We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The resu...We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in Yunnan, with focal depths concentrated in the top 10 km of the crust. The earthquake mechanisms obtained were combined with the global centroid moment tensor solutions of 80 additional earthquakes from 1976 to 2016 to invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme.Results of the stress field inversion confirmed that the Yunnan region is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in a northwest-southeast direction, and they experience a clockwise rotation from north to south, whereas the maximum extensional axes are oriented largely northeast-southwest. The maximum compressional axes are in line with the global positioning system–inferred horizontal velocity field and the southeastward escape of the Sichuan–Yunnan Rhombic Block, whereas the maximum extensional axes are consistent with anisotropy derived from SKS splitting. Against the strike–slip background, normal faulting stress regimes can be seen in the Tengchong volcanic area as well as in other areas with complex crisscrossing fault zones.展开更多
The inversion of modern tectonic stress field in China is made by regions on the basis of focal mechanism data inthe period of 1920-1996. Results of the inversion show that the maximum principal compressive stress σ1...The inversion of modern tectonic stress field in China is made by regions on the basis of focal mechanism data inthe period of 1920-1996. Results of the inversion show that the maximum principal compressive stress σ1 axisstrikes nearly north-south direction in the Tibet Plateau and western Chin4 east-west direction in North China Incentral China, its strikes show a radiate pattern, i.e., north-north east in north part, east-west in central part andnorth-north west in south part. The σ1 axes are often perpendicular to the minimum principal stress σ3 axes, exceptwestern China where the σ1 axes are oblique to the σ3 axes with an acute angle. R is defined by (σ2-σ1)/(σ3-σ1),has the higher values (0.60-0.90) in north part of central China and quickly changes into the lower values(0. 10-0.30) in the Tibet Plateau. Both of the observed and inverted fault planes have strikes varying with locations.Combining stress directions and R value, the stress configuration is divided into 7 groups. Most of the groups showstrike-slip faulting with intermediate R values, which occupies North China and the eastern part of China as well asinner Tibet Plateau. A few of them show reverse faulting with higher R values within western pod of China and thenorth edge of the Tibet Plateau. Normal faulting occurred on the south edge of the Tibet Plateau with smaller Rval nes.展开更多
Using the 78 focal mechanism solutions of the fore shocks, main shock and after shocks of the earthquake sequence for the Yao’an earthquake, the characteristics of the focal faults and stress field for the earthquake...Using the 78 focal mechanism solutions of the fore shocks, main shock and after shocks of the earthquake sequence for the Yao’an earthquake, the characteristics of the focal faults and stress field for the earthquake sequence are analyzed. The results show that the main rupture plane of the Yao’an earthquake sequence is a tectonic fault with N50°W strike and steep dip and all the main shock, the fore shocks and the vast majority of after shocks occurred on the main rupture plane. A tectonic fracture with NNE-NE strike also participated in development process of the sequence. The focal stress field of the sequence dominated by principal compressional stress with nearly horizontal orientation SSE is consistent with the regional tectonic stress field. In the sequence development, the stress field in the focal region was complex with multi-azimuths and multi-action models and the focal rupture showed complex features with multi-directions and multi-patterns.展开更多
A dense seismic network was installed in the capital region of China in recent years,which makes it possible to resolve the focal mechanisms of small earthquakes. We gathered large earthquake focal mechanisms from the...A dense seismic network was installed in the capital region of China in recent years,which makes it possible to resolve the focal mechanisms of small earthquakes. We gathered large earthquake focal mechanisms from the last fifty years and moderate or small earthquake focal mechanisms from between 2002 and 2004,and calculated the present tectonic stress field of the capital region by the grid search method, which weighs different sized earthquakes and can improve the accuracy of the stress field inversion. The analysis of inversion results of different sub-regions shows that the azinuth of the maximum principal compressive stress axis is NE43°- 86° in the Beijing-Zhangjiakou-Datong area,NE38°-86° in the Tangshan area,and NE79°- 81° in the Xingtai area. Inversion results of this paper are similar to previous results,which proves the correctness of the approach. As revealed by the results,the stress field of the capital region is characterized by overall consistency and sub-regional differences. This study provides reference for earthquake mechanism explanation and geodynamics research.展开更多
Focal region field of a two dimensional Gregorian system coated with chiral medium is analyzed at high frequency. Maslov's method is used because the Geometrical Optics approximation fails at focal points. Maslov...Focal region field of a two dimensional Gregorian system coated with chiral medium is analyzed at high frequency. Maslov's method is used because the Geometrical Optics approximation fails at focal points. Maslov’s method combines the simplicity of ray theory and the generality of Fourier transform. Fields patterns are calculated numerically and the results are plotted. The effects of thickness of chiral layer, chirality parameter of the chiral medium and permittivity of the medium are analyzed. The problem of simple dielectric layer is discussed as a special case of this problem.展开更多
Based on the spatial orientation and slip direction of the fault plane solutions, we present the expression of corre- sponding mechanical axis tensor in geographic coordinate system, and then put forward a method for ...Based on the spatial orientation and slip direction of the fault plane solutions, we present the expression of corre- sponding mechanical axis tensor in geographic coordinate system, and then put forward a method for calculating average mechanical axis tensor and its eigenvalues, which involves solving the corresponding eigenequation. The method for deducing mean stress field from T, B, and P axes parameters of a number of focal mechanism solutions has been verified by inverting data of mean stress fields in Fuyun region and in Tangshan region with fitting method of slip direction, and both results are consistent. To study regional average stress field, we need to choose a population of focal mechanism solutions of earthquakes in the massifs where there are significant tectonic struc- tures. According to the focal mechanism solutions of 256 moderate-strong earthquakes occurred in 13 seismic zones of Sichuan-Yunnan region, the quantitative analysis results of stress tensor in each seismic zone have been given. The algorithm of such method is simple and convenient, which makes the method for analyzing tectonic stress field with large amount of focal mechanism solution data become quantified.展开更多
Based on seismic wave records of the Chengdu digital seismic network and Zipingpu reservoir digital seismic network from August 16,2004 to May 12,2008 when the Wenchuan MS8.0 earthquake occurred,the parameters of foca...Based on seismic wave records of the Chengdu digital seismic network and Zipingpu reservoir digital seismic network from August 16,2004 to May 12,2008 when the Wenchuan MS8.0 earthquake occurred,the parameters of focal mechanisms of 486 earthquakes with magnitude larger than M1.6 in the Zipingpu reservoir area were calculated using amplitude ratio method,meanwhile the temporal-spatial variation characteristics of mechanisms and stress field were analyzed based on these parameters.Results show a low ratio of thrust earthquakes and an increased number of strike-slip earthquakes in the reservoir water area in the period from 2006 to 2008.While in the areas far from the reservoir waterfront,the thrust earthquakes took up a high proportion and the strike-slip ones did not increase.The direction of mean principal compressive stress field was deflected and disturbed differently in each area before the Wenchuan MS8.0 earthquake.展开更多
Using the focal mechanism solutions of 24 moderately strong earthquakes in the northern Tianshan area,we carried out system cluster and stress field inversion analysis.The result indicates that,the focal mechanism sol...Using the focal mechanism solutions of 24 moderately strong earthquakes in the northern Tianshan area,we carried out system cluster and stress field inversion analysis.The result indicates that,the focal mechanism solutions of moderately strong earthquakes are mainly dip-slip reverse faulting in the northern Tianshan area.The principal rupture planes of earthquakes are NW-oriented.It is basically consistent with the strike of earthquake structure in its adjacent area.The direction of the principal compression stress P axis is nearly NS,and its inclination angle is small;while the inclination angle of the principal extensional stress T axis is large.It shows that the regional stress field is mainly controlled by the near-NS horizontal compressive stress.The direction of the maximum principal stress shows a gradation process of NNE-NS-NW from east to west.展开更多
The contemporary tectonic stress field in China is obtained on the basis of Chinese stress field database and Harvard CMT catalogue.Result of the inverted tectonic stresses shows that the maximum principal stress axis...The contemporary tectonic stress field in China is obtained on the basis of Chinese stress field database and Harvard CMT catalogue.Result of the inverted tectonic stresses shows that the maximum principal stress axis strikes nearly north-south direction in the west part of Tibet plateau,ENE direction in North China.In Central China,its strikes show a radiated pattern,i.e.,NNE in north part and NNW in south part.The detailed stress field parameters of nearly whole China are given and can be used in geodynamic stress field simulation and earthquake prediction.展开更多
We applied the g CAP algorithm to determine239 focal mechanism solutions 3:0 M We 6:0T with records of dense Chin Array stations deployed in Yunnan,and then inverted 686 focal mechanisms(including 447 previous results...We applied the g CAP algorithm to determine239 focal mechanism solutions 3:0 M We 6:0T with records of dense Chin Array stations deployed in Yunnan,and then inverted 686 focal mechanisms(including 447 previous results) for the regional crustal stress field with a damped linear inversion. The results indicate dominantly strike-slip environment in Yunnan as both the maximum(r1) and minimum(r3) principal stress axes are sub-horizontal. We further calculated the horizontal stress orientations(i.e., maximum and minimum horizontal compressive stress axes: S H and S h, respectively) accordingly and found an abrupt change near *26°N. To the north, S H aligns NW-SE to nearly E-W while S h aligns nearly N-S. In contrast, to the south, both S H and S h rotate laterally and show dominantly fan-shaped patterns. The minimum horizontal stress(i.e., maximum strain axis) S h rotates from NW-SE to the west of Tengchong volcano gradually to nearly E-W in west Yunnan, and further toNE-SW in the South China block in the east. The crustal strain field is consistent with the upper mantle strain field indicated by shear-wave splitting observations in Yunnan but not in other regions. Therefore, the crust and upper mantle in Yunnan are coupled and suffering vertically coherent pure-shear deformation in the lithosphere.展开更多
This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field...This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd:YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd:YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd:YVO4 rectangular crystal for the YVO4/Nd:YVO4 composite crystal and the Nd:YVO4 single crystal are researched respec- tively. Calculating the thermal focal length within the Nd:YVO4 rectangular crystal was done by an analysis of the additional optical path differences (OPD) caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd:YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7 mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd:YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd:YVO4 crystal and the Nd:YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd:YVO4 laser is more advantageous than the laser with Nd:YVO4 single crystal.展开更多
Two earthquakes of Ms=6.0 and Ms=6. 1 consecutively occurred on December 31, 1994 and January 10, 1995 in Beibuwan region, China. By using the generalized reflection-transmission coefficient matrix and the discrete sl...Two earthquakes of Ms=6.0 and Ms=6. 1 consecutively occurred on December 31, 1994 and January 10, 1995 in Beibuwan region, China. By using the generalized reflection-transmission coefficient matrix and the discrete slowness integration method in the calculation of Green’s functions, we obtained the focal mechanisms of these earthquakes using long-period waveforms of regional body waves recorded by the China Digital Seismograph Network (CDSN) by means of moment tensor inversion method in frequency domain. The results inverted indicate that the focal mechanisms of these two earthquakes were similar to each other. Their principal compressional stresses are in NW-SE direction and principal tensional stresses are in NE-SW direction. It turns out that the occurrence of the two earthquakes was controlled by the same tectonic environment related to the collision of the Philippine Plate and the Eurasian Plates. On the other hand, the results imply that the stress field in the seismogenic region has a significant change after the Ms=6.0 earthquake. It may be proposed that the occurrence of the Ms=6. 1 earthquake could be related to the stress field adjustment caused by the Ms=6.0 earthquake.展开更多
基金supported by the Basic Research Fund of the Institute of Earthquake Forecasting,China Earthquake Administration(2015IES010302)the State Key Laboratory of Geodesy and Earth’s Dynamics,Institute of Geodesy and Geophysics,Chinese Academy of Sciences(SKLGED2018-4-3-E)
文摘We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in Yunnan, with focal depths concentrated in the top 10 km of the crust. The earthquake mechanisms obtained were combined with the global centroid moment tensor solutions of 80 additional earthquakes from 1976 to 2016 to invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme.Results of the stress field inversion confirmed that the Yunnan region is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in a northwest-southeast direction, and they experience a clockwise rotation from north to south, whereas the maximum extensional axes are oriented largely northeast-southwest. The maximum compressional axes are in line with the global positioning system–inferred horizontal velocity field and the southeastward escape of the Sichuan–Yunnan Rhombic Block, whereas the maximum extensional axes are consistent with anisotropy derived from SKS splitting. Against the strike–slip background, normal faulting stress regimes can be seen in the Tengchong volcanic area as well as in other areas with complex crisscrossing fault zones.
文摘The inversion of modern tectonic stress field in China is made by regions on the basis of focal mechanism data inthe period of 1920-1996. Results of the inversion show that the maximum principal compressive stress σ1 axisstrikes nearly north-south direction in the Tibet Plateau and western Chin4 east-west direction in North China Incentral China, its strikes show a radiate pattern, i.e., north-north east in north part, east-west in central part andnorth-north west in south part. The σ1 axes are often perpendicular to the minimum principal stress σ3 axes, exceptwestern China where the σ1 axes are oblique to the σ3 axes with an acute angle. R is defined by (σ2-σ1)/(σ3-σ1),has the higher values (0.60-0.90) in north part of central China and quickly changes into the lower values(0. 10-0.30) in the Tibet Plateau. Both of the observed and inverted fault planes have strikes varying with locations.Combining stress directions and R value, the stress configuration is divided into 7 groups. Most of the groups showstrike-slip faulting with intermediate R values, which occupies North China and the eastern part of China as well asinner Tibet Plateau. A few of them show reverse faulting with higher R values within western pod of China and thenorth edge of the Tibet Plateau. Normal faulting occurred on the south edge of the Tibet Plateau with smaller Rval nes.
文摘Using the 78 focal mechanism solutions of the fore shocks, main shock and after shocks of the earthquake sequence for the Yao’an earthquake, the characteristics of the focal faults and stress field for the earthquake sequence are analyzed. The results show that the main rupture plane of the Yao’an earthquake sequence is a tectonic fault with N50°W strike and steep dip and all the main shock, the fore shocks and the vast majority of after shocks occurred on the main rupture plane. A tectonic fracture with NNE-NE strike also participated in development process of the sequence. The focal stress field of the sequence dominated by principal compressional stress with nearly horizontal orientation SSE is consistent with the regional tectonic stress field. In the sequence development, the stress field in the focal region was complex with multi-azimuths and multi-action models and the focal rupture showed complex features with multi-directions and multi-patterns.
基金sponsored by the Special Fund of Fundamental Scientific Research Operating Expenses for Higher School of Central Government(Projects for creation teams ZY20110101)the Special Fund for the Earthquake Scientific Research of China(201208009)National Natural Science Foundation of China(41074072)
文摘A dense seismic network was installed in the capital region of China in recent years,which makes it possible to resolve the focal mechanisms of small earthquakes. We gathered large earthquake focal mechanisms from the last fifty years and moderate or small earthquake focal mechanisms from between 2002 and 2004,and calculated the present tectonic stress field of the capital region by the grid search method, which weighs different sized earthquakes and can improve the accuracy of the stress field inversion. The analysis of inversion results of different sub-regions shows that the azinuth of the maximum principal compressive stress axis is NE43°- 86° in the Beijing-Zhangjiakou-Datong area,NE38°-86° in the Tangshan area,and NE79°- 81° in the Xingtai area. Inversion results of this paper are similar to previous results,which proves the correctness of the approach. As revealed by the results,the stress field of the capital region is characterized by overall consistency and sub-regional differences. This study provides reference for earthquake mechanism explanation and geodynamics research.
文摘Focal region field of a two dimensional Gregorian system coated with chiral medium is analyzed at high frequency. Maslov's method is used because the Geometrical Optics approximation fails at focal points. Maslov’s method combines the simplicity of ray theory and the generality of Fourier transform. Fields patterns are calculated numerically and the results are plotted. The effects of thickness of chiral layer, chirality parameter of the chiral medium and permittivity of the medium are analyzed. The problem of simple dielectric layer is discussed as a special case of this problem.
基金State Key Basic Research Development Program (2004CB418404) and the Joint Seismological Science Foundation of China (105004).
文摘Based on the spatial orientation and slip direction of the fault plane solutions, we present the expression of corre- sponding mechanical axis tensor in geographic coordinate system, and then put forward a method for calculating average mechanical axis tensor and its eigenvalues, which involves solving the corresponding eigenequation. The method for deducing mean stress field from T, B, and P axes parameters of a number of focal mechanism solutions has been verified by inverting data of mean stress fields in Fuyun region and in Tangshan region with fitting method of slip direction, and both results are consistent. To study regional average stress field, we need to choose a population of focal mechanism solutions of earthquakes in the massifs where there are significant tectonic struc- tures. According to the focal mechanism solutions of 256 moderate-strong earthquakes occurred in 13 seismic zones of Sichuan-Yunnan region, the quantitative analysis results of stress tensor in each seismic zone have been given. The algorithm of such method is simple and convenient, which makes the method for analyzing tectonic stress field with large amount of focal mechanism solution data become quantified.
基金sponsored by the National Key Technology R&D Program on Reservoir Earthquake Monitoring and Prediction Technique(2008BAC38B03-0202),China
文摘Based on seismic wave records of the Chengdu digital seismic network and Zipingpu reservoir digital seismic network from August 16,2004 to May 12,2008 when the Wenchuan MS8.0 earthquake occurred,the parameters of focal mechanisms of 486 earthquakes with magnitude larger than M1.6 in the Zipingpu reservoir area were calculated using amplitude ratio method,meanwhile the temporal-spatial variation characteristics of mechanisms and stress field were analyzed based on these parameters.Results show a low ratio of thrust earthquakes and an increased number of strike-slip earthquakes in the reservoir water area in the period from 2006 to 2008.While in the areas far from the reservoir waterfront,the thrust earthquakes took up a high proportion and the strike-slip ones did not increase.The direction of mean principal compressive stress field was deflected and disturbed differently in each area before the Wenchuan MS8.0 earthquake.
基金sponsored by the Subject of City ActiveFault Exploration Program of Urumqi and Joint Foundation of Earthquake Administration of Xinjiang Uygur Autonomous Region (200704),China
文摘Using the focal mechanism solutions of 24 moderately strong earthquakes in the northern Tianshan area,we carried out system cluster and stress field inversion analysis.The result indicates that,the focal mechanism solutions of moderately strong earthquakes are mainly dip-slip reverse faulting in the northern Tianshan area.The principal rupture planes of earthquakes are NW-oriented.It is basically consistent with the strike of earthquake structure in its adjacent area.The direction of the principal compression stress P axis is nearly NS,and its inclination angle is small;while the inclination angle of the principal extensional stress T axis is large.It shows that the regional stress field is mainly controlled by the near-NS horizontal compressive stress.The direction of the maximum principal stress shows a gradation process of NNE-NS-NW from east to west.
基金supported by the National Natural Science Foundation of China (40874022)Public Utility Research Project (200808053)973 program (2008CB425703)
文摘The contemporary tectonic stress field in China is obtained on the basis of Chinese stress field database and Harvard CMT catalogue.Result of the inverted tectonic stresses shows that the maximum principal stress axis strikes nearly north-south direction in the west part of Tibet plateau,ENE direction in North China.In Central China,its strikes show a radiated pattern,i.e.,NNE in north part and NNW in south part.The detailed stress field parameters of nearly whole China are given and can be used in geodynamic stress field simulation and earthquake prediction.
基金supported by the National Natural Science Foundations of China (No.41204040)China National Special Fund for Earthquake Scientific Research in Public Interest (Nos.201008001, 201308011)Most figures were made using GMT (Wessel et al.2013)
文摘We applied the g CAP algorithm to determine239 focal mechanism solutions 3:0 M We 6:0T with records of dense Chin Array stations deployed in Yunnan,and then inverted 686 focal mechanisms(including 447 previous results) for the regional crustal stress field with a damped linear inversion. The results indicate dominantly strike-slip environment in Yunnan as both the maximum(r1) and minimum(r3) principal stress axes are sub-horizontal. We further calculated the horizontal stress orientations(i.e., maximum and minimum horizontal compressive stress axes: S H and S h, respectively) accordingly and found an abrupt change near *26°N. To the north, S H aligns NW-SE to nearly E-W while S h aligns nearly N-S. In contrast, to the south, both S H and S h rotate laterally and show dominantly fan-shaped patterns. The minimum horizontal stress(i.e., maximum strain axis) S h rotates from NW-SE to the west of Tengchong volcano gradually to nearly E-W in west Yunnan, and further toNE-SW in the South China block in the east. The crustal strain field is consistent with the upper mantle strain field indicated by shear-wave splitting observations in Yunnan but not in other regions. Therefore, the crust and upper mantle in Yunnan are coupled and suffering vertically coherent pure-shear deformation in the lithosphere.
文摘This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd:YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd:YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd:YVO4 rectangular crystal for the YVO4/Nd:YVO4 composite crystal and the Nd:YVO4 single crystal are researched respec- tively. Calculating the thermal focal length within the Nd:YVO4 rectangular crystal was done by an analysis of the additional optical path differences (OPD) caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd:YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7 mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd:YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd:YVO4 crystal and the Nd:YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd:YVO4 laser is more advantageous than the laser with Nd:YVO4 single crystal.
文摘Two earthquakes of Ms=6.0 and Ms=6. 1 consecutively occurred on December 31, 1994 and January 10, 1995 in Beibuwan region, China. By using the generalized reflection-transmission coefficient matrix and the discrete slowness integration method in the calculation of Green’s functions, we obtained the focal mechanisms of these earthquakes using long-period waveforms of regional body waves recorded by the China Digital Seismograph Network (CDSN) by means of moment tensor inversion method in frequency domain. The results inverted indicate that the focal mechanisms of these two earthquakes were similar to each other. Their principal compressional stresses are in NW-SE direction and principal tensional stresses are in NE-SW direction. It turns out that the occurrence of the two earthquakes was controlled by the same tectonic environment related to the collision of the Philippine Plate and the Eurasian Plates. On the other hand, the results imply that the stress field in the seismogenic region has a significant change after the Ms=6.0 earthquake. It may be proposed that the occurrence of the Ms=6. 1 earthquake could be related to the stress field adjustment caused by the Ms=6.0 earthquake.