CN111830561B - Method for constructing fault three-dimensional structure based on seismic distribution characteristics - Google Patents
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- G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
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- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
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Abstract
The invention discloses a method for constructing a fault three-dimensional structure based on seismic distribution characteristics, which comprises the steps of firstly, collecting geological information of a region where a target fault is located; discretizing the target fault plane into a plurality of sub fault planes, assuming that seismic events all occur on the sub fault planes, taking the horizontal distance between a seismic source and the sub fault planes as an error, and obtaining a model equation of each sub fault plane by using a least square method; taking the middle point of each sub fault surface as a lattice point of a final result to obtain a three-dimensional structure model of the target fault; obtaining three-dimensional structural features of the target fault based on the gathered geological information and the three-dimensional structural model of the target fault. The method can economically and effectively depict the three-dimensional fine structure of the fault zone, is favorable for researching scientific problems such as geological structure evolution process, earthquake risk assessment, earthquake pregnancy mechanism and the like, and has important theoretical and practical significance.
Description
Technical Field
The invention relates to the technical field of geological disaster research, in particular to a method for constructing a fault three-dimensional structure based on seismic distribution characteristics.
Background
At present, earthquakes frequently occur in active fault areas, high earthquake disaster risks are faced, the three-dimensional structure of the active fault with high resolution and high precision is obtained, a reliable model is provided for earthquake risk assessment, researches on earthquake pregnancy mechanisms and other scientific problems, and earthquake scientific development is promoted. In the prior art, earthquake methods for researching a fault structure mainly comprise a natural earthquake imaging method and an active earthquake source earthquake method, but the two methods are long in time consumption and high in cost, and the three-dimensional fault structure is not precisely depicted. For the method of constraining fault morphology according to seismic distribution characteristics, the prior art also has research, for example, according to the principle that cluster small earthquake occurs in the major earthquake fault plane and the vicinity thereof, the simulated annealing algorithm and the Gauss-Newton algorithm are combined, and a steady estimation method for solving the trend, the dip angle, the position and the error of the major earthquake fault plane by using the intensity of the small earthquake is provided; through seismic clustering analysis, parameters of each sub fault plane are fitted by using partial aftershocks of Landers earthquake occurring in 1992, 6 and 28 months; based on the earthquake repositioning result, the geometrical parameters of 6.6-grade earthquake-induced fault of Xinjiang Jinghe in 2017, 8 months and 9 days are fitted.
However, the constraint of the above research on fault planes is limited to the horizontal direction, and although a scheme of performing layered piecewise fitting on a fault structure by using seismic activity data and constraining in the vertical direction of the fault is also used, the fault constructed by the scheme has the problem that the difference of sub fault planes is large, an intuitive main fault three-dimensional structure model cannot be provided, and the fault partition blocking characteristic cannot be judged.
Disclosure of Invention
The invention aims to provide a method for constructing a fault three-dimensional structure based on seismic distribution characteristics, which can economically and effectively depict a three-dimensional fine structure of a fault zone, thereby being beneficial to researching scientific problems such as a geological structure evolution process, seismic risk assessment, a seismic pregnancy mechanism and the like, and having important theoretical and practical significance.
The purpose of the invention is realized by the following technical scheme:
a method of constructing a fault three-dimensional structure based on seismic profile characteristics, the method comprising:
and 4, acquiring the three-dimensional structural feature of the target fault based on the geological information collected in the step 1 and the three-dimensional structural model of the target fault.
According to the technical scheme provided by the invention, the method can economically and effectively depict the three-dimensional fine structure of the fault zone, thereby being beneficial to researching scientific problems such as geological structure evolution process, earthquake risk assessment, earthquake pregnancy mechanism and the like, and having important theoretical and practical significance.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the description below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic flow chart of a method for constructing a fault three-dimensional structure based on seismic distribution characteristics according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the method of the present invention;
FIG. 3 is a schematic diagram of an exemplary embodiment of an arrangement of an interrupt layer model 1 according to the present invention;
FIG. 4 is a schematic diagram of an exemplary break layer model 2 according to the present invention;
FIG. 5 is a schematic diagram of an exemplary embodiment of a break layer model 3 according to the present invention;
FIG. 6 is a diagram illustrating inversion results of an exemplary discontinuity model 1 according to the present invention;
FIG. 7 is a diagram illustrating inversion results of an exemplary fault model 2 according to the present invention;
FIG. 8 is a diagram illustrating the inversion results of an exemplary discontinuity model 3 according to the present invention;
FIG. 9 is a plot of a Parkfield area station and seismic profile, Calif., in an example of the present invention;
FIG. 10 is a schematic illustration of a Parkfield area seismic profile in an example of the present invention;
FIG. 11 is a schematic diagram of the discretized planar inversion results of Saint Anderson faults in an example of the present invention;
FIG. 12 is a graph illustrating SANDLEIS fault smoothing fault plane results in an exemplary embodiment of the present invention;
FIG. 13 is a graphical illustration of resolution results of Saint Anderson fault inversion in an example of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are 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 only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the present invention will be further described in detail with reference to the accompanying drawings, and as shown in fig. 1, a schematic flow chart of a method for constructing a fault three-dimensional structure based on seismic distribution characteristics according to the embodiment of the present invention is provided, where the method includes:
in the geological information collection process, the seismic distribution data of the target fault are classified, the data belonging to the same main fault belong to the same class, and fitting is performed in a subsequent inversion method respectively.
the process of the step specifically comprises the following steps:
firstly, discretizing the target fault plane into M sub fault planes, wherein the jth sub fault plane is expressed as:
x＝a j ·z+b j ·y+c j (1)
wherein x, y and z are seismic positions; a is j ，b j ，c j Representing parameters controlling the jth sub-fault plane;
the target fault is modeled as follows:
m＝[a 1 ，b 1 ，c 1 ，a 2 ，b 2 ，c 2 ......a m ，b m ，c m ] T (2)
FIG. 2 is a schematic diagram of the method of the present invention, wherein the five-pointed star in FIG. 2 represents the seismic source, the solid line represents the fault, the dashed line represents the horizontal distance between the seismic source and the fault, and the location of the ith seismic event (x) is assumed to occur on the subfraction level i ，y i ，z i ) It should satisfy:
x i ＝a j ·z i +b j ·y i +c j (3)
x i for the data to be fitted, the data set is then:
d＝[x 1 ，x 2 ，......，x n ] T (4)
then, a G matrix is established:
and sets the first order smoothing term L1:
wherein A is a constraint relation parameter between the same attribute parameters of the transversely adjacent sub fault planes; b is a constraint relation parameter between the same attribute parameters of the longitudinally adjacent sub fault planes, and is specifically expressed as follows:
using the horizontal distance between the seismic source and the sublevel as an error to make the seismic source and the sublevel have the same lengthConstraining the model by minimizing the root mean square error
And obtaining a model equation of each sub fault plane.
in this step, the evaluation of the target fault three-dimensional structure model may be performed by a resolution matrix, which is specifically expressed as:
R＝(G T ·G+α 2 ·L1 T ·L1) -1 ·G T ·G (9)
and averaging the parameters belonging to the same plane on the R diagonal line to obtain a final resolution result.
And 4, acquiring the three-dimensional structural feature of the target fault based on the geological information collected in the step 1 and the three-dimensional structural model of the target fault.
In this step, the three-dimensional structural feature of the target fault includes: and the fault plane morphological characteristics reflect geological action characteristics or stress characteristics, earthquake lockout zone distribution characteristics and earthquake danger characteristics.
The following describes and verifies the process of the above method in detail by using specific examples, which specifically include:
1. model testing
The method of the embodiment of the invention is subjected to three fault model tests, and the fault model 1 is respectively generated:
x＝-0.5z-2
-20≤y≤20
-50≤z≤0
and (3) fault model 2:
z＝0.3x 2 -12x+68
-20≤y≤20
-50≤z≤0
the fault model 3:
-20≤y≤20
-50≤z≤0
then, 100 seismic positions are randomly generated in a fault plane, and the generated seismic data x value is added with a random error of a standard normal distribution to obtain test data corresponding to three fault models respectively, as shown in fig. 3, a setting schematic diagram of a fault model 1 in an example of the present invention is shown, fig. 4 is a setting schematic diagram of a fault model 2, and fig. 5 is a setting schematic diagram of a fault model 3, wherein: fig. 3, 4 and 5 (a) are theoretical fault planes; (b) the circles represent random seismic events for the fault plane side view.
The inversion results obtained finally are shown in fig. 6, 7 and 8, fig. 6 is a schematic diagram of the inversion result of the fault model 1 in the example of the present invention, fig. 7 is a schematic diagram of the inversion result of the fault model 2, and fig. 8 is a schematic diagram of the inversion result of the fault model 3, where: fig. 6, 7 and 8 (a) are the discrete fault planes obtained by inversion; (b) calculating a result for the resolution; (c) a final smooth model is obtained for connecting the midpoints of the planes; (d) circles represent random seismic events as a difference from the original theoretical model X direction. From the inversion results, it can be known that: the difference from the original fault plane is small (each lattice point error is within 1 km), and the area with low resolution means that the number of earthquakes is small, and the earthquake locking area can be correspondingly shocked.
The fault simulation result shows that the method provided by the embodiment of the invention has high accuracy, and is feasible and feasible.
2. Performing Fault three-dimensional structure inversion on SanAndrea Fault (SAFZ for short) of California
The saint anderses faults throughout the southwestern, california, usa at the intersection of north american slabs moving south-east and pacific slabs moving north-west, feature a transition fault property with a right-handed walk, as shown in fig. 9 for Parkfield stations and seismic profiles, california, usa in an example of the invention, where: triangles are seismic stations; the very center point is the drilling location of the SAFOD; the solid line is the saint anderlis fault; the colors at different points along the fault represent different depths of the earthquake; the plus sign indicates the cartesian rectangular coordinate system used.
The seismic data used here were 560 earthquakes recorded by 68 temporary ground stations (Zhang et al, 2009) with the Parkfield region centered on a SAFOD well, as shown in fig. 10, which is a schematic diagram of the distribution of the Parkfield region earthquakes in the illustrated example of the present invention, where: in a side view, data in a rectangular frame is reserved, and data in an oval frame is removed; the earthquakes in the rectangular frame are assumed to belong to the same main fault.
By adopting the fault structure constraint method provided by the embodiment of the invention, as shown in fig. 11, a schematic diagram of a discretization plane inversion result of the Saint Anderson fault in the illustrated example of the invention is shown, and a dot represents a seismic event; FIG. 12 is a graph showing the results of the Saint Anderson fault smoothing fault plane in the illustrated example of the present invention, and it can be seen that: the whole Saint Androsts active fault is a nearly vertical main fault as deep as 10km, and the structure is clearer. In the shallow part, the fault trend is parallel to the Y axis, and the observation of the earth surface is met (figure 9); in the deep part, the Y-axis negative direction (northwest) segment is deflected toward the X-axis negative direction (northeast), and the Y-axis positive direction (southeast) segment is deflected toward the X-axis positive direction (southwest). This spiral fault structure result indicates that san andex activity fractures have experienced different periods of geologic structure evolution and stress distribution characteristics.
FIG. 13 is a schematic diagram showing the resolution results of the Saint Anderson fault inversion in the example of the present invention, and the resolution analysis results show that the resolution of the area with the depth of 7-9 km is 0, that is, no earthquake occurs in the station observation time period; the resolution is lower in the area with Y ranging from 0km to 9km and the depth ranging from 6km to 8 km. The low resolution area indicates that the two areas of the fault are likely to be occluded and the earthquake is less likely to occur.
Through the construction of the Saint Anderson fault plane, the fault construction method has the advantages that the fitting result of the fault construction method is high in precision and high in reliability, and the obtained fault three-dimensional structure can provide good model support for researches such as geological structure characteristics, stress characteristics and earthquake pregnancy mechanism characteristics.
It is noted that those skilled in the art will recognize that embodiments of the present invention are not described in detail herein.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (3)
1. A method for constructing a fault three-dimensional structure based on seismic distribution characteristics is characterized by comprising the following steps:
step 1, collecting geological information of a region where a target fault is located, wherein the geological information comprises geological structure characteristics, analysis stress characteristics and fault motion characteristics, and providing reference for construction of a three-dimensional structure of the target fault;
step 2, discretizing the target fault plane into a plurality of sub fault planes, assuming that seismic events all occur on the sub fault planes, taking the horizontal distance between a seismic source and the sub fault planes as an error, and obtaining a model equation of each sub fault plane by using a least square method;
the process of the step 2 specifically comprises the following steps:
firstly, discretizing the target fault plane into M sub fault planes, wherein the jth sub fault plane is expressed as:
x＝a j ·z+b j ·y+C j (1)
wherein x, y and z are seismic positions; a is j ，b j ，c j Representing parameters controlling the jth sub-fault plane;
the target fault is modeled as follows:
m＝[a 1 ，b 1 ，c 1 ，a 2 ，b 2 ，c 2 ......a M ，b M ，c M ] T (2)
assuming that the seismic events all occur on the sub-fault plane, the location (x) of the ith seismic event i ，y i ，z i ) Should be full ofFoot:
x i ＝a j ·z i +b j ·y i +c j (3)
x i for the data to be fitted, the data set is then:
d＝[x 1 ，x 2 ，......，x n ] T (4)
then, a G matrix is established:
and sets the first order smoothing term L1:
wherein A is a constraint relation parameter between the same attribute parameters of the transversely adjacent sub fault planes; b is a constraint relation parameter between the same attribute parameters of the longitudinally adjacent sub fault planes, and is specifically expressed as follows:
constraining the model by minimizing the root mean square error using the horizontal distance of the seismic source from the sub-fault plane as the error, in particular by minimizing
Obtaining a model equation of each sub fault plane;
step 3, taking the middle point of each sub fault surface as a lattice point of a final result to obtain a three-dimensional structure model of the target fault;
and 4, acquiring the three-dimensional structural feature of the target fault based on the geological information collected in the step 1 and the three-dimensional structural model of the target fault.
2. The method for constructing a fault three-dimensional structure based on seismic distribution characteristics as claimed in claim 1, wherein in the geological information collection process of step 1, the seismic distribution data of the target fault are classified, data belonging to the same main fault are assigned to the same class, and are respectively fitted in a subsequent inversion method.
3. The method for constructing fault three-dimensional structure based on seismic distribution characteristics as claimed in claim 1, wherein in step 4, the three-dimensional structure characteristics of the target fault comprise: and the fault plane morphological characteristics reflect geological action characteristics or stress characteristics, earthquake lockout zone distribution characteristics and earthquake danger characteristics.
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