阅读说明：本技术 一种基于地震目录对长断层类型和危险性分段的方法 (Method for segmenting long fault type and danger based on earthquake directory ) 是由 王蕤 韩鹏 孙健维 曾志毅 陈泓燕 常莹 缪淼 于 2020-12-25 设计创作，主要内容包括：本发明公开了一种基于地震目录对长断层类型和危险性分段的方法,包括：获取地震目录；设计空间网格系统,基于断层上的地震目录计算各网格点处的b值,将b值的空间分布作为地下应力状态和断层类型在地震目录中的反映；对断层上的地震目录进行时间窗的划分,并基于不同时间窗内的地震目录计算各网格点处b值,作为该时间窗内的b值空间分布；计算时间窗间的b值的差,将b值的时间变化作为地下应力变化在地震目录中的反映,以判断断层上应力的变化和断层的危险性。本发明通过对断层两侧的地震事件的空间b值分布和b值变化计算,分析b值的空间分布和变化,直观反映断层的断层类型和应力加载状态,直接反映断层的风险性。(The invention discloses a method for segmenting long fault types and dangers based on an earthquake directory, which comprises the following steps: acquiring an earthquake directory; designing a spatial grid system, calculating a b value at each grid point based on a seismic catalog on a fault, and taking the spatial distribution of the b value as the reflection of an underground stress state and a fault type in the seismic catalog; dividing a time window of the seismic catalog on the fault, and calculating the b value at each grid point based on the seismic catalogs in different time windows to serve as the b value spatial distribution in the time window; and calculating the difference of the b values among the time windows, and reflecting the time change of the b value in an earthquake catalogue as the underground stress change so as to judge the stress change on the fault and the fault danger. The method analyzes the spatial distribution and the change of the b value by calculating the spatial b value distribution and the b value change of the seismic events at two sides of the fault, visually reflects the fault type and the stress loading state of the fault and directly reflects the risk of the fault.)

1. A method for segmenting long fault types and hazards based on seismic catalogs, comprising:

acquiring an earthquake directory;

designing a spatial grid system, calculating a b value at each grid point based on a seismic catalog on a fault, and taking the spatial distribution of the b value as the reflection of an underground stress state and a fault type in the seismic catalog;

dividing a time window of the seismic catalog on the fault, and calculating the b value at each grid point based on the seismic catalogs in different time windows to serve as the b value spatial distribution in the time window;

and calculating the difference of the b values among the time windows, and reflecting the time change of the b value in an earthquake catalogue as the underground stress change so as to judge the stress change on the fault and the fault danger.

2. The method of claim 1, wherein the seismic catalog data is acquired by a national seismic grid center.

3. The method of claim 1, wherein said calculating b-values at grid points comprises:

and searching the seismic events around each grid point based on the seismic catalog on the fault or the seismic catalogs in different time windows, and calculating the b value at each grid point.

4. The method of claim 1, wherein said determining changes in stress on faults and fault risk comprises:

and the fault types of the long fault are segmented and distinguished according to the stress state and the stress change of the long fault given by the time change of the b value, and the stress change of each segment of the fault and the danger of each region of the fault are intuitively reflected.

5. A method according to any one of claims 1 to 4, wherein the value of b is calculated using a maximum likelihood method.

6. The method of claim 5, wherein the complete magnitude is calculated using maximum curvature and the b-value is calculated using a seismic catalogue above the complete magnitude.

7. The method of any one of claims 1 to 4, wherein the higher the value of b, the lower the subsurface stress level; the lower the b value, the higher the subsurface stress level.

8. The method of claim 7, wherein b is increased, stress relieved; b value is reduced and stress loading is carried out.

9. The method of any one of claims 1 to 4, wherein the error in the calculation of the b-value is assessed by the standard deviation of the b-value.

10. The method of any one of claims 1 to 4, wherein the significance of the change in b-value is assessed by the Chi-pool information criterion.

Technical Field

The invention relates to the technical field of earthquake risk prediction, in particular to a method for segmenting long fault types and risks based on an earthquake directory.

Background

The stress on the fault is loaded due to the extrusion collision among the plate blocks, and when the stress is loaded to exceed the maximum static friction force on the fault, the fault can generate dislocation and fracture, and further seismic activity is generated.

Conventional fault risk assessment methods include seismic risk assessment modeling and geodetic methods, wherein,

the earthquake risk assessment model method is based on the simulation results of thousands of possible disaster events in the event framework of thousands of years in the past, displays the relationship between the potential damage degree and the disaster occurrence frequency, and can calculate the average value and the extreme value of the damage according to the relationship. From the perspective of the insurance industry, the probabilistic risk assessment model can quantitatively analyze the natural disaster (disaster-causing factor), the vulnerability, the distribution of the insurance target areas and the insurance conditions, and the final output result is the total loss of all the insurance target areas under the insurance conditions.

The disadvantages of the earthquake risk assessment model method are as follows: the time for building the earthquake table network is relatively short, disaster data can be traced back for about one hundred years, but the disaster data is less than one period of a major earthquake, and the risk can be underestimated; also, the transition of the formation activity may cause changes in the seismic activity and risk of the area.

Geodetic measurements are the determination of position, earth shape, gravitational field and their time and space varying surveying activities performed to establish and maintain surveying fiducials and surveying systems. Geodetic surveying may determine ground point locations, earth sphere shape and size, and precision measurements of the earth's gravitational field, the contents of which include triangulation, precision wire measurements, leveling, astronomical measurements, satellite geodetic measurements, gravity measurements, geodetic calculations, and the like.

The geodetic method has the advantages that information is obtained visually, the observation range is wide, the movement rate and loading of the plate are determined through the earth surface displacement, and the earth crust movement is displayed visually; but the disadvantages are: there is a lack of subsurface information and, for areas of weak slip, there is no way to distinguish between the danger zone of slip loss due to high stress concentrations at fault roughness or the safe zone of weak stress loading.

The most intuitive and direct earthquake prediction method is the observation of underground stress, and the most common methods for traditional earth stress observation comprise a stress recovery method, a stress relief method and a hydraulic fracturing method, and also comprise an earth physical method, a geological structure information method, a drilling failure information method, an underground stress mapping method and other observation methods.

However, the above observation methods are all based on drilling construction and logging data, and are difficult to perform continuous observation; the traditional method can realize continuous observation by arranging a stress meter sensor in a deep well obtained by drilling underground, and the method is intuitive and effective and still depends on the drilling technology. The drilling cost is high, the observation window is small, and the depth can reach several kilometers; and the occurrence of major earthquakes can reach less than ten kilometers, and the implementation of earth stress observation is difficult for long faults and large-range risk monitoring.

Disclosure of Invention

In view of the above problems in the prior art, the present invention provides a method for segmenting long fault types and hazards based on seismic catalogs.

The invention discloses a method for segmenting long fault types and dangers based on an earthquake directory, which comprises the following steps:

acquiring an earthquake directory;

designing a spatial grid system, calculating a b value at each grid point based on a seismic catalog on a fault, and taking the spatial distribution of the b value as the reflection of an underground stress state and a fault type in the seismic catalog;

dividing a time window of the seismic catalog on the fault, and calculating the b value at each grid point based on the seismic catalogs in different time windows to serve as the b value spatial distribution in the time window;

and calculating the difference of the b values among the time windows, and reflecting the time change of the b value in an earthquake catalogue as the underground stress change so as to judge the stress change on the fault and the fault danger.

As a further improvement of the invention, the seismic catalogue data is obtained through a national seismic table network center.

As a further improvement of the present invention, the calculating the b value at each grid point includes:

and searching the seismic events around each grid point based on the seismic catalog on the fault or the seismic catalogs in different time windows, and calculating the b value at each grid point.

As a further improvement of the present invention, the determining a change in stress on a fault and a risk of the fault includes:

and the fault types of the long fault are segmented and distinguished according to the stress state and the stress change of the long fault given by the time change of the b value, and the stress change of each segment of the fault and the danger of each region of the fault are intuitively reflected.

As a further improvement of the invention, the b value is calculated by a maximum likelihood method.

As a further improvement of the method, the complete earthquake magnitude is calculated by adopting a maximum curvature method, and the b value is calculated by taking the earthquake directory above the complete earthquake magnitude.

As a further improvement of the invention, the higher the b value, the lower the subsurface stress level; the lower the b value, the higher the subsurface stress level.

As a further improvement of the invention, the b value is increased, and the stress is released; b value is reduced and stress loading is carried out.

As a further improvement of the present invention, the calculation error of the b-value is evaluated by the standard deviation of the b-value.

As a further improvement of the present invention, the significance of the change in b-value was evaluated by the Chi-pool information criterion.

Compared with the prior art, the invention has the beneficial effects that:

the method analyzes the spatial distribution and the change of the b value by calculating the spatial b value distribution and the b value change of the seismic events at two sides of the fault, visually reflects the fault type and the stress loading state of the fault and directly reflects the risk of the fault.

Drawings

FIG. 1 is a flow chart of a method for segmenting long fault types and hazards based on a seismic directory as disclosed in one embodiment of the present invention;

FIG. 2 is a schematic diagram of the magnitude frequency relationship of an earthquake according to an embodiment of the present invention;

FIG. 3 is a schematic illustration of seismic catalog selection as disclosed in one embodiment of the present invention;

FIG. 4 is a schematic diagram of the spatial distribution of b values with time windows 2000.1.1-2008.4.30 according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of the spatial distribution of b values with time windows 2000.1.1-2004.12.31 according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of the spatial distribution of b values with time windows 2004.1.1-2008.4.30 according to an embodiment of the present invention;

FIG. 7 is a schematic illustration of the spatial distribution of b-value variation according to an embodiment of the disclosure;

FIG. 8 is a schematic diagram illustrating a complete spatial distribution of b-value variation according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

The invention is described in further detail below with reference to the attached drawing figures:

as shown in FIG. 1, the invention provides a method for segmenting long fault types and dangers based on a seismic directory, which comprises the following steps:

step 1, acquiring an earthquake catalogue;

the earthquake directory data are obtained through a national earthquake table network center, and comprise a serial number, a magnitude, an origin moment, a latitude, a longitude, a depth and a reference position, wherein the serial number is 1, the magnitude is 5.3, the origin moment is 2020-12-0808: 47:20, the latitude is 22.29, the longitude is 144.95, the depth is 20km, and the reference position is as follows: the area of the volcanic isles of japan.

Step 2, designing a spatial grid system, searching seismic events around each grid point based on a seismic catalogue on a fault, calculating a b value at each grid point, and reflecting the spatial distribution of the b value in the seismic catalogue as an underground stress state and a fault type;

step 3, dividing a time window for the seismic catalog on the fault, searching seismic events around each grid point based on the seismic catalogs in different time windows, and calculating the b value at each grid point as the b value spatial distribution in the time window;

and 4, calculating the difference of the b values among the time windows, taking the time change of the b value as the reflection of the underground stress change in an earthquake catalogue, and carrying out sectional differentiation on the fault type of the long fault according to the stress state and the stress change of the long fault given by the result, so as to visually reflect the stress change of each section of the fault and the danger of each region of the fault.

Furthermore, the method adopts a maximum likelihood method to calculate the b value, simultaneously adopts a maximum curvature method to calculate the complete earthquake magnitude when calculating the b value, and takes the earthquake catalogue above the complete earthquake magnitude to calculate the b value.

Further, in the method for segmenting the long fault type and the danger based on the earthquake catalogue, the principle is that the value b and the underground stress level are in an inverse relation; the higher the b value, the lower the subsurface stress level, and the lower the b value, the higher the subsurface stress level. Due to the fact that stress levels of different types of faults are different, the normal fault stress level is low, the b value is larger than 1, the walk-slip fault stress level is medium, the b value is about 1, and the back-impact fault stress level is high, and the b value is smaller than 1. The b-value decreases when the subsurface stress is loaded and decreases when the subsurface stress is relieved. Therefore, b can only visually reflect the underground stress state, fault type and stress change.

Further, the calculation error of the b-value was evaluated by the standard deviation of the b-value, and the significance of the change in the b-value was evaluated by the Chichi information criterion.

Example (b):

the invention provides a method for segmenting long fault types and dangers based on an earthquake directory, which specifically comprises the following steps:

the earthquake catalogue data updated in real time by the Chinese earthquake platform network can be used for processing the data in real time and rapidly analyzing the risk of the fault.

As shown in FIG. 2, the magnitude frequency relation of an earthquake is:

logN＝a-bM

wherein M is seismic magnitude, N is the number of seismic events with magnitude not less than M, a is constant, and b is constant.

The formula for calculating the value b by adopting the maximum likelihood method is as follows:

and in order to ensure the reliability of the result, the b value is calculated by taking the earthquake catalogue above the perfect earthquake magnitude. Preferably, the complete magnitude is calculated by the maximum curvature method (the maximum curvature of the magnitude-frequency curve shown in fig. 2 is the complete magnitude); in the formula, M_cIn order to complete the magnitude of the vibration,is the seismic magnitude above the perfect seismic magnitude.

In the above example, seismic directories within 60 km on both sides of the fault before the occurrence of the Wenchuan earthquake in 2000 were selected, as shown in FIG. 3. The lines in the region 1(region1) are the main fracture occurring portions when an earthquake occurs, and the lines in the region 2(region2) are the main fracture non-occurring portions when an earthquake occurs.

As shown in fig. 4, in the above embodiment, the grid interval is preferably selected to be 5 km, and the b value of the point is calculated from data of 60 km around the grid point. In the above embodiment, it is preferable to reserve the grid points in which the number of earthquakes is greater than 100. It can be seen that the b value distribution has obvious change, the b value of the main fracture occurrence area is high and is more than 1.2, and the b value of the non-occurrence main fracture area is less than 1.2 and is as low as 0.7. In the above embodiment, the b-value spatial distribution result matches the fault type of the fault, and the epicenter is mainly north in slip type, and gradually changes into reverse fault from south of the fault.

As shown in fig. 5 and 6, the seismic catalog is divided into two time windows of 1 month 1 to 12 months 31 in 2000 and 1 month 1 to 4 months 30 in 2014 to calculate the spatial distribution of the b value. In the above embodiment, it is preferable that the grid interval is 5 km, and the b value at the point is calculated from data of 60 km around the grid point. In the above embodiment, it is preferable to reserve the grid points in which the number of earthquakes is greater than 100. The b value distribution is the same as that of FIG. 4, and corresponds to the fault type of the fault.

As shown in fig. 7, the difference between the results of fig. 6 and fig. 5 indicates that the main fracture occurred in the b-value decreased to reflect the stress accumulation at this stage and the risk increased, and that the main fracture non-occurred in the b-value increased to reflect the stress release at this stage and the risk decreased. This result corresponds to the fracture state of the fault at the time of the earthquake and to the regional risk distribution after the earthquake.

Specifically, using the mathematical statistics method, the formula for P-testing the b value difference in two sample windows using the akage pool information criterion (AIC) is as follows:

in the formula, N₁Number of seismic events in primary fracture incidence zone, N₂Number of seismic events in the primary fracture non-occurrence region, b₁B value of the primary fracture occurrence region, b₁The b value is the value of the area where the primary fracture did not occur.

Probability P of no difference of its samples_bComprises the following steps:

in the above embodiments, it is preferred to retain b value results with confidence intervals greater than 85%. In the primary fracture zone, there were 2 zones with significantly lower b values, reflecting that stress buildup was rapid compared to the other zones. When an earthquake occurs and the fault breaks, the probability of the fault has larger sliding distance and higher risk. The two extreme seismic zones of the occurred Wenchuan earthquake coincide with two zones of significant drop in pre-earthquake b-values.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.