CN114036785A - Deep sea hydrothermal area deep structural stress field simulation method based on ocean hull velocity structure - Google Patents
Deep sea hydrothermal area deep structural stress field simulation method based on ocean hull velocity structure Download PDFInfo
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Abstract
The invention discloses a deep sea hydrothermal area deep structure stress field simulation method based on an ocean shell velocity structure, which comprises the following steps of: firstly, selecting a stress analysis area, and establishing a geometric model of the analysis area; secondly, elastic mechanical parameters are calculated based on the ocean shell sound wave speed structure of the research area, a geomechanical model is built, finite element numerical simulation is carried out on the built geomechanical model, and a deep stress field of the research area is obtained; then, calculating a one-dimensional velocity model by utilizing the ocean shell sound wave velocity structure, repeating the step 3 and the step 4, and calculating a self-weight stress field; and finally, subtracting the self-weight stress field in the step 6 from the stress field in the step 4 to obtain a deep structural stress field of the research area. The method combines the distribution characteristics of the deep tectonic stress field of the submarine hydrothermal area with the geological process, and compared with other methods, the method can quickly establish the complete and high-resolution deep stress field distribution characteristics of the research area, thereby revealing the mechanism of the occurrence of the related geological process of the research area.
Description
Technical Field
The invention relates to the field of deep sea hydrothermal area stress field simulation, in particular to a deep sea hydrothermal area deep structure stress field simulation method based on an ocean shell velocity structure.
Background
In recent years, with the consumption of land mineral resources and the development of deep sea investigation technology, the exploration and development of seabed mineral resources become targets of competitive research and development of various countries, and seabed polymetallic sulfide is a mineral resource with potential commercial exploitation value because of having shallow water depth and being rich in a large amount of heavy metal elements, is expected to become the first object of deep sea exploitation and bears the tomorrow of ocean resources. In 2012, China and the International seabed management office formally sign exploration contracts of multi-metal sulfide exploration areas in the south-west Indian ocean, strives for initiative in future development and utilization of international seabed resource mineral products in China, completes the abandonment of areas in concordance areas, and develops research work on related resource evaluation such as space distribution, scale, occurrence conditions and the like of ore bodies in resource mineral areas.
The hydrothermal circulation process in deep sea is an important factor that submarine sulfide resources can be accumulated on the surface of deep sea, and geological and geophysical related researches show that deep sea hydrothermal circulation dominated by a detached fault is an important type in global hydrothermal circulation, and the high permeability characteristic of the detached fault plays a role of a fluid migration channel in the process of the deep sea hydrothermal circulation. The results of microseismic detection show that: the two sides of the detached fault are the areas with the most frequent geological motions, such as earthquake activity, rock breakage and the like, the rock breakage or sliding process in turn also improves the permeability of the crust, and an upwelling channel is further provided for hydrothermal circulation. Therefore, understanding the mechanism of rock fracture and seismic action is helpful to further understand the deep sea hydrothermal circulation process and reveal the mineralization mechanism of the seabed sulfide mineral.
Currently, research on deep stress fields in deep sea hydrothermal regions is very limited, and most research focuses on inversion of seismic source mechanism solutions. The current seismic source mechanism solution can only solve the stress state of one or more points in the earth crust, the cost of arranging one-time microseismic detection is huge, the inversion result extremely depends on the platform arrangement position and the inversion technology, and the method is a time-consuming and resource-consuming method. In contrast, the numerical simulation method can obtain the stress state of the whole research area, hardly consumes manpower and material resources, is a quick, economic and effective mode, and has important value for understanding the sulfide resource mineralization mechanism, rock fracture, earthquake occurrence and other processes of the deep-sea hydrothermal area.
Disclosure of Invention
The invention aims to provide a method for simulating a deep-sea hydrothermal area deep stress field of an ocean shell velocity structure, which is a method for carrying out stress numerical simulation by utilizing an ocean shell P-wave velocity structure and submarine topography data and disclosing a related geological process occurrence mechanism in the ocean shell of the deep-sea hydrothermal area by combining a geomechanical analysis method according to the distribution characteristics of the deep-sea structural stress field. So as to make a new exploration for understanding the dynamic geological process of the deep-sea hydrothermal area and solve the defects in the prior art. Under the condition of the prior art, the method has the advantages of rapidness, economy and effectiveness.
In order to achieve the purpose, the invention adopts the following technical scheme: a deep sea hydrothermal area deep structure stress field simulation method based on an ocean shell velocity structure is characterized by comprising the following steps:
step 1: selecting a stress analysis area; establishing a geometric model of the analysis area according to the selected area and the submarine topography data;
step 2: calculating elastic mechanical parameters including Poisson's ratio, density and Young modulus based on the ocean shell sound wave velocity structure of the stress analysis region, and establishing a geomechanical model;
and step 3: and setting boundary conditions, loading loads, gridding the model and carrying out finite element numerical simulation on the established geomechanical model. Setting boundary conditions by combining with specific geological structure conditions of a stress analysis region; in order to adapt to the characteristics of the fluctuation of the submarine topography, a free mesh division strategy is adopted in the gridding process of the model; and the load applied inside the model is a gravity load and is loaded on each grid point to obtain a simulated self-weight stress field.
And 4, step 4: the method comprises the following steps that an ocean shell sound wave velocity structure in a stress analysis area is a two-dimensional velocity model, and a one-dimensional velocity model is established for the velocity value of each depth being equal to the average value of the velocity of the two-dimensional model at the depth; repeating the process of the step 2-3, and simulating to obtain a self-weight stress field of the stress analysis area;
and 5: and 3, subtracting the self-weight stress field obtained by the simulation in the step 4 from the self-weight stress field obtained by the simulation in the step 3 to obtain a deep structural stress field of the stress analysis region, and analyzing the stress state of the stress analysis region.
Further, in step 2, the ocean shell acoustic velocity structure is obtained by inversion calculation of seismic waves acquired by a submarine seismograph.
Further, the specific calculation formula for calculating the elasticity parameter by using the ocean shell sound wave velocity structure shown in step 2 is as follows:
μ＝Vs 2ρ (5)
E＝μ(3λ+2μ)/(λ+μ) (6)
in the above formulae (1) to (6), VPAnd VsRespectively representing the propagation speeds of longitudinal waves and shear waves in a stratum medium, and the unit is m/s; sigma is the Poisson's ratio of the rock, and the ratio of the absolute value of the transverse positive strain to the absolute value of the axial positive strain; ρ represents the density of the rock in g/cm3(ii) a λ is Lame constant, μ is shear modulus, E is Young's modulus, in N/m2(ii) a In combination with equations (1) - (6), the density, Young's modulus and Poisson's ratio of the rock can all be determined according to the longitudinal wave velocity VPAnd (6) calculating.
Further, the setting method of the boundary condition in step 3 is as follows: the south boundary and the north boundary respectively apply 8mm/y and 7mm/y expansion rates, the upper boundary applies hydrostatic pressure according to the depth of the sea bed, a calculation formula is represented by a formula (7), and the lower boundary is fixed.
Fs＝ρgh (7)
In the above formula FsExpressed as hydrostatic pressure in Pa, ρ expressed as sea water density in kg/m3。
Further, in step 3, the calculation of the gravity load value is obtained according to a global gravity acceleration calculation formula of the IEC standard, wherein the calculation formula is as follows:
in the formula (I), the compound is shown in the specification,
as the latitudeThe value is in degrees, north latitude is positive, Z is altitude, in meters, above the horizontal plane is positive, and g represents acceleration of gravity.
Further, the stress analysis region one-dimensional velocity model extraction in step 4 is specifically as follows: a two-dimensional velocity model to be researched is selected, a certain depth d is given, all velocity values of the depth are extracted, and an average value is calculated to be used as the velocity value of the one-dimensional model at the depth. And sequentially calculating the speed average value of each depth to obtain a one-dimensional speed model corresponding to the two-dimensional speed model.
Further, the stress state analysis method in the step 5 specifically includes: extracting a first main stress field according to a simulation result, considering that a positive value of the first main stress represents tension and a negative value represents tension by solid mechanics, combining the simulation result of the stress with a geological phenomenon of a stress analysis area, analyzing an earth dynamic process mechanism of the stress analysis area, and revealing the processes of rock earthquake generation and fluid migration in the ocean shell, wherein the specific mode is as follows:
(1) simulating the distribution characteristics of the stress field according to the established model and the boundary condition;
(2) extracting a first principal stress sigma 1 distribution diagram;
(3) the tensile stress (sigma 1 is more than 0) is corresponding to the tensile fracture of the rock, induces earthquake, causes the low-speed abnormality of earthquake wave P wave and provides a channel for the migration of fluid;
(4) the compressive stress (sigma 1 is less than 0) corresponds to the rock compaction action, and causes the high-speed abnormality of the seismic wave P wave. The invention has the beneficial effects that: the method combines the distribution characteristics of the deep structural stress field of the submarine hydrothermal area with the geological process, and provides a finite element simulation method of the deep stress field of the submarine hydrothermal area based on the ocean shell velocity structure.
Drawings
FIG. 1 is a flow chart of the implementation of the present invention.
FIG. 2 is a submarine topography of a research area during the practice of the present invention, black lines indicate the location of the test at a depth of 13km from sea surface to below sea surface, 40km in the north-south direction, and white asterisks in the middle indicate the location of sulfide mines.
Fig. 3 is a geometric diagram of a model built during the implementation of the present invention, the black line representing the position of the detached fault, the upper surface being the sea floor, corresponding to the position of the black line L1 in fig. 2.
Fig. 4 is a diagram of a two-dimensional ocean hull velocity map established in the practice of the present invention.
Fig. 5 is a one-dimensional ocean hull velocity structure diagram established in the practice of the present invention.
FIG. 6 is a diagram of elastic parameters established when simulating a total stress field in the process of implementing the invention, from top to bottom, Young's modulus (MPa) and density (kg/m) respectively3) Poisson's ratio.
Fig. 7 is a total stress field S1 resulting from the practice of the present invention.
FIG. 8 is a diagram of elastic parameters of a model established when a self-weight stress field is simulated in the implementation process of the invention, wherein the elastic parameters are Young's modulus (MPa) and density (kg/m) from top to bottom respectively3) Poisson's ratio.
Fig. 9 is a deadweight stress field S2 resulting from the practice of the present invention.
FIG. 10 is a tectonic stress field, S1-S2, resulting from the practice of the present invention, with the open circles representing seismic source locations.
Detailed Description
The embodiments of the present invention will be described in detail below with reference to the drawings and specific examples, and the implementation steps, functions and advantages of the present invention can be easily understood by those skilled in the art from the description. The invention can also be applied to other types of mine finding work on the seabed, and technicians can adjust various details, such as the acquisition modes of various data, the accuracy of topographic data and the like, according to different application scenes on the premise of not departing from the spirit of the invention. It should be noted that any detail modification made by those skilled in the art within the scope of the claims falls within the protection scope of the present invention.
Referring to the flow chart of fig. 1, the present invention provides a deep sea hydrothermal area deep tectonic stress field simulation method based on ocean hull velocity structure, including the following steps:
step 1: selecting a stress analysis area, and generally selecting an area near a deep sea sulfide mining area;
step 2: establishing a geometric model of an analysis area according to the selected area and the submarine topography data; the depth selection should consider the thickness of the crust of the study area, the depth of the earthquake, the depth of the detached fault and the like, and the depth of the model should be greater than the maximum depth of the detached fault under the condition that the maximum depth of the P-wave velocity structure data allows. The upper surface of the model is the submarine topography of the research area, and the left and right boundaries are generally rectangular boundaries which can be changed according to specific research targets.
And step 3: elastic mechanical parameters (Poisson ratio, density and Young modulus) are calculated based on the ocean shell sound wave speed structure in the research area, and a geomechanical model is built. The method for calculating the elasto-mechanical parameters by using the acoustic velocity is obtained from a result of Thomas M.Brocher in 2005, and the method requires that the acoustic velocity is in a rock medium of 1500-:
μ＝Vs 2ρ (5)
E＝μ(3λ+2μ)/(λ+μ) (6)
in the above formulae (1) to (6), VPAnd VsRespectively representing the propagation speeds of longitudinal waves and shear waves in a stratum medium, and the unit is m/s; sigma is the Poisson's ratio of the rock, and the ratio of the absolute value of the transverse positive strain to the absolute value of the axial positive strain; ρ represents the density of the rock in g/cm3(ii) a λ is Lame constant, μ is shear modulus, E is Young's modulus, in N/m2. Combining the formulas (1) to (6), the elastic parameters (density, Young modulus and Poisson's ratio) of the rock can be determined according to the longitudinal wave velocity VPAnd (6) calculating.
In the step 3, the crustal acoustic velocity structure is obtained by geophysical exploration in the early stage, particularly seismic exploration, and the required model resolution can be constructed in an interpolation or sampling mode according to the requirement on the resolution in the simulation process; the calculation in the step 3 is to calculate the Poisson's ratio and the Young's modulus according to the longitudinal wave velocity and combining the formulas (1) and (2), then calculate the transverse wave velocity, the Lame constant and the shear modulus for the pair by using the formulas (3), (4) and (5), and finally substitute the formula (6) to calculate the Young's modulus. The use conditions of the equations (1) to (6) are that the velocity of the longitudinal wave is in the range of 1500m/s to 8500m/s, and the above process converts the velocity model into a geomechanical model. The vast majority of the sound wave velocity of the seabed stratum is within the range, and the method has wide applicability.
And 4, step 4: setting boundary conditions, loading loads and model gridding for the established geomechanical model, and selecting a calculation method to carry out finite element numerical simulation. The boundary conditions are set in combination with the specific geological structure conditions of the research area. The setting method comprises the following steps: the south boundary and the north boundary respectively apply 8mm/y and 7mm/y expansion rates, the upper boundary applies hydrostatic pressure according to the depth of the sea bed, a calculation formula is represented by a formula (7), and the lower boundary is fixed.
Fs＝ρgh (7)
In the above formula FsExpressed as hydrostatic pressure in Pa, ρ expressed as sea water density in kg/m3。
As shown in fig. 2, for the subject being southwestern indian ocean longman 2605050in the example of the invention, the black line in fig. 2 represents the location of the test at a depth of 13km from sea surface to below sea surface, 40km from north to south, and the middle white asterisk is the location of the sulfide ore field. A two-dimensional north-south model and a depth model are established, the geometric diagram of the model is shown in fig. 3, the black line represents the position of the detached fault, and the upper surface is the sea floor corresponding to the position of the black line L1 in fig. 2. The constructed two-dimensional ocean hull velocity structure diagram is shown in fig. 4. The expansion rate of 7mm/y is respectively applied to two sides by taking the middle ridge as the center, the hydrostatic pressure corresponding to the specific seawater depth is applied to the sea bottom surface, and the lower bottom surface is set as a constraint surface. In order to adapt to the characteristics of the fluctuation of the submarine topography, a free mesh division strategy is adopted in the gridding process of the model, and the method can be almost suitable for any submarine model. The load applied inside the model is gravity load and is loaded on each grid point, the value is calculated according to the global gravity acceleration calculation formula of the IEC standard, and the calculation formula is as follows:
wherein the content of the first and second substances,
is latitude value in degrees, north latitude is positive, Z is altitude in meters, above the horizontal plane is positive, and g represents acceleration of gravity.
The elastic parameter graph established in simulating the total stress field is shown in FIG. 6, which is from top to bottom, Young's modulus (MPa) and density (kg/m)3) Poisson's ratio. The total stress field is shown in fig. 7.
The operation flow implemented in the step (4) is specifically as follows:
1) giving the elastic parameters obtained by calculation in the step 3 to the geometric model established in the step 2, and establishing an elastic mechanical model;
2) setting boundary conditions, wherein the loading of the boundary conditions is required according to the specific geological conditions of the research area, and taking the hot liquid area of Indian dragon in southwest as an example in the embodiment of the invention. The upper boundary is the sea floor, the hydrostatic pressure generated by loading seawater is loaded, the hydrostatic pressure of each point is related to the depth of the sea floor, and the specific formula is represented by (7); the left and right sides are expressed as expansion rate boundaries, and geological and geophysical research results show that the expansion of the area is asymmetrical in the north-south direction, the south side (8mm/y) is slightly larger than the north side (7mm/y), the simulation of the embodiment takes the middle ridge as the center, and the north and south sides are respectively loaded with the expansion rates of 8mm/y and 7 mm/y; the lower boundary of the model is a fixed interface.
3) The load is a gravity load, and a gravity acceleration g is applied to each grid point, and the calculation of the value can be obtained by the formula (8).
4) The model is gridded, and models suitable for the fluctuation change of the boundary terrain, such as triangular meshes and hexagonal meshes, can be selected, the grid division precision can meet the analysis of a target task, and the precision of 'fine' is selected in the embodiment. The gridding mode of the model adopts free gridding and adopts finite element mode to solve, and the equation adopted by numerical simulation is a stress balance equation:
in the above formula, σ: normal stress in Pa; τ: shear force in Pa; x, Y, Z: external forces in three directions, in units of N, Z is gravity, in units of N, X, Y is set to 0;
and 5: establishing a one-dimensional model according to a two-dimensional speed model of a research area, wherein the speed value of each depth is equal to the average value of the speed of the two-dimensional model at the depth;
as shown in FIG. 5, the specific way of establishing the one-dimensional velocity model according to the two-dimensional velocity model in step 5 is: selecting a certain depth d1, adding the velocity values of all the depths in the two-dimensional model to obtain an average value, and obtaining v01,v01Is the velocity value of the one-dimensional velocity model at that depth. And then, the average speed of each depth value is sequentially obtained, so that the whole one-dimensional speed model corresponding to the two-dimensional model can be obtained.
Step 6: repeating the processes of the steps 2, 3 and 4 by using the one-dimensional velocity model obtained in the step 5, and calculating to obtain a self-weight stress field of the research area; the elastic parameter diagram of the model established when simulating the dead weight stress field is shown in FIG. 8, which is from top to bottom respectively Young's modulus (MPa) and density (kg/m)3) Poisson's ratio. The deadweight stress field is shown in fig. 9.
In the process of repeating the steps 2, 3 and 4 in the step 6, the stress field numerical simulation of the one-dimensional velocity model is completely the same as that of the two-dimensional velocity model in the steps 2, 3 and 4, only the solid mechanical parameters corresponding to the models are different, and the calculation process of the solid mechanical parameters is shown by the formula in the step 3, so that the purpose of controlling the variables is to ensure the consistency of the numerical processes of the two times. The method specifically comprises the following steps: only the elastic parameters of the model are changed, and all the parameters of boundary load, grid division, solution mode, submarine topography and the like are the same.
And 7: subtracting the self-weight stress field obtained in the step 6 from the stress field obtained by simulation in the step 4 to obtain a deep structural stress field of the research area;
the stress interphase method in the step 7 is to subtract the self-weight stress field obtained in the step 6 from the stress field obtained in the step 4, to obtain the stress field generated by the combined action of gravity and the structure in the step 4, and to obtain the stress field generated by the deep structure action by subtracting the stress field generated by the action of gravity in the step 6 from the stress field obtained in the step 4. As shown in fig. 10, the open circles in the figure represent seismic source locations.
And 8: and (4) extracting the simulation result in the step (7), analyzing the stress state of the research area, and revealing the mechanism of the occurrence of the related geological processes in the ocean shells, such as rock cracking, earthquake occurrence and other processes.
The stress state analysis parameter provided in step 8 is generally the first principal stress σ 1, and different parameters may also be extracted according to different analysis targets. According to the research of geomechanics, the following are considered: positive values of the first principal stress represent a state of tension and negative values of the first principal stress represent a state of compression, the distribution of tension and pressure being closely related to the processes of rock fracture, earthquake occurrence, fluid migration and the like.
The concrete mode is as follows:
(1) simulating the distribution characteristics of the stress field according to a given model and boundary conditions;
(2) extracting a first principal stress sigma 1 distribution diagram;
(3) the tensile stress (sigma 1 is more than 0) is corresponding to the tensile fracture of the rock, induces earthquake, causes the low-speed abnormality of earthquake wave P wave and provides a channel for the migration of fluid;
(4) the compressive stress (sigma 1 is less than 0) corresponds to the rock compaction action, and causes the high-speed abnormality of the seismic wave P wave.
The above-described embodiments are intended to illustrate rather than to limit the invention, and any modifications and variations of the present invention are within the spirit of the invention and the scope of the appended claims.
Claims (7)
1. A deep sea hydrothermal area deep structure stress field simulation method based on an ocean shell velocity structure is characterized by comprising the following steps:
step 1: selecting a stress analysis area; establishing a geometric model of the analysis area according to the selected area and the submarine topography data;
step 2: calculating elastic mechanical parameters including Poisson's ratio, density and Young modulus based on the ocean shell sound wave velocity structure of the stress analysis region, and establishing a geomechanical model;
and step 3: and setting boundary conditions, loading loads, gridding the model and carrying out finite element numerical simulation on the established geomechanical model. Setting boundary conditions by combining with specific geological structure conditions of a stress analysis region; in order to adapt to the characteristics of the fluctuation of the submarine topography, a free mesh division strategy is adopted in the gridding process of the model; and the load applied inside the model is a gravity load and is loaded on each grid point to obtain a simulated self-weight stress field.
And 4, step 4: the method comprises the following steps that an ocean shell sound wave velocity structure in a stress analysis area is a two-dimensional velocity model, and a one-dimensional velocity model is established for the velocity value of each depth being equal to the average value of the velocity of the two-dimensional model at the depth; repeating the process of the step 2-3, and simulating to obtain a self-weight stress field of the stress analysis area;
and 5: and 3, subtracting the self-weight stress field obtained by the simulation in the step 4 from the self-weight stress field obtained by the simulation in the step 3 to obtain a deep structural stress field of the stress analysis region, and analyzing the stress state of the stress analysis region.
2. The deep-sea hydrothermal-section deep tectonic stress field simulation method of claim 1, characterized in that: in the step 2, the ocean shell acoustic velocity structure is obtained by inversion calculation of seismic waves acquired by a submarine seismograph.
3. The deep-sea hydrothermal-section deep tectonic stress field simulation method of claim 1, characterized in that: the specific calculation formula for calculating the elastic parameters by using the ocean shell sound wave velocity structure shown in the step 2 is as follows:
μ＝Vs 2ρ (5)
E＝μ(3λ+2μ)/(λ+μ) (6)
in the above formulae (1) to (6), VPAnd VsRespectively representing the propagation speeds of longitudinal waves and shear waves in a stratum medium, and the unit is m/s; sigma is the Poisson's ratio of the rock, and the ratio of the absolute value of the transverse positive strain to the absolute value of the axial positive strain; ρ represents the density of the rock in g/cm3(ii) a λ is Lame constant, μ is shear modulus, E is Young's modulus, in N/m2(ii) a In combination with equations (1) - (6), the density, Young's modulus and Poisson's ratio of the rock can all be determined according to the longitudinal wave velocity VPAnd (6) calculating.
4. The deep-sea hydrothermal-section deep tectonic stress field simulation method of claim 3, characterized in that: the setting method of the boundary condition in the step 3 comprises the following steps: the south boundary and the north boundary respectively apply 8mm/y and 7mm/y expansion rates, the upper boundary applies hydrostatic pressure according to the depth of the sea bed, a calculation formula is represented by a formula (7), and the lower boundary is fixed.
Fs＝ρgh (7)
In the above formula FsExpressed as hydrostatic pressure in Pa, ρ expressed as sea water density in kg/m3。
5. The deep-sea hydrothermal-section deep tectonic stress field simulation method of claim 1, characterized in that: in step 3, the calculation of the gravity load value is obtained according to a global gravity acceleration calculation formula of the IEC standard, wherein the calculation formula is as follows:
in the formula (I), the compound is shown in the specification,
is latitude value in degrees, north latitude is positive, Z is altitude in meters, above the horizontal plane is positive, and g represents acceleration of gravity.
6. The deep-sea hydrothermal-section deep tectonic stress field simulation method of claim 1, characterized in that: the specific way of extracting the stress analysis region one-dimensional velocity model in the step 4 is as follows: a two-dimensional velocity model to be researched is selected, a certain depth d is given, all velocity values of the depth are extracted, and an average value is calculated to be used as the velocity value of the one-dimensional model at the depth. And sequentially calculating the speed average value of each depth to obtain a one-dimensional speed model corresponding to the two-dimensional speed model.
7. The deep-sea hydrothermal-section deep tectonic stress field simulation method of claim 1, characterized in that: the stress state analysis method in the step 5 specifically comprises the following steps: extracting a first main stress field according to a simulation result, considering that a positive value of the first main stress represents tension and a negative value represents tension by solid mechanics, combining the simulation result of the stress with a geological phenomenon of a stress analysis area, analyzing an earth dynamic process mechanism of the stress analysis area, and revealing the processes of rock earthquake generation and fluid migration in the ocean shell, wherein the specific mode is as follows:
(1) simulating the distribution characteristics of the stress field according to the established model and the boundary condition;
(2) extracting a first principal stress sigma 1 distribution diagram;
(3) the tensile stress (sigma 1 is more than 0) is corresponding to the tensile fracture of the rock, induces earthquake, causes the low-speed abnormality of earthquake wave P wave and provides a channel for the migration of fluid;
(4) the compressive stress (sigma 1 is less than 0) corresponds to the rock compaction action, and causes the high-speed abnormality of the seismic wave P wave.
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