Seabed earthquake positioning method for communication submarine cable networking
By using submarine cable networking and distributed acoustic sensing technology, the problem of insufficient accuracy in submarine earthquake positioning was solved, achieving high-precision submarine earthquake positioning, reducing costs and improving the feasibility of the project.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUN YAT SEN UNIV
- Filing Date
- 2025-11-27
- Publication Date
- 2026-05-26
AI Technical Summary
Existing technologies lack sufficient accuracy in locating submarine earthquakes, especially in deep-sea areas where the deployment density is insufficient, making marine earthquake monitoring and location difficult and costly.
By utilizing submarine communication cables, power spectral density analysis and signal enhancement frequency band processing are used to extract the P-wave and S-wave phase travel times of the seismic waveform. Combined with distributed acoustic sensing technology, the epicentral distance and hypocenter are calculated, and precise positioning is achieved using the multi-station circle drawing method and double-difference travel time algorithm.
It achieves high-precision seabed seismic positioning, equivalent to the accuracy of simultaneous observation by hundreds of OBSs, reducing observation costs and improving engineering feasibility.
Smart Images
Figure CN122085366A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of marine seismic exploration technology, and in particular to a method for seabed seismic location using a communication submarine cable network. Background Technology
[0002] Currently, seafloor earthquake monitoring and location primarily relies on seafloor seismometer (OBS) networks. This involves first deploying seismometers on the seabed, then calculating the location of the seismic source by inverting the travel times of shear waves and shear waves received by the seismometers, or by calculating the propagation paths of seismic rays in the subsurface medium and cross-correlating this with the actual seismic data received by the OBS. Accurate OBS location of seafloor earthquake sources requires the simultaneous deployment of a large number of OBSs. However, this technology faces numerous challenges in practical applications, such as the difficulty of deploying equipment in harsh marine environments, technical bottlenecks in the real-time transmission of large volumes of observational data, and extremely high deployment and maintenance costs in deep-sea areas. These limitations directly result in insufficient OBS deployment density in marine areas, especially in the deep sea, thus leading to insufficient accuracy in seafloor earthquake location using existing technologies.
[0003] A search of existing technical literature revealed a patent application (application number 202010462557.2) entitled "A Seafloor Seismograph Time Difference Positioning Device and Method." This patent describes a method for deploying a seafloor seismograph according to a designed operational point. After the seismograph lands, artificial seismic sources are used to generate seismic signals in a cross-shaped pattern around the deployment point. The seismograph is then retrieved after the operation is completed. Using the time and location navigation information from the artificial seismic source generation, a common receiving point gather corresponding to the station to which the seismograph belongs is extracted from the continuously recorded data sequence of the seafloor seismograph and saved in SU or SEGY format. A search grid is defined around the deployment point using a search radius and grid spacing. A theoretical time difference model is constructed by selecting any two shots. The SU or SEGY format data of the hydrophone components of the seafloor seismograph are read, and the measured time difference of the shot pair is calculated based on a cross-correlation algorithm. The theoretical time difference models for all shot pairs are iteratively calculated and superimposed on the measured time difference. The final coordinate value corresponding to the minimum value of the superimposed time difference model is the positioning result. However, this patent has problems such as the need for extensive deployment and deployment of the seabed seismograph, and the difficulty of deployment in deep-sea areas, resulting in insufficient accuracy in seabed seismic positioning. Summary of the Invention
[0004] Therefore, it is necessary to provide a submarine earthquake location method using submarine cable networking to address the aforementioned technical problems and achieve high-precision submarine earthquake location.
[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a method for submarine seismic location in a communication submarine cable network, the method comprising: S1: When the first submarine cable and the second submarine cable detect seismic waves, the first seismic wave data and the second seismic wave data are obtained respectively. Power spectral density analysis is performed on the first seismic wave data and the second seismic wave data respectively to obtain the first signal enhancement frequency band and the second signal enhancement frequency band. The seismic wave signal detected by the first submarine cable is stronger than the seismic wave signal detected by the second submarine cable. S2: Process the first seismic wave data according to the first signal enhancement frequency band to obtain the first seismic waveform; process the second seismic wave data according to the second signal enhancement frequency band to obtain the second seismic waveform. S3: Extract the phase travel time of the first seismic waveform and the second seismic waveform respectively to obtain the first P-wave phase travel time and the first S-wave phase travel time corresponding to the first seismic waveform, and the second P-wave phase travel time and the second S-wave phase travel time corresponding to the second seismic waveform. Calculate the first phase travel time difference and the second phase travel time difference based on the first P-wave phase travel time and the first S-wave phase travel time, the second P-wave phase travel time and the second S-wave phase travel time. S4: Obtain the first P-wave velocity model and the first S-wave velocity model corresponding to the first submarine cable, obtain the second P-wave velocity model and the second S-wave velocity model corresponding to the second submarine cable, and calculate the first epicentral distance and the second epicentral distance based on the first P-wave velocity model, the first S-wave velocity model and the first phase travel time difference, the second P-wave velocity model, the second S-wave velocity model and the second phase travel time difference, respectively. S5: Two preliminary hypocenters are calculated based on the first epicentral distance and the second epicentral distance. The correct preliminary hypocenter is determined based on the S-wave phase travel time of the first or second S-wave phase of the submarine cable at the beginning and end of the cable.
[0006] Preferably, before step S1, the method further includes numbering each channel in the first submarine cable and the second submarine cable and reading their geographic coordinates.
[0007] Preferably, the first submarine cable and the second submarine cable identify seismic waves through their respective generated space-time-strain rate maps.
[0008] Preferably, obtaining the first signal enhancement frequency band and the second signal enhancement frequency band includes: Power spectral density analysis was performed on the first seismic wave data to obtain the first signal enhancement frequency band. The first seismic wave data consisted of seismic wave data acquired from all channels in the first submarine cable. Power spectral density analysis was performed on the second seismic wave data to obtain the second signal enhancement frequency band. The second seismic wave data is the seismic wave data obtained from the second submarine cable with a clear seismic wave signal channel. The clear seismic wave signal channel is determined based on the space-time-strain rate diagram.
[0009] Preferably, step S2 includes: The first seismic wave data is filtered according to the first signal enhancement frequency band to obtain the first seismic waveform; The second seismic wave data is sequentially superimposed with channel seismic wave data, filtered according to the second signal enhancement frequency band, and denoised using wavelet transform thresholding to obtain the second seismic waveform.
[0010] Preferably, obtaining the first P-wave phase travel time and the first S-wave phase travel time corresponding to the first seismic waveform, and the second P-wave phase travel time and the second S-wave phase travel time corresponding to the second seismic waveform, includes: The first earthquake waveform was extracted using the PhaseNet-DAS neural network model to obtain the first P-wave phase travel time and the first S-wave phase travel time; The second seismic waveform was manually extracted to obtain the travel time of the second P-wave phase and the travel time of the second S-wave phase.
[0011] Preferably, obtaining the second P-wave phase travel time and the second S-wave phase travel time corresponding to the second seismic waveform includes: The second seismic waveform was extracted using the STA / LTA method to obtain the travel time of the second P-wave phase and the travel time of the second S-wave phase.
[0012] Preferably, the formula for calculating the epicentral distance is as follows:
[0013] in, Indicates the distance from the epicenter. This represents the P-wave velocity model. Represents the S-wave velocity model. This indicates the travel time difference of the seismic phase.
[0014] Preferably, the first epicentral distance includes the epicentral distances of all channels in the first submarine cable, and the second epicentral distance includes the epicentral distances of channels in the second submarine cable with clear seismic wave signals. Two preliminary hypocenters are calculated based on the first and second epicentral distances, including: Using the epicentral distance of each channel in the first epicentral distance and the second epicentral distance as the radius, and the channel corresponding to the epicentral distance as the center, draw circles in the spherical coordinate system to obtain the first epicentral distance circle group corresponding to the first submarine cable and the second epicentral distance circle group corresponding to the second submarine cable. By taking the midpoint of the two intersecting regions of the first and second epicentral distance circles, two preliminary hypocenters are obtained.
[0015] Preferably, after step S5, the method further includes: The correct preliminary hypocenter was calculated using a double-difference travel time algorithm to obtain the accurate hypocenter.
[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a submarine earthquake location method using a communication cable network. It utilizes existing submarine communication optical cables combined with distributed acoustic sensing technology to identify and locate seismic waves. The location accuracy is equivalent to that of hundreds of OBSs observing simultaneously. Such a scale of OBS is difficult to deploy in the ocean, thus solving the problem of insufficient OBS coverage in the ocean leading to insufficient submarine earthquake location accuracy. Furthermore, it has lower observation costs and higher engineering feasibility. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of a submarine earthquake location method for a communication submarine cable network in one embodiment. Figure 2 This is a schematic diagram of the first seismic waveform obtained by filtering the Xiamen submarine cable (No. 3) cable from 1Hz to 4.5Hz using a submarine earthquake location method for communication cable networking in one embodiment. Figure 3 This is a waveform diagram of channel 6055 of the Hainan-Hong Kong submarine cable (No. 1) in the submarine earthquake location method of communication submarine cable network in one embodiment. Figure 4 This is a schematic diagram of two intersecting areas generated by the multi-station circular positioning method for submarine seismic location in a communication submarine cable network embodiment. Figure 5 This is an enlarged schematic diagram of one intersection area of a submarine seismic location method for a communication submarine cable network in one embodiment; Figure 6 This is a schematic diagram illustrating a submarine earthquake location method for communication cable networks in one embodiment, which uses S-wave phase travel time to determine the true location of the earthquake source. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.
[0019] Example 1 like Figure 1 As shown in the figure, this embodiment proposes a method for submarine seismic location using submarine communication cable networks. The method includes: S1: When the first submarine cable and the second submarine cable detect seismic waves, the first seismic wave data and the second seismic wave data are obtained respectively. Power spectral density analysis is performed on the first seismic wave data and the second seismic wave data respectively to obtain the first signal enhancement frequency band and the second signal enhancement frequency band. The seismic wave signal detected by the first submarine cable is stronger than the seismic wave signal detected by the second submarine cable. The specific implementation of this step is as follows: the submarine cable is laid in the sea area near Wenchang, Hainan, Sanjiao Island, Zhuhai, and Gulangyu, Xiamen. In this embodiment, the Xiamen submarine cable (No. 3) and the Hainan-Hong Kong submarine cable (No. 1) are used to locate the earthquake that occurred in the sea area east of Taiwan on May 5, 2025 (UTC: 2025-05-05 10:53:27), with an initial location of (23.9°N, 121.967°E). The Xiamen submarine cable (No. 3) is the first submarine cable, and the Hainan-Hong Kong submarine cable (No. 1) is the second submarine cable. After the earthquake, it was first identified on the space-time-strain rate map generated on the Xiamen submarine cable (No. 3). Similarly, two minutes of data were added to this time period to generate the space-time-strain rate map for the Hainan-Hong Kong submarine cable (No. 1). Seismic waves were identified on the space-time-strain rate map generated on the submarine cable, and the first and second seismic wave data were obtained. Based on the space-time-strain rate map, it can be seen that the seismic wave signal identified on the Xiamen submarine cable (No. 3) was stronger than that identified on the Hainan-Hong Kong submarine cable (No. 1). Power spectral density analysis was performed on the data collected on the Xiamen submarine cable (No. 3) before the earthquake and the data collected during the earthquake (first seismic wave data). The results showed that the Xiamen submarine cable... The signal in the 1Hz-4.5Hz frequency band on (③) was enhanced, which is the first signal enhancement frequency band. Channels with relatively clear seismic wave signals were extracted from the data collected from the Hainan-Hong Kong submarine cable (①). The channels with clear seismic wave signals were determined based on the space-time-strain rate diagram (the segments with good coupling between the seabed and the submarine cable in the space-time-strain rate diagram), which were channels 4916, 6055, and 7035. Then, power spectral density analysis was performed on the data before and after these channels, a total of 30 channels, for the data before and during the earthquake (the second seismic wave data). The results showed that the signal in the 1.74Hz-4.88Hz frequency band on the Hainan-Hong Kong submarine cable (①) was enhanced during the earthquake, which is the second signal enhancement frequency band.
[0020] S2: Process the first seismic wave data according to the first signal enhancement frequency band to obtain the first seismic waveform; process the second seismic wave data according to the second signal enhancement frequency band to obtain the second seismic waveform. The specific implementation of this step is as follows: For the Xiamen submarine cable (No. 3), based on the obtained first signal enhancement frequency band, the first seismic wave data is directly bandpass filtered from 1Hz to 4.5Hz to obtain relatively clear seismic P-waves and S-waves, i.e., the first seismic waveform, as shown below. Figure 2 As shown; for the Hainan-Hong Kong submarine cable (No. 1), based on the obtained second signal enhancement frequency band, the three channels 4916, 6055, and 7035 of the second seismic wave data on the Hainan-Hong Kong submarine cable (No. 1) are first superimposed with the seismic wave data of the previous and next five channels, then bandpass filtered from 1.74Hz to 4.88Hz, and finally denoised by continuous wavelet transform combined with thresholding, to obtain relatively clear seismic waveforms on the three channels, i.e., the second seismic waveforms. Taking the 6055th channel as an example, as shown... Figure 3 As shown.
[0021] S3: Extract the phase travel time of the first seismic waveform and the second seismic waveform respectively to obtain the first P-wave phase travel time and the first S-wave phase travel time corresponding to the first seismic waveform, and the second P-wave phase travel time and the second S-wave phase travel time corresponding to the second seismic waveform. Calculate the first phase travel time difference and the second phase travel time difference based on the first P-wave phase travel time and the first S-wave phase travel time, the second P-wave phase travel time and the second S-wave phase travel time. The specific implementation of this step is as follows: The PhaseNet-DAS neural network model is used to extract the first phase travel time of the first seismic waveform of all channels in the Xiamen submarine cable (No. 3) to obtain the first P-wave phase travel time and the first S-wave phase travel time corresponding to the first seismic waveform. The first phase travel time difference is calculated based on the first P-wave phase travel time and the first S-wave phase travel time. The second seismic waveforms of the three channels 4916, 6055 and 7035 on the Hainan-Hong Kong submarine cable (No. 1) are manually extracted to obtain the second P-wave phase travel time and the second S-wave phase travel time corresponding to the second seismic waveform. The second phase travel time difference is calculated based on the second P-wave phase travel time and the second S-wave phase travel time.
[0022] S4: Obtain the first P-wave velocity model and the first S-wave velocity model corresponding to the first submarine cable, obtain the second P-wave velocity model and the second S-wave velocity model corresponding to the second submarine cable, and calculate the first epicentral distance and the second epicentral distance based on the first P-wave velocity model, the first S-wave velocity model and the first phase travel time difference, the second P-wave velocity model, the second S-wave velocity model and the second phase travel time difference, respectively. The specific implementation of this step is as follows: Based on the AK135 geological velocity model of the study area and the epicentral distance calculation formula, the distance from the receiving channel to the source on the two submarine cables is calculated, i.e., the epicentral distance. The distance from all channels of the Xiamen submarine cable (No. 3) to the source is the first epicentral distance, and the distance from the source of the three channels 4916, 6055 and 7035 on the Hainan-Hong Kong submarine cable (No. 1) to the source is the second epicentral distance.
[0023] S5: Two preliminary hypocenters are calculated based on the first epicentral distance and the second epicentral distance. The correct preliminary hypocenter is determined based on the S-wave phase travel time of the first or second S-wave phase of the submarine cable at the beginning and end of the cable.
[0024] The specific implementation of this step is as follows, such as Figure 4 , Figure 5 As shown, after obtaining the epicentral distance of the channel on each submarine cable, circles are drawn in spherical coordinates using a multi-station circular positioning method based on the first and second epicentral distances. This yields a first epicentral distance circle group corresponding to the first submarine cable and a second epicentral distance circle group corresponding to the second submarine cable. The two circles have two intersecting regions. The center points of these two intersecting regions are taken as two preliminary hypocenters, namely (27.67°N, 119.8°E) and (23.94°N, 121.86°E). After obtaining the two preliminary hypocenters, it is determined which preliminary hypocenter is the true hypocenter location. Figure 6 As shown, based on the S-wave travel times at port 1 and port 2 of the Xiamen submarine cable (No. ③) (the S-wave travel times of the first and last channels of the submarine cable), it was determined that the travel time from the source to Port 1 was longer than that to Port 2. Therefore, the source was closer to Port 2, which is consistent with the situation of the submarine cable at (23.94°N, 121.86°E). Finally, we determined (23.94°N, 121.86°E) as the source location and excluded (27.67°N, 119.8°E).
[0025] Example 2 This embodiment further supplements the description of the submarine earthquake location method for communication submarine cable networking proposed in Embodiment 1.
[0026] Before step S1, the process also includes numbering each channel in the first submarine cable and the second submarine cable and reading their geographic coordinates.
[0027] The specific implementation of this step is as follows: Before the earthquake occurs, each receiving channel on the submarine cable needs to be numbered and the geographical coordinates of each channel need to be read. In addition, the P-wave velocity model and S-wave velocity model of the study area near the first and second submarine cables are obtained according to the AK135 model.
[0028] The second P-wave phase travel time and the second S-wave phase travel time corresponding to the second seismic waveform are obtained, including: The second seismic waveform was extracted using the STA / LTA method to obtain the travel time of the second P-wave phase and the travel time of the second S-wave phase.
[0029] The formula for calculating the epicentral distance is as follows:
[0030] in, Indicates the distance from the epicenter. This represents the P-wave velocity model. Represents the S-wave velocity model. This indicates the travel time difference of the seismic phase.
[0031] Example 3 This embodiment further supplements the description of the submarine earthquake location method for communication submarine cable networking proposed in the above embodiment.
[0032] After step S5, the following also includes: The correct preliminary hypocenter was calculated using a double-difference travel time algorithm to obtain the accurate hypocenter.
[0033] The specific implementation of this step is as follows: Based on the double-difference time-travel algorithm, the preliminary locations of all earthquakes are input to obtain the precise source locations of all earthquakes. The principle of the double-difference time-travel algorithm is as follows: based on ray theory, earthquake events... To the passage Time of departure:
[0034] Its first-order Taylor expansion:
[0035]
[0036] in It is to observe the time travel. It calculates the travel time. It calculates the difference between the parameters of the two seismic sources:
[0037] The difference between the observed and calculated travel times of the two events is the sum of the four parameters of the total source parameters. for:
[0038] By simultaneously solving the equations generated from all the seismic event pairs in each channel, we obtain a set of equations:
[0039] The requirement is that all four source parameters change to zero. Solving this system of equations using the LSQT method (least squares) yields the relative values of the four source parameters for the two earthquake sources, which represent the relative positions of the two sources. The preliminary source location is known; the precise source location is the preliminary source location plus the four relative values: the preliminary source location is... Solving this system of equations yields the following relative positions: The precise hypocenter of the earthquake is:
[0040]
[0041] Since this embodiment does not analyze depth, the accurate source result only provides latitude and longitude information. The double-difference travel time method is used to eliminate variations in near-surface and stratum velocities, reducing positioning errors. The final accurate positioning result is (23.9203°N, 121.8888°E). According to the official initial positioning (23.9°N, 121.967°E), the positioning error for this earthquake is (±0.0203°N, ±0.0782°E), which is equivalent to the error generated by hundreds of OBS simultaneous positioning.
Claims
1. A method for submarine seismic location using submarine cable networks, characterized in that, include: S1: When the first submarine cable and the second submarine cable detect seismic waves, the first seismic wave data and the second seismic wave data are obtained respectively. Power spectral density analysis is performed on the first seismic wave data and the second seismic wave data respectively to obtain the first signal enhancement frequency band and the second signal enhancement frequency band. The seismic wave signal detected by the first submarine cable is stronger than the seismic wave signal detected by the second submarine cable. S2: Process the first seismic wave data according to the first signal enhancement frequency band to obtain the first seismic waveform; process the second seismic wave data according to the second signal enhancement frequency band to obtain the second seismic waveform. S3: Extract the phase travel time of the first seismic waveform and the second seismic waveform respectively to obtain the first P-wave phase travel time and the first S-wave phase travel time corresponding to the first seismic waveform, and the second P-wave phase travel time and the second S-wave phase travel time corresponding to the second seismic waveform. Calculate the first phase travel time difference and the second phase travel time difference based on the first P-wave phase travel time and the first S-wave phase travel time, the second P-wave phase travel time and the second S-wave phase travel time. S4: Obtain the first P-wave velocity model and the first S-wave velocity model corresponding to the first submarine cable, obtain the second P-wave velocity model and the second S-wave velocity model corresponding to the second submarine cable, and calculate the first epicentral distance and the second epicentral distance based on the first P-wave velocity model, the first S-wave velocity model and the first phase travel time difference, the second P-wave velocity model, the second S-wave velocity model and the second phase travel time difference, respectively. S5: Two preliminary hypocenters are calculated based on the first epicentral distance and the second epicentral distance. The correct preliminary hypocenter is determined based on the S-wave phase travel time of the first or second S-wave phase of the submarine cable at the beginning and end of the cable.
2. The submarine seismic location method for communication submarine cable networking according to claim 1, characterized in that, Before step S1, the process also includes numbering each channel in the first submarine cable and the second submarine cable and reading their geographic coordinates.
3. The submarine seismic location method for communication submarine cable networking according to claim 2, characterized in that, The first and second submarine cables identified seismic waves through their respective generated space-time-strain rate maps.
4. The submarine seismic location method for communication submarine cable networking according to claim 3, characterized in that, The first signal enhancement band and the second signal enhancement band are obtained, including: Power spectral density analysis was performed on the first seismic wave data to obtain the first signal enhancement frequency band. The first seismic wave data consisted of seismic wave data acquired from all channels in the first submarine cable. Power spectral density analysis was performed on the second seismic wave data to obtain the second signal enhancement frequency band. The second seismic wave data is the seismic wave data obtained from the second submarine cable with a clear seismic wave signal channel. The clear seismic wave signal channel is determined based on the space-time-strain rate diagram.
5. The submarine seismic location method for communication submarine cable networking according to claim 4, characterized in that, Step S2 includes: The first seismic wave data is filtered according to the first signal enhancement frequency band to obtain the first seismic waveform; The second seismic wave data is sequentially superimposed with channel seismic wave data, filtered according to the second signal enhancement frequency band, and denoised using wavelet transform thresholding to obtain the second seismic waveform.
6. The submarine seismic location method for communication submarine cable networking according to claim 5, characterized in that, The first P-wave phase travel time and the first S-wave phase travel time corresponding to the first seismic waveform, and the second P-wave phase travel time and the second S-wave phase travel time corresponding to the second seismic waveform are obtained, including: The first earthquake waveform was extracted using the PhaseNet-DAS neural network model to obtain the first P-wave phase travel time and the first S-wave phase travel time; The second seismic waveform was manually extracted to obtain the travel time of the second P-wave phase and the travel time of the second S-wave phase.
7. The submarine seismic location method for communication submarine cable networking according to claim 5, characterized in that, The second P-wave phase travel time and the second S-wave phase travel time corresponding to the second seismic waveform are obtained, including: The second seismic waveform was extracted using the STA / LTA method to obtain the travel time of the second P-wave phase and the travel time of the second S-wave phase.
8. The submarine seismic location method for communication submarine cable networking according to claim 1, characterized in that, The formula for calculating the epicentral distance is as follows: in, Indicates the distance from the epicenter. This represents the P-wave velocity model. Represents the S-wave velocity model. This indicates the travel time difference of the seismic phase.
9. The submarine seismic location method for communication submarine cable networking according to claim 4, characterized in that, The first epicentral distance includes the epicentral distances of all channels in the first submarine cable, and the second epicentral distance includes the epicentral distances of channels in the second submarine cable with clear seismic wave signals. Two preliminary hypocenters are calculated based on the first and second epicentral distances, including: Using the epicentral distance of each channel in the first epicentral distance and the second epicentral distance as the radius, and the channel corresponding to the epicentral distance as the center, draw circles in the spherical coordinate system to obtain the first epicentral distance circle group corresponding to the first submarine cable and the second epicentral distance circle group corresponding to the second submarine cable. By taking the midpoint of the two intersecting regions of the first and second epicentral distance circles, two preliminary hypocenters are obtained.
10. The submarine seismic location method for communication submarine cable networking according to claim 1, characterized in that, After step S5, the following also includes: The correct preliminary hypocenter was calculated using a double-difference travel time algorithm to obtain the accurate hypocenter.