Alternating electromagnetic field earthquake monitoring observation station network

Abstract

The invention discloses an alternating electromagnetic field earthquake monitoring observation station network, which comprises an alternating electromagnetic observation station network which is used for receiving electromagnetic field signals of a high-power artificial source and a natural source and is composed of a plurality of receiving stations, and the electromagnetic field signals of the artificial source and the natural source are received through a plurality of observation stations which are arranged based on an earthquake distribution trend. Processing observation data, including spectral analysis on an observed electromagnetic field time sequence, to obtain a frequency spectrum and an auto-power spectrum of each electromagnetic field component and a cross-power spectrum among different components, and further calculating parameters such as impedance reflecting underground electrical properties, apparent resistivity and impedance phase; the method comprises the following steps of: performing inversion on apparent resistivity, impedance phase and the like of different frequencies to obtain electrical structure parameters of different underground depths. The method observes and utilizes signals of an alternating electromagnetic field wide frequency range most sensitive to earthquakes; an observation station network is arranged in an earthquake active area, a key defensive area and the like to carry out long-term continuous observation so as to realize comprehensive three-dimensional monitoring of an earthquake.

Description

Technical Field

[0001] The present invention relates to the technical field of seismic monitoring, and particularly to an alternating electromagnetic field seismic monitoring network that simultaneously receives artificial sources and natural sources. Background Art

[0002] China is located in two major earthquake zones globally, with high seismic activity frequency, large intensity, shallow focal depth, and wide distribution. In seismic monitoring and prediction, the magnetotelluric method is an important geophysical method. Methods for seismic monitoring include direct current resistivity sounding monitoring, geomagnetic field monitoring, and geoelectric field monitoring, etc.

[0003] Although there is no network for seismic monitoring using alternating electromagnetic fields yet, through mobile observations or temporary single-point observations, etc., a large number of abnormal phenomena have been discovered in the frequency band of alternating electromagnetic fields. Existing monitoring methods include the direct current resistivity sounding method, geomagnetic field observation method, and geoelectric field method. Among them, the direct current resistivity sounding method draws on the electrical sounding method for ore deposit exploration. It sends direct current into the ground through electrodes at both ends of AB, measures the voltage value through MN, and obtains the resistivity of the ground using the observation device coefficient. By studying the change of resistivity over time, seismic monitoring and prediction are carried out. The disadvantages of the direct current resistivity sounding method are: (1) Due to being shielded by high-resistance layers underground, the exploration depth is shallow, and the underground structure it reflects is only a few hundred meters deep, unable to reach the depth of more than 10 kilometers of most shallow-focus earthquakes; (2) It can only monitor the change of underground resistivity and cannot monitor the change of spatial electromagnetic fields; (3) The observed is a direct current constant field and cannot observe the alternating field; (4) It is often affected by non-seismic factors such as seasonal changes, weather changes, and grounding metal facilities in the site.

[0004] Geomagnetic field observation uses traditional geomagnetic observation methods, and dozens of observation stations have also been set up across the country. Geomagnetic observation is divided into two categories. One is to observe the basic field, that is, to observe the absolute magnetic field of the earth, mainly for the study of the global geomagnetic field. The other is to use fluxgate instruments to observe the changing magnetic field, but the frequency range is low, and the highest sampling rate is 1 Hz or 60 seconds. By observing the change of the geomagnetic field over time, seismic abnormal phenomena are studied. The disadvantages are: (1) The observed absolute field or very low-frequency magnetic field does not include the alternating electromagnetic field in the frequency band above 1 Hz where many seismic abnormal phenomena occur; (2) There is little analysis of the alternating field component and its spectrum changing over time in geomagnetic observation, and it mainly reflects the magnetic field above the ground and is not sensitive to the underground electrical properties and their changes; (3) Since the electric field is not observed synchronously, the impedance or resistivity of the underground and its changes cannot be monitored; (4) Since the magnetic field signal mainly comes from the magnetosphere and ionosphere above the earth, the random change characteristics are obvious, and due to being often affected by other interferences, it masks the identification of the anomalies caused by seismic activities.

[0005] The seismic station has built the geoelectric field method, which observes the natural electric field or voltage between two electrodes at a certain distance. Its observation device is similar to the Figure 1 MN measurement device. The measured signal is a natural source field, mainly the earth-induced electric field generated by magnetic field changes, which is different from the artificial source signal observed by the DC resistivity method. The highest sampling rate of the observed signal is 1 Hz. Minute values are usually used in geoelectric field stations in China, and the effective signal frequency band range is below 1 Hz. By studying the change of the observed electric field over time, earthquake prediction and monitoring are studied. The defects are as follows: (1) It is difficult to detect short-term earthquake anomalies of alternating electromagnetic fields above 1 Hz by observing the electric field with a very low frequency; (2) Since only the electric field is observed, it is impossible to determine whether the observed signal is generated by the observation system itself or caused by the change of the external field; (3) The observed electric field is greatly affected by the earth's surface, the vicinity of the observation point, and the electromagnetic field sources above the ground, and is not sensitive enough to the underground electrical changes; (4) The observed electric field has strong randomness and is easily interfered, which affects the identification of earthquake anomaly phenomena.

[0006] Using a single station or a small number of stations, semi-continuous or mobile magnetotelluric observations are carried out. This method observes the natural source electromagnetic fields of 5 (2 horizontal electric fields and 2 horizontal magnetic field components that are mutually orthogonal, and 1 vertical magnetic field component) or 4 electromagnetic field components (observing 2 mutually orthogonal horizontal electric fields and 2 horizontal magnetic field components). By analyzing the frequency spectrum of the alternating electromagnetic field, the frequency spectrum of the electromagnetic field is obtained, and then the impedance and apparent resistivity that reflect the underground electrical properties are obtained. The main purpose is to observe the underground resistivity changes in the area where the station is located and study the earthquake anomaly phenomena that may be caused by earthquakes. The defects of single-point magnetotelluric mobile observations are as follows: (1) These stations are mobile observation points and are repeatedly observed within a certain period of time without continuous observation. There are very few observation points, generally only one or two measurement points; (2) Only natural source signals are observed, and it is easily affected by electromagnetic field interference caused by human activities, which is not conducive to the identification of anomalies that may be related to earthquakes; (3) Only the changes of typical parameters such as underground resistivity are studied, and the changes of electromagnetic fields from space and underground are not concerned. Therefore, an alternating electromagnetic field earthquake monitoring observation network is needed. Summary of the Invention

[0007] The purpose of the present invention is to provide an alternating electromagnetic field earthquake monitoring observation network based on the simultaneous observation of artificial sources and natural sources, which simultaneously monitors the electric and magnetic fields of natural sources and artificial sources and the continuous changes of underground structures over time, and obtains earthquake precursors and related electromagnetic information.

[0008] To achieve the above purpose, the present invention is implemented according to the following technical solutions:

[0009] In the first aspect of the present invention, a seismic monitoring observation network for simultaneously receiving artificial source and natural source alternating electromagnetic fields is provided, including multiple stations for receiving high-power artificial source electromagnetic fields and natural source electromagnetic signals. The underground resistivity anomaly and electromagnetic field anomaly in the seismic source area are processed through the observation data of multiple stations arranged based on the seismic distribution trend to obtain electromagnetic anomaly information beneficial to earthquake prediction, including the following steps:

[0010] By performing spectral analysis on the observed electromagnetic field time series, the frequency spectrum and auto-power spectrum of each electromagnetic field component, as well as the cross-power spectrum of different components, can be obtained, and the impedance reflecting the underground electrical properties, as well as the apparent resistivity and impedance phase parameters, are calculated;

[0011] Invert the apparent resistivity, etc., to obtain the electrical structure parameters of the underground, and determine the alternating electromagnetic field earthquake through the abnormal change of the parameters of the underground electrical structure;

[0012] The formula for calculating the impedance from the frequency spectrum of each component of the electromagnetic field is as follows:

[0013] Ex = Zxx Hx + ZxyHy

[0014] Ey = Zyx Hx + ZyyHy

[0015] Hz = A Hx + B Hy

[0016] In the formula, Zxx, Zxy, Zyx, Zyy are impedance tensor elements, and A and B are magnetic field transfer functions;

[0017] The apparent resistivity and impedance phase can be calculated from the impedance tensor elements by the following formula:

[0018] ρ ij = 0.2T|Z ij | 2

[0019] φ ij = arctan(Z ij )

[0020] Among them, ρ ij represents the apparent resistivity, φ ij represents the impedance phase, and the subscript ij represents x or y.

[0021] Through the apparent resistivity and impedance phase, the underground electrical structure information of the observation station can be qualitatively analyzed and the resistivity structure of the underground can be quantitatively inverted.

[0022] Furthermore, the observed quantities include the north-south electric field Ex component, the magnetic field component Hx component, the east-west electric field Ey component, the magnetic field component Hy component, and the vertical magnetic field component Hz component.

[0023] For the measurement of electric field components, cables are used to connect the instrument and the grounding electrodes that are 25 - 50 meters apart to collect electric field signals, and for the magnetic field, an inductive magnetic probe is used to receive magnetic field signals.

[0024] Furthermore, the station equipment adopts 10 - channel observations, among which 5 channels are used for continuous 24 - hour observations of the natural field at low frequencies, and the other 5 channels are used for segmented observations of artificial sources in different frequency bands and for high - and medium - frequency natural sources during non - artificial source observation periods.

[0025] To ensure the rapid transmission of observation data, electromagnetic field signals are received at different sampling rates in different time periods. For artificial source data, signals are emitted at fixed time periods in the morning and evening, and the receiver uses different sampling rates to receive artificial source emission signals of different frequencies; for the low - frequency natural source signals, the receiver continuously observes for 24 hours at a lower sampling rate. For the high - and medium - frequency natural source signals, during the non - artificial source signal emission period, they are received once every 10 minutes, and at least 4 segments of 4096 data samples are collected respectively to ensure the uniform distribution of high - and medium - frequency data throughout the day.

[0026] Furthermore, the effective frequency range of the natural source electromagnetic field observed by the network covers 0.001 - 1000 Hz, and the effective frequency range of the artificial source electromagnetic field is 0.1 - 300 Hz.

[0027] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0028] The present invention observes and utilizes the signals in the frequency range of the alternating electromagnetic field that is most sensitive to earthquakes. By deploying an observation network in earthquake - active areas and key defense areas for long - term continuous observation, it can observe both natural source electromagnetic field signals and artificial source electromagnetic field signals, and can observe both the underground electrical structure and its changes, as well as the spatial electromagnetic field and its changes, so as to achieve comprehensive three - dimensional monitoring of earthquakes.

[0029] The present invention can carry out the comparison of ground - based observation and satellite - based observation data and their anomalies, and can also utilize satellite - based observation of the electromagnetic field signals artificially emitted on the ground; it can also be used for the observation and research of underground resources and deep - crustal structures; it is beneficial to study the mechanism of the full - space seismic electromagnetic anomaly response of the lithosphere - atmosphere - ionosphere. In addition, it can carry out interdisciplinary research and applications in the fields of communication and space electromagnetic environment, etc.

[0030] The present invention expands the distribution range of the network and tries to cover all strong earthquake - active areas and key monitoring areas as much as possible.

[0031] 1) For artificial source signals, the emission equipment can be improved to expand the frequency range towards both high - and low - frequency ends.

[0032] 2) Different forms of emission sources can be adopted, such as magnetohydrodynamic transmitters, nuclear - power - supplied transmitters, industrial - power - supplied transmitters, etc., while the receiving network scheme remains basically unchanged. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the composition of the alternating electromagnetic field network of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0034] Figure 2 It is a schematic diagram of the composition of the observation systems of each station of the electromagnetic network of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0035] Figure 3 It is the time series of the electromagnetic field signals of 5 components and 4 frequencies of natural sources and artificial sources that can be received by a certain station in the network of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0036] The 5 components are Ex, Ey, Hx, Hy, Hz from top to bottom, and artificial source signals of 4 frequencies (F1 - F4) are emitted within 1.5 hours;

[0037] Figure 4 It is the electromagnetic field processing and analysis process of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0038] Figure 5 It is a distribution map of 15 stations in a certain network area of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0039] Figure 6 It is the apparent resistivity and impedance phase curves of the Jinggu Station in a certain network area of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0040] Figure 7 It is a distribution map of the Hx spectrum plane at 216 Hz in a certain network area of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0041] Figure 8 It is a plane contour map of the apparent resistivity at 120 Hz in a certain area of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0042] Figure 9 It is a resistivity distribution map at a depth of 15 km obtained by inversion of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0043] Figure 10 It is a resistivity distribution map at different depths (1 km, 2 km, 5 km, 10 km, 15 km) obtained by inversion in a certain area of an alternating electromagnetic field seismic monitoring and observation network according to the present invention;

[0044] Figure 11The variation of the spectrum of the Hx component at 4 Hz at the Jinggu station before and after the 5.1-magnitude Litang earthquake that occurred at 1:23 on September 23, 2016, in a seismic monitoring and observation network of an alternating electromagnetic field for the present invention. Detailed implementation manners

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] The following defines the abbreviations and key terms involved in the present technical solution:

[0047] Alternating electromagnetic field: An electromagnetic field that changes with time, and its research and application conform to the law of electromagnetic induction

[0048] Station network: An observation network composed of many stations arranged within a certain range on the ground for a certain or certain needs

[0049] Seismic electromagnetic anomaly: An electromagnetic field phenomenon of abnormal background change related to seismic activity

[0050] Electromagnetic field spectrum: The electromagnetic field in the frequency domain obtained by spectral analysis of the electromagnetic field signal in the time domain

[0051] Apparent resistivity, impedance phase: The impedance reflecting the underground resistivity structure calculated from the electromagnetic field data observed on the ground. The resistivity data further calculated is called apparent resistivity; the phase calculated from the real part and the imaginary part of the impedance element; the underground resistivity distribution can be obtained through techniques such as inversion.

[0052] Resistivity: A parameter reflecting the conductive property of rock minerals, related to the composition, porosity, structure, water content, etc. of rock minerals

[0053] "Cloud map": Drawing on terms in fields such as meteorology, reflecting the spatial distribution characteristics of regional physical properties such as electromagnetic field spectrum, resistivity, etc.

[0054] Seismic anomaly three-dimensional monitoring: Monitoring seismic anomaly phenomena from multiple aspects using multiple parameters to more accurately identify anomaly phenomena.

[0055] The schematic diagram of the composition of the alternating electromagnetic field station network is as Figure 1 shown.

[0056] Figure 1T: High-power artificial source electromagnetic field signal transmitter; R: A network composed of various stations, the distribution can be regular, of any shape, or arranged according to earthquake distribution or structure; Wa: The propagation path of the artificial source electromagnetic field in the waveguide layer, which can reach a distance of thousands of kilometers; Wn: The propagation of the natural source electromagnetic field to the ground network area; Wi: The artificial source and the natural source electromagnetic fields are transmitted underground; Ws: When an earthquake occurs, the electromagnetic field excited by the seismic activity propagates to the ground, and the electrical properties such as resistivity in the seismic source area also change.

[0057] As Figure 1 shown, the alternating electric field network on the ground can observe both natural source electromagnetic field signals and artificial source electromagnetic field signals. The alternating electric field network can be arranged within a range of thousands of kilometers on the ground. When an earthquake occurs, the resistivity in the seismic source area will change, which can be observed through the ground network. The seismic source area also excites electromagnetic field anomalies, which can also be observed through the ground network. Since the network layout range is very large, the spatial distribution differences and characteristics of the electromagnetic field anomalies can be comprehensively analyzed. By observing the underground resistivity anomalies and the electromagnetic field anomalies observed on the ground, the characteristics of the anomalies can be analyzed three-dimensionally to identify the authenticity of the anomalies. High-power artificial source signals can significantly suppress the influence of other interference factors.

[0058] Schematic diagram of the observation system composition of each station of the electromagnetic network is as Figure 2 , the receiving equipment of the observation station can be arranged inside the seismic station, or in other places outside the seismic station, or in the blank area for observation when needed. The observed quantities include 5 components, namely the north-south electric field (Ex), magnetic field (Hx) components, the east-west electric field (Ey), magnetic field (Hy) components, and the vertical magnetic field component (Hz). For the measurement of the electric field component, cable wires are used to connect the instrument and the grounding electrodes 50 - 100 meters apart to collect signals, and the magnetic field is received by an inductive magnetic probe (magnetic rod). In order to continuously observe without interruption and prevent interference caused by power electricity, solar power supply is adopted, and the observation host is placed in a room or other windproof and rainproof facilities or containers (referred to as the observation room).

[0059] The station equipment uses 10-channel observations. Among them, 5 channels are used for continuous 24-hour observation of the natural field at low frequencies, and the other 5 channels are used for segmented high-frequency and medium-frequency natural source observations during the artificial source frequency band observation and non-artificial source observation periods. In this way, the same set of instruments can simultaneously observe the electromagnetic field signals of natural sources and artificial sources. To ensure the rapid transmission of observation data, electromagnetic field signals are received at different sampling rates at different times. For artificial source data, signals are emitted during fixed periods in the morning and evening, and the receiver uses different sampling rates to receive artificial source emission signals of different frequencies. For the low-frequency signals of natural sources, the receiver uses a lower sampling rate for continuous 24-hour observation. For the high-frequency and medium-frequency signals of natural sources, during the non-artificial source signal emission period, they are received once every 10 minutes, and at least 4 segments of 4096 data samples are collected respectively to ensure the uniform distribution of high- and medium-frequency data throughout the day.

[0060] The effective frequency range of the natural source electromagnetic field observed by the network covers 1000~0.001Hz, and the effective frequency range of the artificial source electromagnetic field is 300~0.1Hz. The observed data can be transmitted to the data processing, analysis and prediction departments through wired or wireless networks, and the data is processed and analyzed in real time or quasi-real time.

[0061] The original time series of the observed natural field and artificial source field signals are as Figure 2 . The abscissa represents time, and the ordinate represents the signal amplitude. The figure shows the artificial source signals of 4 frequencies and the natural source signals between and outside them. The amplitude of the artificial source signals is greater than that of the natural source signals.

[0062] As Figure 3 shown, by performing spectral analysis on the observed electromagnetic field time series, the frequency spectrum of each electromagnetic field component can be obtained, and then parameters such as impedance reflecting the underground electrical properties, apparent resistivity, and impedance phase can be calculated. These parameters are the basic parameters reflecting the underground electrical properties, spatial electromagnetic fields, and their changes. By inverting the apparent resistivity, etc., the underground electrical structure can be obtained, so the observation network can directly monitor the abnormal changes in the underground electrical structure.

[0063] The formulas for calculating impedance from the frequency spectra (Ex, Ey, Hx, Yy, and Hz) of each component of the electromagnetic field are as follows:

[0064] Ex = Zxx Hx + ZxyHy

[0065] Ey = Zyx Hx + ZyyHy

[0066] Hz = A Hx + B Hy

[0067] In the formula, Zxx, Zxy, Zyx, and Zyy are impedance tensor elements, and A and B are magnetic field transfer functions. The apparent resistivity and impedance phase can be calculated from the impedance tensor elements using the following formula:

[0068] ρ ij = 0.2T|Z ij | 2 φ ij = arctan(Z ij )

[0069] where ρ ij represents apparent resistivity, φ ij represents impedance phase, and the subscript ij represents x or y.

[0070] Apparent resistivity, impedance phase, and magnetic field transfer function can qualitatively analyze the underground electrical structure information of observation stations and quantitatively invert the resistivity structure underground.

[0071] The data processing and analysis process can be represented as follows. Using the alternating electromagnetic field network method, it is distributed in the seismically active area (a certain region) and the capital circle area, with 15 stations in each area. Figure 4 It is a distribution map (marked in yellow) of 15 stations in the network area of a certain region. Figure 5 It is a distribution map (marked in yellow) of 15 stations in the network area of a certain region.

[0072] Figure 6 It shows the apparent resistivity and impedance phase curves obtained from the Jinggu Station in the network of a certain region. These are the basic parameters for earthquake anomaly detection in ground observation data. It reflects the underground electrical structure. By inverting these parameters, the underground electrical distribution, i.e., the electrical structure, can be obtained. If the underground structure does not change, the underground electrical structure is stable, and the apparent resistivity curve and phase curve will not change. When an earthquake or the like occurs and the underground structure changes, then the apparent resistivity phase parameters will also change.

[0073] In the observed frequency range, an electromagnetic field energy cloud map in planar distribution can be calculated for a spectrogram including 5 components. This spectrogram is similar to the "cloud map" in meteorology. Under normal circumstances, the cloud map should be stable. When an anomaly caused by an earthquake or the like occurs, the cloud map will change, thereby enabling the identification of the frequency and region where the anomaly appears. Figure 7 What is given is the planar distribution map of the Hx spectrum at 216 Hz in a certain network area. Similar cloud maps can also be obtained for other components.

[0074] It is like the cloud Figure 1 of the above electromagnetic field power spectrum. A cloud map reflecting the underground electrical structure at different depths can also be obtained. When an anomaly occurs, the frequency and region where the anomaly appears can be identified from the map. Figure 8 It is the planar contour map of the apparent resistivity ρ yx at 120 Hz in a certain region.

[0075] By inverting the apparent resistivity, phase, etc. calculated from ground observations, the underground electrical (resistivity) structure of the network area can be obtained (such asFigure 9 ) When the underground structure remains unchanged, the inverted underground resistivity distribution is stable. When an earthquake or other event occurs, the underground structure is damaged and fractured, the porosity of the rock changes, and the distribution of underground fluids also changes. Therefore, the underground resistivity will also change.

[0076] Resistivity distribution maps at different depths, based on Figure 10 , when seismic anomalies occur, in addition to identifying the areas where the anomalies occur, it is also possible to identify the depths at which the anomalies occur, and conduct seismic anomaly monitoring from a three-dimensional perspective.

[0077] For a certain earthquake, it is also possible to analyze the data of each station included in the network, and deeply explore whether there are abnormal changes in the parameters of the corresponding stations before and after the earthquake, so as to study the characteristics of abnormal parameters before and after the earthquake and contribute to earthquake prediction. Figure 11 It shows the change in the spectrum of the Hx component at 4 Hz of the Jinggu Station before and after the M5.1 LITANG earthquake that occurred at 1:23 on September 23, 2016. Among them, the black line represents the change in the natural source spectrum, and the red line represents the change in the artificial source spectrum. As can be seen from the figure, it is difficult to find obvious abnormal changes in the natural source spectrum, while in the artificial source spectrum, three days before the earthquake, the spectrum began to gradually increase, and returned to normal values after the earthquake.

[0078] The alternating electromagnetic field network is proposed to address the shortcomings of existing methods. Its advantages include: (1) It can not only observe the underground electrical structure and its continuous changes, with a depth reaching below the depths of most earthquake hypocenters, even below the crust, but also monitor the changes in electromagnetic fields from space and underground on the ground, constituting a true three-dimensional observation; (2) The observed frequency band range of the alternating electromagnetic field is very wide. Currently, the high-frequency band reaches several thousand hertz, and the low-frequency band can reach below 1000 seconds, covering the main frequency bands where seismic anomalies have been found before and their adjacent frequency bands; (3) The observation is carried out in a network mode, and many stations simultaneously observe in a range of thousands of kilometers. It is possible to compare the characteristics of electromagnetic anomaly data in different regions (seismic regions and regions far from earthquakes), which is conducive to capturing the locations, spatial distributions, and temporal variation characteristics of seismic anomalies; (4) It can observe both natural source electromagnetic fields and artificial source electromagnetic fields. Currently, the signals of high-power artificial source electromagnetic fields propagate thousands of kilometers through the waveguide layer between the Earth and the ionosphere, with a frequency band range of 300 - 0.1 Hz. The development of future technologies can make the frequency band wider; (5) By observing artificial source signals, the influence of interference signals can be suppressed to a great extent, highlighting useful signals and improving the ability to identify and capture seismic anomalies; (6) Long-term continuous observation of the network can compare data at different times (day and night, different dates, different seasons, earthquake and non-earthquake times, etc.), which is conducive to comparing and identifying the authenticity of seismic anomalies and is conducive to identifying and capturing the temporal distribution characteristics of seismic anomalies.

[0079] The above content is only an example and illustration of the structure of the present invention. Those skilled in the art to which the present technology pertains can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the structure of the invention or exceed the scope defined by this claim book, and they shall fall within the protection scope of the present invention.

Claims

1. An alternating electromagnetic field earthquake monitoring observation network, characterized in that , including multiple stations that receive high-power artificial source electromagnetic fields and natural source electromagnetic signals, the underground resistivity anomaly and electromagnetic field anomaly in the earthquake source area are processed through the observation data of multiple stations arranged based on the earthquake distribution trend, and electromagnetic anomaly information that is conducive to earthquake prediction is obtained, including the following steps: By performing spectrum analysis on the observed electromagnetic field time series, the spectrum and autopower spectrum of each electromagnetic field component, as well as the cross-power spectrum of different components, can be obtained, and the impedance reflecting the underground electrical properties, as well as the apparent resistivity and impedance phase parameters can be calculated; Invert the apparent resistivity and other parameters to obtain the underground electrical structure parameters, and judge the alternating electromagnetic field earthquake through the abnormal changes in the parameters of the underground electrical structure; The formula for calculating impedance from the spectrum of electromagnetic field observations is as follows: Ex=Zxx Hx+ZxyHy Ey=Zyx Hx+ZyyHy Hz=A Hx+B Hy Where Zxx, Zxy, Zyx, and Zyy are impedance tensor elements, and A and B are magnetic field transfer functions; The apparent resistivity and impedance phase can be calculated from the impedance tensor elements using the following formula: ρ ij =0.2T|Z ij | 2 φ ij =arctan(Z ij ) Among them, ρ ij represents the apparent resistivity, φ ij represents the impedance phase, and the subscript ij represents x or y; The apparent resistivity and impedance phase can be used to qualitatively analyze the underground electrical structure information of the observation station and quantitatively invert the underground resistivity structure.

2. The alternating electromagnetic field seismic monitoring observation network according to claim 1, characterized in that: The observed quantities include the north-south electric field Ex component, the magnetic field component Hx component, the east-west electric field Ey component, the magnetic field component Hy component, and the vertical magnetic field component Hz component.

3. The alternating electromagnetic field seismic monitoring observation network according to claim 1, characterized in that: The electric field measurement uses cables to connect the instrument and ground electrodes 30-50 meters apart to collect mutually perpendicular horizontal electric field signals. The magnetic field uses an inductive magnetic field sensor to receive mutually perpendicular three-component magnetic field signals corresponding to the direction of the electric field.

4. The alternating electromagnetic field seismic monitoring observation network according to claim 1, characterized in that: The station equipment uses 10 observation channels, of which 5 are used for 24-hour low-frequency continuous observation of natural fields, and the other 5 are used for artificial source frequency band observation and natural source high-frequency and medium-frequency segmented observation during non-artificial source observation periods.

5. The alternating electromagnetic field seismic monitoring observation network according to claim 1, characterized in that: To ensure fast transmission of observation data, electromagnetic field signals are received in different time periods using high and low sampling rates. For artificial source data, signals are transmitted during fixed time periods in the morning and evening, and the receiver uses different sampling rates to receive artificial source transmission signals of different frequencies. For natural source low-frequency signals, the receiver uses a low-frequency dedicated channel for 24-hour continuous observation. The high and medium frequencies of natural source signals are received every 10 minutes during the non-artificial source signal transmission period, and at least 4 segments of 4096 data samples are collected to ensure that the high and medium frequency data are evenly distributed throughout the day.

6. The alternating electromagnetic field seismic monitoring observation network according to claim 1, characterized in that: The effective frequency range of natural source electromagnetic fields observed by the network covers 0.001 to 1000 Hz, and the effective frequency range of artificial source electromagnetic fields is 0.1 to 300 Hz.

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