CN113687422B - Aftershock sequence deleting method based on fault buffer zone - Google Patents
Aftershock sequence deleting method based on fault buffer zone Download PDFInfo
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Abstract
The invention provides a aftershock sequence deletion method based on a fault buffer zone, which is characterized in that a typical earthquake is selected as a main earthquake, the space-time distribution and the fracture trend of the aftershock are combined, the space difference of a geological structure is considered, a fracture buffer zone empirical formula is provided, the fault buffer zone is used as an aftershock space window to improve the space window selection mode of the K-K aftershock deletion method, the aftershock deletion function in earthquakes with different seismic levels is realized, the aftershock deletion is more reliable, the deleted aftershock sequence has clustering performance and stronger geological theoretical explanation. The invention solves the relation between aftershock and fracture distribution, improves the limitation of setting the space window by the K-K method, adjusts the reasonability of the setting of the space window, restores the geological characteristics of the area to a greater extent, ensures that the deleted aftershock sequence has better contact degree with the actual earthquake occurrence distribution, and improves the aftershock deleting effect in the earthquakes with different seismic levels.
Description
Technical Field
The invention belongs to the technical field of seismic data processing, and particularly relates to a fault buffer zone-based aftershock sequence deleting method.
Background
Aftershocks refer to a series of earthquakes that occur after the occurrence of a major shock. The existence of aftershock sequences in the seismic sequences can influence the principal shock analysis, and the elimination of aftershocks is the premise and the basis for performing seismic statistical analysis. The existing K-K method judges the time and the space position of aftershock by using a relational expression according to the aftershock space and the time window related to the main shock magnitude, and deletes all other events listed in a certain specified distance and time from a large-magnitude event in an earthquake directory; most of the existing methods are based on experience model building, and aftershocks can be deleted quickly for the whole earthquake catalogue. However, the spatial range of the aftershocks selected by the method is a circular area with the principal seismic center as the origin, and also includes aftershocks occurring in different areas adjacent to the geological structure, so that seismic groups unrelated to the principal shock cannot be eliminated, and the influence of the aftershocks in the seismic centers of different magnitudes on the analysis of the principal shock is caused.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the aftershock sequence deleting method based on the fault buffer zone is used for deleting aftershocks in earthquakes with different seismic magnitudes.
The technical scheme adopted by the invention for solving the technical problems is as follows: a method for deleting aftershock sequences based on fault buffer zones comprises the following steps:
s1: setting the epicenter position of the major earthquake as a target area;
s2: importing a fracture database of a target area, and selecting a fracture zone closest to a principal earthquake as a main fracture;
s3: screening seismic catalogs meeting the conditions through a K-K method time window, and importing the screened seismic catalogs;
s4: taking the main fracture as a line element, and extending outwards according to the buffer distance R to serve as a buffer zone of the main fracture;
s5: establishing a multi-ring buffer zone according to the distribution condition of the earthquake around the main fracture, and adjusting the buffer distance R until the generated buffer zone area contains the earthquake distributed along the main fracture trend;
s6: fitting a buffer zone empirical formula of the major earthquake magnitude M and the buffer distance R by a least square method:
logR＝0.2621M-0.2682；
s7: and (4) taking the buffer zone as a aftershock space window, and deleting the earthquakes smaller than the main earthquake magnitude in the buffer zone area.
According to the scheme, in the step S2, the specific steps are as follows: if the seismic magnitude is M and the fracture length is L, the formula of the seismic magnitude and the fracture length is:
M＝3.3+2.1logL；
the effective length is obtained by intercepting the fracture by taking the epicenter of the main earthquake as the center, and the larger the earthquake magnitude is, the longer the corresponding effective length is.
Further, in step S2, the fracture cutting method includes three methods:
the first method is two-end interception, the effective length of a main fracture corresponding to a main earthquake is calculated by using a formula of earthquake magnitude and fracture length, a point is selected on the main fracture, and half of the effective length is respectively extended to two sides to obtain a new sub-fracture based on the main fracture as an effective fracture;
the second is far-end interception, after points are determined on the main fracture, if the length of a broken line at one end of the points does not meet the requirement of being equal to half of the effective length, one side of the shorter broken line length of the points is reserved, and interception is carried out from the end point of the longer broken line length at the other side, so that the total length of the sub-fractures is equal to the length of the corresponding effective fracture of the earthquake;
and in the third case, not intercepting the main fracture, and taking the main fracture as an effective fracture if the length of the broken line on two sides of the point does not meet the requirement of being equal to half of the effective length after the point is determined on the main fracture.
According to the scheme, in the step S3, the K-K method for screening the seismic catalog comprises the following specific steps:
s31: let the aftershock magnitude be m, the distance between the principal shock and the aftershock be R, the time be Δ t, and the space window distance be R0Interval of time window is T0(ii) a When the following relation is satisfied, judging M to be the aftershock of M:
r≤R0(M)；Δt≤T0(M)；m＜M
s32: using the coordinate of the main earthquake center as the center of a circle and the distance R of a space window0And (4) deleting the earthquakes with the inner seismic level smaller than the main seismic level.
According to the scheme, in the step S5, the specific steps are as follows:
s51: taking the inflection point of the main fracture as the center of a circle and the buffer distance as the radius, sequentially drawing circles with the same radius along the inflection point of the main fracture, and drawing an envelope curve outside the series of circles to establish a buffer zone;
s52: respectively establishing buffer zones at different buffer distances;
s53: and performing aftershock analysis on the earthquakes with different seismic magnitudes, and determining the buffer distance corresponding to each seismic magnitude.
A computer storage medium having stored therein a computer program executable by a computer processor, the computer program executing a fault buffer zone based aftershock sequence deletion method according to any one of claims 1 to 5.
The beneficial effects of the invention are as follows:
1. the invention discloses a fault buffer zone-based aftershock sequence deletion method, which comprises the steps of selecting a plurality of typical earthquakes from earthquake catalog data of the past year as principal earthquakes, combining aftershock space-time distribution and fracture trend, considering spatial difference of geological structures, sequentially establishing fracture buffer zones, providing a fracture buffer zone empirical formula, and improving a spatial window selection mode of a K-K aftershock deletion method by using a fault buffer zone as an aftershock spatial window, so that the function of deleting the aftershocks in earthquakes with different seismic levels is realized, the aftershocks are deleted more reliably, and the deleted aftershock sequences have clustering and stronger geological theoretical explanation.
2. The invention considers the correlation between the aftershock space-time distribution and the actual geological structure and fracture, eliminates the seismic groups irrelevant to the main shock, and improves the effect of deleting the aftershock in the earthquakes with different seismic levels.
3. The invention solves the relation between aftershock and fracture distribution, improves the limitation of setting the space window by the K-K method, greatly adjusts the reasonability of setting the space window, restores the geological characteristics of the area to a greater degree, and ensures that the deleted aftershock sequence has better contact degree with the actual earthquake occurrence distribution.
Drawings
FIG. 1 is a CX zone seismic and fracture distribution plot of an embodiment of the present invention.
FIG. 2 is a flow chart of the fault buffer based K-K algorithm according to the embodiment of the invention.
Fig. 3 is a WC area fracture diagram of an embodiment of the present invention.
FIG. 4 is a graph of fractures in the northeast region of XZMN in accordance with an embodiment of the present invention.
FIG. 5 is a graph showing the fracture at the QHGH-XH junction in accordance with an embodiment of the present invention.
FIG. 6 is a diagram of a fracture buffer zone build-up of an embodiment of the present invention.
FIG. 7 is a diagram illustrating adjustment of fracture buffer zones according to an embodiment of the present invention.
FIG. 8 is a PME-MJ fracture buffer band diagram of an embodiment of the present invention.
FIG. 9 is a QH-TTH fracture buffer band diagram according to an embodiment of the present invention.
FIG. 10 is a QHGH-TGM fragmentation buffer band diagram of an embodiment of the present invention.
FIG. 11 is a XJWQ fracture buffer band diagram of an embodiment of the invention.
FIG. 12 is a YNJG fracture buffer band diagram in accordance with an embodiment of the present invention.
FIG. 13 is a XZLZ fracture buffer band diagram of an embodiment of the invention.
Fig. 14 is a SCDF fracture buffer band diagram according to an embodiment of the present invention.
FIG. 15 is a fracture buffer band diagram of YNLJ in accordance with an embodiment of the present invention.
Fig. 16 is a XJHT fragmentation buffer band diagram of an embodiment of the invention.
FIG. 17 is a XZZB fragmentation buffer band diagram of an embodiment of the invention.
Fig. 18 is an SCYA fragmentation buffer band diagram of an embodiment of the invention.
FIG. 19 is a SCAB fracture buffer band diagram of an embodiment of the present invention.
Figure 20 is an XJWQ fragmentation buffer band diagram of an embodiment of the invention.
Fig. 21 is a KLSFSL fracture buffer band diagram of an embodiment of the invention.
Fig. 22 is a QHYS fragmentation buffer band diagram of an embodiment of the invention.
FIG. 23 is a XJYT fragmentation buffer band diagram in accordance with an embodiment of the present invention.
Fig. 24 is a XZMN fracture buffer band diagram of an embodiment of the present invention.
FIG. 25 is a diagram of a fragmentation buffer band for YNLC-GM-CY in accordance with an embodiment of the present invention.
Figure 26 is a SCWC fracture buffer band diagram according to an embodiment of the invention.
FIG. 27 is a plot of a fit function for an embodiment of the present invention.
Fig. 28 is a KLSK fragmentation buffer band diagram of an embodiment of the invention.
FIG. 29 is a SCABXJ fracture buffer band diagram of an embodiment of the invention.
Fig. 30 is a XJHJ fragmentation buffer band diagram of an embodiment of the invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Referring to fig. 1, a method of an embodiment of the present invention includes the steps of:
according to the characteristic that the earthquake space distribution is closely related to the fracture trend, the occurrence of the earthquake and the fracture distribution have extremely high correlation, and the space range selected by the aftershock of the K-K method can be reduced. Taking the CX region ms8.0 earthquake as an example, referring to fig. 1, the earthquake space position is closely related to the fracture zone trend. The earthquake occurrence frequency is higher in the area with dense fracture zones, and conversely, the earthquake occurrence frequency is lower in the part with sparse fracture zones. Mainly because after the main earthquake occurs, the aftershocks usually occur on the same fracture surface as the main earthquake, and due to coulomb stress transfer (coulomb stress transfer), the stress variation can also cause the aftershocks to occur at other fracture zones, but the number of the earthquakes distributed around the fracture zone near the main earthquake is relatively the largest.
Based on the characteristic that the seismic space position is closely related to the trend of the fracture zone, the invention provides the concept of fracture buffer zone. And taking the fault corresponding to the earthquake closest to the main earthquake center as the main earthquake-initiating fracture of the earthquake, simplifying the fault into a linear unit, extending a certain distance outwards by taking the linear unit as the center to form a closed polygon as a fracture buffer zone, and improving the space window selection mode of the classical K-K residual earthquake deletion method based on the fracture buffer zone.
K-K algorithm
The K-K algorithm judges whether the earthquake is aftershock or not according to the distance and the post-earthquake time window, deletes the aftershock, firstly screens the earthquake catalogue meeting the conditions through the time window, then uses the main earthquake center coordinate as the circle center, and uses the space window distance R0And (4) deleting the earthquakes with the inner seismic level smaller than the main seismic level. The K-K algorithm deletes aftershocks by setting aftershock space and time window related to the principal shock magnitude through an empirical method, setting the principal shock magnitude as M, the aftershocks as M, the distance between the two earthquakes as R, the time as delta t, and the space window distance as R0Time window interval of T0. M is the aftershock of M when the following relation is satisfied:
r≤R0(M)；Δt≤T0(M)；m＜M
improved K-K algorithm
Referring to fig. 2, the fault buffer area-based improved K-K algorithm selects a fracture closest to a specific principal vibration as a main fracture according to the specific principal vibration, and then determines a buffer zone of the main fracture by extending a certain distance outwards from a line element determined by the main fracture, that is, a residual vibration space. This method takes into account the correlation of aftershocks with the primary fracture and the geologic formation properties of the different zones.
The improved K-K algorithm based on the fault buffer zone firstly needs to determine the position of the occurrence of the main earthquake, then the fracture database of the target area is imported, and a fracture zone closest to the position of the main earthquake, namely the fracture corresponding to the main earthquake, is searched. Then, the earthquake catalogue screened by the K-K method time window is imported, so that the earthquake can be found to be distributed very densely along the trend of the main fracture zone, and the main fracture zone is taken as a line element, and a certain distance is extended outwards to be used as a buffer zone. The buffer distance is continuously adjusted according to the distribution of the earthquake on the main fracture zone until the generated buffer zone area can approximately contain the earthquake around the main fracture zone, the buffer radius at the moment is the space window of the improved method, and the earthquake which is smaller than the main earthquake magnitude in the buffer zone area is the aftershock sequence to be deleted.
The space window deleting aftershock determined based on the fracture buffer zone needs to determine the outward extending distance of the fracture buffer zone, the main shock fracture length and the like. The method selects 20 earthquakes of Ms7.0-8.0 which occur in nearly 40 years, takes the earthquakes as the principal earthquakes, determines the space position and the length of the principal fracture by utilizing a time window provided by a K-K method, counts the space windows determined by different fracture buffer zones, compares the space windows with the K-K method for deleting aftershocks, and fits a correlation function of the principal seismic level and the buffer distance by least squares.
Determination of the length and spatial position of a fracture
And searching a fracture zone close to the epicenter in the fracture list as a fracture (main fracture) corresponding to the main earthquake by taking the shortest distance from the epicenter to the fracture as a target. Many times, a seismic fracture is not a complete fracture, but only a part of one fracture needs to be intercepted by taking the epicenter as the center to obtain the effective fracture length, an empirical formula of the seismic magnitude and the fracture length is adopted for calculation, and when the seismic magnitude is larger, the corresponding fracture length is also longer. Where M represents the seismic magnitude, L represents the fracture length, in Km:
M＝3.3+2.1logL；
the determination of the effective fracture spatial location is discussed in three cases. The first method is two-end interception, the effective length of a main fracture corresponding to the main earthquake is obtained through calculation by using the formula, one point is selected on the main fracture, half of the effective length extends to two sides respectively, and a new sub-fracture based on the main fracture is obtained and is the required effective fracture. For example, in the WC area ms8.0 earthquake, see fig. 3, the corresponding main fracture is a YX-BC reverse fracture (black polygonal line), a point on the main fracture corresponding to the shortest distance from the epicenter to the black polygonal line is obtained by calculation, and the newly obtained sub-fractures (gray polygonal lines) are effective fractures by respectively extending the point to half of the corresponding effective length from the point to both ends. The second is far-end interception, after a point is determined on the main fracture, when the length of a broken line at one end of the point cannot meet half of the effective length corresponding to the earthquake, one side of the point with the shorter broken line length is reserved, interception is carried out from the end point of the other side with the longer broken line length, and finally the total length of the sub-fractures is required to be equal to the length of the effective fracture corresponding to the earthquake. For example, referring to fig. 4, when the ms7.6 earthquake occurs in the northeast of XZMN, the corresponding main fracture is a wlwlwlh south-TTH edge fracture (black broken line), a point on the main fracture zone corresponding to the shortest distance from the epicenter to the black broken line is calculated, and the length of the right broken line cannot satisfy half of the corresponding effective fracture length, so that the length of the right broken line of the point is reserved, a certain length is cut from the left side of the point, and finally, the length of the sub-fracture (gray broken line) is equal to the effective fracture length, which is the required effective fracture. And in the third case, no interception is carried out, after points are determined on the main fracture, the length of the broken line on two sides of each point is found not to meet the requirement of being equal to half of the effective fracture, and the main fracture is selected to be not intercepted and taken as the effective fracture. For example, when the Ms7.1 earthquake at the QHGH-XH junction is taken as an example, referring to FIG. 5, the corresponding main fracture is QHGH basin north edge fracture, the length of the broken line at both sides of the point does not meet the condition, and the main fracture (gray broken line) is an effective fracture without cutting.
The fracture buffer zone for the earthquake distributed along the main fracture trend is contained as much as possible, sometimes, the target cannot be accurately realized only by setting one buffer distance, and then the buffer distance is continuously adjusted by establishing the multi-ring fracture buffer zone to achieve the optimal result. For example, in an XJWQ east region ms7.1 earthquake, a corresponding main fracture is found, the main fracture is formed by a series of inflection points, the upper inflection point of the main fracture is taken as a circle center, a certain distance is taken as a radius, the radius is a buffer distance, circles with the same radius are made along the inflection points of the fracture zone in sequence, an envelope curve is formed outside the series of circles, and a buffer zone is established, namely the fracture buffer zone, as shown in fig. 6. And establishing fracture buffer zones with different buffer radiuses, looking at fig. 7, searching different buffer distances corresponding to different seismic levels in Ms7.0-8.0 for earthquakes with different seismic levels, and fitting a function related to the seismic levels and the buffer distances.
And (3) selecting 20-year seismic catalog data to perform an experiment of the aftershock elimination algorithm, wherein the total number of the earthquakes is 69714. The integrity seismic level of the seismic directory is Ms3.0, and the directory has 2772 seismic examples containing Ms5.0 above Ms5.0 and 461 seismic examples containing Ms6.0 above Ms6.0. Fracture distribution data is a fracture distribution data set, and the data comprises 1966 pieces of fracture information, including fracture name, inflection point coordinates and other information. And performing aftershock statistical analysis on fracture buffer areas of typical Ms7.0-7.1 earthquake, Ms7.2 earthquake, Ms7.4 earthquake, Ms7.6 earthquake and Ms8.0 earthquake.
Determining Ms7.0-7.1 earthquake fracture buffer zone
Fig. 8 to 13 show information of main fracture, aftershock distribution and the like of the ms7.0 and 7.1 earthquakes, and the earthquake point positions of different magnitude shown in the figures are earthquake sequences left after being screened by a time window of a K-K method. The circular area is a space range for deleting aftershocks corresponding to the principal shock selected by the K-K method space window, and the dotted line area is a fracture buffer zone formed according to effective fracture. The earthquake corresponding to the graph 8 occurs near the West end of the MJ fracture basin in the North part of the PME structure, the earthquake is distributed very densely along the effective fracture trend, the effective fracture is taken as a line element, a fracture buffer zone is extended outwards, the earthquake sequence along the effective fracture trend is included as far as possible, and the aftershock related to the principal earthquake can be selected when the buffer distance is equal to 36 Km. In aftershock sequences screened by the fracture buffer zone, the seismic magnitude is concentrated between Ms3.0-4.8, the aftershock quantity attenuates year by year, the seismic source depth is different from 4-16Km, and the figure shows that the aftershock sequences screened by the fracture buffer zone are more concentrated than the sequences screened by a circular space region of a K-K method and can reflect the correlation between the aftershock sequences and the fracture trend.
From fig. 9 to 13, a plot of fracture buffer zones for several earthquakes of ms7.1 is shown. The earthquake corresponding to fig. 9 occurs in the area between the southwest of the QH and the TTH edge, the buffering distance is 39Km, the magnitude of the aftershock sequence is 3.4, and the depth of the aftershock source is-1 Km as the depth of the principal shock source. The seismic data of the place are less due to the limitation of observation conditions, and the size of the buffer distance is determined according to the aftershock distribution of other Ms7.1 earthquakes; FIG. 10 depicts an earthquake near TGM at the southwest edge of the QHGH trap basin, with a buffer distance of 39Km to achieve better results, and the aftershock level is mainly 3-4; the earthquake in FIG. 11 is the Ms7.1 earthquake of XJWQ, the best effect is achieved when the buffering distance is set to 39Km, the seismic level span of the aftershock of the earthquake is large, the aftershock is abundant from 3.0 to 6.4 levels, and the attenuation is slow; the earthquake corresponding to FIG. 12 occurs in YNJG, the aftershock magnitude is more than 3-4, but there are also some 5-6 larger magnitudes, and the depth of the seismic source is relatively larger; the earthquake corresponding to the figure 13 occurs on the XZLZ, the buffering distance is 39Km, the aftershock distribution takes the main earthquake as the center, the aftershock distribution extends along the north-west direction and the south-east direction of the main earthquake, the maximum aftershock magnitude is 5.6, and the depth of the earthquake source is generally shallow. In summary, when the buffering distance is set to 39Km, the aftershock elimination effect on the ms7.1 earthquake is good.
Determining Ms7.2 seismic fracture buffer
Fig. 14 shows an ms7.2-level earthquake of the SCDF, where the spatial distribution of aftershocks presents northwest-direction stripes, and the buffering radius is assumed to be 42Km, which is better in effect, and the obtained aftershock sequence has a smaller magnitude, and the seismic source depth is generally smaller, but the depth of the aftershock seismic source among them reaches 27 Km; the earthquake corresponding to the earthquake in the graph 15 occurs in YNLJ, the LJ-DJ fracture is represented as a positive fracture with a left-handed motion component, along the fracture, the differential motion between YL-HBXS mountain lifting and mountain front fracture and cave-in enables the fracture to represent strong activity, the buffer distance is tried by using 42Km, the aftershocks are distributed in the north-south direction, the maximum aftershock level is 6.3, and the corresponding seismic source depth is also large and is 33 Km; the earthquake corresponding to fig. 16 occurs in XJHT, 42Km is used as a buffer distance, the range of a fracture buffer zone is in a boundary region, data at a long time is missing, a part of earthquake sequence is not included, aftershocks are mostly distributed in the southwest direction of the main earthquake, the magnitude of the aftershocks is lower, no obvious distribution dominant direction exists, no earthquake table exists in the 200Km range of the epicenter, the monitoring capability is weak, the result of the epicenter extrapolation is that the magnitude of the aftershocks is generally lower, and the determination of the buffer distance is further determined by means of other earthquakes of the same magnitude; FIG. 17 is an earthquake with a smaller aftershock level occurring in XZZB; the earthquake corresponding to fig. 18 occurs in SCYA, and this earthquake is a thrust fracture in nature of the seismic source, and as can be seen from the aftershock distribution, many peripheral earthquake events are dense, and are also in the areas where this earthquake is seriously damaged, and the earthquake shows the south-west trend distribution along the fracture; the earthquake in FIG. 19 occurs in SCAB, the aftershock activity of the earthquake has the characteristics of less medium-strength aftershock number and larger difference between the maximum aftershock and the principal shock magnitude, the aftershock sequence is in NW-SE trend on the plane, all Ms7.2 earthquakes are comprehensively considered, and the effect is better when the buffer distance is 42 Km.
Determining Ms7.4 seismic fracture buffer
The earthquake of fig. 20 occurs in XJWQ, if the earthquake is selected by the method of selecting the main fracture, the earthquake should be a short SS fracture in the figure, but the earthquake distributed along the fracture zone is very few, so the earthquake distribution condition around the main earthquake is selected to be observed, and a more suitable main fracture is further selected. Finding that the number of earthquakes along the periphery of the KZKAET fracture is the most intensive, and then trying to use the KZKAET fracture as a main fracture, determining an effective fracture by using a previous method, drawing a fracture buffer zone, adjusting, selecting 48Km as a buffer distance, and distributing aftershocks along one side of the fracture in the buffer zone; FIG. 21 shows that the earthquake is located near KLSFSL in the epicenter, the AEJ fracture zone is formed by multiple nearly parallel fractures, the earthquake is considered to be caused by that the GZC fracture of the AEJ fracture zone is subjected to tension fracture with a slip component under the action of near NS force, the buffering distance is selected to be 48Km, so that the earthquake is better contained, the aftershock sequence is more quickly attenuated, and the earthquake is mainly distributed in XZRT and XJ partial areas; FIG. 22 shows that the earthquake occurs in QHYS, the maximum aftershock magnitude is Ms6.6, the area where the aftershocks are most concentrated is located in the area where the principal shock moves west again, the aftershock spatial distribution of the earthquake gradually shrinks west with time, and the buffering distance is set to 48Km, which is also suitable; FIG. 23 shows an earthquake with XJYT, aftershocks are distributed in the southwest direction and extend along a single fracture side, the depth of the earthquake source is more than 5-10Km, the aftershocks are formed by fracturing the southwest direction of the main earthquake to the single fracture side, and a better effect can be achieved when the buffering distance is set to 48Km in the view of a plurality of Ms7.4 earthquakes.
Determining Ms7.6 seismic fracture buffer
The earthquake corresponding to the figure 24 occurs in the XZMN, the buffering radius of 54Km is tried, the effect is good, the aftershock magnitude is small and is about Ms5, and the attenuation speed of the sequence along with time is high; the earthquake corresponding to the graph 25 occurs at the YNLC-GM-CY junction, the fracture closest to the major earthquake center is an ML-LC fracture, but a buffer zone is drawn along the fracture zone, the effect is not good, the distribution of the earthquake near the major earthquake is observed, the fracture distribution along LL-LC is found to be denser, the buffer zone is tried to be drawn by the fracture, when the buffer distance is set to be 54Km, the peripheral dense earthquake cluster can be included, the maximum aftershock level is found to be 7.2, the earthquake can also be considered as a double major earthquake aftershock type, the aftershock seismic source depth is shallow, and the strong aftershock is frequent.
Determining the Ms8.0 seismic fracture buffer
Referring to fig. 26, the 8.0-level strong earthquake of SCWC is selected for the earthquake of ms8.0, the epicenter is located at 103.4 ° E and 31 ° N, the depth of the earthquake source is 14Km, the selected main fracture is YX-BC fracture, the effective fracture interception mode is that each of two ends is intercepted, when the buffer distance is 66Km, the inclusion effect is better, the aftershocks are mostly generated in the areas near the main earthquakes such as SCWC, BC and MZ, the number of aftershocks is slowly attenuated along the time change, the number of aftershocks is large but the earthquake level is generally not large, and the aftershocks are densely distributed along the NE of the main earthquake.
Fitting the major shock fracture buffer
Performing aftershock analysis on earthquakes with different seismic levels, and determining different buffer distances corresponding to the seismic levels; in order to more accurately analyze the relation between the main seismic magnitude and the buffering distance and test the applicability of the main seismic magnitude and the buffering distance for deleting aftershocks in earthquakes with other seismic magnitudes, a function of the seismic magnitude and the buffering distance is fitted. It can be seen from FIG. 27 that the fit is good, the SSE and RMSE are low, and the R-square is close to 1:
logR＝0.2621M-0.2682。
inspection of major shock fracture buffers
The statistics of Ms7.0-8.0 earthquake are carried out, the improved algorithm based on the fracture buffer zone is applied to 3 representative earthquakes of Ms8.1, 6.8 and 5.9, and aftershock sequences selected by a K-K method are used as comparison to verify the effectiveness and the applicability of the method for deleting aftershocks at different earthquake magnitudes. The earthquake in fig. 28 occurs in KLSK, which is the largest magnitude earthquake occurring in 70 years, the buffering distance is calculated by using the formula to be 71.58Km, and it can be seen from fig. 28 that the fracture buffering zone considers the fracture walking direction, compared with the K-K method, the earthquake-resistant method can more intensively and effectively select the aftershock sequence, the aftershocks are intensively distributed along the effective fractures, the number of the aftershocks is continuously attenuated along with the change of the years, and the magnitude of the earthquake is generally smaller; FIG. 29 shows that the earthquake occurs in SCABXJ, the buffering distance is 32.67Km, the aftershock is centrally distributed at 5Km around the principal shock, the maximum aftershock magnitude is 5.4, and the rest magnitudes are between 3-4; in the figure 30, the earthquake occurs in the XJHJ, the buffer distance is 18.98Km, the magnitude of the aftershock sequence is lower, and the distribution is concentrated, so that the earthquake with lower magnitude can be presumed to delete the aftershock rapidly and accurately by the method. From three application cases, the method considers the fracture trend, and the selected aftershock sequence is more accurate.
The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications based on the principles and design concepts disclosed herein are intended to be included within the scope of the present invention.
Claims (5)
1. A aftershock sequence deleting method based on a fault buffer zone is characterized by comprising the following steps: the method comprises the following steps:
s1: setting the epicenter position of the major earthquake as a target area;
s2: introducing a fracture database of a target area, and selecting a fracture zone closest to a major earthquake as a major fracture;
s3: screening seismic catalogs meeting the conditions through a K-K method time window, and importing the screened seismic catalogs;
s4: taking the main fracture as a line element, and extending outwards according to the buffering distance R to be used as a buffering belt of the main fracture;
s5: establishing a multi-ring buffer zone according to the distribution condition of the earthquake around the main fracture, and adjusting the buffer distance R until the generated buffer zone area contains the earthquake distributed along the main fracture trend; the method comprises the following specific steps:
s51: taking the inflection point of the main fracture as the center of a circle, taking the buffering distance as the radius, sequentially making circles with the same radius along the inflection point of the main fracture, and drawing an envelope curve outside the series of circles to establish a buffering zone;
s52: respectively establishing buffer zones at different buffer distances;
s53: performing aftershock analysis on earthquakes of different seismic magnitudes, and determining the buffer distance corresponding to each seismic magnitude;
s6: fitting a buffer zone empirical formula of the major earthquake magnitude M and the buffer distance R by a least square method:
logR＝0.2621M-0.2682；
s7: and (5) taking the buffer zone as a aftershock space window, and deleting the earthquakes smaller than the principal shock level in the buffer zone area.
2. The aftershock sequence deletion method based on the fault buffer zone as claimed in claim 1, characterized in that: in the step S2, the specific steps are as follows: if the seismic magnitude is M and the fracture length is L, the formula of the seismic magnitude and the fracture length is:
M＝3.3+2.1logL；
the effective length is obtained by intercepting the fracture by taking the epicenter of the main earthquake as the center, and the larger the earthquake magnitude is, the longer the corresponding effective length is.
3. The method for deleting the aftershock sequence based on the fault buffer zone as claimed in claim 2, characterized in that: in step S2, the cutting and breaking modes include three types:
the first method is two-end interception, the effective length of a main fracture corresponding to a main earthquake is calculated by using a formula of earthquake magnitude and fracture length, one point is selected on the main fracture, and half of the effective length is respectively extended to two sides to obtain a new sub-fracture based on the main fracture as an effective fracture;
the second is far-end interception, after points are determined on the main fracture, if the length of a broken line at one end of the points does not meet the requirement of being equal to half of the effective length, one side of the shorter broken line length of the points is reserved, and interception is carried out from the end point of the longer broken line length at the other side, so that the total length of the sub-fractures is equal to the length of the corresponding effective fracture of the earthquake;
and in the third case, not intercepting the main fracture, and taking the main fracture as an effective fracture if the length of the broken line on two sides of the point does not meet the requirement of being equal to half of the effective length after the point is determined on the main fracture.
4. The aftershock sequence deletion method based on the fault buffer zone as claimed in claim 1, characterized in that: in the step S3, the K-K method for screening the seismic catalog specifically comprises the following steps:
s31: let the aftershock magnitude be m, the distance between the main shock and the aftershock be R, the time be Δ t, and the space window distance be R0Interval of time window is T0(ii) a Judging M to be the aftershock of M when the following relational expression is satisfied:
r≤R0(M)；Δt≤T0(M)；m＜M
s32: using the coordinate of the main earthquake center as the center of a circle and the distance R of a space window0And (4) deleting the earthquakes with the inner seismic level smaller than the main seismic level as the radius.
5. A computer storage medium, characterized in that: stored therein is a computer program executable by a computer processor, the computer program performing a fault buffer zone based aftershock sequence deletion method as claimed in any one of claims 1 to 4.
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