A P and S wave velocity model is obtained for the crust in the region along the Longmenshan fault zone, Sichuan Province, China, by using data from a refraction profiling survey carried out in this region and those fr...A P and S wave velocity model is obtained for the crust in the region along the Longmenshan fault zone, Sichuan Province, China, by using data from a refraction profiling survey carried out in this region and those from local earthquakes. 202 local earthquakes along the fault zone are based on this velocity model, location errors being estimated to be about 1.5 km. The present relocations fairly improved the accuracy of hypocenter locations for earthquakes in this area, which is recognized from small scatter of data in the arrival time distance diagram compared with that for the original locations in the Earthquake Catalogue of Sichuan Seismic Network. The obtained hypocenter distribution shows that shallow earthquakes, confined to the upper crust in the depth range from 3 km to 22 km, are actively occurring along the main fault of the Longmenshan fault zone. The velocity model and the location method are presently used quite effective for precisely locating local earthquakes such as those in Sichuan Province. Installation of these with the real time processing system developed by Tohoku University in the Sichuan Telemetered Seismic Network would help to improve the location accuracy of events beneath the network.展开更多
This paper discusses the inversion of velocity structure and hypocenters location in the Beijing Tianjin Tangshan Zhangjiakou area by genetic algorithm. The hypocenters location of sele...This paper discusses the inversion of velocity structure and hypocenters location in the Beijing Tianjin Tangshan Zhangjiakou area by genetic algorithm. The hypocenters location of selected earthquakes and crustal structure of this area are obtained using the travel time data of local earthquakes acquired by the Telemetered Seismic Network of Northern China. The mean and standard residuals of hypocenter location acquired by this method are much less than those provided by the report of respective earthquakes. The crustal structure of the first and the second layers obtained interpret the outline of the plain and mountain area in the region successfully and the crustal structure of the third layer nearly coincides with the Moho discontinuity obtained by artificial seismic sounding. These show the genetic algorithm is effective to the inversion of hypocenter location and three dimensional velocity structure.展开更多
We investigated correlation of the slope of the initial part of P-wave envelope, hypocenter depth and plate boundaries by B-Δ method, which is used to determine epicentral distances in the Japan Meteorological Agency...We investigated correlation of the slope of the initial part of P-wave envelope, hypocenter depth and plate boundaries by B-Δ method, which is used to determine epicentral distances in the Japan Meteorological Agency and Japan Railway Company earthquake early warning(EEW) systems. The Tohoku region was chosen as the study region. 19,899 strong motion data for 265 events with magnitudes in the range from 5.0 to 7.6 from KiK-net(Kiban Kyoshin network) had been collected. The coefficient c to investigate is obtained from the linear relation between log B and log Δ. Compared to the hypocenter depth, the coefficients c of events is more likely to decide by the spatial correlation of the plate boundaries. The differences are likely to be due to earthquake characteristics, since deeper events in the subducting slabs the structural effects are likely to be larger than or comparable to those for shallow crust events.展开更多
Identification of precise hypocenter location is useful in order to improve the faults plane orientation and seismic zone analysis. In the study area, relocated hypocenter of earthquakes in Koyna-Warna region (KWR) fr...Identification of precise hypocenter location is useful in order to improve the faults plane orientation and seismic zone analysis. In the study area, relocated hypocenter of earthquakes in Koyna-Warna region (KWR) from the short period recorded data from 6th January 2010 to 28th May 2010 by using Cross-Correlation waveform results in Double Difference Hypocenter method [1]. The results show the significant improvement in hypocenter location and orientation in earthquake hypocenters, which is correlated with local faults plane orientation in study region. From the observations the earthquake hypocenters are lying in the depth between 3 to 8 km. The result which identified three faults plane orientation in NNW-SSE direction and also identified new fractures in NE-SW directions between the faults plane orientation with short duration data sets the first time in India.展开更多
In this paper a method of relocating hypocenter in inhomogeneous medium is introduced.Based on the velocity from the latest results on the crust and mantle structure of the Bohai Sea and its adjacent areas,by using th...In this paper a method of relocating hypocenter in inhomogeneous medium is introduced.Based on the velocity from the latest results on the crust and mantle structure of the Bohai Sea and its adjacent areas,by using the data recorded in Shandong,Hebei,Beijing,and Liaoning networks around the Bohai Sea we apply the method to relocate hypocenter parameters of 598 events occurring in the Bohai Sea and its adjacent areas.The accuracy of hypocenter relocation is discussed.We present the results of events ML≥4.0 in the Bohai Sea in recent years and discussed the distribution of focal depths.展开更多
In order to improve reliability of probabilistic seismic hazard analysis, shallow earthquake (depth <70 km) data, recorded with orientation precision grades 1 and 2 by modern instrument and containing depth informa...In order to improve reliability of probabilistic seismic hazard analysis, shallow earthquake (depth <70 km) data, recorded with orientation precision grades 1 and 2 by modern instrument and containing depth information after 1970, are selected as statistical samples, meanwhile, North China seismic region, Central China seismic region, South China seismic region, Xinjiang seismic region and Qinghai-Xizang Plateau seismic region are chosen as statistical units to study the depth distribution characteristics of shallow earthquakes. Considering the differences of depth distribution characteristics of earthquakes with different magnitudes, the following magnitude intervals are adopted to analyze earthquakes with different magnitude scales, respectively: M S=2.0～2.9, M S=3.0～3.9, M S=4.0～4.9, M S=5.0～5.9 and M S=6.0～6.9. The results show that hypocenter depths are normally distributed by and large around the mean depth of the corresponding seismic region. The probabilistic distribution curves of earthquake depth in West China are wider than those in East China. The probabilistic distribution deviation, σ, of West China is greater than those of East China, that is, earthquakes in West China have a wider range in terms of depth. There is also a tendency that the absolute value of mean hypocenter depth increases with the magnitude by and large.展开更多
Located on the foothills of Alborz mountains,in northern Iran,the city of Tehran is surrounded by many active faults that have caused destructive earthquakes in the past.Two earthquakes magnitudes 4.1 and 3.6 occurred...Located on the foothills of Alborz mountains,in northern Iran,the city of Tehran is surrounded by many active faults that have caused destructive earthquakes in the past.Two earthquakes magnitudes 4.1 and 3.6 occurred on 13th August 2015,known as Javadabad earthquakes,affected the SE Alborz region near Tehran.In this study,we relocated 780 events with magnitude 2.0 and larger that occurred during 1996-2015,which provides an enhanced image of seismicity in the region.We manually re-picked 6845 P-wave and 4675 S-waves arrival times on 41 seismic stations encompassing the SE Alborz regions.We then used our arrival times to relocate the earthquakes using a probabilistic method.Then we focus on improving the picked arrival times by cross-correlating the waveforms of P-and S-waves for event pairs with similar waveforms.The differential times of event pairs for all observations were weighted based on the quality of correlations.We computed more than 220,000 and 140,000 differential times for P-and S-wave records,respectively,and selected pairs of waveforms with coefficients of 0.7 or higher.Finally,in order to minimize the effect of inaccurate velocity structure,we applied the double-difference location method.展开更多
Studying the inner structure of intraplate earthquakes originating in aseismic areas,which are poorly covered by seismic networks or as historical earthquakes is usually the only way to get knowledge about their sourc...Studying the inner structure of intraplate earthquakes originating in aseismic areas,which are poorly covered by seismic networks or as historical earthquakes is usually the only way to get knowledge about their source mechanisms,which is partially essential for a deeper understanding of intraplate geodynamics.The epicentral zones of earthquakes are situated in hard-toreach areas,so,using active seismic methods for such purposes is unreasonable or even impossible because of high cost and logistical difficulties.We propose a novel approach that combines diverse passive seismic methods,which allows us to get sufficient information about geological environment structure for such task solutions.As an example,we investigated the inner structure of platform earthquake epicentral zone originated up north of Russia.We used four passive seismic methods:microseismic sounding method,passive seismic interferometry,HVSR method,and microseismic activity method.We show that passive seismic data,recoded in the same installation and processed by these different methods,can provide sufficient information about structure of studied environment,needed to explain source mechanism.In sum,the hypocenter zone is presented by intersection of vertical faults and a lateral fractured zone in the middle crust.Results were confirmed by comparison with results by active seismic methods.展开更多
ased on the empirical formulation formed from coda observations, the digital waveforms from 33 local events with magnitude ML ranging between 2.1 and 3.5, recorded at Changli station of Beijing Telemetered Seismograph...ased on the empirical formulation formed from coda observations, the digital waveforms from 33 local events with magnitude ML ranging between 2.1 and 3.5, recorded at Changli station of Beijing Telemetered Seismographic Network from 1989 to 1991, are used to compute coda Q for the Changli region and the source factors of all earthquakes by single-station coda method. Furthermore, assuming a certain source model, we have obtained the station site frequency response and source spectra, as well as source parameters such as corner frequencies, seismic moments and stress drops and so on. Their variations with time are monitored before and after larger earthquakes. Because the coda method can more effectively reduce the influence of source radiation pattern and a particular propagation path than direct wave method, more data can be used and more accurate results can be obtained, which provided a possible approach to study the source properties and reveal the variation of source parameters before larger earthquakes.展开更多
Through the accurate determination of hypocenter location, the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with M S=5 0 occurr...Through the accurate determination of hypocenter location, the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with M S=5 0 occurred along the middle segment of Longmenshan fault zone on November 30, 1999, the distribution of focal depth section, the stress release and seismicity features are given to reveal the earthquake-generating structure of the earthquake sequence. The obtained results show the activity features for this sequence as follows: ① There is no obvious foreshock, the accumulated strain energy releases in nearly pulse way, fluctuation of the seismic activity level is not quite evident during the duration of the sequence, and the statistical relation between the large events and the small events is less compatible with the traditional G-R estimation; ② The epicenters of the earthquake sequence are not distributed on the main Longmenshan piedmont faults emerging out ground, but near the hidden Longmenshan piedmont faults. The direction of epicenter distribution is not very coincident with the fault strikes. The microscopic epicenters are relatively far from the macroscopic epicenters. The focal depths range from 5km to 16km; ③ The fractures of focal fault plane with the NE strike appear out the strike-slip displacement with a few overthrust components under the major principal compressive stress of NNE direction. From these, we consider it should be paid more attentions to the underground hidden faults near the ground fault zone on a large scale for their generating earthquake risk.展开更多
After the establishment of the seismic observation network of southern Okinawa in August,1988 by the JMA(Japan Meteorological Agency),many hypocenters of earthquakes have been located.However,due to the small number o...After the establishment of the seismic observation network of southern Okinawa in August,1988 by the JMA(Japan Meteorological Agency),many hypocenters of earthquakes have been located.However,due to the small number of observation stations and narrow configuration of the array,the hypocenters lo-cated contain some systematic errors.Numerical experiments on the extent of the errors and the reliabilityof the JMA seismic observation network showed that the obtained hypocenters deeper than 100 km werereliable,but that for the obtained hypocenters shallower than 100 km,only the epicenters were reliable.展开更多
The hypocentral depths of more than 200 Chinese earthquakes, of magnitudes from M 8.6 to M 3.0, are calculated from macroseismic data carried on earthquake catalogs, by using the formula for macroseismic hypocen...The hypocentral depths of more than 200 Chinese earthquakes, of magnitudes from M 8.6 to M 3.0, are calculated from macroseismic data carried on earthquake catalogs, by using the formula for macroseismic hypocentral depths and the formula for general solution of macroseismic hypocentral depths. The results are plotted on maps to show their geographical distribution. It can be seen that most Chinese earthquakes are shollow ones. Of the 200 earthquakes calculated, 162(81.0%) hypocenters are shallower than 9 km, of which 111 (55.5%) hypocenters are shallower than 5 km. Such shallow earthquakes are mostly distributed in the provinces near to the North South Earthquake Belt, while the rest are scattered in the other provinces(except Zhejiang province). Earthquakes of medium(between 10 and 20 km) depth are relatively few (32 in number, 15.0%); they are distributed along the North South Earthquake Belt, and the western part of Xinjiang Uygur Autonomous Region and in provinces Shaanxi, Shanxi and Shandong (along the Tanlu Fracture Zone, crossing the sea to northeast China). Deep earthquakes are rare, being scattered in south Yunnan and the east end of Inner Mongolia Uygur Autonomous Region.展开更多
It is accepted as a well-known fact that in different places on the Earth’s crust,a similar anthropogenic impact causes a dissimilar response.Seismic zoning maps are not designed to predict such geodynamic hazards as...It is accepted as a well-known fact that in different places on the Earth’s crust,a similar anthropogenic impact causes a dissimilar response.Seismic zoning maps are not designed to predict such geodynamic hazards as rock bursts,induced earthquakes,reactivation of tectonic faults,etc.,and therefore require careful adjustments in places of intense impact on the subsurface strata.In this regard,we consider the classification of the Earth’s crustal areas according to the degree of geodynamic hazard,i.e.its potential geodynamic response to anthropogenic intervention.This classification is based on the concept that there exists a critically stressed layer within the Earth’s crust.It is believed that such a critically stressed layer within the Earth’s crust extends from the Earth’s surface to a certain depth,and each point depends on the nature of the interaction between crustal blocks of different hierarchical levels.From this perspective,anthropogenic impact,such as mining operations,represents a direct impact upon the critically stressed zone.We recognize the hypothesis that the thicker the critical stressed rock layer,the stronger the response might be to anthropogenic intervention,as it has more accumulated energy.Four categories of geodynamic threat have been found and mapped.To verify this classification,the manifestations of the geodynamic hazards were studied.The intensity of geodynamic hazard increased from the first area to the fourth area.The phenomenon of large induced seismic events with hypocenters at great depths is explained on the basis of this theory,and could be associated with anthropogenic impacts from the surface directly on the regional zone of the critically stressed rock massif.The approach can be used to assess the geodynamic consequences of human exposure to the Earth’s crust.展开更多
The concept of ＂numerical Green’s functions＂ （NGF or Green’s function database） is developed. The basic idea is： a large seismic fault is divided into subfaults of appropriate size, for which synthetic Green’s...The concept of ＂numerical Green’s functions＂ （NGF or Green’s function database） is developed. The basic idea is： a large seismic fault is divided into subfaults of appropriate size, for which synthetic Green’s functions at the surface （NGF） are calculated and stored. Consequently, ground motions from arbitrary kinematic sources can be simulated, rapidly, for the whole fault or parts of it by superposition. The target fault is a simplified, vertical model of the Newport-Inglewood fault in the Los Angeles basin. This approach and its functionality are illustrated by investigating the variations of ground motions （e.g. peak ground velocity and synthetic seismograms） due to the source complexity. The source complexities are considered with two respects： hypocenter location and slip history. The results show a complex behavior, with dependence of absolute peak ground velocity and their variation on source process directionality, hypocenter location, local structure, and static slip asperity location. We concluded that combining effect due to 3-D structure and finite-source is necessary to quan- tify ground motion characteristics and their variations. Our results will facilitate the earthquake hazard assessment projects.展开更多
It is now common practice to perform simultaneous traveltime inversion for the velocity field and the reflector geometry in reflection/refraction tomography, or the velocity field and the hypocenter locations in regio...It is now common practice to perform simultaneous traveltime inversion for the velocity field and the reflector geometry in reflection/refraction tomography, or the velocity field and the hypocenter locations in regional earthquake tomography, but seldom are all three classes of model parameters updated simultaneously. This is mainly due to the trade-off between the different types of model parameters and the lack of different seismic phases to constrain the model parameters. Using a spherical-coordinate ray tracing algorithm for first and later（primary reflected） arrival tracing algorithm in combination with a popular linearized inversion solver, it is possible to simultaneously recover the three classes of model parameters in regional or global tomographic studies. In this paper we incorporate the multistage irregular shortest-path ray tracing algorithm（in a spherical coordinate system） with a subspace inversion solver to formulate a simultaneous inversion algorithm for triple model parameters updating using direct and later arrival time information.Comparison tests for two sets of data（noise free and added noise） indicate that the new triple-class parameter inversion algorithm is capable of obtaining nearly the same results as the double-class parameter inversion scheme. Furthermore,the proposed multi-parameter type inversion method is not sensitive to a modest level of picking error in the traveltime data, and also performs well with a relatively large uncertainty in earthquake hypocentral locations. This shows it to be a feasible and promising approach in regional or global tomographic applications.展开更多
The relationships between energy, amplitude and frequency of eanhquake are correlative with the property of the seismic source. And the grade of the correlativity can be used as an index to distinguish the types of st...The relationships between energy, amplitude and frequency of eanhquake are correlative with the property of the seismic source. And the grade of the correlativity can be used as an index to distinguish the types of strong earth quakes. Primarily the strong earthquake can be divided into three types of main-after earthquakes, double-main earthquakes and swarm of strong earthquake. There are similarity and a certain repeatability at the quantificational indexes of hypocenter property between the same type of strong earthquakes, which supply basis for the forecast of subsequent strong shocks. The reference indexes of after strong shock forecast which are valuable for the applica tions of the method of type-divided forecast come from the analysis about more than fifty strong shock wide-band (BPZ wave) recording data of CDSN from 1988 to 1997.展开更多
We applied the double-difference earthquake rdocation algorithm to 1348 earthquakes with Ms ≥2.0 that occurred in the northern Tianshan region, Xinjiang, from April 1988 to June 2003, using a total of 28701 P- and S-...We applied the double-difference earthquake rdocation algorithm to 1348 earthquakes with Ms ≥2.0 that occurred in the northern Tianshan region, Xinjiang, from April 1988 to June 2003, using a total of 28701 P- and S-wave arrival times recorded by 32 seismic stations in Xinjiang. Aiming to obtain most of these Ms ≥ 2.0 earthquakes relocations, and considering the requirements of the DD method and the condition of data, we added the travel time data of another 437 earthquakes with 1.5 ≤ Ms 〈 2.0. Finally, we obtained the relocation results for 1253 earthquakes with Ms ≥2.0, which account for 93 % of all the 1348 earthquakes with Ms ≥ 2.0 and includes all the Ms ≥ 3.0 earthquakes. The reason for not relocating the 95 earthquakes with 2.0 ≤ Ms 〈 3.0 is analyzed in the paper. After relocation, the RMS residual decreased from 0.83s to 0.14s, the average error is 0.993 km in E-W direction, 1.10 km in N- S direction, and 1.33 km in vertical direction. The hypocenter depths are more convergent than before and distributed from 5 km to 35 kin, with 94% being from 5km to 35 kin, 68.2% from 10 km to 25 kin. The average hypocenter depth is 19 kin.展开更多
文摘A P and S wave velocity model is obtained for the crust in the region along the Longmenshan fault zone, Sichuan Province, China, by using data from a refraction profiling survey carried out in this region and those from local earthquakes. 202 local earthquakes along the fault zone are based on this velocity model, location errors being estimated to be about 1.5 km. The present relocations fairly improved the accuracy of hypocenter locations for earthquakes in this area, which is recognized from small scatter of data in the arrival time distance diagram compared with that for the original locations in the Earthquake Catalogue of Sichuan Seismic Network. The obtained hypocenter distribution shows that shallow earthquakes, confined to the upper crust in the depth range from 3 km to 22 km, are actively occurring along the main fault of the Longmenshan fault zone. The velocity model and the location method are presently used quite effective for precisely locating local earthquakes such as those in Sichuan Province. Installation of these with the real time processing system developed by Tohoku University in the Sichuan Telemetered Seismic Network would help to improve the location accuracy of events beneath the network.
文摘This paper discusses the inversion of velocity structure and hypocenters location in the Beijing Tianjin Tangshan Zhangjiakou area by genetic algorithm. The hypocenters location of selected earthquakes and crustal structure of this area are obtained using the travel time data of local earthquakes acquired by the Telemetered Seismic Network of Northern China. The mean and standard residuals of hypocenter location acquired by this method are much less than those provided by the report of respective earthquakes. The crustal structure of the first and the second layers obtained interpret the outline of the plain and mountain area in the region successfully and the crustal structure of the third layer nearly coincides with the Moho discontinuity obtained by artificial seismic sounding. These show the genetic algorithm is effective to the inversion of hypocenter location and three dimensional velocity structure.
基金supported by the Director Foundation of the Institute of Seismology,China Earthquake Administration,China(IS200756046)
文摘We investigated correlation of the slope of the initial part of P-wave envelope, hypocenter depth and plate boundaries by B-Δ method, which is used to determine epicentral distances in the Japan Meteorological Agency and Japan Railway Company earthquake early warning(EEW) systems. The Tohoku region was chosen as the study region. 19,899 strong motion data for 265 events with magnitudes in the range from 5.0 to 7.6 from KiK-net(Kiban Kyoshin network) had been collected. The coefficient c to investigate is obtained from the linear relation between log B and log Δ. Compared to the hypocenter depth, the coefficients c of events is more likely to decide by the spatial correlation of the plate boundaries. The differences are likely to be due to earthquake characteristics, since deeper events in the subducting slabs the structural effects are likely to be larger than or comparable to those for shallow crust events.
文摘Identification of precise hypocenter location is useful in order to improve the faults plane orientation and seismic zone analysis. In the study area, relocated hypocenter of earthquakes in Koyna-Warna region (KWR) from the short period recorded data from 6th January 2010 to 28th May 2010 by using Cross-Correlation waveform results in Double Difference Hypocenter method [1]. The results show the significant improvement in hypocenter location and orientation in earthquake hypocenters, which is correlated with local faults plane orientation in study region. From the observations the earthquake hypocenters are lying in the depth between 3 to 8 km. The result which identified three faults plane orientation in NNW-SSE direction and also identified new fractures in NE-SW directions between the faults plane orientation with short duration data sets the first time in India.
基金This project was sponsored by the Earthquake Science Foundation, China
文摘In this paper a method of relocating hypocenter in inhomogeneous medium is introduced.Based on the velocity from the latest results on the crust and mantle structure of the Bohai Sea and its adjacent areas,by using the data recorded in Shandong,Hebei,Beijing,and Liaoning networks around the Bohai Sea we apply the method to relocate hypocenter parameters of 598 events occurring in the Bohai Sea and its adjacent areas.The accuracy of hypocenter relocation is discussed.We present the results of events ML≥4.0 in the Bohai Sea in recent years and discussed the distribution of focal depths.
文摘In order to improve reliability of probabilistic seismic hazard analysis, shallow earthquake (depth <70 km) data, recorded with orientation precision grades 1 and 2 by modern instrument and containing depth information after 1970, are selected as statistical samples, meanwhile, North China seismic region, Central China seismic region, South China seismic region, Xinjiang seismic region and Qinghai-Xizang Plateau seismic region are chosen as statistical units to study the depth distribution characteristics of shallow earthquakes. Considering the differences of depth distribution characteristics of earthquakes with different magnitudes, the following magnitude intervals are adopted to analyze earthquakes with different magnitude scales, respectively: M S=2.0～2.9, M S=3.0～3.9, M S=4.0～4.9, M S=5.0～5.9 and M S=6.0～6.9. The results show that hypocenter depths are normally distributed by and large around the mean depth of the corresponding seismic region. The probabilistic distribution curves of earthquake depth in West China are wider than those in East China. The probabilistic distribution deviation, σ, of West China is greater than those of East China, that is, earthquakes in West China have a wider range in terms of depth. There is also a tendency that the absolute value of mean hypocenter depth increases with the magnitude by and large.
文摘Located on the foothills of Alborz mountains,in northern Iran,the city of Tehran is surrounded by many active faults that have caused destructive earthquakes in the past.Two earthquakes magnitudes 4.1 and 3.6 occurred on 13th August 2015,known as Javadabad earthquakes,affected the SE Alborz region near Tehran.In this study,we relocated 780 events with magnitude 2.0 and larger that occurred during 1996-2015,which provides an enhanced image of seismicity in the region.We manually re-picked 6845 P-wave and 4675 S-waves arrival times on 41 seismic stations encompassing the SE Alborz regions.We then used our arrival times to relocate the earthquakes using a probabilistic method.Then we focus on improving the picked arrival times by cross-correlating the waveforms of P-and S-waves for event pairs with similar waveforms.The differential times of event pairs for all observations were weighted based on the quality of correlations.We computed more than 220,000 and 140,000 differential times for P-and S-wave records,respectively,and selected pairs of waveforms with coefficients of 0.7 or higher.Finally,in order to minimize the effect of inaccurate velocity structure,we applied the double-difference location method.
基金funded by the Russian Federation Ministry of Science and Higher Education according to the research project FUUW-2025-0033 of the FECIAR UrB RASthe Arkhangelsk branch of the Territorial Fund of Geological Information for the North-Western Federal District for providing geological and geophysical reports for the objects under consideration。
文摘Studying the inner structure of intraplate earthquakes originating in aseismic areas,which are poorly covered by seismic networks or as historical earthquakes is usually the only way to get knowledge about their source mechanisms,which is partially essential for a deeper understanding of intraplate geodynamics.The epicentral zones of earthquakes are situated in hard-toreach areas,so,using active seismic methods for such purposes is unreasonable or even impossible because of high cost and logistical difficulties.We propose a novel approach that combines diverse passive seismic methods,which allows us to get sufficient information about geological environment structure for such task solutions.As an example,we investigated the inner structure of platform earthquake epicentral zone originated up north of Russia.We used four passive seismic methods:microseismic sounding method,passive seismic interferometry,HVSR method,and microseismic activity method.We show that passive seismic data,recoded in the same installation and processed by these different methods,can provide sufficient information about structure of studied environment,needed to explain source mechanism.In sum,the hypocenter zone is presented by intersection of vertical faults and a lateral fractured zone in the middle crust.Results were confirmed by comparison with results by active seismic methods.
文摘ased on the empirical formulation formed from coda observations, the digital waveforms from 33 local events with magnitude ML ranging between 2.1 and 3.5, recorded at Changli station of Beijing Telemetered Seismographic Network from 1989 to 1991, are used to compute coda Q for the Changli region and the source factors of all earthquakes by single-station coda method. Furthermore, assuming a certain source model, we have obtained the station site frequency response and source spectra, as well as source parameters such as corner frequencies, seismic moments and stress drops and so on. Their variations with time are monitored before and after larger earthquakes. Because the coda method can more effectively reduce the influence of source radiation pattern and a particular propagation path than direct wave method, more data can be used and more accurate results can be obtained, which provided a possible approach to study the source properties and reveal the variation of source parameters before larger earthquakes.
文摘Through the accurate determination of hypocenter location, the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with M S=5 0 occurred along the middle segment of Longmenshan fault zone on November 30, 1999, the distribution of focal depth section, the stress release and seismicity features are given to reveal the earthquake-generating structure of the earthquake sequence. The obtained results show the activity features for this sequence as follows: ① There is no obvious foreshock, the accumulated strain energy releases in nearly pulse way, fluctuation of the seismic activity level is not quite evident during the duration of the sequence, and the statistical relation between the large events and the small events is less compatible with the traditional G-R estimation; ② The epicenters of the earthquake sequence are not distributed on the main Longmenshan piedmont faults emerging out ground, but near the hidden Longmenshan piedmont faults. The direction of epicenter distribution is not very coincident with the fault strikes. The microscopic epicenters are relatively far from the macroscopic epicenters. The focal depths range from 5km to 16km; ③ The fractures of focal fault plane with the NE strike appear out the strike-slip displacement with a few overthrust components under the major principal compressive stress of NNE direction. From these, we consider it should be paid more attentions to the underground hidden faults near the ground fault zone on a large scale for their generating earthquake risk.
文摘After the establishment of the seismic observation network of southern Okinawa in August,1988 by the JMA(Japan Meteorological Agency),many hypocenters of earthquakes have been located.However,due to the small number of observation stations and narrow configuration of the array,the hypocenters lo-cated contain some systematic errors.Numerical experiments on the extent of the errors and the reliabilityof the JMA seismic observation network showed that the obtained hypocenters deeper than 100 km werereliable,but that for the obtained hypocenters shallower than 100 km,only the epicenters were reliable.
文摘The hypocentral depths of more than 200 Chinese earthquakes, of magnitudes from M 8.6 to M 3.0, are calculated from macroseismic data carried on earthquake catalogs, by using the formula for macroseismic hypocentral depths and the formula for general solution of macroseismic hypocentral depths. The results are plotted on maps to show their geographical distribution. It can be seen that most Chinese earthquakes are shollow ones. Of the 200 earthquakes calculated, 162(81.0%) hypocenters are shallower than 9 km, of which 111 (55.5%) hypocenters are shallower than 5 km. Such shallow earthquakes are mostly distributed in the provinces near to the North South Earthquake Belt, while the rest are scattered in the other provinces(except Zhejiang province). Earthquakes of medium(between 10 and 20 km) depth are relatively few (32 in number, 15.0%); they are distributed along the North South Earthquake Belt, and the western part of Xinjiang Uygur Autonomous Region and in provinces Shaanxi, Shanxi and Shandong (along the Tanlu Fracture Zone, crossing the sea to northeast China). Deep earthquakes are rare, being scattered in south Yunnan and the east end of Inner Mongolia Uygur Autonomous Region.
基金partially used the materials obtained during grant implementation No.GК-1406(2009)of the Russian Ministry of Science and Education
文摘It is accepted as a well-known fact that in different places on the Earth’s crust,a similar anthropogenic impact causes a dissimilar response.Seismic zoning maps are not designed to predict such geodynamic hazards as rock bursts,induced earthquakes,reactivation of tectonic faults,etc.,and therefore require careful adjustments in places of intense impact on the subsurface strata.In this regard,we consider the classification of the Earth’s crustal areas according to the degree of geodynamic hazard,i.e.its potential geodynamic response to anthropogenic intervention.This classification is based on the concept that there exists a critically stressed layer within the Earth’s crust.It is believed that such a critically stressed layer within the Earth’s crust extends from the Earth’s surface to a certain depth,and each point depends on the nature of the interaction between crustal blocks of different hierarchical levels.From this perspective,anthropogenic impact,such as mining operations,represents a direct impact upon the critically stressed zone.We recognize the hypothesis that the thicker the critical stressed rock layer,the stronger the response might be to anthropogenic intervention,as it has more accumulated energy.Four categories of geodynamic threat have been found and mapped.To verify this classification,the manifestations of the geodynamic hazards were studied.The intensity of geodynamic hazard increased from the first area to the fourth area.The phenomenon of large induced seismic events with hypocenters at great depths is explained on the basis of this theory,and could be associated with anthropogenic impacts from the surface directly on the regional zone of the critically stressed rock massif.The approach can be used to assess the geodynamic consequences of human exposure to the Earth’s crust.
基金funding from the International Quality Network:Georisk (Ger-man Academic Exchange Service),and the Elite Gradu-ate College THESIS (Bavarian Government)support from the European Hu-man Resources Mobility Program (Research Training Network SPICE)
文摘The concept of ＂numerical Green’s functions＂ （NGF or Green’s function database） is developed. The basic idea is： a large seismic fault is divided into subfaults of appropriate size, for which synthetic Green’s functions at the surface （NGF） are calculated and stored. Consequently, ground motions from arbitrary kinematic sources can be simulated, rapidly, for the whole fault or parts of it by superposition. The target fault is a simplified, vertical model of the Newport-Inglewood fault in the Los Angeles basin. This approach and its functionality are illustrated by investigating the variations of ground motions （e.g. peak ground velocity and synthetic seismograms） due to the source complexity. The source complexities are considered with two respects： hypocenter location and slip history. The results show a complex behavior, with dependence of absolute peak ground velocity and their variation on source process directionality, hypocenter location, local structure, and static slip asperity location. We concluded that combining effect due to 3-D structure and finite-source is necessary to quan- tify ground motion characteristics and their variations. Our results will facilitate the earthquake hazard assessment projects.
基金partially supported by the Doctoral Programming Research Fund of Higher Education, Chinese Ministry of Education (No. 20110205110010)
文摘It is now common practice to perform simultaneous traveltime inversion for the velocity field and the reflector geometry in reflection/refraction tomography, or the velocity field and the hypocenter locations in regional earthquake tomography, but seldom are all three classes of model parameters updated simultaneously. This is mainly due to the trade-off between the different types of model parameters and the lack of different seismic phases to constrain the model parameters. Using a spherical-coordinate ray tracing algorithm for first and later（primary reflected） arrival tracing algorithm in combination with a popular linearized inversion solver, it is possible to simultaneously recover the three classes of model parameters in regional or global tomographic studies. In this paper we incorporate the multistage irregular shortest-path ray tracing algorithm（in a spherical coordinate system） with a subspace inversion solver to formulate a simultaneous inversion algorithm for triple model parameters updating using direct and later arrival time information.Comparison tests for two sets of data（noise free and added noise） indicate that the new triple-class parameter inversion algorithm is capable of obtaining nearly the same results as the double-class parameter inversion scheme. Furthermore,the proposed multi-parameter type inversion method is not sensitive to a modest level of picking error in the traveltime data, and also performs well with a relatively large uncertainty in earthquake hypocentral locations. This shows it to be a feasible and promising approach in regional or global tomographic applications.
文摘The relationships between energy, amplitude and frequency of eanhquake are correlative with the property of the seismic source. And the grade of the correlativity can be used as an index to distinguish the types of strong earth quakes. Primarily the strong earthquake can be divided into three types of main-after earthquakes, double-main earthquakes and swarm of strong earthquake. There are similarity and a certain repeatability at the quantificational indexes of hypocenter property between the same type of strong earthquakes, which supply basis for the forecast of subsequent strong shocks. The reference indexes of after strong shock forecast which are valuable for the applica tions of the method of type-divided forecast come from the analysis about more than fifty strong shock wide-band (BPZ wave) recording data of CDSN from 1988 to 1997.
基金Joint Earthquake Science Foundation of China (104001)
文摘We applied the double-difference earthquake rdocation algorithm to 1348 earthquakes with Ms ≥2.0 that occurred in the northern Tianshan region, Xinjiang, from April 1988 to June 2003, using a total of 28701 P- and S-wave arrival times recorded by 32 seismic stations in Xinjiang. Aiming to obtain most of these Ms ≥ 2.0 earthquakes relocations, and considering the requirements of the DD method and the condition of data, we added the travel time data of another 437 earthquakes with 1.5 ≤ Ms 〈 2.0. Finally, we obtained the relocation results for 1253 earthquakes with Ms ≥2.0, which account for 93 % of all the 1348 earthquakes with Ms ≥ 2.0 and includes all the Ms ≥ 3.0 earthquakes. The reason for not relocating the 95 earthquakes with 2.0 ≤ Ms 〈 3.0 is analyzed in the paper. After relocation, the RMS residual decreased from 0.83s to 0.14s, the average error is 0.993 km in E-W direction, 1.10 km in N- S direction, and 1.33 km in vertical direction. The hypocenter depths are more convergent than before and distributed from 5 km to 35 kin, with 94% being from 5km to 35 kin, 68.2% from 10 km to 25 kin. The average hypocenter depth is 19 kin.
