CN115657130A - Method for evaluating seismic capability of active fault based on hydrofracturing ground stress measurement technology - Google Patents
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Abstract
The method for evaluating the earthquake generating capacity of the active fault based on the hydrofracturing ground stress measurement technology provided by the invention firstly creatively provides a technical framework for evaluating the earthquake generating capacity of the active fault based on the actually measured ground stress state; the earthquake risk assessment method based on the ground stress state is perfected by utilizing the ground stress measurement data and combining an environmental shear stress formula to assess the earthquake capability of the active fault, so that the application range of the method can be further expanded, and a foundation is laid for realizing the development from the assessment of the risk to the earthquake prediction.
Description
Technical Field
The invention relates to the technical field of active fault seismic capability assessment, in particular to a method for assessing active fault seismic capability based on a hydrofracturing ground stress measurement technology.
Background
The hydrofracturing ground stress measuring method (HF for short) is one of the recommended ground stress measuring methods of international rock mechanics society, and HF is used for fracturing complete rock by using high-pressure water and obtaining pressure-time curve, according to which the fracture pressure P can be determined b Re-opening pressure P r And closing pressure P s (equal to the minimum level of principal stress S h ) According to S h The maximum horizontal principal stress S can be obtained H Selecting the last 3 times of the fracturing curve, and respectively determining P by using dt/dp, maskat method, gradual change method and double tangent method s The average value of 3 methods is used as the final value, and the detailed data processing method and qualityThe amount of control can be referred to (Meng et al, 2015). S v The vertical principal stress is equal to the density of the overlying rock mass multiplied by the thickness of the covering layer; s. the h -a minimum level principal stress; s H -maximum horizontal principal stress; maximum shear stress: average of the difference between the maximum principal stress and the minimum principal stress, three-way principal stress: s. the H ，S h And S v (ii) a The ground stress state is one of the main factors affecting the earthquake occurrence and the stability of the crust of the area, and the Bayer criterion and the ratio (mu) of the maximum shearing stress to the average principal stress are utilized m ) It is possible to judge the earthquake risk of the known active fracture.
At present, when the earthquake risk of the active fault is evaluated, the frame in the prior art can only evaluate whether the active fault has the risk, but can not accurately and quantitatively evaluate the earthquake generating capacity of the active fault and can not provide enough useful information for earthquake prediction; and there is currently no prior art for assessing active fault seismicity based on geostress.
Therefore, the technical personnel in the field are dedicated to develop a method for evaluating the earthquake-causing capacity of the active fault based on the hydrofracturing ground stress measurement technology, and the method aims to solve the problems of the defects in the prior art.
Disclosure of Invention
In view of the above defects in the prior art, the technical problem to be solved by the present invention is that in the prior art, the earthquake-inducing capability of the active fault cannot be evaluated, only whether the active fault is dangerous or not can be evaluated, the earthquake-inducing capability of the active fault cannot be quantitatively evaluated more accurately, and sufficient useful information cannot be provided for earthquake prediction.
In order to achieve the aim, the invention discloses a method for evaluating the earthquake-generating capacity of an active fault based on a hydrofracturing ground stress measurement technology, which comprises the following steps:
s1, collecting seismic geological data and ground stress measurement data;
s2, processing the ground stress measurement data collected in the S1;
s3, according to the measurement data obtained by processing in the step 2, calculating to obtain the maximum shear stress on the critical depth after executing the corresponding step;
s4, substituting the formula into an environmental shear stress formula to estimate the magnitude of the earthquake;
s5, estimating the magnitude of earthquake by combining historical earthquake and structural geological data;
the result of the mechanism solution of the seismic source shows that most earthquakes are shear fracture, namely the fracture of rock under the action of shear stress, so that the level of the shear stress of a region plays an important role in the inoculation of the earthquake; then, deducing an environmental shear stress calculation formula for estimating and constructing a shear stress formula according to the dislocation theory;
the environmental shear stress formula is as follows:
wherein tau is 0 Is an environmental shear stress, corresponding to the tectonic shear stress when an earthquake occurs, M W The moment magnitude is C, the constant is C, and the value range is 0.10-0.16;
the critical depth, namely the shear stress is constant value after exceeding a certain depth until the seismic source depth, and the certain depth is the critical depth;
the step S1, collecting seismic geological data and ground stress measurement data, including actually measured ground stress measurement data, published relevant ground stress measurement data and seismic geological data;
the processing of step S2 is performed based on the collected data of step S1, and can be divided into a case with pre-earthquake ground stress measurement data and a case without pre-earthquake ground stress measurement data;
in the step S2, if the corresponding data processing is carried out, the pre-earthquake ground stress measurement data is not available, and then the step S3A1 and the step S3A2 are carried out in sequence;
S3A1, performing linear fitting on the ground stress data;
step 3A2, calculating the maximum shear stress on the critical depth;
in the step S2, if there is a pre-earthquake ground stress measurement data after performing corresponding data processing, then steps S3B1, S3B2, S3B3, and S3B4 are sequentially performed;
S3B1, performing linear fitting on the pre-earthquake ground stress measurement data;
S3B2, substituting the environmental shear stress formula into the environmental shear stress formula to estimate the critical depth;
S3B3, performing linear fitting on the data of the research area;
step S3B4, calculating the maximum shear stress on the critical depth;
the pre-earthquake ground stress measurement data comprises: measuring depth, S h Minimum horizontal principal stress, S H Maximum horizontal principal stress, S v Perpendicular principal stress, P 0 Hydrostatic pressure,. Mu. m -the ratio of the maximum shear stress to the mean principal stress;
the step S3A1 is carried out under the condition that the geostress measurement data before the strong earthquake does not exist, and at the moment, the linear fitting is directly carried out on the collected geostress data; after linear fitting, S can be obtained H 、S h 、S v The three-dimensional main stress changes along with the depth, and fitting correlation coefficients; therefore, three-dimensional main stress on the depth of 800m can be obtained, and the maximum shear stress can be further calculated;
the critical depth of step S3A2 is preferably 800m, which is a preference obtained by referring to the results of Zoback studies on San Andreas faults;
step S3A2, calculating the maximum shear stress, by substituting the formula between the three-dimensional principal stress and the depth obtained in step S3A1 into the numerical value of the critical depth, the value of the three-dimensional principal stress at the depth can be obtained, and the average value of the difference between the maximum principal stress and the minimum principal stress is the magnitude of the maximum shear stress;
the step S3B1 is performed on the premise that the pre-earthquake ground stress data exists after the processing and analysis in the step S2; performing linear fitting on the processed ground stress data;
step S3B2, estimating the critical depth, firstly, substituting the magnitude of the strong earthquake into an environmental shear stress formula, and then obtaining tau corresponding to the magnitude according to the formula 0 The value is then linearly fitted to the ground stress measurement data to obtain the change of the three-dimensional stress along with the depthThe formula further calculates the change formula of the shear stress with the depth, and then the formula is used for measuring the value of tau 0 The critical depth can be calculated by the substitution;
the step S3B3 of performing linear fitting on the data of the research area is performed after the step S3B2 of obtaining the critical depth, and after the critical depth is obtained, respectively performing fitting on the newly obtained three-dimensional main stress to obtain a fitting formula;
step S3B4, calculating the maximum shear stress at the critical depth is performed after the fitting formula is obtained in step S3B3, and the critical depth calculated in step S3B2 is substituted into the new fitting formula obtained in step S3B3, so that the stress value at the critical depth can be calculated, the formula of the change of the shear stress with the depth is further solved, and then the maximum shear stress at the critical depth can be calculated;
step S4 is performed after step S3A2 or step S3B4 is completed and the value of the maximum shear stress is obtained, and the value of the maximum shear stress obtained in the previous step is substituted into the environmental shear stress formula for calculation, so that the moment magnitude M can be obtained W The value of (d); the magnitude is preliminarily estimated;
in the step S5, the estimation of the seismic level is finally completed by combining the historical earthquake and the tectonic geological data collected in the step S1 and the related data obtained by calculation in the step S4;
further, the critical depth calculated in step S3B2 should be not less than 800m;
further, in the step S3B2, a constant C in the formula of the introduced environmental shear stress formula is C =0.16 (which may be adjusted according to actual conditions);
by adopting the scheme, the method for evaluating the earthquake-generating capacity of the active fault based on the hydrofracturing ground stress measuring technology disclosed by the invention has the following advantages:
(1) The method for evaluating the earthquake-generating capacity of the active fault based on the hydrofracturing ground stress measurement technology innovatively provides a technical framework for evaluating the earthquake-generating capacity of the active fault based on the ground stress for the first time, utilizes the ground stress measurement data in combination with an environmental shear stress formula to evaluate the earthquake-generating capacity of the active fault, and has important inspiration significance for establishing a method with physical significance;
(2) The method for evaluating the earthquake-inducing capacity of the active fault based on the hydrofracturing ground stress measurement technology supplements and perfects a method for evaluating the earthquake risk based on the ground stress, so that the earthquake-inducing capacity of the active fault can be quantitatively evaluated, the defect that only the risk can be evaluated in the traditional evaluation is overcome, and more data which can be collected and informed can be provided for earthquake prediction through the quantitative evaluation; a foundation is laid for realizing more accurate earthquake prediction;
in conclusion, the method for evaluating the earthquake capability of the active fault based on the hydrofracturing ground stress measurement technology disclosed by the invention innovatively provides a technical framework for evaluating the earthquake capability of the active fault based on the ground stress for the first time, utilizes the ground stress measurement data in combination with an environmental shear stress formula to evaluate the earthquake capability of the active fault, can quantitatively evaluate the earthquake capability of the active fault, gets rid of the defect that the traditional evaluation can only evaluate dangerousness, and can provide more credible data for earthquake prediction through quantitative evaluation; and a foundation is laid for realizing more accurate earthquake prediction.
The conception, the specific technical solutions and the technical effects produced by the present invention will be further described with reference to the following detailed description so as to fully understand the objects, the features and the effects of the present invention.
Drawings
FIG. 1 is a schematic diagram of a technical scheme for evaluating the earthquake-inducing capacity of an active fault based on a hydrofracturing ground stress measurement technology;
FIG. 2 is a graph of principal stress versus depth for ZK7 and ZKl3 boreholes in example 1 of the present invention;
fig. 3 is a graph of principal stress versus depth for GYl and GY2 boreholes in example 3 of the present invention.
Detailed Description
The following describes several preferred embodiments of the present invention to make the technical contents thereof clearer and easier to understand. The invention may be embodied in many different forms of embodiments, which are intended to be illustrative only, and the scope of the invention is not intended to be limited to the embodiments shown herein.
Example 1 evaluation of seismic Capacity of active Fault on the coast of Penglai, shandong, by the method of the invention
Firstly, S1, collecting seismic geological data and ground stress measurement data; as the earthquake frequently happens to the Shandong long island, the geostress measurement of 2 drill holes is carried out in a Penglai about 40km away from the long island, so as to collect relevant earthquake geological data and geostress measurement data; wherein the geostress measurements for both boreholes are shown in table l;
TABLE I measurement of the ground stress of the borehole
Tallle 1 Results of in-silu stress mleasuremlent in boreholes
Note: s v -a vertical stress; s v The unit weight of the overlying rock is taken to be 2.70g/cm 3 ；P 0 -hydrostatic pressure. K a -the ratio of the mean horizontal principal stress to the vertical stress; k Hmax Ratio of maximum horizontal principal stress to vertical principal stress, K' under effective stress conditions Hmax ；μ m -ratio of maximum shear stress to mean principal stress.
Subsequently, step S2 is executed, the geostress measurement data collected in step S1 is processed, and after analysis and processing, if it is determined that the embodiment 1 belongs to the case where there is no geostress measurement data before a strong earthquake, steps S3A1 and S3A2 are sequentially executed subsequently;
then, step S3A1 is performed to perform linear fitting on the pre-earthquake ground stress measurement data, that is, the data in table 1 obtained in example 1 is subjected to linear fitting, and S can be obtained after the linear fitting H 、S h 、S v The characteristic that the three-dimensional main stress changes along with the depth and a fitting correlation coefficient; the fitted equation and schematic are shown in fig. 2; wherein the fit equation in example 1 is:
S H ＝4.6565+0.038Z r＝0.73
S h ＝3.134+0.022Z r＝0.77
wherein the maximum shear stress is the average of the differences between the two horizontal principal stresses, i.e., (S) H -S v ) /2), the maximum shear stress is 7.16MPa at a depth of 800m;
then, executing the step S4, substituting the step into an environmental shear stress formula to estimate the magnitude of the earthquake; substituting into the environmental shear stress formula in FIG. 2 to obtain a corresponding moment magnitude of 4.6;
finally, executing the step S5, and estimating the magnitude of the earthquake by combining the historical earthquake and the structural geological data; by combining the geological history data of the earthquake occurring near the latest Penglai, it can be further determined that the upper limit of the earthquake magnitude of the research area of the coastal area of Shandong Penglai in this embodiment 1 is M w 4.6 level conclusion.
Example 2 evaluation of Wenchuan earthquake Activity Fault earthquake Generation Capacity by Using the method of the present invention
Firstly, S1, collecting seismic geological data and ground stress measurement data; step S2, processing the collected ground stress measurement data after the data collection is finished;
because there are actually measured data before the Wenchuan earthquake, there are relevant information before the strong earthquake, so after the step S2 is processed, it is the geostress measured data before the strong earthquake, therefore carry on the step S3B1 subsequently, S3B2, S3B3, S3B4 sequentially;
in example 2, the collected and utilized data are the shear stress data measured by hanging the plate ZK1 on the epicenter of Guo \21855, liang et al (2009); based on the collected data, the data acquisition module is used to acquire the data,
linear fitting is carried out on the ground stress data, a formula between the maximum shear stress and the depth can be obtained after the linear fitting, and fitting correlation coefficients are as follows:
τ＝-11.015+0.041Z r＝0.905
in the fitting formula, the relevant meaning parameters are as follows: tau is the maximum shear stress, r is the correlation coefficient of fitting, Z is the depth, the unit is m, and as can be seen from the formula, the correlation coefficient of the ground stress of the two holes along with the change of the depth is 0.905, and the fitting correlation is good; after obtaining the functional relationship between the maximum shear stress and the depth,
S3B2, estimating the critical depth, namely, firstly, substituting the magnitude of the strong shock into an environmental shear stress formula, then, obtaining a value tau 0 corresponding to the magnitude of the shock according to the formula, then, carrying out linear fitting on the ground stress measurement data to obtain a three-dimensional stress change formula along with the depth, further, solving the shear stress change formula along with the depth, and then, substituting tau 0 to calculate the critical depth;
then, step 3B4 is carried out, the maximum shear stress on the critical depth is calculated, the critical depth obtained by the step 3B2 is substituted into the new fitting formula obtained by the step 3B3, the stress value on the critical depth can be calculated, then the maximum shear stress on the critical depth can be calculated, the maximum shear stress can be deduced through simple calculation, and the magnitude of the shear stress is 21.79MPa in the critical depth;
then, step S4 is executed, that is, the formula of the environmental shear stress in FIG. 2 is substituted, and the magnitude of the moment is M W 7.85；
Finally, step S5 is executed, and the historical earthquake is combined, so that the evaluation method and the Wenchuan M are used W 7.9 are substantially close, it can be seen that the shear stress state before the earthquake is close to the occurrence M W Grade 7.9 earthquake.
Example 3 evaluation of Activity fracture seismic Capacity of Mongolian fracture zone by the method of the invention
Firstly, S1, collecting seismic geological data and ground stress measurement data; wherein the in situ stress measurements for the three boreholes are tabulated as shown in table 2;
TABLE 2 in-situ stress measurement results Table
Table 1 Results of in-situ stress measurement in borehole
Note: (1) s. the h -a minimum level principal stress; s. the H -maximum horizontal principal stress; s v -a vertical principal stress; s. the v The volume weight of the overlying rock is taken as: 2.70g/cm 3 ；P 0 -hydrostatic pressure. Mu.s m -the ratio of the maximum shear stress to the mean principal stress; the units of stress are all MPa; r = (σ) 1 -σ 2 )/(σ 1 -σ 3 )，σ 1 、σ 2 、σ 3 The maximum principal stress, the intermediate principal stress, and the minimum principal stress, respectively. The burial depths of ZK1, ZK2 and ZK3 are 384m, 384m and 354m respectively. Gran is granite spangle rock; gra-ton is Marble cloud amphibolite; gne-grazing gneiss; qua quartz vein.
Subsequently, step S2 is executed, the geostress measurement data collected in step S1 is processed, and after analysis and processing, if it is determined that the embodiment 3 belongs to the case where there is no geostress measurement data before a strong earthquake, steps S3A1 and S3A2 are sequentially executed subsequently;
step S3A1 is executed under the condition that the pre-earthquake ground stress measurement data does not exist, and at the moment, the collected ground stress data is directly subjected to linear fitting; after linear fitting, S can be obtained H 、S h 、S v The three-dimensional main stress changes along with the depth, and fitting correlation coefficients;
the fitting formula in example 3 was such that,
τ＝-0.475+0.009Z r＝0.848
in the fitting formula, the relevant meaning parameters are as follows: tau is the maximum shear stress, r is the correlation coefficient of fitting, Z is the depth, the unit is m, the correlation coefficient of the stress of the two holes along with the change of the depth is 0.848, and the fitting correlation is good;
then, step S3A2 is executed to calculate the maximum shear stress, which is to substitute the formula between the three-dimensional principal stress and the depth obtained in step S3A1 into the value of the critical depth to obtain the value of the three-dimensional principal stress at the depth, wherein the average value of the difference between the maximum principal stress and the minimum principal stress is the value of the maximum shear stress, and the maximum shear stress is the average value of the difference between the two horizontal principal stresses, i.e., (S) ((S) H -S v ) /2), the maximum shear stress is 6.73MPa at a depth of 800m;
then, executing the step S4, substituting the step into an environmental shear stress formula to estimate the magnitude of the earthquake; in the shear stress state of this embodiment 3, the corresponding earthquakeStage M W 4.5 grade;
finally, executing the step S5, and estimating the magnitude of the earthquake by combining the historical earthquake and the structural geological data; by combining historical data on geology of earthquakes occurring near the recently Mongolian fracture zone, namely 'directory of recent earthquakes in China (the year 1912-1990, ms are more than or equal to 4.7)', the method can be further determined, and is consistent with the frequently occurring moderate and strong earthquakes in a research area.
The historical earthquake shows that the earthquake density in the research area is very small, the earthquake mostly occurs in the vicinity of a fracture zone of Mongolian, ms3.3 earthquake occurs in the vicinity of the xanthium mountains from 1912 to 1990, 5.1 earthquake occurs in the xanthium mountains in 1995, and 3-time 5 earthquake in Feiyan county (the earthquake occurs earlier than 1912).
Example 4 evaluation of Activity Fault seismogenic Capacity of Lushan by the method of the invention
Firstly, S1, collecting seismic geological data and ground stress measurement data; collecting related seismic geological data and geostress measurement data near a GQX-1 hole about 20km away from M6.1 seismic epicenter of Lushan; wherein shear stress values measured for the deep portions of the two boreholes are as shown in table 3;
TABLE 3 GQX-1 crustal stress measurement results
Step S2 is executed subsequently, the geostress measurement data collected in step S1 is processed, and after analysis and processing, if the condition that the embodiment 3 belongs to the condition that the geostress measurement data exists before a strong earthquake is judged, the steps S3B1, S3B2, S3B3 and S3B4 are executed subsequently in sequence;
step S3B1 is executed to perform linear fitting on the pre-earthquake ground stress measurement data, that is, the measurement data in table 3 obtained in embodiment 4 is subjected to linear fitting, so that the change of the shear stress with the depth can be obtained.
In the fitting formula of example 4,
wherein the maximum shear stress is the average of the differences between the two horizontal principal stresses, i.e., (S) H -S v ) /2), the maximum shear stress is 12.8MPa at a depth of 800m;
after the functional relation between the maximum shearing stress and the depth is obtained, the step S3B2 is carried out to estimate the critical depth, firstly, the vibration level of the strong earthquake is brought into the environmental shearing stress formula, and at the moment, tau corresponding to the vibration level can be obtained according to the formula 0 The value is then linearly fitted to the measured ground stress data to obtain the change formula of the three-dimensional stress with the depth, the change formula of the shear stress with the depth is further calculated, and then tau is added 0 The critical depth can be calculated by the substitution;
then, step S3B4 is performed to calculate the maximum shear stress at the critical depth, the critical depth calculated in step S3B2 is substituted into the new fitting formula obtained in step S3B3, and the stress value at the critical depth can be calculated, and then the maximum shear stress at the critical depth can be calculated,
then, executing the step S4, substituting the step into an environmental shear stress formula to estimate the magnitude of the earthquake; in the shear stress state of the embodiment 3, the corresponding earthquake magnitude is M W Grade 6.3;
finally, executing the step S5, and estimating the magnitude of the earthquake by combining the historical earthquake and the structural geological data; the evaluation results can be obtained, which are related to M occurring near the goaf of Malus hupehensis W The 5.9-grade earthquake basically coincides.
Example 5 evaluation of Activity Fault seismic Capacity in Guangyuan region by the method of the invention
Firstly, S1, collecting seismic geological data and ground stress measurement data; wherein the in situ stress with respect to both boreholes varies with depth as shown in FIG. 3;
subsequently, step S2 is executed, the geostress measurement data collected in step S1 is processed, and after analysis and processing, if it is determined that the embodiment 5 belongs to the case where there is no geostress measurement data before a strong earthquake, steps S3A1 and S3A2 are sequentially executed subsequently;
step S3A1 is executed under the condition that the geostress measurement data before the strong earthquake does not exist, and at the moment, the linear fitting is directly carried out on the collected geostress data; after linear fitting, S can be obtained H 、S h 、S v The three-dimensional main stress changes along with the depth, and fitting correlation coefficients;
the fitting equation in example 3 is shown in figure 3,
then, step S3A2 is executed to calculate the maximum shear stress, which is the value of the three-way principal stress at the depth obtained by substituting the formula between the three-way principal stress and the depth obtained in step S3A1 into the value of the critical depth, and the average value of the difference between the maximum principal stress and the minimum principal stress is the value of the maximum shear stress, wherein the maximum shear stress is the average value of the difference between the two horizontal principal stresses, i.e., (S) H -S v ) /2), the maximum shear stress of two holes is 17.97MPa and 8.67MPa respectively when the depth is 800m;
then, executing the step S4, substituting the step into an environmental shear stress formula to estimate the magnitude of the earthquake; in the shear stress state of this embodiment 5, the corresponding seismic magnitudes are M respectively W 7.3 and M W 5.12；
Finally, step S5 is executed, and the magnitude of the earthquake is estimated by combining the historical earthquake and the tectonic geological data; the combination of the relevant historical data of the earthquake occurring near the recent Guangyuan can further confirm that the earthquake is matched with the historical earthquake of the research area: since 2008, the maximum magnitude of the region was M W 6.1 (USGS data), ranging from about 50km from the borehole; grade 5.4 earthquakes occurred in 2017.
And (3) comprehensive analysis: in examples 1, 3 and 5, the technical route of the invention based on the pre-earthquake ground stress measurement data without strong earthquake is completed, the fault earthquake generating capability is evaluated by the measuring technology based on the hydrofracture ground stress, and in example 1, the method of the invention is used for obtaining that although the earthquake occurs frequently near the Paulie, the upper limit of the earthquake magnitude of the earthquake is M W 4.6 level conclusion and experienceThe history seismic record can be verified, and the evaluation accuracy is high by adopting the method;
in example 3, according to the book of recent earthquakes in China (Gong Yuan 1912-1990, ms.gtoreq.4.7), in example 3, it was described that, in the vicinity of the fracture zone of Mount Mongolia, ms3.3 earthquake occurred in the vicinity of the Groshan from 1912 to 1990, 5.1 earthquake occurred in the Groshan in 1995, and the earlier earthquake (earlier than 1912) was 3-times 5 earthquake in Fisher county;
in example 5, measurements from two boreholes showed that the magnitude generating capability was between M W 5.12 and M W 7.3, although 2008M W 6.1 seismic magnitude greater than M W 5.12, but the earthquake-triggered fault is not the same fault as the fault evaluated by drilling, and the error between the evaluation seismic level and the actual seismic level is less than 1 level, so that the method verifies that after the evaluation by the method, the earthquake-triggered capacity of the active fault can be quantitatively evaluated, and the prediction is more accurate.
In the embodiments 2 and 4, the technical route based on the earthquake stress measurement data without strong earthquake is completed, and in the embodiment 2, the conclusion that the magnitude of the Wenchuan moment is Mw7.85 can be obtained, the conclusion is basically similar to the actual situation, and the earthquake stress prediction method has good earthquake intensity prediction capability; in the embodiment 4, in the evaluation of the active fault seismic capability of lushan, the difference amplitude between the evaluation result and the actual result is 6%, and the difference amplitude is basically consistent with the actual seismic activity condition;
through the embodiment, the capability of the research area for generating earthquake magnitude is in positive correlation with the magnitude of the shear stress, and the larger the shear stress is, the stronger the earthquake generating capability is;
the method of the invention estimates the earthquake generating capacity of the active fault based on the ground stress measurement data and has strong consistency with the actual result, which shows that the method has practicability and rationality.
In summary, according to the technical scheme, a technical framework for evaluating the earthquake generating capacity of the active fault based on the ground stress measurement technology of the hydraulic fracture is innovatively provided for the first time, and the method for evaluating the earthquake generating capacity of the active fault by combining ground stress measurement data with an environmental shear stress formula can be used for quantitatively evaluating the earthquake generating capacity of the active fault, so that the defect that only danger can be evaluated in the traditional evaluation is overcome, and more credible data can be provided for earthquake prediction through quantitative evaluation; and a foundation is laid for realizing more accurate earthquake prediction.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations can be devised by those skilled in the art in light of the above teachings. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (8)
1. A method for evaluating the earthquake generating capacity of an active fault based on a hydrofracturing ground stress measurement technology is characterized by comprising the following steps:
s1, collecting seismic geological data and ground stress measurement data;
s2, processing the ground stress measurement data collected in the S1;
s3, according to the measurement data obtained by processing in the step 2, calculating to obtain the maximum shear stress on the critical depth after executing the corresponding step;
s4, substituting the formula into an environmental shear stress formula to estimate the magnitude of the earthquake;
s5, estimating the magnitude of earthquake by combining historical earthquake and structural geological data;
the environmental shear stress formula is as follows: lg τ 0 ＝0.15M ω + C, wherein τ 0 Is an environmental shear stress, corresponding to the tectonic shear stress when an earthquake occurs, M W The moment magnitude is C, the constant is C, and the value range is 0.10-0.16.
2. The method of assessing the seismicity of an active fault as claimed in claim 1,
the step S1, collecting seismic geological data and ground stress measurement data, including actually measured ground stress measurement data, published relevant ground stress measurement data and seismic geological data;
the processing of step S2 is performed based on the collected data of step S1, and can be divided into a case with pre-earthquake ground stress measurement data and a case without pre-earthquake ground stress measurement data.
3. The method of assessing active fault seismicity of claim 1,
step 3, according to the measurement data processed in step 2, dividing the measurement data into two situations, namely pre-earthquake ground stress measurement data and non-pre-earthquake ground stress measurement data;
in the step S2, after the corresponding data processing, there is no pre-earthquake ground stress measurement data, and then the step S3A1 and the step S3A2 are sequentially performed;
S3A1, performing linear fitting on the ground stress data;
and S3A2, calculating the maximum shear stress on the critical depth.
4. The method of assessing active fault seismicity of claim 1,
in the step S2, if there is a pre-earthquake ground stress measurement data after performing corresponding data processing, then steps S3B1, S3B2, S3B3, and S3B4 are sequentially performed;
S3B1, performing linear fitting on the pre-earthquake ground stress measurement data;
S3B2, substituting the environmental shear stress formula into the environmental shear stress formula to estimate the critical depth;
S3B3, performing linear fitting on the data of the research area;
S3B4, calculating the maximum shear stress on the critical depth;
the pre-earthquake ground stress measurement data comprises: measuring depth, S h Minimum horizontal principal stress, S H Maximum horizontal principal stress, S v Perpendicular principal stress, P 0 Hydrostatic pressure,. Mu. m -ratio of maximum shear stress to mean principal stress.
5. The method of assessing the seismicity of an active fault as claimed in claim 1,
the step S3A1 is carried out under the condition that the pre-earthquake ground stress measurement data does not exist, and at the moment, the linear fitting is directly carried out on the collected ground stress data; after linear fitting, S can be obtained H 、S h 、S v The three-dimensional main stress changes along with the depth, and fitting correlation coefficients; therefore, three-dimensional main stress on the depth of 800m can be obtained, and the maximum shear stress can be further calculated;
in the step S3A2, the maximum shear stress is calculated by substituting the formula between the three-dimensional principal stress and the depth obtained in the step S3A1 into the value of the critical depth, so as to obtain the value of the three-dimensional principal stress at the depth, and the average value of the difference between the maximum principal stress and the minimum principal stress is the value of the maximum shear stress.
6. The method of assessing the seismicity of an active fault as claimed in claim 1,
the step S3B1 is performed on the premise that the pre-earthquake ground stress data exists after the processing and analysis in the step S2; performing linear fitting on the processed ground stress data;
step S3B2, estimating the critical depth, firstly, substituting the magnitude of the strong earthquake into an environmental shear stress formula, and then obtaining tau corresponding to the magnitude according to the formula 0 The value is then linearly fitted to the measured ground stress data to obtain the change formula of the three-dimensional stress with the depth, the change formula of the shear stress with the depth is further calculated, and then tau is added 0 The critical depth can be calculated by the substitution;
the step S3B3 of performing linear fitting on the data of the research area is performed after the step S3B2 of obtaining the critical depth, and after the critical depth is obtained, respectively performing fitting on the newly obtained three-dimensional principal stress to obtain a fitting formula;
the step S3B4 of calculating the maximum shear stress at the critical depth is performed after the fitting formula is obtained in the step S3B3, the critical depth calculated in the step S3B2 is substituted into the new fitting formula obtained in the step S3B3, and then the stress value at the critical depth can be calculated, the formula of the change of the shear stress with the depth is further calculated, and then the maximum shear stress at the critical depth can be calculated.
7. The method of assessing active fault seismicity of claim 1,
step S4 is performed after step S3A2 or step S3B4 is completed and the value of the maximum shear stress is obtained, and the value of the maximum shear stress obtained in the previous step is substituted into the environmental shear stress formula for calculation, so that the moment magnitude M can be obtained W The value of (d); the magnitude is preliminarily estimated;
and step S5, combining the historical earthquake and the tectonic geological data collected in step S1 and the related data obtained by calculation in step S4 to finally complete the estimation of the magnitude of earthquake.
8. The method of assessing the seismicity of an active fault as claimed in claim 1,
the critical depth calculated in step S3B2 should be not less than 800m;
in step S3B2, the constant C in the formula of the introduced environmental shear stress formula is C =0.16 (which may be adjusted according to actual conditions).
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