Apparatus, system and method for providing earthquake information through distributed optical fiber sensing - Patents.com

Abstract

A method for determining maximum earth acceleration includes providing a DFOS instrument connected to at least one optical fiber and recording DFOS data with the DFOS instrument, the DFOS data including strain data along the at least one optical fiber, and the method also includes transforming the strain data into complex Fourier coefficients, scaling the complex Fourier coefficients, applying an inverse transform to the scaled Fourier coefficients, and selecting a maximum value from an output of the inverse transform to identify a maximum earth acceleration at a location along the at least one optical fiber.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 157,789, filed March 7, 2021, the entirety of which is incorporated herein by reference. [Background technology]

[0002] Ten years after the 9.0 magnitude earthquake that struck off the Tohoku coast of Japan on March 11, 2011, and the Christchurch, New Zealand earthquake in 2011, seismic events remain a pressing challenge for densely populated cities around the world. Earthquakes pose significant risks to both human life and infrastructure. Catastrophic structural collapse during the initial earthquake shock is often followed by a deadly series of secondary hazards, such as tsunamis, landslides, liquefaction, and aftershocks. In many cases, these secondary hazards are more deadly than the initial shock. The large economic losses associated with infrastructure damage impose an unsustainable burden on home and structure owners, as well as private and public financial institutions that provide earthquake insurance.

[0003] Traditionally, sparse networks of seismometers are used to quantify the magnitude of ground motion from earthquakes. A small number of seismometers, often located in peri-urban areas or away from human habitations or workplaces, are typically generalized to the entire city. In reality, ground motion varies dramatically across a city depending on the directionality of the seismic waves as well as the local geology, sediment thickness, and soil conditions. Current information on ground motion from sparse networks of seismometers is insufficient to provide the desired resolution at the address level.

[0004] Because information from seismographs after a major earthquake is incomplete, engineers and seismologists are dispatched to survey street addresses after a major earthquake to determine the extent of damage, often looking for cracks in walls inside and outside the structure or other visual evidence of damage. These surveys are highly inefficient and often delay the restoration of transportation systems and critical infrastructure by a day or more. Many structures are not surveyed, so the burden of proof for documenting damage falls on the structure owners.

[0005] Furthermore, while the system is intended to assess large earthquakes (e.g., magnitude M>6.5-7.0), frequent earthquakes of relatively small magnitude (M2.0-M6.5) resulting in repeated light to moderate shaking can make it difficult to assess the long-term structural integrity of buildings and, from an insurance perspective, difficult to establish a causal link between earthquake claims and damages. Summary of the Invention

[0006] Embodiments of the present disclosure provide methods, systems, and apparatus that enable analysis of the effects of earthquakes, such as the magnitude of earthquake motion amplitude, high-risk areas, and the presence or absence of secondary natural hazards such as tsunamis and liquefaction.

[0007] Those skilled in the art will appreciate that with regard to seismology, today, detection is not the primary concern. There are many ways to detect that an earthquake has occurred. For example, an external earthquake service can be used from a mobile device to confirm that an earthquake has occurred. Shortly after a damaging earthquake occurs, the most valuable information is not the detection of the earthquake, but the impact of the earthquake. In particular, embodiments provide methods, systems, and devices that characterize the type, typology, and magnitude of earthquake motion, and how it has affected buildings and other infrastructure. In this regard, embodiments present methods, devices, and systems that improve prediction of earthquake risk in populated areas with spatial resolution (so-called "peak ground acceleration by address") that allows assessment of individual house numbers (e.g., buildings and designated areas).

[0008] In embodiments, methods, apparatus, and systems utilize Distributed Fiber Optic Sensing (DFOS) measurements made along optical fibers (such as communications fiber infrastructure) at high resolution (e.g., 1 meter resolution) to provide quantitative information regarding potential building damage, structural integrity, liquefaction, potential secondary disasters, and economic damage caused by seismic energy.

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Like reference numerals represent like elements. The accompanying drawings are not necessarily drawn to scale. Some figures have been simplified by omitting selected features for the purpose of more clearly showing other essential features. Such omission of elements in some figures does not necessarily indicate the presence or absence of a particular element in any of the exemplary embodiments, unless expressly disclosed in the corresponding written description. [Brief description of the drawings]

[0010] [Figure 1] 1 illustrates an example of a DFOS device for transmitting and receiving laser light in accordance with an embodiment of the disclosed subject matter. [Diagram 2] 1 illustrates a non-limiting example of a method for calculating peak ground acceleration according to an embodiment of the disclosed subject matter. [Diagram 3] 1 illustrates a non-limiting example of a method for calculating peak ground acceleration based on a regional seismic velocity model, according to an embodiment of the disclosed subject matter. [Figure 4A] 1 illustrates a non-limiting example of a method for quantifying the effects of seismic motion in accordance with an embodiment of the disclosed subject matter. [Figure 4B] 1 illustrates a non-limiting example of a method for quantifying the effects of seismic motion in accordance with an embodiment of the disclosed subject matter. [Diagram 5]1 shows a seismogram section from a DFOS recording performed in accordance with an embodiment of the disclosed subject matter. [Figure 6] 1 illustrates an example geographical spread at multiple bearings and distances calculated in accordance with an embodiment of the disclosed subject matter. [Figure 7A] 1 shows measurements of DFOS data obtained in accordance with an embodiment of the disclosed subject matter. [Figure 7B] 1 shows measurements of DFOS data obtained in accordance with an embodiment of the disclosed subject matter. [Figure 7C] 1 shows measurements of DFOS data obtained in accordance with an embodiment of the disclosed subject matter. [Figure 7D] 1 shows measurements of DFOS data obtained in accordance with an embodiment of the disclosed subject matter. [Figure 7E] 1 shows measurements of DFOS data obtained in accordance with an embodiment of the disclosed subject matter. [Figure 7F] 1 shows measurements of DFOS data obtained in accordance with an embodiment of the disclosed subject matter. [Figure 8] 1 illustrates peak ground acceleration calculated for a portion of a city in accordance with an embodiment of the disclosed subject matter. [Figure 9] 1 shows a compilation of results obtained according to embodiments of the disclosed subject matter. [Figure 10] 1 illustrates a method for self-assessing earthquake-induced effects according to an embodiment of the disclosed subject matter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Referring to FIG. 1, a DFOS instrument 100 shines light into an optical fiber 150 and records the returning energy 110 as a function of time. The light can be any type, such as a simple pulse, a chirped pulse, or a continuous wave. In an embodiment, the light is laser light. In a further embodiment, the laser light is in the infrared or near infrared frequency range. The energy returned from the optical fiber sensing path may be Rayleigh scattered as a result of light scattering characteristics along the length of the optical fiber, or the returning energy may result from Brillouin or Raman transitions from the incident wavelength. The returning light may be analyzed optically, digitally, or both. The output of this process is a data set, referred to herein as DFOS data or DFOS record, that includes values ​​for the optical fiber state at specific time samples at all sensor locations in the fiber.

[0012] In an embodiment, the statistics of the telecommunication receiver itself are collected as input dates for DFOS to extract information related to the condition of the fiber, such as polarization characteristics and time of flight from one end to the other, which may convey information about the time rate of change of the fiber length, or the stress or strain state of the fiber at a point or over the entire length, without a dedicated instrument at one end. It will be understood that the strain includes geodetic strain, which can be measured by the geodetic strain response. After an earthquake, the surface of the earth near the epicenter moves, possibly laterally or up and down across a fault. This movement is called geodetic strain.

[0013] In one embodiment, the DFOS instrument may be an interrogator unit ("IU"), such as the unit for distributed acoustic sensing described in WO2018 / 045433A1 (herein incorporated by reference in its entirety).

[0014] For some DFOS, there is no physical fixed length of sensor location. In principle, the gauge length is the distance along the optical fiber for which one DFOS value has sensitivity. For example, in some types of pulsed Rayleigh-based DFOS, the gauge length may be 10m and the recorded data may be strain. In this case, the 10m gauge length becomes the "reference length" and any displacement larger than that causes strain. The gauge length can affect many aspects of the measurement, including the quality of the measurement, the gain of the measurement, the finest spatial size that can be analyzed without spatial aliasing, and the amount of DFOS data recorded. The gauge length can be set in hardware and / or software. If the gauge length is set in software, DFOS data can be recorded at multiple gauge lengths.

[0015] DFOS measurements are affected by the movement and deformation of the optical fiber itself, and by the movement and deformation of the surrounding area. For example, during an earthquake, the soil compresses and thickens as seismic waves travel near the earth's surface, and this movement is transmitted to the optical fiber.

[0016] DFOS measurements can be made wherever a continuous optical fiber exists and one end can be connected to a DFOS instrument. The fiber may be oriented in any direction and may be wrapped helically around a central cylinder (e.g. wrapped around a bridge pier or around a building foundation) to introduce multiple motion / deformation components into each gauge length of the DFOS measurement. Existing optical fiber installed for other purposes may be used for DFOS measurements. Multiple fibers may be connected in series and used for DFOS in one instrument, and multiple DFOS channels (analyzed by the same or separate DFOS instruments) may be used to record DFOS data in the same vicinity.

[0017] DFOS measurements made along the fiber pathway provide quantitative information on the displacement, velocity, acceleration, and / or strain resulting from earthquake ground motion, and therefore provide data that directly quantifies damage to structures, liquefaction, and risk to structural integrity.

[0018] In various embodiments, DFOS measurements are taken before (e.g., several seconds before), during, and after the seismic waves arrive at a particular location. It will be appreciated that the particular location may be a location in a populated area, and the spatial resolution may be on the order of a meter (e.g., 1 meter) so that particular structures can be identified.

[0019] Earthquakes often occur some distance from human habitation and infrastructure. For example, most of the major earthquakes off the coast of Japan, New Zealand, and British Columbia, Canada, occurred more than 100 km away from coastal cities. In embodiments, long lengths of fiber (e.g., hundreds of kilometers long) deployed at sea and on land for communications can also be used to detect these remote earthquakes at any point along the fiber by optical signals traveling at the speed of light in the fiber.

[0020] In an embodiment, DFOS equipment is installed in a land-based urban data center and connected to a long (e.g., 100 km) offshore fiber route. If an earthquake occurs 100 km offshore, at the seaward end of the fiber, the use of DFOS measurements may present a scenario in which the use of DFOS provides an early warning of the earthquake. In this example, the P-waves (longitudinal waves), which travel the fastest through the Earth from the earthquake site, cause deformation of the undersea fiber, and this deformation of the undersea fiber is detected and quantified by the DFOS measurements. With a sensing length of 100 km of optical fiber, the system can issue an alert with an earthquake warning 16.7 seconds before the P-waves reach the city (assuming a P-wave speed of 6 km / s). The arrival of the most damaging Rayleigh and surface waves is slightly delayed due to their relative slowness compared to the P-waves. Therefore, this method may allow up to 50 seconds of warning for densely populated areas (assuming a Rayleigh wave speed of 2 km / s). It will thus be appreciated that the employment of DFOS on existing or newly installed fiber optic cables extending to or beyond the epicenter of an earthquake can detect the occurrence of an earthquake and provide warning to populated areas before the earthquake's P and surface waves reach the city. It will further be appreciated that direct observation of ground conditions at the epicenter location (promisingly enhanced by the large-scale deployment of DFOS on communication fiber cables) can provide dense geotechnical data that can be used to predict the likelihood of a major earthquake before it occurs.

[0021] In an embodiment, DFOS measurements are used to provide information regarding the type, direction, and / or amplitude and duration of earthquake motion (e.g., in terms of peak ground acceleration (PGA)). It will be apparent to one skilled in the art of seismology, earthquake science, or signal processing that the measurement amplitude obtained with the proposed method will be greatest during earthquake timing based on historical earthquake records in urban areas. Thus, even in the absence of earthquake detection schemes, DFOS measurements according to the present disclosure can be used to provide a measurement method to inform about the effects of earthquake motion.

[0022] This applies to both general and specific use of the method in the case of a single earthquake or sequence of earthquakes. For example, to clarify what is meant by a general use case, consider an owner of a building or an insurer of the building property in an earthquake-prone region of New Zealand. The owner or insurer may be interested in the statistical distribution of peak ground acceleration (PGA) of nearby or his own buildings, due to the frequent occurrence of low-level earthquakes each year, without any catastrophic damage events. In this case, DFOS measurements may be continuously recorded and analyzed to calculate the average PGA level, or the mean and standard deviation, or another statistical measure, of a segment of fiber near the target building, ensuring that a statistical perspective of the data is calculated over a period of time that may extend over years. To clarify what is meant by a specific use case of the method, consider how an owner or insurer of the same or a different building may want to know the PGA value during a damaging main shock, or during a main shock and all subsequent aftershocks in a main shock and aftershock sequence. All measurements of PGA can be obtained from DFOS. As is evident from this description, the PGA measurements during the calculations can be performed continuously (e.g., every minute) to satisfy both general and specific single earthquake use cases.

[0023] In an embodiment, the DFOS data is used to estimate acceleration (A) by recording the strain from DFOS at multiple locations of the fiber array. In an embodiment, the multiple locations are all locations within the fiber array. The PGA is determined from the relationship in Equation 1 below.

number

[0024] DFOS data may be sampled uniformly in distance and time. In an embodiment, DFOS data is sampled spatially at approximately 1-10 m and at fine time increments of 100-1000 samples per second. As a result, a two-dimensional Fourier transform (FFT2) can be used to convert any particular seismic phase from the seismic arrivals into a quantity from which acceleration can be calculated. Thus, the previous equation can be rewritten as:

number

number

number

number

[0025] FIG. 2 illustrates a non-limiting example of a method for calculating peak ground acceleration according to an embodiment of the subject matter of the present disclosure. At S200, the process begins. At S210, DFOS data is recorded and stored. The DFOS data includes strain data, which may include strain amplitude. A two-dimensional Fourier transform is then applied at S220 to convert the strain data into complex Fourier coefficients. At S230, the Fourier coefficients are then multiplied by the quantity ω / k, which has the effect of scaling the original data with the apparent velocity as per Equation 4. At S240, the data is then brought back into the space-time domain using a two-dimensional inverse Fourier transform, differentiated in time and multiplied by −1 (negation) to obtain a data set with units of acceleration A as per Equation 5. At S250, the maximum value of A in each channel is selected and considered as the peak ground acceleration at that location in the optical fiber.

[0026] In another embodiment, an alternative method of calculating the peak ground acceleration is described. This alternative method involves a regional seismic velocity model that is used to estimate u by ray tracing using the approximate location of the epicenter (latitude, longitude, and depth within 5 km depending on the radial distance from the DFOS measurement location) and the shear wave velocity (V s While the approximate location of an earthquake can be obtained from seismometers and other non-DFOS sensors, DFOS sensing is used to quantify the earthquake's effects on an area of ​​interest and on specific objects within the area of ​​interest (structures, bridges, roads, etc.). s The value of can be known from geological surveys, soil sampling, photogrammetry, or aerial imagery, or from information available from geological maps or other archives of geological information. In these embodiments, the representative angles (θ) that the seismic waves make with the horizontal plane in the area of ​​the DFOS array calculated during ray tracing are stored. These representative angles are used to estimate, for example, u, using the following formula:

number

[0027] 3 illustrates a non-limiting example of a method for calculating peak ground acceleration based on a regional seismic velocity model. The process begins at S300. DFOS data is continuously recorded and stored at S310. In an embodiment, the data is recorded in a circular buffer, with new data overwriting older data. This allows for analysis of relevant data while reducing storage requirements. An earthquake is detected at S320. As discussed above, this detection can be by non-DFOS measurements, such as by seismometer measurements. This detection triggers analysis of the recorded DFOS data at S310.

[0028] The seismic ray paths are then ray traced in the S330. This requires input of the earthquake's epicenter and local geological information, which can be loaded from external archives of this information, for example those published by the US Geological Survey (USGS). Ray tracing is an application of Snell's law, which describes how seismic waves are refracted as they pass from one material layer to the next according to the angle of incidence at the interface between the layers. Wherever the target DFOS fiber channel is present, the result of ray tracing is an estimate of the angle of incidence θ at the surface.

[0029] Next, in S340, the value of θ obtained in S330 is used to calculate the underground shear wave velocity V near the DFOS fiber channel. s to calculate u as in Equation 6. In embodiments, the underground near the DFOS fiber is within 5 m, 10 m, 100 m, or 500 m of the DFOS fiber.

[0030] Finally, in S350, the time derivative is applied to the recorded DFOS measurements of strain and multiplied by u to obtain a data set in units of acceleration A. The maximum value of A in each channel is taken as the maximum ground acceleration at that location in the optical fiber selected in S360.

[0031] If hospitals, bridges, tunnels, and other critical infrastructure record strong vibrations at specific frequencies known to cause structural vibrations, additional safety protocols can be implemented such as shutting down electricity, automatic gas shutoff valves, opening elevator doors, etc. This can be accomplished on a building-by-building and address-by-address basis wherever fiber used for DFOS is present.

[0032] Referring to FIG. 4A, a non-limiting example of a method for detecting and quantifying earthquake effects based on degradation of optical fiber signal strength is shown. At S410, DFOS data is recorded and stored. The stored data is analyzed at S415 using quantitative measurements of signal amplitude within a passband of the dominant frequency range of earthquakes (0.5-150 Hz for local earthquakes, 0.005-5 Hz for regional and near-field earthquakes). The result of this analysis can be an estimate of the expected amplitude at the propagation distance beyond the measured area based on the understanding that the radiation of surface waves resembles an inverse square law. In some embodiments, a general or specialized attenuation model is employed to predict the expected ground motion levels at a given location or city using DFOS amplitude measurements, such as the model proposed by Anderson and Hart (1978), which describes the extrinsic and intrinsic attenuation effects of layered soils.

[0033] If the quantitative measurements are above a predefined threshold in S420, an earthquake is presumed to have occurred. If not, the process loops back. Degradation of the signal amplitude may also be caused by physical effects other than earthquakes, such as vehicle traffic, construction, excavation, or other noise or energy added in the vicinity of the optical fiber recording data for DFOS. Thus, verification of earthquake occurrence is performed in S430. This may include querying one or more computer systems storing earthquake data to determine whether an earthquake has been detected by other sensors.

[0034] If an earthquake is identified at S430, the process proceeds to S440 where the earthquake impact is quantified for specific locations, such as buildings and bridges, that are within sensing distance of the optical fiber. The quantification of the impact may follow the process shown in Figure 2 and described above. Specifically, the process may already include recorded DFOS data and processing may continue to S220.

[0035] In other embodiments, even if a dedicated DFOS fiber is not deployed near a location of interest, such as the hospital in the above example, seismic motion measurements and calculations can be made based on other existing fiber communication infrastructure. Referring now to Figure 4B, the steps are similar to Figure 4A, except for the differences highlighted below.

[0036] In one embodiment, a communications fiber that does not have a dedicated DFOS interrogator unit is configured to continuously monitor the quality of signals transmitted and received over the fiber (e.g., signal-to-noise ratio or scattering measurements). This process is similar to the process of FIG. 4A, except that an assessment of signal quality occurs at S416. This assessment may be continuous and may include measuring the signal-to-noise ratio of the optical signals received and recorded by the DFOS system 100. The quality measurement (e.g., SNR) is compared to a threshold at S421. If the quality degrades to a predetermined level, it is determined that a physical change in the fiber has occurred, such as due to seismic energy from an earthquake, and data available to DFOS is recorded in a storage device. Recording can occur before or after signal quality detection. In an embodiment, a smaller amount of data is stored at S410 before a signal quality degradation is detected. After a signal quality degradation is detected, a larger amount of data is stored for analysis. This allows analysis of the recorded data in case an earthquake actually caused the degradation of signal quality (rather than road construction or other events), while many, if not all, fiber optic communication devices are able to perform this data collection since local storage capacity remains small and inexpensive. If the degradation was caused by an earthquake, the data stored in the fiber optic communication device can be analyzed to determine a quantitative measure of the seismic motion along the communication fiber.

[0037] In an embodiment, a spatial resolution of 100m is achievable to allow accurate calculation of seismic motion for locations of interest within 100m of the fiber cable. Beyond this distance, soil conditions may change, reducing the accuracy of the fiber measurements. The density of DFOS seismic motion measurements can be used to plan safe locations in cities where seismic motion is minimized during earthquakes. Thus, a database of calculated seismic motions is created that stores DFOS seismic motion measurements indexed by location. This allows identification of locations where no dangerous seismic motion occurs (whether due to natural ground characteristics or specific man-made mitigation measures).

[0038] Referring now to FIG. 5, the illustrated plot shows a seismogram section from a DFOS recording performed in accordance with an embodiment of the disclosed subject matter. Darker colors indicate stronger seismic motion. The white lines are the focal times when fault motions that generate the seismic waves occurred. Pulses of seismic energy become visible some time later on the DFOS channels represented along the optical distance [km] on the x-axis: P-waves and S-waves. The first energy to arrive are P-waves at about Time=80 seconds. The second pulse of energy about 35-40 seconds later at Time=120 seconds are S-waves or surface waves. Due to the geometry of the source and receiver, there is a curvature in the arrival of these waves. There is also a large variation in amplitude. Channels around 5-16 km optical distance record stronger seismic motions than the channels immediately preceding or following them. This is a result of ground amplification, an effect that is captured by measurements of peak ground acceleration. This is valuable information for urban planners, building owners, and geotechnical engineers who design, build, and / or develop building codes based on the anticipated hazards posed by peak ground acceleration levels in their areas.

[0039] Figure 6 shows an example geographical distribution at multiple orientations and distances near the M5.9 earthquake that occurred in Melbourne, Australia on September 21, 2021. Each location at the offset labeled here is DFOS data recorded during this period, and the respective data are shown in Figures 7A-7F. The earthquake occurred approximately 130 km east-northeast of central Melbourne.

[0040] 7A-7F show measurements of DFOS data from a magnitude 5.9 earthquake that occurred in Melbourne, Australia in 2021. The left vertical axis represents time in seconds, and the horizontal axis represents optical distance in kilometers. The scale on the right side of each figure represents the power spectral density, which corresponds to the grayscale shading of each figure. The high amplitude incoming energy spreads from one side of the array to the next. There are also clear differences between segments of the fiber array. In FIG. 7A, the illustrated plot shows a seismogram section from a DFOS recording in Melbourne, Australia, performed in accordance with an embodiment of the disclosed subject matter. In FIG. 7B, the illustrated plot shows a seismogram section from a DFOS recording offshore Victoria, Australia, performed in accordance with an embodiment of the disclosed subject matter. In FIG. 7C, the illustrated plot shows a seismogram section from a DFOS recording in another area offshore Australia, performed in accordance with an embodiment of the disclosed subject matter. In FIG. 7D, the illustrated plot shows a seismogram section from a DFOS recording in another area Adelaide, Australia, performed in accordance with an embodiment of the disclosed subject matter. In Figure 7E, the illustrated plot shows a seismogram section from a DFOS recording in another area of ​​Sydney, Australia, performed in accordance with an embodiment of the disclosed subject matter. In Figure 7F, the illustrated plot shows a seismogram section from a DFOS recording in another area of ​​Sydney, Australia, performed in accordance with an embodiment of the disclosed subject matter. In each of Figures 7A-7F, the dark horizontal signal arriving between about Time=20 seconds and Time=380 seconds indicates seismic energy from the earthquake.

[0041] Figure 8 shows the calculated results for a fiber in central Melbourne that recorded the 2021 Melbourne, Australia, M5.9 earthquake. Every independent DFOS sensor records a unique seismogram that is converted from raw strain units to acceleration units, and a peak sample is selected and plotted within the range shown. This allows the maximum ground acceleration to be calculated at a finer granularity of street address, called PGA by address.

[0042] The street-level PGA results can be aggregated and overlaid on a map of the area of ​​interest. See Figure 9, which shows an example of a graphical earthquake report with a map of central Melbourne overlaid with street-level PGA values ​​(relative amplitude is represented by greyscale shading, with darker being lower amplitude and lighter being higher amplitude).

[0043] In an embodiment, DFOS measurements during vibration are used to provide information about the interior of the building on a floor-by-floor basis using fiber optic cables running through the building. Modern buildings often have fiber optic cables for communication. These cables are subject to deformation due to the seismic motion of the structure during an earthquake. Single-port or multi-port DFOS instruments can be placed at one end of a single or multiple fiber optic cables running throughout the building, and DFOS data can be recorded continuously or in a rolling buffer that is processed after an earthquake is detected. Analysis of DFOS data from a building can clearly quantify the impact of an earthquake on individual subparts of the building (exterior walls, columns, floor joists, ceiling joists, etc.). For example, if the story displacements of lower floors are smaller than those of higher floors, this type of DFOS data can be used to assess the magnitude of the relative story displacements. Alternatively, DFOS data can be recorded from fibers running vertically and horizontally to calculate a horizontal-vertical deformation time series. By recording multiple components in a grid, the rotation of the structure can be calculated through the calculation of the spatial derivative of the strain in each component of the recording. In an embodiment, a specific maximum acceleration and / or displacement of one or more of these subparts may be calculated based on DFOS data and then compared to an acceptable threshold (such as a threshold provided by an architect or building engineer).

[0044] FIG. 10 illustrates a non-limiting example of a self-assessment process for infrastructure, such as a building or bridge, based on the effects of an earthquake event. In one embodiment, the automated building self-assessment is performed by a DFOS system. The process begins in S1000. As described above, the DFOS system is connected to a fiber optic cable running through the building and can continuously record and analyze DFOS data to calculate the displacement and / or acceleration of building components. This process can be performed on a periodic schedule, such as every 10 minutes, denoted as T in S1005. In an embodiment, T is 1 hour, 12 hours, or 24 hours. In an embodiment, the process is performed continuously, i.e., from 0 seconds until the T period has elapsed, at which point the process proceeds to S1010.

[0045] At S1010, DFOS data is recorded and stored. It will be appreciated that the recorded data may represent a period T or another duration. At S1020, resonant peaks of the target structure (such as a building or bridge) are calculated based on the DFOS data obtained at S1010. Historical values ​​of the resonant peaks are stored in a data storage. These values ​​may include pre-calculated values, may be engineering parameters calculated based on the design of the structure from a finite element model simulation of the structure, or may be a general structural design. At S1030, the archived values ​​are retrieved from the data storage and compared to the DFOS-based values ​​at S1040. The output of S1040 may be a difference value between the calculated value and the archived value. At S1050, the difference value is compared to a threshold value. The threshold value may be an engineering parameter calculated based on a finite element simulation of the structure, or may be a value set by safety regulations. In an embodiment, the threshold value is adaptive and decreases based on historical measurements. This accounts for the possible accumulation of structural effects on the structure, which may be cumulative. In an embodiment, the system may include tolerance thresholds for acceleration and / or displacement of various subcomponents, compare the calculated values ​​to the thresholds, and generate an alert in S1060 if one or more thresholds are exceeded. It will be appreciated that this allows a structure to self-assess at least the initial damage that may be caused by an earthquake, and quickly identify structures that require further investigation by structural engineers to ensure the safety of the structure. The alert may be transmitted to one or more designated recipients over a wired or wireless network. In an embodiment, if a structure is the monitored structure, the one or more designated recipients are occupants of the structure.

[0046] After vibrations, DFOS measurements can be used to provide post-earthquake warnings regarding the structural integrity of buildings and infrastructure. For example, if the measured vibrations exceed a safety threshold for a structure or bridge, the structure or infrastructure may be automatically red-tagged to prevent unintentional human access or use. Natural eigenmode resonances (frequency peaks in the vibration and torsion of a structure) can be measured and compared to pre-earthquake resonances. This information can be used to provide warnings regarding damage to structures.

[0047] Secondary hazards often occur in rapid succession following damaging ground motion as a result of physical surface processes initiated by the earthquake. In an embodiment, DFOS measurements of soil vibrations are used to facilitate liquefaction investigations or refine the scale of liquefaction investigations in a targeted and strategic manner to improve resource utilization.

[0048] Further embodiments of the disclosed subject matter are as follows: According to a first further embodiment, there is provided a method of determining a maximum Earth acceleration, the method comprising: providing a DFOS instrument connected to at least one optical fiber; recording DFOS data with the DFOS instrument, the DFOS data including strain data along the at least one optical fiber; converting the strain data to complex Fourier coefficients; scaling the complex Fourier coefficients; applying an inverse transform to the scaled Fourier coefficients; and selecting a maximum value from an output of the inverse transform to identify a maximum Earth acceleration at a location along the at least one optical fiber. According to a second further embodiment, there is provided the method of the first further embodiment, wherein converting the strain data to complex Fourier coefficients comprises applying a two-dimensional Fourier transform to the strain data. According to a third further embodiment, there is provided the method of the first further embodiment, wherein applying the inverse transform comprises applying a two-dimensional inverse Fourier transform to the scaled Fourier coefficients.

[0049] According to a fourth further embodiment, a method for determining a peak ground acceleration based on a regional seismic velocity model is provided, the method comprising: providing a DFOS device connected to at least one optical fiber; recording DFOS data including strain data along the at least one optical fiber with the DFOS device; detecting an earthquake occurrence; ray tracing a seismic wave path from the earthquake occurrence site to the optical fiber to determine an angle of incidence of seismic energy at the earth's surface where the optical fiber is installed; calculating a ground apparent velocity measurement based on the determined angle of incidence and a ground shear velocity around the optical fiber; applying a time derivative to the calculated apparent velocity measurement to obtain a ground acceleration measurement; and selecting a maximum value from the output of the application to identify a peak ground acceleration at a location along the at least one optical fiber. According to a fifth further embodiment, the method of the fourth further embodiment is provided, wherein the ground apparent velocity is a velocity in a horizontal direction. According to a sixth further embodiment, the method of the fourth further embodiment is provided, wherein detecting an earthquake occurrence is not based on DFOS data.

[0050] According to a seventh further embodiment, there is provided a method for determining characteristics of seismic motion caused by an earthquake, the method comprising: recording DFOS data with a DFOS instrument, including strain data along at least one optical fiber; analyzing the recorded DFOS data to obtain a quantitative measure of signal amplitude of the DFOS data; comparing the quantitative measure of the signal amplitude to a predefined threshold; preliminarily determining that an earthquake has occurred if the quantitative measure exceeds the predefined threshold; and quantifying the effect of the earthquake. According to an eighth further embodiment, there is provided the method of the seventh further embodiment, further comprising verifying that an earthquake has occurred after the preliminarily determining and before the quantifying. According to a ninth further embodiment, there is provided the method of the eighth further embodiment, wherein analyzing the recorded DFOS data comprises measuring signal amplitude within a passband of a dominant frequency of the earthquake. According to a tenth further embodiment, there is provided the method of the ninth further embodiment, wherein the dominant frequency is in the range of 0.5-156 Hz for local earthquakes. According to an eleventh further embodiment, there is provided the method of the ninth further embodiment, wherein the dominant frequency is in the range of 0.005-5 Hz for regional and shallow earthquakes. According to a twelfth further embodiment, there is provided the method of the ninth further embodiment, wherein the verifying is based on non-DFOS measurements. According to a thirteenth further embodiment, there is provided the method of the ninth further embodiment, wherein the verifying is based on analysis of the recorded DFOS data. According to a fourteenth further embodiment, there is provided the method of the ninth further embodiment, wherein the quantifying comprises determining a peak ground acceleration of the ground proximate the at least one optical fiber.According to a fifteenth further embodiment, the method of the fourteenth further embodiment is provided, in which determining the maximum ground acceleration comprises transforming the strain data of the DFOS data into complex Fourier coefficients, scaling the complex Fourier coefficients, applying an inverse transform to the scaled Fourier coefficients, and selecting a maximum value from an output of the inverse transform to identify the maximum ground acceleration at a location along the at least one optical fiber. According to a sixteenth further embodiment, the method of the fifteenth further embodiment is provided, in which converting the strain data into complex Fourier coefficients comprises applying a two-dimensional Fourier transform to the strain data. According to a seventeenth further embodiment, the method of the fifteenth further embodiment is provided, in which applying the inverse transform comprises applying a two-dimensional inverse Fourier transform to the scaled Fourier coefficients.

[0051] According to an eighteenth further embodiment, a method for determining characteristics of seismic motion caused by an earthquake is provided, the method comprising: recording DFOS data including strain data along at least one optical fiber with a DFOS instrument; measuring a signal quality of the DFOS data; comparing the signal quality of the measured DFOS data to a predefined threshold; preliminarily determining that an earthquake has occurred if the measured signal quality is below a predefined threshold; and quantifying the effect of the earthquake. According to a nineteenth further embodiment, the method of the eighteenth further embodiment is provided, further comprising verifying that an earthquake has occurred after the preliminarily determining and before the quantifying. According to a twentieth further embodiment, the method of the nineteenth further embodiment is provided, wherein the measuring of the signal quality comprises determining a signal-to-noise ratio of the DFOS data. According to a twenty-first further embodiment, the method of the nineteenth further embodiment is provided, wherein the measuring of the signal quality is applied to the recorded DFOS data. According to a twenty-second further embodiment, the method of the nineteenth further embodiment is provided, wherein the measuring of the signal quality is applied to the DFOS data simultaneously with recording the DFOS data. According to a twenty-third further embodiment, there is provided the method of the nineteenth further embodiment, in which the quantifying comprises determining a maximum ground acceleration of the ground proximate the at least one optical fiber. According to a twenty-fourth further embodiment, there is provided the method of the twenty-third further embodiment, in which the determining the maximum ground acceleration comprises transforming the strain data of the DFOS data into complex Fourier coefficients, scaling the complex Fourier coefficients, applying an inverse transform to the scaled Fourier coefficients, and selecting a maximum value from an output of the inverse transform to identify a maximum ground acceleration at a location along the at least one optical fiber. According to a twenty-fifth further embodiment, there is provided the method of the twenty-fourth further embodiment, in which the transforming the strain data into complex Fourier coefficients comprises applying a two-dimensional Fourier transform to the strain data.According to a twenty-sixth further embodiment, there is provided the method of the twenty-fifth further embodiment, wherein applying the inverse transform comprises applying a two-dimensional inverse Fourier transform to the scaled Fourier coefficients.

[0052] According to a twenty-seventh further embodiment, there is provided a method for assessing the effect of seismic motion on a structure, the method comprising: recording DFOS data with a DFOS instrument, including strain data along at least one optical fiber; calculating a resonant peak of the structure based on the DFOS data; storing the calculated resonant peak in a storage device that archives resonant peak values ​​associated with the structure; retrieving the archived resonant peak value from the storage device; detecting a change, represented by a change value, between the retrieved archived value and the resonant peak calculated based on the DFOS data; comparing the change value to a threshold; and generating an alarm if the detected change exceeds the threshold. According to a twenty-eighth further embodiment, there is provided the method of the twenty-seventh further embodiment, further comprising installing the at least one optical fiber in the vicinity of the structure. According to a twenty-ninth further embodiment, there is provided the method of the twenty-eighth further embodiment, wherein the at least one optical fiber is inside or under the structure. According to a thirtieth further embodiment, there is provided the method of the twenty-seventh further embodiment, wherein the method is repeated on a schedule. According to a thirty-first further embodiment, there is provided the method of the thirty-first further embodiment, wherein the period of the schedule is between 5 minutes and 48 hours. According to a thirty-second further embodiment, there is provided the method of the thirty-first further embodiment, wherein the period of the schedule is 10 minutes, 60 minutes, 12 hours, or 24 hours. According to a thirty-third further embodiment, there is provided the method of the thirty-first further embodiment, wherein the period of the schedule is adaptive and decreases in duration depending on the results of the comparison. According to a thirty-fourth further embodiment, there is provided the method of the twenty-seventh further embodiment, wherein the structure is a building, a bridge, or a tower. According to a thirty-fifth further embodiment, there is provided the method of the twenty-seventh further embodiment, wherein engineering design parameters based on the design of the structure are stored in a storage device.According to a further embodiment of a thirty-sixth aspect, the method of the thirty-fifth aspect is provided, wherein the storage device stores a plurality of resonant peak values ​​associated with the structure, each of the resonant peak values ​​being associated with at least one of a timestamp and a duration. According to a further embodiment of a thirty-seventh aspect, the method of the thirty-sixth aspect is provided, further comprising accumulating the detected change values ​​over time to identify an accumulated change value representing a change between a last calculated resonant peak and an oldest resonant peak value stored in the storage device. According to a further embodiment of a thirty-eighth aspect, the method of any of the twenty-seventh to thirty-seventh aspects is provided, wherein the seismic motion is caused by an earthquake. According to a further embodiment of a thirty-ninth aspect, the method of the twenty-seventh aspect is provided, wherein the threshold is adaptive and decreases over time. According to a further embodiment of a fortieth aspect, the method of the twenty-seventh aspect is provided, wherein generating the alarm includes transmitting a signal over a wired or wireless network. According to a further embodiment of a fortieth aspect, the method of the twenty-seventh aspect is provided, wherein generating the alarm includes outputting a message audible to a human inside the structure. According to a forty-second further embodiment, there is provided the method of the forty-first further embodiment, wherein the human audible message includes information regarding potential damage to the structure.

[0053] According to a further embodiment of 43, there is provided a method of generating an earthquake alert at a first location remote from a second location that is an epicenter of an earthquake, the method comprising: measuring DFOS data at the first location of an optical fiber extending from the first location to an area surrounding the second location; calculating from the DFOS data an indication that an earthquake has occurred at the second location; and generating an alert at the first location indicating that the earthquake has occurred. According to a further embodiment of 44, there is provided a method of the further embodiment of 43, in which the first location is outside a populated area and the second location is within a populated area. According to a further embodiment of 45, there is provided a method of the further embodiment of 44, in which the first location is offshore. According to a further embodiment of 46, there is provided a method of the further embodiment of 44, in which the first location is in a rural area. According to a further embodiment of 47, there is provided a method of the further embodiment of 44, in which the second location is in an urban area. According to a forty-eighth further embodiment, the method of the forty-third further embodiment is provided, wherein generating the alert occurs before the earthquake P-waves and / or damaging seismic motion arrive at the first location. According to a forty-ninth further embodiment, the method of the forty-third further embodiment is provided, wherein measuring the DFOS data comprises transmitting light from a DFOS device to the optical fiber and receiving refracted or reflected light from the optical fiber. According to a fifty-first further embodiment, the method of the forty-third further embodiment is provided, wherein measuring the DFOS data comprises transmitting light from an optical communication device to the optical fiber and receiving refracted light from the optical fiber. According to a fifty-first further embodiment, the method of the forty-third further embodiment is provided, wherein measuring the DFOS data comprises measuring strain. According to a fifty-second further embodiment, the method of the forty-third further embodiment is provided, wherein measuring the DFOS data comprises measuring seismic motion. According to a fifty-third further embodiment, the method of the forty-third further embodiment is provided, wherein calculating comprises calculating a magnitude of the earthquake.According to a further embodiment of a fifty-fourth aspect, the method of the further embodiment of a forty-third aspect is provided, in which the calculating comprises calculating a geographical position of the second location. According to a further embodiment of a fifty-fifth aspect, the method of the further embodiment of a forty-third aspect is provided, in which the calculating comprises calculating a peak ground acceleration of the second location. According to a further embodiment of a fifty-sixth aspect, the method of the further embodiment of a forty-third aspect is provided, in which the calculating comprises calculating a peak ground acceleration of the first location. According to a further embodiment of a fifty-seventh aspect, the method of the further embodiment of a forty-third aspect is provided, in which the calculating comprises calculating a peak ground acceleration of a location within a predetermined distance of the optical fiber. According to a further embodiment of a fifty-eighth aspect, the method of the further embodiment of a fifty-seventh aspect is provided, in which the predetermined distance is between 50 meters and 500 meters. According to a further embodiment of a fifty-ninth aspect, the method of the further embodiments of a fifth to eighth aspect is provided, in which the predetermined distance is 100 meters. According to a sixtieth further embodiment, there is provided the method of any of the forty-third to fifty-ninth further embodiments, wherein measuring the DFOS data comprises selecting a portion of an unlit or unused optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network.

[0054] According to a sixty-first further embodiment, there is provided a method of quantifying the effects of an earthquake originating at a first location, the method comprising: measuring DFOS data with a DFOS system at a second location offset from the first location during the earthquake; and using the measured DFOS data to calculate at least one of peak ground acceleration, peak ground velocity, maximum ground displacement, maximum peak ground strain, maximum ground strain rate, maximum spectral acceleration, and / or earthquake intensity. According to a sixty-second further embodiment, there is provided a method of the sixty-first further embodiment, further comprising: recording the measured DFOS data; receiving notification that an earthquake has occurred; and, in response to the received notification, using the recorded measured DFOS data to calculate at least one of the earthquake magnitude, moment, strain, strain rate, geodetic deformation, location, depth, focal mechanism, radiation pattern, moment tensor, finite fault area of ​​slip, slip velocity, and rupture velocity of the occurring earthquake. According to a further embodiment of a 63rd aspect, there is provided a method of a further embodiment of a 62nd aspect, further comprising generating an alert from the DFOS system based on the calculating and transmitting the generated alert to a receiver in a populated area. According to a further embodiment of a 64th aspect, there is provided a method of a further embodiment of a 61st aspect, wherein measuring the DFOS data comprises transmitting and receiving DFOS signals over a single telecommunications fiber that is used simultaneously for DFOS seismic sensing and for carrying telecommunications traffic. According to a further embodiment of a 65th aspect, there is provided a method of a further embodiment of a 61st aspect, wherein measuring the DFOS data occurs during the occurrence of the earthquake and the calculating occurs after the occurrence of the earthquake. According to a further embodiment of a 66th aspect, there is provided a method of a further embodiment of a 61st aspect, wherein measuring the DFOS data and the calculating occur during the occurrence of the earthquake. According to a further embodiment of a 67th aspect, there is provided a method of a further embodiment of a 61st aspect, wherein the calculating represents a physical effect at the second location.According to a further embodiment of a 68th aspect, a method of a further embodiment of a 61st aspect is provided, in which a DFOS device is located at the second location. According to a further embodiment of a 69th aspect, a method of a further embodiment of a 61st aspect is provided, in which the calculating represents physical effects at a third location located between the first location and the second location. According to a further embodiment of a 70th aspect, a method of a further embodiment of a 61st aspect is provided, in which the measuring of the DFOS data includes transmitting light from the DFOS system to an optical fiber and receiving refracted light from the optical fiber, and the calculating represents physical effects at a third location located within a predetermined distance from the optical fiber. According to a further embodiment of a 71st aspect, a method of a further embodiment of a 61st aspect is provided, in which the measuring of the DFOS data includes transmitting light from the DFOS system to an optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of a 72nd aspect, a method of a further embodiment of a 61st aspect is provided, in which the measuring of the DFOS data includes transmitting light from an optical communication device to an optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of a seventy-third aspect, there is provided the method of the seventy-first aspect, wherein the predetermined distance is between 50 meters and 500 meters. According to a further embodiment of a seventy-fourth aspect, there is provided the method of the seventy-third aspect, wherein the predetermined distance is 100 meters. According to a further embodiment of a seventy-fifth aspect, there is provided the method of the sixty-seventh aspect, wherein the second location is at least one site of a building, a data center, a hospital, an airport, a critical infrastructure, a road, a bridge, a tunnel, a residence, a hotel, other structure, or a building subject to seismic motion. According to a further embodiment of a seventy-sixth aspect, there is provided the method of any of the sixty-first to seventy-fifth aspects, wherein measuring the DFOS data includes selecting a portion of an unlit or unused optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network.

[0055] According to a seventy-seventh further embodiment, there is provided a method of quantifying an earthquake effect, the method comprising measuring DFOS data at least during the occurrence of the earthquake, and using the measured DFOS data to calculate at least one of a direction of seismic motion during the occurrence of the earthquake and a duration of the seismic motion during the occurrence of the earthquake. According to a seventy-eighth further embodiment, there is provided the method of the seventy-seventh further embodiment, wherein measuring the DFOS data comprises transmitting light from a DFOS device to an optical fiber and receiving refracted light from the optical fiber. According to a seventy-ninth further embodiment, there is provided the method of the seventy-seventh further embodiment, wherein measuring the DFOS data comprises transmitting light from an optical communication device to an optical fiber and receiving refracted light from the optical fiber. According to an eightieth further embodiment, there is provided the method of any of the seventy-seventh to seventy-ninth further embodiments, wherein measuring the DFOS data comprises selecting a portion of an unlit or unused optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network.

[0056] According to an eighty-first further embodiment, a method for analyzing the effects of an earthquake on a structure is provided, the method comprising: measuring DFOS data at least during the occurrence of the earthquake; calculating eigenmode resonance values ​​of the structure from the measured DFOS data; and determining a quantity representative of the vibration strength of the structure from the eigenmodes. According to an eighty-second further embodiment, the method of the eighty-first further embodiment is provided, in which measuring the DFOS data comprises transmitting light from a DFOS device to an optical fiber and receiving refracted light from the optical fiber, the optical fiber extending a predetermined distance from the structure or passing through the structure. According to an eighty-third further embodiment, the method of the eighty-first further embodiment is provided, in which measuring the DFOS data comprises transmitting light from a DFOS device to an optical fiber and receiving refracted light from the optical fiber. According to an eighty-fourth further embodiment, the method of the eighty-first further embodiment is provided, in which measuring the DFOS data comprises transmitting light from an optical communication device to an optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of an 85th aspect, there is provided a method of a further embodiment of an 81st aspect, wherein the measuring of the DFOS data is performed during vibrations caused by the earthquake. According to a further embodiment of an 86th aspect, there is provided a method of a further embodiment of an 81st aspect, wherein the calculating is performed during vibrations caused by the earthquake. According to a further embodiment of an 87th aspect, there is provided a method of a further embodiment of an 85th aspect, wherein the calculating is performed after vibrations caused by the earthquake have ceased. According to a further embodiment of an 88th aspect, there is provided a method of a further embodiment of an 81st aspect, wherein the determining comprises comparing an eigenmode of the structure calculated after the occurrence of the earthquake with an eigenmode of the structure before the earthquake. According to a further embodiment of an 89th aspect, there is provided a method of a further embodiment of an 88th aspect, further comprising relating a change in the eigenmode to a change in a state of structural health of the structure.According to a 90th further embodiment, there is provided the method of any of the 81st to 89th further embodiments, wherein measuring the DFOS data comprises selecting a portion of an unlit or unused optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network.

[0057] According to a further embodiment of a 91st, a method is provided for generating a safety alert for a structure in the aftermath of an earthquake, the method comprising: measuring DFOS data at least during an earthquake; calculating a safety score for the structure based on the measured DFOS data; and generating a safety alert based on the safety score. According to a further embodiment of a 92nd, a method is provided for the 91st, wherein the safety score is based on a comparison of a peak ground acceleration calculated from the measured DFOS data and a peak ground acceleration rating of the structure. According to a further embodiment of a 93rd, a method is provided for the 91st, wherein the safety alert includes a representation of the calculated safety score. According to a further embodiment of a 94th, a method is provided for the 91st, wherein the safety alert is classified into a plurality of severity levels, and the generating is based on the severity level. According to a further embodiment of a 95th, a method is provided for the 94th, further comprising sending the generated safety alert to a recipient selected based on the severity level. According to a further embodiment of a 96th aspect, there is provided a method of a further embodiment of a 91st aspect, wherein the safety alert indicates whether the structure is safe for human occupants to enter. According to a further embodiment of a 97th aspect, there is provided a method of a further embodiment of a 91st aspect, wherein measuring the DFOS data includes transmitting light from a DFOS system to an optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of a 98th aspect, there is provided a method of a further embodiment of a 91st aspect, wherein measuring the DFOS data includes transmitting light from an optical communication device to an optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of a 99th aspect, there is provided a method of a further embodiment of a 98th aspect, further including storing the measured DFOS data in a storage device in response to detecting a physical change in the optical fiber.According to a 100th further embodiment, there is provided the method of any of the 91 to 99 further embodiments, wherein measuring the DFOS data comprises selecting a portion of an unlit or unused optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network.

[0058] According to a further embodiment of 101, there is provided a method of detecting damage to a structure, the method comprising: measuring DFOS data on an optical fiber in or near the structure; calculating a physical quantity representing at least one of a story displacement of the structure, a peak ground acceleration of a bottom or side of the structure, a peak ground acceleration of a component of the structure itself, and liquefaction based on the measured DFOS; comparing the calculated physical quantity to a specification of the structure; and generating an alert indicating potential damage to the structure based on the calculated physical quantity and the specification of the structure. According to a further embodiment of 102, there is provided a method of the further embodiment of 101, wherein measuring the DFOS data comprises transmitting light from a DFOS system to an optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of 102, there is provided a method of the further embodiment of 101, wherein measuring the DFOS data comprises transmitting light from an optical communication device to an optical fiber and receiving refracted light from the optical fiber. According to a further embodiment 104, there is provided the method of any of the further embodiments 102 to 103, wherein the optical fiber extends below the structure. According to a further embodiment 105, there is provided the method of any of the further embodiments 102 to 103, wherein the optical fiber extends through the structure. According to a further embodiment 106, there is provided the method of the further embodiment 105, wherein the optical fiber extends through multiple stories of the structure. According to a further embodiment 107, there is provided the method of the further embodiment 106, wherein the optical fiber wraps around a perimeter of a base of the structure. According to a further embodiment 108, there is provided the method of any of the further embodiments 101 to 107, wherein measuring the DFOS data includes selecting a portion of an unlit or unused optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network.

[0059] According to a further embodiment of 109, a method of detecting damage to an infrastructure is provided, the method comprising: measuring DFOS data on an optical fiber in or near the infrastructure; calculating a physical quantity representing at least one of a story displacement of a building, a peak ground acceleration at a bottom or side of the building, a peak ground acceleration of a component of the infrastructure itself, and liquefaction based on the measured DFOS; comparing the calculated physical quantity to a specification of the infrastructure; and generating an alert indicating potential infrastructure damage based on the calculated physical quantity and the specification of the infrastructure. According to a further embodiment of 110, the method of the further embodiment of 109 is provided, wherein measuring the DFOS data comprises transmitting light from a DFOS system to an optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of 111, the method of the further embodiment of 109 is provided, wherein measuring the DFOS data comprises transmitting light from an optical communication device to an optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of 112, the method of the further embodiment of 110 or 111 is provided. According to a further embodiment of 113, in which the optical fiber extends below the infrastructure, the method of the further embodiment of 110 or 111 is provided, in which the optical fiber extends through the infrastructure. According to a further embodiment of 114, the method of the further embodiment of 113 is provided, in which the optical fiber extends through a plurality of horizontal levels of the infrastructure. According to a further embodiment of 115, the method of the further embodiment of 113 is provided, in which the optical fiber wraps around a perimeter of a foundation of the infrastructure. According to a further embodiment of 116, the method of any one of the further embodiments of 109 to 115 is provided, in which the infrastructure includes at least one of a building, a bridge, a road, a monument, a street light, a construction site, a mine, an underground structure, a tunnel, a mass transit terminal, an airport, a train station, a factory, and a seaport.According to a 117th further embodiment, there is provided the method of any one of the 109th to 116th further embodiments, wherein measuring the DFOS data comprises selecting a portion of an unlit or unused optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network. According to a 118th further embodiment, there is provided a DFOS device comprising an optical transmitter configured to transmit light to the optical fiber, a receiver configured to receive light from the optical fiber, and a controller configured to perform the method defined in any of the 43rd to 117th further embodiments. According to a 119th further embodiment, there is provided a system for processing earthquake data comprising one or more DFOS devices according to the 118th further embodiment and one or more optical fibers operatively connected to the one or more DFOS devices. According to a 120th further embodiment, there is provided a method for detecting an occurrence of an earthquake comprising measuring DFOS data on an optical fiber located within a sensing distance of a seismic source of the earthquake and analyzing the DFOS data to detect that the earthquake has occurred. According to a further embodiment of a 121st aspect, there is provided a method of a further embodiment of a 120th aspect, further comprising connecting a DFOS device to the optical fiber, and measuring the DFOS data comprises transmitting light from the DFOS device to the optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of a 122nd aspect, there is provided a method of a further embodiment of a 120th aspect, further comprising transmitting light from an optical communication device to the optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of a 123rd aspect, there is provided a method of a further embodiment of a 120th aspect, further comprising calculating a magnitude of the earthquake from an analysis of the DFOS data. According to a further embodiment of a 124th aspect, there is provided a method of a further embodiment of a 120th aspect, further comprising measuring the DFOS data comprises measuring strain.According to a 125th further embodiment, there is provided the method of the 120th further embodiment, wherein measuring the DFOS data comprises measuring seismic motion. According to a 126th further embodiment, there is provided the method of any one of the 120th to 125th further embodiments, wherein measuring the DFOS data comprises selecting an unlit or unused portion of the optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network.

[0060] According to a further embodiment of a 127, there is provided a method of analyzing the effects of an earthquake by a DFOS system, the method comprising: capturing DFOS data with the DFOS system; storing the captured DFOS data; receiving an external notification from the DFOS system that the earthquake has occurred; and analyzing the stored DFOS data to quantify the effects of the earthquake. According to a further embodiment of a 128, there is provided the method of the further embodiment of a 127, wherein the capturing is continuous in time. According to a further embodiment of a 129, there is provided the method of any one of the further embodiments of a 127 to 128, wherein the storing includes overwriting previously stored DFOS data, with new DFOS data overwriting the oldest DFOS data. According to a further embodiment of a 130, there is provided the method of any one of the further embodiments of a 127 to 129, wherein the capturing includes emitting light into an optical fiber and receiving light from the optical fiber. According to a further embodiment of a 131, there is provided the method of any one of the further embodiments of a 127 to a 130, wherein receiving the notification comprises receiving a signal emitted from a seismometer. According to a further embodiment of a 132, there is provided the method of any one of the further embodiments of a 127 to a 131, wherein receiving the notification comprises receiving a signal from a wireless network. According to a further embodiment of a 133, there is provided the method of any one of the further embodiments of a 127 to a 132, wherein the signal is a processed output of a geophone. According to a further embodiment of a 134, there is provided the method of any one of the further embodiments of a 127 to a 133, wherein analyzing the stored DFOS data comprises calculating a peak Earth acceleration. According to a further embodiment of a 135, there is provided the method of any one of the further embodiments of a 127 to a 133, wherein analyzing the stored DFOS data comprises measuring a geodetic strain response in an area within a sensing distance of the optical fiber.

[0061] According to a further embodiment of item 136, there is provided a method for determining a peak ground acceleration at a first location, the method comprising: providing an optical fiber extending unidirectionally within a first distance from the first location for a second distance; calculating an apparent velocity of the ground where the optical fiber is horizontally located based on DFOS data; and differentiating the apparent velocity with respect to time to obtain an acceleration. According to a further embodiment of item 137, there is provided the method of the further embodiment of item 136, wherein the first distance is less than 100 meters and the second distance is greater than 100 meters.

[0062] According to a further embodiment of a 138th, there is provided a method of visually representing earthquake effects on a plurality of different locations within a geographical region, the method comprising: providing at least one optical fiber within a sensing distance of the geographical region; calculating a peak ground acceleration value for each of the plurality of different locations based on DFOS data; and overlaying the calculated peak ground acceleration values ​​on a map representing the plurality of locations. According to a further embodiment of a 139th, there is provided a method of a further embodiment of a 138th, wherein calculating the peak ground acceleration value comprises capturing DFOS data from the at least one optical fiber with a DFOS system; calculating an apparent velocity of the ground where the optical fiber is horizontally located based on the DFOS data; and differentiating the apparent velocity with respect to time to obtain an acceleration.

[0063] According to a further embodiment of a 140th aspect, there is provided a method for detecting the occurrence of an earthquake, comprising measuring DFOS data on an optical fiber located within a sensing distance of an epicenter of the earthquake, and analyzing the DFOS data to detect the occurrence of the earthquake. According to a further embodiment of a 141st aspect, there is provided a method of a further embodiment of a 140th aspect, further comprising connecting a DFOS device to the optical fiber, and measuring the DFOS data comprises transmitting light from the DFOS device to the optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of a 142nd aspect, there is provided a method of a further embodiment of a 140th aspect, further comprising transmitting light from an optical communication device to the optical fiber and receiving refracted light from the optical fiber. According to a further embodiment of a 143rd aspect, there is provided a method of a further embodiment of a 140th aspect, further comprising calculating a magnitude of the earthquake from an analysis of the DFOS data. According to a further embodiment of a 144th aspect, there is provided a method of a further embodiment of a 140th aspect, wherein measuring the DFOS data comprises measuring strain. According to a further embodiment of 145, there is provided the method of the further embodiment of 140, wherein measuring the DFOS data comprises measuring seismic motion. According to a further embodiment of 146, there is provided the method of any one of the further embodiments of 140 to 145, wherein measuring the DFOS data comprises selecting a portion of an unlit or unused optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network.

[0064] It is thus apparent that there has been provided, in accordance with the present disclosure, a distributed fiber optic sensing system, apparatus, and method. The present disclosure is susceptible to many alternatives, modifications, and variations. Features of the disclosed embodiments can be combined, rearranged, omitted, etc., within the scope of the invention to produce additional embodiments. Furthermore, certain features may be used to advantage without the concomitant use of other features. Accordingly, applicants intend to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present invention.

Claims

1. 1. A method for determining peak ground acceleration comprising the steps of: providing a DFOS device connected to at least one optical fiber; recording DFOS data with the DFOS instrument, the DFOS data including strain data along the at least one optical fiber; Transforming the strain data into complex Fourier coefficients; Scaling the complex Fourier coefficients; applying an inverse transform to the scaled Fourier coefficients; selecting a maximum value from an output of the inverse transformation to identify the maximum earth acceleration at a location along the at least one optical fiber; The method includes:

2. The method of claim 1 , wherein transforming the strain data into complex Fourier coefficients comprises applying a two-dimensional Fourier transform to the strain data.

3. The method of claim 1 , wherein applying the inverse transform comprises applying a two-dimensional inverse Fourier transform to the scaled Fourier coefficients. analysing the recorded DFOS data to obtain a quantitative measure of signal amplitude of the DFOS data; comparing the quantitative measure of the signal amplitude to a predetermined threshold; making a preliminary determination that an earthquake has occurred if the quantitative measurement value exceeds the predetermined threshold value; Quantifying the effects of earthquakes determining characteristics of seismic motion caused by said earthquake by The method of claim 1 further comprising:

5. The method of claim 4 , further comprising verifying that the earthquake has occurred after said predetermining and before said quantifying.

6. The method of claim 4 , wherein analyzing the recorded DFOS data includes measuring the signal amplitude within a passband of dominant frequencies of the earthquake.

7. Calculating a resonance peak of a structure based on the DFOS data, storing the calculated resonant peaks in a storage device that archives resonant peak values ​​associated with the structure; Retrieving archived resonance peak values ​​from said storage device; Detecting a change, represented by a change value, between the retrieved archive value and a resonant peak calculated based on the DFOS data; comparing the change value to a threshold value; generating an alert when the detected change exceeds the threshold. assessing the effect of earthquake motion on the structure by The method of claim 1 further comprising:

8. The method of claim 7 , wherein the method is repeated according to a schedule.

9. The method of claim 8 , wherein the duration of the schedule is adaptive and decreases in duration depending on the results of the comparison.

10. 8. The method of claim 7, further comprising accumulating the detected change values ​​over time to identify a cumulative change value representative of a change between a last calculated resonant peak and an oldest resonant peak value stored in the memory device.

11. The method of claim 7 , wherein the threshold is adaptive and decreases over time.

12. Receiving notification that an earthquake has occurred; In response to the received notification, using the DFOS data to calculate at least one of the following: seismic magnitude, moment, strain, strain rate, geodetic deformation, location, depth, focal mechanism, radiation pattern, moment tensor, finite fault area of ​​slip, slip velocity, and rupture velocity of the occurring earthquake; The method of claim 1 further comprising:

13. generating an alert from the DFOS system based on said calculating; transmitting said generated alert to a receiver in a populated area; The method of claim 12 further comprising:

14. The method of claim 12 , wherein the calculating represents a physical effect at a second location or a physical effect at a third location located between the first location and the second location.

15. 15. The method of any one of claims 1 to 14, wherein measuring the DFOS data comprises selecting a portion of an unlit or unused optical spectrum from an otherwise lit optical fiber, or selecting a polarization eigenmode from an otherwise lit optical fiber, or selecting an entire dark fiber from an established dedicated telecommunications network. Using the DFOS data to calculate at least one of a direction of seismic motion during an earthquake and a duration of the seismic motion during the earthquake. Quantifying the impact of the earthquake by The method of claim 1 further comprising:

17. Calculating resonance values ​​of natural modes of a structure from the DFOS data; determining a quantity representative of the strength of vibration of the structure from said natural modes; analyzing the effect of an earthquake on the structure by The method of claim 1 further comprising:

18. The method of claim 17 , wherein the determining comprises comparing eigenmodes of the structure calculated after the earthquake occurs with eigenmodes before the earthquake.

19. The method of claim 18 , further comprising relating changes in the natural modes to changes in a state of structural health of the building.

20. Calculating a safety score for the structure based on the DFOS data; generating a safety alert based on said safety score; generating a safety alert for said structure in the aftermath of an earthquake by The method of claim 1 further comprising:

21. 21. The method of claim 20, wherein the safety score is based on a comparison of the peak ground acceleration calculated from the DFOS data to a peak ground acceleration rating of the structure.

22. Calculating physical quantities representing at least one of the following based on the DFOS data: a story displacement of a structure, a peak ground acceleration at a lower or side portion of the structure, a peak ground acceleration of a component of the infrastructure itself, and liquefaction; Comparing the calculated physical quantities to a specification of the infrastructure; generating an alert indicating potential infrastructure damage based on the calculated physical quantities and the infrastructure specifications; Detecting damage to said infrastructure by The method of claim 1 further comprising:

23. Calculating a maximum ground acceleration value for each of a plurality of different locations based on the DFOS data; overlaying the calculated peak ground acceleration values ​​onto a map representative of the plurality of different locations. a visual representation of the earthquake effects on said plurality of different locations within a geographic region by The method of claim 1 further comprising:

Images