A method for monitoring large plate crust deformation by GNSS baseline time series

Abstract

The application provides a method for monitoring the deformation of large plates in the earth's crust using GNSS baseline timing, belonging to the field of crust deformation monitoring. First, the area of large plates to be monitored and the GNSS monitoring stations within it are determined, and the quality of the monitoring data of each station is evaluated. Then, the arc length between the monitoring stations is calculated, and the change of the arc length over time is calculated. Next, the relative motion between large plates and the deformation degree of local areas are analyzed to obtain the overall situation and details of the deformation. In addition, further analysis of the baseline results can be performed, and monitoring and analysis can be performed through different stations and directions. This method can effectively monitor the deformation of large plates in the earth's crust, which is helpful for the study of crustal structure and earthquake warning, and has wide application value.

Description

Technical Field

[0001] The present invention belongs to the field of crustal deformation monitoring, and more specifically relates to a method for monitoring large plate crustal deformation using GNSS baseline time series. Background Art

[0002] Since the advent of GNSS technology, using two GNSS stations on Earth to create a geodetic line between them and continuously monitoring changes in its length has replaced traditional baseline timing monitoring. This led to the development of GNSS baseline timing. This technique is primarily used to monitor crustal deformation because it eliminates the need for traditional steel baselines. As long as there are GNSS stations, GNSS baseline timing can theoretically be used. Its convenience and universality significantly surpass those of traditional baseline timing monitoring.

[0003] A primary use of GNSS baseline time series in seismic research is to monitor large-scale crustal deformation, such as the relative motion between large plates, indicating acceleration, deceleration, and stabilization, thereby providing a reference for other monitoring methods. However, using baselines to monitor large-scale crustal deformation currently presents a major problem: it is unclear what crustal deformation the baselines represent.

[0004] The Earth is generally considered to be more like an ellipsoid than a sphere. Therefore, baseline calculations often assume an ellipsoidal shape. However, this approach is very complex to calculate the geodesic of the ellipsoid, and it is difficult to obtain a precise theoretical solution. It requires iterative approximations, which are computationally inefficient. This can be very time-consuming when calculating a large number of baselines.

[0005] The relative movement of large plates was determined based on baselines obtained from only two stations. This led to different results if different stations were selected, resulting in an unclear interpretation. Over time, this method was gradually marginalized. Summary of the Invention

[0006] The technical problem to be solved by the present invention is how to effectively monitor the overall and local conditions of crustal deformation of large plates, especially to accurately display the detailed changes in crustal deformation, so as to end the doubts about the unclear internal deformation information and baseline results of the baseline, improve the monitoring accuracy and scientific nature of crustal movement, and at the same time provide accurate and reliable data support for earthquake prediction, geological research and other fields.

[0007] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions: the method comprises:

[0008] (1) Determine the large plate area to be monitored and the GNSS monitoring stations within it;

[0009] (2) Calculate the arc length between monitoring stations (not the elliptical arc length), and calculate the change of the arc length over time;

[0010] (3) Analyze the relative motion between large plates and the deformation degree of local areas, and obtain the overall deformation and details;

[0011] Select the two stations farthest apart as the baseline reference to obtain the most comprehensive change;

[0012] After obtaining the baseline result, further form the baseline graph of adjacent stations to separately analyze the result of each baseline, and compare the deformation rates of different regions by the method of normalized calculation.

[0013] In one scheme, the determination of the large plate area to be monitored and the GNSS monitoring stations therein includes evaluating the monitoring data quality of each monitoring station, so as to ensure that the data quality of the selected monitoring station is high, the data loss is little, and the station time sequence fluctuation is controlled within 10 mm.

[0014] In one scheme, the calculation of the arc length between monitoring stations includes calculating the arc length of each day according to the position change of each day, and subtracting the arc length of the first monitoring day from all the arc lengths, so as to obtain the time sequence of the change of the arc length over time, that is, the GNSS baseline.

[0015] In one scheme, the analysis of the relative motion between large plates and the deformation degree of local areas includes linear fitting according to the baseline time sequence to obtain the slope of the straight line, that is, the overall change rate of the baseline;

[0016] The change rate is divided by the arc length between two points to obtain the baseline deformation rate per unit time and per unit length; and the normalized deformation rate of the baseline of different GNSS stations is represented by color.

[0017] In one scheme, when the relative motion information in other directions is to be understood, corresponding stations are selected in other directions, and the same steps are performed to monitor and analyze the relative motion.

[0018] In one scheme, the method includes analyzing the baseline result, displaying the baseline result between adjacent stations, calculating the deformation rate per unit time and per unit length of each baseline, revealing the deformation degree difference between different regions, and further revealing the detailed change of the large plate crust shape.

[0019] In one scheme, the method calculates the earth as a sphere, and the error of the calculation result is 0.02 mm-0.04 mm compared with the calculation result of the earth as an ellipsoid

[0020] The present application has the following beneficial effects:

[0021] The present invention provides a method for monitoring the crustal deformation of large plates using GNSS baseline time series. Through precise calculation and data analysis, it can accurately reflect the deformation of the crust of large plates, effectively solving the problem of unclear understanding of crustal deformation when calculating the baseline in the prior art.

[0022] This method not only monitors the relative movement between large plates, but also examines the degree of deformation in local areas, facilitating the acquisition of both the overall situation and details of the deformation. An adaptive algorithm is used to calculate the GNSS baseline, ensuring accuracy and algorithm performance.

[0023] In previous calculations, technicians always calculated according to the shape of the earth itself (ellipsoid), but the disadvantage of doing so is that the geodesic calculation of the ellipsoid is very troublesome, and no theoretical accurate solution can be obtained. Therefore, in the calculation process, an iterative algorithm is adopted to perform multiple iterations, and multiple iterations will cause the calculation speed to be too slow. The present application directly regards the earth as a perfect sphere for calculation, and does not need to adopt the method of multiple iterations to continue calculating, which greatly speeds up the calculation speed. Moreover, the error between the calculated result and the result calculated by multiple iterations of the ellipsoid is between 0.02mm-0.04mm. This result error is extremely small. Greatly improves the calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Comparison of baseline timing results of two GNSS stations under the sphere and ellipsoid;

[0025] Figure 2 This is a schematic diagram of the physical meaning of the GNSS baseline;

[0026] Figure 3 A schematic diagram of a general scheme of the present invention;

[0027] Figure 4 The baseline timing results for the baseline group are shown in Figure 2. Due to the squeezed background, the original baseline timings are shortened, and the baseline timings in the figure are the result of delinearization. DETAILED DESCRIPTION

[0028] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The drawings illustrate exemplary embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those understood by those skilled in the art to which the present invention pertains. The terms used in the present specification are for the purpose of describing specific embodiments only and are not intended to limit the present invention. To facilitate understanding of the present invention, a more comprehensive description of the present invention will be provided below with reference to the accompanying drawings. Typical embodiments of the present invention are shown in the drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0030] The essence of GNSS baseline timing is a geometric problem, and its meaning is clear: it reflects the relationship between the distance between two points over time; its physical meaning is: the total amount of deformation between the two points in the direction of the line connecting the two points (such as Figure 2 ).for example, Figure 2 For points A and B, the GNSS baseline timing results reflect the total deformation between points A and B in the direction of the line connecting them. The GNSS baseline timing cannot reflect the deformation to the left of point A and to the right of point B, that is, the deformation outside of AB. Furthermore, the specific details of the deformation between points A and B are not reflected. The GNSS baseline timing can only reflect the total deformation between the two points. In summary, the physical meaning of the GNSS baseline timing has three aspects: it only reflects (1) the direction of the line connecting the two points, (2) the deformation between the two points, and (3) the total deformation.

[0031] Assuming the Earth to be a sphere, the calculation of geodesics does not require iteration and the calculation process can be completed instantly. This saves a lot of time in the calculation of massive baselines. Moreover, the difference between the baseline under the sphere and the baseline under the ellipsoid is less than 5%, which is completely sufficient for analyzing large-scale crustal deformation. Figure 1 The baselines for the two stations were obtained using a distance of approximately 4,750 kilometers. The blue line in the figure above represents the baseline using a sphere, while the orange line represents the baseline using an ellipsoid. The figure below shows the difference between the two results. Generally, the greater the distance, the greater the difference between the geodesics for the sphere and ellipsoid. As shown in the figure, the two results are almost identical, indicating that the sphere model is fully adequate.

[0032] Specifically for the surrounding plates, if the station is inside the plate, since the plate pushes the Eurasian plate, the point can be called an active point, and the point inside the Eurasian plate can be called a passive point. Figure 2 If the active point A pushes the passive point B, then the physical meaning of the GNSS baseline time series shows that the baseline result reflects the total deformation between AB. If A and B are both in the rigid region, then the baseline result reflects the deformation of the continuous deformation region between the two rigid blocks. However, how the deformation changes within the region is unclear. Figure 2Curve 1, Curve 2, Curve 3, or more complex curves cannot be obtained using only the GNSS baseline timing between AB.

[0033] The pattern of the Indian plate pushing the Tibetan Plateau Figure 2 Regardless of whether the study is about the northwest or northeast push, if the active point is Bangalore (IISC) in India, and the passive point is located in the Eurasian block or the Mongolian Plateau, the GNSS baseline time series will reveal the total push of the Indian plate in the northwest and northeast directions.

[0034] Based on the above conclusions, some baselines may not reflect the Indian plate's push on the entire Tibetan Plateau. For example, the baseline from Bangalore (IISC) to Lhasa (LHAS) reflects the northeastern push of the Indian plate south of Lhasa, not the entire Tibetan Plateau. The Indian plate's push north of Lhasa is not reflected.

[0035] Further, in order to refine Figure 2 To understand the deformation between points A and B, we can insert a series of stations (if available) between A and B. These stations divide the area between A and B into multiple smaller regions. The deformation of these smaller regions can be obtained by using the GNSS baseline timing between these multiple points. The level of detail in the deformation distribution between A and B depends on the station density between A and B.

[0036] Based on the above understanding, this patent application provides a general solution for monitoring large plate crustal deformation using GNSS baseline time series:

[0037] The process of baseline calculation:

[0038] (1) First, calculate the length of the arc between the two stations. Given that the longitude and latitude of the two stations are (l1, b1) and (l2, b2), and the radius of the earth is R, then the length S of the arc between the two points is:

[0039] S=R·arccos[cos(b1)·cos(b2)·cos(l1-l2)+sin(b1)·sin(b2)];

[0040] (2) Then, based on the temporal changes of the two stations, i.e., the daily changes in the station positions, the daily latitude and longitude of the stations are obtained;

[0041] (3) In this way, the arc length between two points on each day can be obtained. Subtracting the arc length of the first day of monitoring from all arc lengths can give the relative change process of the arc length, thereby obtaining the time series of the arc length change over time. The change process of arc length over time is the GNSS baseline.

[0042] Program process introduction:

[0043] S1. Data Collection: Data comes primarily from two sources: the China Crustal Movement Observation Network and the Chinese Continental Tectonic Environment Monitoring Network (this data is not publicly available, but can be obtained within the seismic system upon request. The data format is included at the end of this document). The other source is the IGS (International GNSS Service) global data, which is publicly available (the data format is included at the end of this document).

[0044] First determine the large plate area to be monitored. For example, if you want to monitor the relative movement between the Indian Plate and the Qinghai-Tibet Plateau (such as Figure 3 ), first determine whether there are GNSS stations with good monitoring quality on the large plate, such as the IISC on the Indian plate, which has very good monitoring quality; there are also some stations on the Qinghai-Tibet Plateau, such as XZRK, QHTT, DLHA, and DXIN, which have generally good quality. There should also be a station farther across the Qinghai-Tibet Plateau, ULAB, which also has very good monitoring quality. The so-called stations with good monitoring quality meet the following requirements: (1) There are very few missing stations; (2) The station timing fluctuation is basically controlled within 10mm. Then proceed according to the following process:

[0045] (1) Determine the direction of relative motion of the large plate to be monitored. Figure 3 We focus on the relative motion of the Indian Plate in the northeast direction and the Tibetan Plateau, and try to select GNSS stations in this direction.

[0046] (2) Select the two sites that are farthest apart as the baseline and analyze the baseline results.

[0047] (3) Then press Figure 3 In this way, baselines are made between adjacent sites, baseline results are displayed, baseline results of each section are analyzed, and the deformation rate per unit time and per unit length of each baseline section is calculated in a normalized manner.

[0048] (4) Analyze the baseline results: From 3, we can obtain: the total deformation characteristics between the two stations that are farthest apart, in the direction of the line connecting the two stations; from 4, we can obtain the deformation details, and the richness of the details depends on the number of GNSS stations inserted in the middle. If there are more stations in the middle, the details of the relative movement will be richer; finally, through normalization calculation, we can compare the deformation degree between different sections, which section deforms faster, which section deforms slower, and other information. The specific process of normalization is: (1) First, linearly fit the baseline time series to obtain the slope of the straight line, which is the overall change rate V of the baseline; (2) V is divided by the arc length between the two points, so that the baseline deformation rate value per unit time and unit length is obtained, and the normalized deformation rate of the baseline of different GNSS stations is represented by color.

[0049] If you want to obtain relative motion information in other directions, follow the above scheme to select points in other directions, make the longest baseline, then make segmented baselines, normalize, and compare vertically and horizontally.

[0050] Through the above scheme, we can truly obtain the overall and local information of the relative movement between large plates. The degree of detail of the information obtained depends on the density of GNSS stations. This scheme can put an end to the previous debate on "information about internal deformation of baselines" and "baseline results are unclear". For example Figure 4 yes Figure 3 Baseline results: Connecting the Bangalore (IISC)-Ulaanbaatar (ULAB) baseline reveals a significant acceleration of compression since 2020. This suggests a region of compressional acceleration between Bangalore (IISC) and Ulaanbaatar (ULAB) in the northeast direction, but the location of this region is unknown because baselines only reflect overall deformation. Using the baseline set again, we see that the acceleration since 2020 has occurred in the region between Dingxin (DXIN) and Ulaanbaatar (ULAB). All GNSS baseline time series south of Dingxin (DXIN) exhibit stable compressional loading. The results indicate that the northeastern thrust of the Indian plate is being absorbed by the Tibetan Plateau, but at varying rates. The region between QHTT and DLHA exhibits the highest rate of deformation absorption, while the region north of DXIN has the lowest rate. However, since 2020, the region north of the Alxa Block has exhibited acceleration of compression. This provides a complete and accurate representation of both the overall and local details of the relative motion between the Indian plate and the Tibetan Plateau.

[0051] The data format of the "China Crustal Movement Observation Network" and the "China Continental Tectonic Environment Monitoring Network" is as follows:

[0052]

[0053] The first row shows the units used for the data solution. The second row shows the initial longitude, latitude, elevation, and station name for the station. The next two rows show the sudden change at a specific point in time. Below that is the station's time series: the first column shows GNSS time, the second column shows the year, the third column shows the accumulated days, the fourth, fifth, and sixth columns show the northing, easting, and vertical displacements, and the last three columns show the error in the fourth, fifth, and sixth columns, all in meters.

[0054] "IGS" station data format:

[0055]

[0056] The contents of each column are: site name, specific year, month and day of observation, GNSS time, Julian day, GNSS week, day of the week, initial easting value, easting change value, initial northing value, northing change value, initial vertical value, vertical change value, then the corresponding error, and the last three items are latitude, longitude and elevation, in meters.

[0057] Data processing: First, the data from the "China Crustal Movement Observation Network", "China Continental Tectonic Environment Monitoring Network" and "IGS" data are converted into the following formats:

[0058]

[0059] The first row shows the station's longitude, latitude, elevation, and station name. The next column shows GNSS time, the second shows the year, the third shows the accumulated days, the fourth, fifth, and sixth columns show the easting, northing, and vertical displacements, and the last three columns show the northing, easting, and vertical displacement errors, all in millimeters. This converted data facilitates baseline calculations.

[0060] Those skilled in the art will appreciate that all or part of the processes in the above-described method embodiments can be implemented by instructing related hardware through a computer program. The program can be stored in a computer-readable storage medium, and when executed, the program can include the processes in the above-described method embodiments. The storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

[0061] It should be understood that the detailed description of the technical solutions of the present invention using the preferred embodiments above is illustrative and not restrictive. A person skilled in the art, after reading the present specification, may modify the technical solutions described in the embodiments or replace some of the technical features therein with equivalents; such modifications or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for monitoring large plate crustal deformation using GNSS baseline time series, characterized by: The method includes: (1) Determine the large plate area to be monitored and the GNSS monitoring stations within it; (2) Calculate the arc length between monitoring stations and calculate the change of arc length over time; (3) Analyze and reveal the relative motion between large plates and the degree of deformation in local areas, and obtain the overall situation and details of the deformation; The two sites that are furthest apart were selected as baseline references to yield the most comprehensive picture of changes; After obtaining the baseline results, a baseline map of adjacent sites is further formed to analyze the results of each baseline segment separately, and the deformation rates of different areas are compared by normalized calculation method; The analysis reveals the relative motion between large plates and the degree of deformation in local areas, including linear fitting based on the baseline time series to obtain the slope of the line, that is, the rate of change of the overall baseline; The baseline deformation rate per unit time and unit length is obtained by dividing the rate of change by the arc length between the two points. The baseline normalized deformation rate of different GNSS stations is represented by color. The method described herein considers the earth to be a perfect sphere for calculation, and the error between the calculation result obtained by considering the earth to be an ellipsoid and the calculation result is 0.02mm-0.04mm.

2. The method for monitoring large plate crustal deformation using GNSS baseline time series according to claim 1, characterized in that: The determination of the large area to be monitored and the GNSS monitoring stations therein includes evaluating the quality of monitoring data at each monitoring station to ensure that the data quality of the selected monitoring stations is high, with little data missing, and that the station timing fluctuation is controlled within 10 mm.

3. The method for monitoring large plate crustal deformation using GNSS baseline time series according to claim 1, characterized in that: The calculation of the arc length between the monitoring sites includes calculating the arc length of each day based on the daily site position changes, and subtracting the arc length of the first day of monitoring from all arc lengths to obtain a time series of arc length changes over time, namely the GNSS baseline.

4. The method for monitoring large plate crustal deformation using GNSS baseline time series according to claim 1, characterized in that: When understanding the relative motion information in different directions, select corresponding sites in different directions and perform the same steps to monitor and analyze the relative motion.

5. The method for monitoring large plate crustal deformation using GNSS baseline time series according to claim 1, characterized in that: The method includes analyzing the baseline results, displaying the baseline results between adjacent stations, calculating the deformation rate per unit time and unit length of each baseline segment, revealing the differences in deformation degrees between different regions, and further revealing the detailed changes in the crustal morphology of large plates.

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