Method for monitoring large-plate earth crust deformation by using GNSS baseline time sequence

Abstract

The invention provides a method for monitoring large-plate crustal deformation by using a GNSS baseline time sequence, and belongs to the field of crustal deformation monitoring. The method comprises the following steps: firstly, determining a to-be-monitored large plate area and GNSS monitoring stations in the large plate area, and evaluating the monitoring data quality of each station; then, the arc length between the monitoring stations is calculated, and the changing process of the arc length along with time is calculated; then, analyzing and revealing the relative motion condition between the large plates and the deformation degree of a local area, and obtaining the overall condition and details of the obtained deformation; in addition, the baseline result can be further analyzed, and monitoring and analysis are carried out through different stations and directions. The method can effectively monitor the deformation of the large-plate earth crust, facilitates earth crust structure research and earthquake early 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, by using two GNSS stations on the earth, making a geodesic between the two stations, and then continuously monitoring the length change of the geodesic, the traditional baseline time series monitoring can be replaced, and thus the GNSS baseline time series technical means has emerged. This means is mostly applied to monitoring crustal deformation because its advantage is that it does not need to be restricted to the traditional steel baseline. As long as there are GNSS stations, theoretically, GNSS baseline time series can be made, and its convenience and universality are much better than the traditional baseline time series monitoring.

[0003] One of the main uses of GNSS baseline time series in earthquake research is to monitor large-scale crustal deformation, such as the relative movement between large plates, whether it is accelerating / decelerating / stable, so as to provide a reference basis for other monitoring means. However, there is a main problem when using the baseline to monitor large-scale crustal deformation currently: it is not clear what the crustal deformation reflected by the baseline is exactly.

[0004] Generally, it is considered that the earth is more like an ellipsoid compared to a spherical shape. Therefore, when calculating the baseline, it is also assumed that the earth is an ellipsoid. However, the disadvantage of doing so is that the calculation of the geodesic of the ellipsoid is very troublesome, and the theoretical exact solution cannot be obtained either. It can only be continuously approximated by iteration, and the calculation efficiency is relatively low. When there are many baselines to be calculated, a lot of time is spent.

[0005] Judging the relative movement change of large plates only from the baselines obtained from two stations. As a result, if different stations are selected, the obtained results are often different, and finally it falls into a situation of "not being able to explain clearly". Over time, this method has been 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 situations of large plate crustal deformation, especially to accurately display the detailed changes of 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 fields such as earthquake prediction and geological research.

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

[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 (instead of the elliptical arc length), and calculate the change process of the arc length over time;

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

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

[0012] After obtaining the baseline results, further form the baseline map of adjacent stations to analyze the results of each baseline separately, and compare the deformation rates of different regions through the method of normalization calculation.

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

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

[0015] In one solution, the analysis and revelation of the relative movement between large plates and the deformation degree of local areas include performing linear fitting according to the baseline time series to obtain the straight line slope, that is, the overall change rate of the baseline;

[0016] Divide the change rate by the arc length between two points to obtain the baseline deformation rate per unit time and per unit length; and use colors to represent the normalized deformation rates of the baselines of different GNSS stations.

[0017] In one solution, when understanding the relative movement information in other directions, select the corresponding stations in other directions and perform the same steps for the monitoring and analysis of relative movement.

[0018] In one solution, the method includes the analysis of the baseline results, the display of the baseline results between adjacent stations, the calculation of the deformation rate per unit time and per unit length of each baseline, the revelation of the difference in the deformation degree between different regions, and further the revelation of the detailed change situation of the crustal morphology of large plates.

[0019] In one solution, the method calculates by considering the earth as a perfect sphere, and the error from the result of calculating by considering the earth as an ellipsoid is 0.02 mm - 0.04 mm

[0020] Advantages of the present invention:

[0021] A method for monitoring large - plate crustal deformation using GNSS baseline time series provided by the present invention can accurately reflect the crustal deformation of large plates through precise calculations and data analysis, effectively solving the problem of unclear understanding of crustal deformation in the existing technology when calculating baselines.

[0022] This method can not only monitor the relative movement between large plates, but also view the deformation degree of local areas, facilitating the acquisition of the overall situation and details of the deformation. An adaptive algorithm is used to calculate GNSS baselines, ensuring the accuracy of the calculation and the performance of the algorithm.

[0023] In previous calculations, technicians always calculated according to the shape of the Earth itself (ellipsoid), but the disadvantage of this is that the calculation of the geodetic line of the ellipsoid is very troublesome and the theoretical exact solution cannot be obtained. Therefore, in the calculation process, an iterative algorithm is used for multiple iterations, and multiple iterations will lead to too slow calculation speed. This application directly regards the Earth as a perfect sphere for calculation, without the need to use the method of multiple iterations to continue the calculation, greatly accelerating the calculation speed, and the error between the calculation result and the result calculated by multiple iterations of the ellipsoid is between 0.02 mm and 0.04 mm. This result error is extremely small, greatly improving the calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a comparison diagram of GNSS site baseline time series results under a sphere and an ellipsoid;

[0025] Figure 2 It is a schematic diagram of the physical meaning of GNSS baselines;

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

[0027] Figure 4 It is the baseline time series result of the baseline group. Due to the compression background, the original baseline time series are all shortened, and the baseline time series in the figure are all the results after detrending. DETAILED DESCRIPTION OF THE INVENTION

[0028] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Typical embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0029] Unless otherwise defined, all technical and scientific terms used in this invention have the same meanings as those understood by those skilled in the technical field to which this invention pertains. The terms used in the description of this invention in this specification are only for the purpose of describing specific embodiments and are not intended to limit this invention. To facilitate the understanding of this invention, the following will provide a more comprehensive description of this invention with reference to the relevant drawings. The drawings show typical embodiments of this invention. However, this invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of this invention more thorough and comprehensive.

[0030] The essence of GNSS baseline time series is a geometric problem, and its meaning is clear: it reflects the change relationship of the distance between two points over time; its physical meaning is: in the direction of the line connecting these two points, the total deformation amount between the two points (such as Figure 2 ). For example, Figure 1 for points A and B in, the GNSS baseline time series result reflects the total deformation amount between A and B in the direction of the line connecting A and B. The deformation conditions in the areas to the left of point A and to the right of point B, that is, the areas outside AB, cannot be reflected by the GNSS baseline time series; and the specific details of the deformation between points A and B cannot be reflected either. The GNSS baseline time series can only reflect the total deformation amount between the two points. To sum up: The physical meaning of the GNSS baseline time series has three points: it only reflects (1) in the direction of the line connecting two points, (2) between two points, and (3) the total deformation amount.

[0031] Assume the Earth to be a sphere, so that the calculation of the geodesic does not require iteration, and the calculation process can be said to be completed instantly. This saves a large amount of time in the calculation of a large number of baselines. Moreover, the difference between the baselines under the sphere and under the ellipsoid is less than 5%, which is completely sufficient for analyzing large-scale crustal deformation. For example, Figure 1 , for the baselines obtained by selecting two stations with a relatively large distance apart, the two stations are about 4750 kilometers apart. The blue line in the upper figure is the baseline result under the sphere, and the orange line is the baseline result under the ellipsoid; the lower figure is the difference between the two results. Generally, the farther the distance, the greater the difference between the geodesics under the sphere and under the ellipsoid. From the results in the figure, the two results are almost coincident, indicating that the sphere model is completely sufficient.

[0032] Specifically for the surrounding plates, if the station is within the plate, since the plate pushes against the Eurasian plate, this point can be called an active point, and the points within the Eurasian plate can be called passive points. For example, Figure 2, if the active point A pushes against the passive point B, then according to the physical meaning of the GNSS baseline time series, the baseline result reflects the total deformation between AB; if both A and B are in a rigid region, then the baseline result reflects the deformation of the continuous deformation region between the two rigid blocks, but how this deformation changes within the region, whether it is the curve 1, curve 2 or curve 3 in the figure or a more complex curve, cannot be obtained only from the GNSS baseline time series between AB.

[0033] The mode of the Indian plate pushing against the Qinghai-Tibet Plateau is related to Figure 2 corresponding. Whether studying the pushing effect in the northwestern or northeastern direction, the active point is selected as Bangalore (IISC) within India. If the passive point is selected within the relatively rigid Eurasian block or the Mongolian Plateau, then the total pushing amounts of the Indian plate in the northwestern and northeastern directions can be obtained from the GNSS baseline time series.

[0034] Based on the above conclusions, some baselines may not be able to reflect the pushing of the Indian plate on the entire Qinghai-Tibet Plateau. For example, the baseline from Bangalore (IISC) to Lhasa (LHAS). From the above understanding, the baseline reflects the pushing effect of the Indian plate in the northeastern direction to the area south of Lhasa, rather than the pushing effect on the entire Qinghai-Tibet Plateau. The pushing effect of the Indian plate on the area north of Lhasa cannot be reflected.

[0035] Furthermore, in order to refine Figure 2 the specific situation of the deformation between points A and B, a series of stations (if any) can be inserted by connecting A and B. These stations divide the area between AB into multiple small areas, and the deformation of these small areas can be obtained through the GNSS baseline time series between multiple points. The detailed degree of 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 presents a general scheme for monitoring the crustal deformation of large plates using GNSS baseline time series:

[0037] The process of baseline calculation:

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

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

[0040] (2) Then, based on the time series changes of these two stations, that is, the daily position changes of the stations, the latitudes and longitudes of the stations can be obtained every day.

[0041] (3) In this way, the arc length between two points each day can be obtained. Subtracting the arc length of the first day of monitoring from all the arc lengths gives the relative change process of the arc length, from which a time series of the arc length changing with time is obtained. The changing process of the arc length with time is the GNSS baseline.

[0042] Introduction to the solution process:

[0043] S1. Data collection: The data mainly comes from two sources. One is the data of the "China Crustal Movement Observation Network" and the "Mainland China Tectonic Environment Monitoring Network" (this data is not publicly available, but can be applied for within the earthquake system. The data format is placed at the end of the document). The other is the global data of IGS (International GNSS Service), which is publicly available (the data format is placed at the end of the document).

[0044] First, determine the large plate area to be monitored. For example, to monitor the relative movement between the Indian Plate and the Tibetan Plateau (such as Figure 3 ), it is necessary to first determine whether there are GNSS stations with good monitoring quality on the large plate. For example, there is IISC on the Indian Plate, and the monitoring quality of the station is very good; there are also some stations on the Tibetan Plateau, such as XZRK, QHTT, DLHA, and DXIN, with generally good quality. There is also a farther station ULAB across the Tibetan Plateau, with good monitoring quality. The so-called stations with very good monitoring quality meet the following conditions: (1) There are very few missing data; (2) The time series fluctuations of the stations are basically controlled within 10 mm. Then, operate according to the following process:

[0045] (1) Determine a certain direction of the relative movement of the large plate to be monitored. Such as Figure 3 , what we are concerned about is the relative movement of the Indian Plate in the northeast direction with respect to the Tibetan Plateau. Then, try to select GNSS stations in this direction.

[0046] (2) Select the two farthest stations to form a baseline and analyze the baseline results.

[0047] (3) Then, in the Figure 3 way, form baselines between adjacent stations, display the baseline results, analyze the baseline results of each segment, and at the same time calculate the deformation rate per unit time and per unit length of each segment of the baseline after normalization.

[0048] (4) Analyze the baseline results: From (3), the overall deformation characteristics in the direction of the line connecting the two farthest stations can be obtained; from (4), the deformation details can be obtained, and the richness of the details shown depends on the number of GNSS stations inserted in the middle. If there are more intermediate stations, the details of the relative movement will be richer; finally, through normalization calculations, the deformation degrees of different segments can be compared, such as which segment deforms faster and which segment deforms slower. (The specific process of normalization is: (1) First, linearly fit the baseline time series to obtain the slope of the straight line, and this slope is the overall change rate V of the baseline; (2) Divide V by the arc length between the two points, so as to obtain the baseline deformation rate value per unit time and per unit length, and different GNSS stations' baseline normalization deformation rates are represented by colors.)

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

[0050] Through the above scheme, the overall and local information of the relative movement between large plates can be truly obtained. The degree of detail display of information acquisition depends on the density of GNSS stations. This scheme can end the previous debates on "internal deformation information of the baseline" and "unclear baseline results". For example Figure 4 Yes Figure 3 The baseline result is: For the baseline connecting Bangalore (IISC) - Ulaanbaatar (ULAB), it can be seen that there has been an obvious acceleration of compression since 2020, which indicates that there is a compression acceleration area in the range from Bangalore (IISC) to Ulaanbaatar (ULAB) in the northeast direction. However, it is not known where this compression area is because the baseline only reflects the overall deformation. By using the baseline group, it can be seen that the compression acceleration since 2020 appears in the area between Dingxin (DXIN) - Ulaanbaatar (ULAB). The time series of each GNSS baseline south of Dingxin (DXIN) shows stable compression loading. The results show that the northeastward pushing effect of the Indian plate is absorbed by the Qinghai-Tibet Plateau, but the absorption rates in different regions are different. Among them, the region between QHTT and DLHA has the highest absorption deformation rate, and the region north of DXIN has the lowest absorption rate. However, since 2020, there has been a phenomenon of compression acceleration in the area north of the Alxa block. In this way, the overall and local details of the relative movement between the Indian plate and the Qinghai-Tibet Plateau are displayed completely and accurately.

[0051] Data formats of "China Crustal Movement Observation Network" and "China Mainland Tectonic Environment Monitoring Network":

[0052]

[0053] The first line is the unit of data calculation. The second line is the initial longitude, latitude, elevation, and station name of the site. The next two lines are the jumps at a certain time point when the site changes over time. Then follows the time series of the site, where the first column is the GNSS time, the second column is the year, the third column is the day of the year, and the fourth, fifth, and sixth columns are the displacements in the north, east, and vertical directions. The last three columns are the errors of the data in the fourth, fifth, and sixth columns, with the unit of "meter".

[0054] Data format of "IGS" stations:

[0055]

[0056] The content of each column is respectively: station name, specific year, month, and day of observation, GNSS time, Julian day, GNSS week, day of the week, initial eastward value, eastward change value, initial northward value, northward change value, initial vertical value, vertical change value, then the corresponding errors, and the last three items are latitude, longitude, and elevation, with the unit of "meter".

[0057] Data processing first converts the data of "China Crustal Movement Observation Network" and "China Mainland Tectonic Environment Monitoring Network" and "IGS" data into the following form:

[0058]

[0059] The first line is the longitude, latitude, elevation, and station name of the site. The first column below is the GNSS time, the second column is the year, the third column is the day of the year, and the fourth, fifth, and sixth columns are the displacements in the east, north, and vertical directions. The last three columns are the displacement errors in the north, east, and vertical directions, with the unit of "millimeter". The converted data facilitates baseline calculation.

[0060] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The said program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above various methods. Among them, the said storage medium can be a magnetic disk, an optical disc, a read-only memory (ROM), or a random access memory (RAM), etc.

[0061] It should be understood that the detailed description of the technical solutions of the present invention with the aid of the preferred embodiments above is illustrative rather than restrictive. Those of ordinary skill in the art can modify the technical solutions recorded in each embodiment on the basis of reading the specification of the present invention, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims

1. A method for monitoring large plate crust 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 the monitoring stations and calculate the change of arc length over time; (3) Analyze and reveal the relative movement 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 farthest apart were selected as baseline references to yield the most comprehensive picture of change; After obtaining the baseline results, a baseline map of adjacent sites is further formed to analyze the results of each section of the baseline separately, and the deformation rates of different areas are compared by normalized calculation method.

2. The method for monitoring large plate crust deformation using GNSS baseline time series according to claim 1, characterized in that: The determination of the large plate 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, data missing is small, and station timing fluctuations are controlled within 10 mm.

3. The method for monitoring large plate crust 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 according to the daily site position change, and subtracting the arc length of the first day of monitoring from all arc lengths, so as to obtain a time series of arc length changes over time, namely, the GNSS baseline.

4. The method for monitoring large plate crust deformation using GNSS baseline time series according to claim 1, characterized in that: The analysis described reveals the relative motion between the large plates and the degree of deformation in the local area, 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; Divide the rate of change by the arc length between the two points to obtain the baseline deformation rate per unit time and unit length; Colors are used to represent the baseline normalized deformation rates of different GNSS stations.

5. The method for monitoring large plate crust deformation using GNSS baseline time series according to claim 1, characterized in that: When the relative motion information in different directions is known, corresponding stations are selected in different directions and the same steps are performed to monitor and analyze the relative motion.

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

7. The method of monitoring large plate crust deformation using GNSS baseline time series according to claim 1, characterized in that: The method described herein considers the earth to be a perfect sphere for calculation, and the error between the method described herein and the method described herein that considers the earth to be an ellipsoid for calculation is 0.02 mm to 0.04 mm.

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