Seabed earthquake positioning method before seismic wave by using linear communication submarine cable
By utilizing submarine communication optical cables and distributed acoustic sensing technology, seismic wavefront information on the submarine cables was extracted, solving the problem of insufficient coverage density of submarine seismographs, achieving high-precision submarine earthquake positioning, reducing costs, and expanding the monitoring range.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUN YAT SEN UNIV
- Filing Date
- 2025-11-28
- Publication Date
- 2026-05-12
AI Technical Summary
The existing seabed seismometers have insufficient coverage density, resulting in insufficient accuracy in locating seabed earthquakes. Furthermore, the real-time data transmission and high costs limit the large-scale application of the monitoring network.
By utilizing existing submarine communication optical cables and distributed acoustic sensing technology, differential equations are constructed by acquiring the spatial-time-strain rate map and S-wave velocity model of the submarine cables. Seismic wavefront information is then extracted using the PhaseNet-DAS neural network to achieve submarine earthquake location.
It has improved the accuracy of submarine earthquake location to the level of 0.01° on Earth coordinates, reduced costs, expanded the monitoring range, and solved the long-standing problem of a lack of marine earthquake data.
Smart Images
Figure CN122018006A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of submarine earthquake location technology, and more specifically, to a method for submarine earthquake location using seismic wavefronts via a straight-line communication submarine cable. Background Technology
[0002] Currently, high-precision monitoring of submarine seismic activity, especially earthquake swarms with clustered seismic activity, mainly relies on high-precision array systems deployed on the seabed, with the core equipment being seabed seismometers. This technology aims to capture key phases such as P-waves and S-waves generated by earthquakes to accurately invert core parameters such as the spatial location of the seismic source, the depth of origin, and the fault rupture mechanism, thereby providing crucial data support for earthquake mechanism research, tsunami warning, and exploration of marine geological structures.
[0003] However, despite the maturity of the technology in principle, its large-scale application and operational use face a series of severe challenges brought about by the complex marine environment: ① Equipment deployment and survivability challenges: The deployment and retrieval of seabed seismometers heavily rely on expensive research vessels. In harsh sea conditions, the accurate deployment and long-term stability of the equipment face significant challenges. Complex seabed topography, strong ocean currents, marine organism attachment, and bottom sediment migration can all lead to equipment displacement, capsizing, or even damage, significantly reducing the reliability of data acquisition. ② Technical bottlenecks in real-time data transmission: Most existing seabed seismometers adopt a "self-contained" working mode, meaning that data is collected and stored internally, then retrieved and downloaded after the mission cycle. This method results in a severe lag in seismic data acquisition, failing to meet the urgent real-time requirements of applications such as tsunami warnings. Although real-time transmission systems based on submarine optical cables exist, their construction and maintenance costs are astronomical, and their high technical complexity makes large-scale deployment difficult, creating a huge gap between monitoring capabilities and real-time requirements. ③ High lifecycle costs: From equipment research and development, offshore deployment, to long-term operation and maintenance and data retrieval, the entire technology chain is extremely expensive. This directly limits the number of stations that can be put into use, resulting in a limited coverage area of the monitoring network and a much lower array spacing (i.e., coverage density) than terrestrial networks, further leading to insufficient positioning accuracy for submarine earthquakes. Summary of the Invention
[0004] This invention provides a seabed earthquake location method using seismic wavefronts of straight-line communication submarine cables, which solves the problems of insufficient coverage density of seabed seismographs (OBS) in the prior art, which prevents the acquisition of a large amount of effective seabed seismic data, and the problem of insufficient seabed earthquake location accuracy caused by the inability of a single submarine cable to obtain accurate S-wave travel time difference.
[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: This invention provides a method for locating seabed earthquakes using seismic wavefronts via a straight-line communication submarine cable, comprising the following steps: Before the earthquake, the geographic coordinates and S-wave velocity model of each receiving channel of the submarine cable were obtained; after the earthquake, the space-time-strain rate map of the submarine cable was obtained. The first seismic wave is obtained based on the space-time-strain rate diagram. Based on the first seismic wave, the wavefront information of the earthquake on the submarine cable is obtained; Based on the S-wave velocity model, a differential equation representing the relationship between the distance along the optical cable and the component of the seismic wave propagation velocity along the fiber direction is constructed using the linear wavefront method. Based on the differential equation and wavefront information, the positional relationship between the epicenter and the reference point of the submarine cable is obtained, where the reference point of the submarine cable is the endpoint of the submarine cable. The coordinates of the epicenter are obtained based on the geographical coordinates of each receiving channel of the submarine cable and the positional relationship between the epicenter and the reference point of the submarine cable.
[0006] Furthermore, based on the AK135 model, the S-wave velocity model of the study area near the submarine cable was obtained.
[0007] Furthermore, based on the first seismic wave, the wavefront information of the earthquake on the submarine cable is obtained, including: Density analysis was performed on the power spectrum of the first seismic wave before and during seismic wave reception to obtain the signal enhancement frequency band when the seismic wave arrived. Based on the signal enhancement frequency band, the first seismic wave is bandpass filtered to obtain the second seismic wave; Phase travel time extraction was performed on the second seismic wave to obtain the wavefront information of the earthquake on the submarine cable.
[0008] Furthermore, the phase travel time of the second seismic wave is extracted to obtain the wavefront information of the earthquake on the submarine cable, including: The second seismic wave is input into the PhaseNet-DAS neural network to obtain the wavefront information of the earthquake on the submarine cable.
[0009] Furthermore, based on the aforementioned S-wave velocity model, a differential equation representing the relationship between the distance along the optical cable and the component of the seismic wave propagation velocity along the fiber direction is constructed using the linear wavefront method, including: The formula for calculating the component of seismic wave propagation velocity along the fiber direction is:
[0010] In the formula, This represents the component of the seismic wave propagation velocity along the fiber optic direction; This represents the S-wave velocity model, and represents the actual propagation velocity of the seismic wave. The azimuth angle between the position of a virtual sensor element on the submarine cable and the direction of seismic wave propagation is represented by tan. θ= ( x+L ) / D,L This represents the horizontal distance from the epicenter to the submarine cable reference point. D This indicates the vertical distance from the epicenter to the submarine cable reference point; Will To determine the distance along the fiber optic cable Taking the second derivative, we obtain the differential equation: .
[0011] Furthermore, based on the aforementioned differential equation and wavefront information, the positional relationship between the epicenter and the submarine cable reference point is obtained, including: Solving the differential equation yields the first expression; Integrating the first expression with respect to time yields the second expression; Based on the wavefront information and the second expression, the positional relationship between the epicenter and the submarine cable reference point is obtained.
[0012] Furthermore, the first expression is:
[0013] In the formula, Represents a constant.
[0014] Furthermore, the second expression is:
[0015] In the formula, Indicates the distance along the optical cable The arrival time of the received seismic signal is given by the wavefront information. This indicates the arrival time of the seismic signal received by the submarine cable reference point.
[0016] Furthermore, based on the geographical coordinates of each receiving channel of the submarine cable and the positional relationship between the epicenter and the reference point of the submarine cable, the coordinates of the epicenter are obtained, including: according to and the calculated D and L The difference in latitude and longitude between the epicenter location and the reference point of the submarine cable is obtained. The coordinates of the epicenter are obtained based on the latitude and longitude of the submarine cable reference point and the difference in latitude and longitude between the epicenter and the submarine cable reference point.
[0017] Furthermore, based on the latitude and longitude of the submarine cable reference point and the difference in latitude and longitude between the epicenter and the submarine cable reference point, the coordinates of the epicenter are obtained, including: The coordinates of the epicenter are obtained by adding the latitude and longitude difference between the reference point and the reference point to the reference point.
[0018] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: This invention proposes a seabed seismic location method utilizing the wavefront of seismic waves from a straight-line communication submarine cable. By combining existing submarine communication optical cables with distributed acoustic sensing technology, it solves the problem of insufficient OBS coverage in the ocean, which leads to inadequate seabed seismic location accuracy, thus improving the accuracy of seabed seismic location. The final positioning accuracy reaches the level of 0.01° in Earth coordinates. Furthermore, since OBS is difficult to deploy and has high operating costs in the ocean, this invention only requires existing submarine optical cables for positioning, making it more cost-effective and feasible than traditional large-scale OBS deployment. Finally, this solution helps to address the long-standing problem of missing data from marine seismic networks, providing a new observation technology for marine geological development and tomographic imaging. Attached Figure Description
[0019] Figure 1 A flowchart illustrating a seabed seismic location method using seismic wavefronts via a straight-line communication submarine cable, provided in an embodiment of the present invention; Figure 2 A schematic diagram of a theoretical model for seismic wavefront positioning of a straight-line communication submarine cable provided in an embodiment of the present invention; Figure 3 A schematic diagram showing the location of the earthquake and the location of the submarine cable as provided in an embodiment of the present invention; Figure 4 A schematic diagram showing the specific location of the submarine cable and the location of the reference point provided in an embodiment of the present invention; Figure 5 A waterfall diagram of the received seismic signal after filtering, provided in an embodiment of the present invention; Figure 6 Linear fitting of the extracted seismic S-wave front information provided in the embodiments of the present invention. Detailed Implementation
[0020] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent. To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.
[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.
[0022] The first embodiment of the present invention provides a method for locating seabed earthquakes using seismic wavefronts via a straight-line communication submarine cable, such as... Figure 1 As shown, it includes the following steps: Before the earthquake, the geographic coordinates and S-wave velocity model of each receiving channel of the submarine cable were obtained; after the earthquake, the space-time-strain rate map of the submarine cable was obtained. The first seismic wave is obtained based on the space-time-strain rate diagram. Based on the first seismic wave, the wavefront information of the earthquake on the submarine cable is obtained; Based on the S-wave velocity model, a differential equation representing the relationship between the distance along the optical cable and the component of the seismic wave propagation velocity along the fiber direction is constructed using the linear wavefront method. Based on the differential equation and wavefront information, the positional relationship between the epicenter and the reference point of the submarine cable is obtained, where the reference point of the submarine cable is the endpoint of the submarine cable. The coordinates of the epicenter are obtained based on the geographical coordinates of each receiving channel of the submarine cable and the positional relationship between the epicenter and the reference point of the submarine cable.
[0023] In a further embodiment, the S-wave velocity model of the study area near the submarine cable is obtained based on the AK135 model.
[0024] In a further embodiment, based on the first seismic wave, wavefront information of the earthquake on the submarine cable is obtained, including: Density analysis was performed on the power spectrum of the first seismic wave before and during seismic wave reception to obtain the signal enhancement frequency band when the seismic wave arrived. Based on the signal enhancement frequency band, the first seismic wave is bandpass filtered to obtain the second seismic wave; Phase travel time extraction of the second seismic wave yields the wavefront information of the earthquake along the submarine cable, i.e., the distance along the optical cable. And seismic waves to Arrival time at the location .
[0025] In a further embodiment, the second seismic wave is subjected to phase travel time extraction to obtain the wavefront information of the earthquake on the submarine cable, including: The second seismic wave is input into the PhaseNet-DAS neural network to obtain the wavefront information of the earthquake on the submarine cable.
[0026] The second embodiment of the present invention, based on the first embodiment and the S-wave velocity model, uses the linear wavefront method to construct a differential equation representing the relationship between the distance along the optical cable and the component of the seismic wave propagation velocity along the optical fiber direction, including: Earthquake location is achieved using the linear wavefront method, simplifying the entire earthquake propagation process to... Figure 2 The model shown. (As shown in the image) Figure 2 As shown in the figure D This represents the vertical distance from the epicenter to the fiber optic reference point. L The distance from the epicenter to the reference point of the submarine cable is denoted as . Based on the shorter arrival times of seismic waves at both ends of the cable, the end with the shorter arrival time can be used as the reference point. The dashed line represents the seismic wave emitted from the epicenter, and the arrow indicates the component of the earthquake propagation velocity along the fiber optic direction. The formula relating this component to the actual seismic wave propagation velocity is:
[0027] In the formula, This represents the component of the seismic wave propagation velocity along the fiber optic direction; This represents the S-wave velocity model, and represents the actual propagation velocity of the seismic wave. The azimuth angle between the position of a virtual sensor element on the submarine cable and the direction of seismic wave propagation is represented by tan. θ= ( x+L ) / D,L This represents the horizontal distance from the epicenter to the submarine cable reference point. D This represents the vertical distance from the epicenter to the reference point of the submarine cable, which is the shortest endpoint when the seismic wave arrives. Applying the above formula to the distance along the optical cable Differentiate, since It is a function of spatial location, at different locations on the optical cable. Affected by azimuth angle, It is also a function of space, which can be written as tan θ= ( x+ L ) / D For scenarios where the fiber optic cable length is much shorter than R1 and R2 (the distance from the earthquake source to both ends of the straight-line communication submarine cable), it can make... θ = θ 1≈ θ 2. After differentiation, we obtain the first-order derivative formula:
[0028] By transforming the first-order derivative formula, we obtain the following equation:
[0029] Taking the derivative of the above with respect to distance, we obtain the second derivative of velocity with respect to distance, resulting in the following equation:
[0030] Substituting the first-order derivative formula into the above, we obtain the differential equation:
[0031] In a further embodiment, based on the differential equation and wavefront information, the positional relationship between the epicenter and the submarine cable reference point is obtained, including: Solving the differential equation yields the first expression; Integrating the first expression with respect to time yields the second expression; Based on the wavefront information and the second expression, the positional relationship between the epicenter and the submarine cable reference point is obtained.
[0032] In a further embodiment, the differential equation can be viewed as a second-order ordinary differential equation. By solving this ordinary differential equation, the first expression is obtained as follows:
[0033] In the formula, Represents a constant.
[0034] In a further embodiment, it can be seen that the first expression is a representation about and The equation, but actually Solving this equation is not easy, so we need to integrate the first expression with respect to time to obtain a solution with respect to time. The second expression of the equation is:
[0035] In the formula, Indicates the distance along the optical cable The arrival time of the received seismic signal is given by the wavefront information. This indicates the arrival time of the seismic signal received at the submarine cable reference point. As can be seen from the above formula, D and L This reflects information about the location of the epicenter. This indicates the arrival time (time of arrival) of the seismic signal received by the first virtual sensor element (fiber optic reference point). and It is the wavefront information of the seismic signals received by the entire submarine optical cable (i.e., the arrival time of the seismic signals received at different locations on the optical cable).
[0036] In a further embodiment, the coordinates of the epicenter are obtained based on the geographical coordinates of each receiving channel of the submarine cable and the positional relationship between the epicenter and the reference point of the submarine cable, including: according to and the calculated D andL The difference in latitude and longitude between the epicenter location and the reference point of the submarine cable is obtained. The coordinates of the epicenter are obtained based on the latitude and longitude of the submarine cable reference point and the difference in latitude and longitude between the epicenter and the submarine cable reference point.
[0037] In a further embodiment, the coordinates of the epicenter are obtained based on the latitude and longitude of the submarine cable reference point and the difference in latitude and longitude between the epicenter and the submarine cable reference point, including: The coordinates of the epicenter are obtained by adding the latitude and longitude difference between the reference point and the reference point to the reference point.
[0038] The earthquake location method of this embodiment can achieve the following objectives: (1) High positioning accuracy: the positioning accuracy of a single submarine cable reaches the level of 0.01° in Earth coordinates; (2) It has a wide monitoring range, and submarine cable network positioning can locate earthquakes in areas not covered by OBS; (3) Low implementation cost, positioning can be achieved using only existing communication submarine cables, without the need for a large number of submarine seismographs; (4) It helps to solve the long-standing problem of lack of marine earthquake data.
[0039] The third embodiment of the present invention uses the Changqin Island submarine cable to locate an earthquake that occurred on March 13, 2022 (UTC: 2022_0313_18:28:47) in the waters off Huidong, Guangdong Province, with an initial location of (22.51°N, 115.04°E). The earthquake location and the submarine cable location are as follows: Figure 3 The specific location of the submarine cable is shown by the red dot and red line. Figure 4 As shown by the solid yellow line, the specific positioning steps can be as follows: 1. First, observe the strain rate changing over time using the space-time-strain rate map generated on the Changqin Island submarine cable to identify earthquakes; 2. Based on previous deployment plans, a straight section of the submarine cable within a nautical mile radius was selected for study, namely... Figure 4 The solid yellow line segment; 3. Select the second endpoint of the submarine cable as the reference point, i.e. Figure 4 As shown by the black pentagram in the middle, the reference point coordinates are (22.167°N, 113.789°E); 4. Power spectral density analysis was performed on the data collected by the Changqin Island submarine cable before and during the earthquake. The results showed that the signal in the 2Hz-10Hz frequency band on the Changqin Island submarine cable was enhanced during the earthquake. 5. Based on the enhanced signal frequency band received by the submarine cable during earthquakes obtained in step 4, filtering the seismic data collected by the Xiamen submarine cable from 2Hz to 10Hz yields a clearer seismic waveform, which can then be saved as a file. The filtered waterfall plot is shown below. Figure 5 As shown; 6. Based on the relatively clear seismic waveform file of the Changqin Island submarine cable obtained in step 5, the phase travel time of P-wave and S-wave is extracted using the PhaseNet-DAS neural network model, and the phase travel time is saved as a wavefront information file. The first column of the file is the length of the submarine cable, and the wavefront arrival time along the length of the submarine cable is saved as the second column. 7. Perform linear fitting on the S-wavefront information file obtained in step 6. The fitted straight line is as follows: Figure 6 As shown by the red line, the fitted line expression is: t = -0.2118x + 40.332, R² = 0.997; 8. Save the obtained fitted line information to a file, and then solve it according to the equation in the second expression. D and L The values are 35km and 132km respectively; 9. Based on the results obtained in step 8 D and L The value, expressed by the formula r=(L 2 +D 2 ) 1 / 2 The epicenter distance of this earthquake was obtained r =136km; 10. Based on the results obtained in step 8 D and L The value, according to the formula tan θ= ( x+L ) / D The offset angle θ = 0.375° of this earthquake relative to the axial direction of the submarine cable reference point was obtained. 11. Based on the epicentral distance and reference point position obtained in step 10, draw a circle with the reference point as the center and the epicentral distance as the radius, with the hypocenter on the circle; 12. Based on the offset angle relative to the optical cable axis obtained in step 10 θ The location of this earthquake was determined to be (24.405°N, 121.9°E), with an error of (±0.0277°N, ±0.0179°E) compared to the initial location provided by the authorities.
[0040] The same or similar labels correspond to the same or similar parts; The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.
Claims
1. A method for locating seabed earthquakes using seismic wavefronts via a straight-line communication submarine cable, characterized in that, Includes the following steps: Before the earthquake, the geographic coordinates and S-wave velocity model of each receiving channel of the submarine cable were obtained; after the earthquake, the space-time-strain rate map of the submarine cable was obtained. The first seismic wave is obtained based on the space-time-strain rate diagram. Based on the first seismic wave, the wavefront information of the earthquake on the submarine cable is obtained; Based on the S-wave velocity model, a differential equation representing the relationship between the distance along the optical cable and the component of the seismic wave propagation velocity along the fiber direction is constructed using the linear wavefront method. Based on the differential equation and wavefront information, the positional relationship between the epicenter and the reference point of the submarine cable is obtained, where the reference point of the submarine cable is the endpoint of the submarine cable. The coordinates of the epicenter are obtained based on the geographical coordinates of each receiving channel of the submarine cable and the positional relationship between the epicenter and the reference point of the submarine cable.
2. The seabed seismic location method using seismic wavefronts via a straight-line communication submarine cable according to claim 1, characterized in that, The S-wave velocity model of the study area near the submarine cable was obtained based on the AK135 model.
3. The seabed seismic location method using seismic wavefronts of a straight-line communication submarine cable according to claim 1, characterized in that, Based on the first seismic wave, the wavefront information of the earthquake on the submarine cable is obtained, including: Density analysis was performed on the power spectrum of the first seismic wave before and during seismic wave reception to obtain the signal enhancement frequency band when the seismic wave arrived. Based on the signal enhancement frequency band, the first seismic wave is bandpass filtered to obtain the second seismic wave; Phase travel time extraction was performed on the second seismic wave to obtain the wavefront information of the earthquake on the submarine cable.
4. The seabed seismic location method using seismic wavefronts via a straight-line communication submarine cable according to claim 3, characterized in that, Phase travel time extraction of the second seismic wave yielded wavefront information of the earthquake on the submarine cable, including: The second seismic wave is input into the PhaseNet-DAS neural network to obtain the wavefront information of the earthquake on the submarine cable.
5. The seabed seismic location method using seismic wavefronts of a straight-line communication submarine cable according to claim 4, characterized in that, Based on the S-wave velocity model, a differential equation representing the relationship between the distance along the optical cable and the component of the seismic wave propagation velocity along the fiber direction is constructed using the linear wavefront method, including: The formula for calculating the component of seismic wave propagation velocity along the fiber direction is: In the formula, This represents the component of the seismic wave propagation velocity along the fiber optic direction; This represents the S-wave velocity model, and represents the actual propagation velocity of the seismic wave. The azimuth angle between the position of a virtual sensor element on the submarine cable and the direction of seismic wave propagation is represented by tan. θ= ( x+L ) / D,L This represents the horizontal distance from the epicenter to the submarine cable reference point. D This indicates the vertical distance from the epicenter to the submarine cable reference point; Will To determine the distance along the fiber optic cable Taking the second derivative, we obtain the differential equation: 。 6. The seabed seismic location method using seismic wavefronts of a straight-line communication submarine cable according to claim 5, characterized in that, Based on the differential equation and wavefront information, the positional relationship between the epicenter and the submarine cable reference point is obtained, including: Solving the differential equation yields the first expression; Integrating the first expression with respect to time yields the second expression; Based on the wavefront information and the second expression, the positional relationship between the epicenter and the submarine cable reference point is obtained.
7. The seabed seismic location method using seismic wavefronts of a straight-line communication submarine cable according to claim 6, characterized in that, The first expression is: In the formula, Represents a constant.
8. The seabed seismic location method using seismic wavefronts of a straight-line communication submarine cable according to claim 7, characterized in that, The second expression is: In the formula, Indicates the distance along the optical cable The arrival time of the received seismic signal is given by the wavefront information. This indicates the arrival time of the seismic signal received by the submarine cable reference point.
9. The submarine seismic location method using seismic wavefronts of a straight-line communication submarine cable according to any one of claims 5-8, characterized in that, Based on the geographical coordinates of each receiving channel of the submarine cable and the positional relationship between the epicenter and the reference point of the submarine cable, the coordinates of the epicenter are obtained, including: according to and the calculated D and L The difference in latitude and longitude between the epicenter location and the reference point of the submarine cable is obtained. The coordinates of the epicenter are obtained based on the latitude and longitude of the submarine cable reference point and the difference in latitude and longitude between the epicenter and the submarine cable reference point.
10. The seabed seismic location method using seismic wavefronts of a straight-line communication submarine cable according to claim 9, characterized in that, The coordinates of the epicenter are obtained based on the latitude and longitude of the submarine cable reference point and the difference in latitude and longitude between the epicenter and the submarine cable reference point, including: The coordinates of the epicenter are obtained by adding the latitude and longitude difference between the reference point and the reference point.