Recently, the phase compensation technique has allowed the ultrasound to propagate through the skull and focus into the brain. However, the temperature evolution during treatment is hard to control to achieve effectiv...Recently, the phase compensation technique has allowed the ultrasound to propagate through the skull and focus into the brain. However, the temperature evolution during treatment is hard to control to achieve effective treatment and avoid over-high temperature. Proposed in this paper is a method to modulate the temperature distribution in the focal region. It superimposes two signals which focus on two preset different targets with a certain distance. Then the temperature distribution is modulated by changing triggering time delay and amplitudes of the two signals. The simulation model is established based on an 82-element transducer and computed tomography (CT) data of a volunteer's head. A finite- difference time-domain (FDTD) method is used to calculate the temperature distributions. The results show that when the distances between the two targets respectively are 7.5-12.5 mm on the acoustic axis and 2.0-3.0 mm in the direction perpendicular to the acoustic axis, a focal region with a uniform temperature distribution (64-65 ℃) can be created. Moreover, the volume of the focal region formed by one irradiation can be adjusted (26.8-266.7 mm3) along with the uniform temperature distribution. This method may ensure the safety and efficacy of HIFU brain tumor therapy.展开更多
A method estimating the stress level in the focal region of an earthquake is proposed here. Taking the 2001 M=8.1 Western Kunlun Mountain Pass earthquake as an example, we estimate its stress level in the focal region...A method estimating the stress level in the focal region of an earthquake is proposed here. Taking the 2001 M=8.1 Western Kunlun Mountain Pass earthquake as an example, we estimate its stress level in the focal region before and after it by this method. The results show that the stress level in the focal region just prior to the initiation of this event is approximately 6.3-8 MPa, and about 5-6.7 MPa remained in the focal region after its occurrence. The stress in the focal region decreased by roughly twenty percent after this event.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
There are put forward in this paper the principle of using artificial neural networks to determine the featureswhich reflect seismotectonics and seismicity of the potential focal regions and the method to divide quant...There are put forward in this paper the principle of using artificial neural networks to determine the featureswhich reflect seismotectonics and seismicity of the potential focal regions and the method to divide quantitativelythe potential focal regions. The calculation of the actual data of North China area shows that it may fully reveal the relations between the potential focal regions and their controling characteristics by the method, of which the principle is concise and convenient to apply, the calculated results reasonable, the division in a meticulous way and the achievement practicable.展开更多
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
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
Based on the spatial orientation and slip direction of the fault plane solutions, we present the expression of corresponding mechanical axis tensor in geographic coordinate system, and then put forward a method for ca...Based on the spatial orientation and slip direction of the fault plane solutions, we present the expression of corresponding 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 structures. 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
An earthquake with magnitude 6.6 occurred on November 16,1983 in the Kaoiki,Hawii.The hierarchical clustering analyses were made by stages for the focal mechanism solutions of 74 earthquakes with M≥3.0 in this area f...An earthquake with magnitude 6.6 occurred on November 16,1983 in the Kaoiki,Hawii.The hierarchical clustering analyses were made by stages for the focal mechanism solutions of 74 earthquakes with M≥3.0 in this area from 1977 to 1985,it was found that each type of focal mechanism is roughly with invariable percentage,and that the strike-slip events including the mainshock,which did not appear in other stages,occurred in the stage around M=6.6 mainshock.The dominant types in the other stages were depressed in the period around the mainshock. This is a believable precursor phenomena.orientation of the principal axes of stress field was inversed by fitting slip vector based on the focal mechanisms in the different periods.The results show that the stress field around the main shock with M=6.6 was more stable,its maximum and minimum principal axes is nearly horizontal in EW and NS direction respectively,the middle one is nearly vertical.The middle principal axis of stress field in the other periods appeared to be horizontal and the corresponding seismic rupture horizontally slip with a small dip.The significant difference between the stress field of source region in the period around the strong shock and that in the other periods shows that the seismogeny and occurrence of the strong shock were controlled by the variation of stress field.The characteristic environment factors of Kaoiki region and its effects were discussed.展开更多
Small earthquake data from the Pishan MS6.5 aftershocks is collected by the Xinjiang Regional Digital Seismic Observation Network.Five parameters of the focal region are obtained by micro genetic inversion:stress dro...Small earthquake data from the Pishan MS6.5 aftershocks is collected by the Xinjiang Regional Digital Seismic Observation Network.Five parameters of the focal region are obtained by micro genetic inversion:stress dropΔσof 75.95 bars,quality factor parameters Q0of 186.33 andηof 0.26,geometric attenuation parameters R1of 72.18km and R2of 139.70km.We calculate the Fourier spectrum and combine it with the random phase spectrum to get the ground motion time history,and build the strong motion acceleration attenuation relationship.The strong ground motion acceleration attenuation of the Pishan area is thus obtained.Because of the insufficiency of strong ground motion records,we added the records from the Wuqia MS6.9 earthquake on October 5,2008,the Akto MS6.2 earthquake on October 6,2008,and the Lop MS6.0 earthquake on March 9,2012 to the data.The comparison of the calculation results and the empirical attenuation relationships with strong ground motion records reveal that the strong motion data of Pishan and Lop earthquakes is higher than the empirical attenuation relationships.The Wuqia MS6.9 earthquake strong motion data is consistent with Yu Yanxiangs(2013)short axis result,and lower than the present result.展开更多
On the basis of about 300 earthquake wave forms observed in the Shidian MS=5.9 sequences on April 12, 2001 recorded in Kunming Digital Seismic Network, the spectra of shear wave have been used to estimate the focal pa...On the basis of about 300 earthquake wave forms observed in the Shidian MS=5.9 sequences on April 12, 2001 recorded in Kunming Digital Seismic Network, the spectra of shear wave have been used to estimate the focal parameters of these earthquake sequences. The results show that within the magnitude range of 1.5~5.3, the seis-mic moments are 1010~1016 N?m, the corner frequencies are 0.2~0.8 Hz, radii of the focal rupture are 200~2 500 m and the stress drops are 0.1×105~20×105Pa. Through the statistical analyses of variation of corner frequency fc and stress drop ?σ with time, it is discovered that the average corner frequency of the foreshock sequences is obviously lower than that of the aftershock sequences. Contrarily, the average stress drops ?σ of the foreshock sequences are clearly higher than that of the aftershocks. It is considered that these variation characteristics of av-erage corner frequency and stress drops before and after the main shock have index significance to the precursory information before a strong earthquake. The higher stress drops for the foreshock sequences show that the higher shear stresses have been stored in the area of main shock. After the main shock, most of the stresses have been released, so the aftershock sequences show a rupture process of lower stresses.展开更多
We selected the 103 M_L≥2. 5 earthquake waveform data from the Inner Mongolia-Ningxia border during 2009-2015,which was recorded by the Inner Mongolia Digital Seismic Networks and used the simplex method, Hyposat met...We selected the 103 M_L≥2. 5 earthquake waveform data from the Inner Mongolia-Ningxia border during 2009-2015,which was recorded by the Inner Mongolia Digital Seismic Networks and used the simplex method, Hyposat method, double difference location method,and deterministic method (PTD) for the determination of focal depth,and compared the results. The CAP moment tensor inversion method is used to determine the focal depths of the Alxa Left Banner M5. 8 and M4. 2 earthquakes. The final results of the focal depth by the deterministic method (PTD) and the double difference location method fit well with the tectonic characteristics of the Inner Mongolia-Ningxia border area,but those of the simplex method and the Hyposat method do not. The average depth of the Inner Mongolia-Ningxia border seismic tectonic zone is 13. 32 ± 8 km.展开更多
In this paper, using focal mechanism solutions of moderate-strong earthquakes in Yunnan and its adjacent areas, and based on the statistical analysis of the parameters of focal mechanism solutions, we discussed in det...In this paper, using focal mechanism solutions of moderate-strong earthquakes in Yunnan and its adjacent areas, and based on the statistical analysis of the parameters of focal mechanism solutions, we discussed in detail the earthquake fault types and the characteristics of the modern tectonic stress field in the Yunnan region. The results show that most moderate-strong earthquakes occurring in the Yunnan region are of the strike-slip type, amounting to 80% of the total. Normal faulting and normal with strike-slip and reverse and reverse with strike-slip earthquakes is almost equivalent in proportion, about 8% each. The tectonic stress field of the Yunnan region is near-horizontal, and the dips of earthquake fault planes are large. There are three main dynamic sources acting on the Yunnan region: one is the NE, NNE and NNW-directed acting force from Myanmar, Laos and Vietnam; the second is the SE-SSE directed force from the Sichuan and Sichuan-Yunnan rhombus block and the third is the NW-NNW directed force from the South China block. These three acting forces have controlled the faulting behavior of the main faults and the characteristics of strong earthquake activity of Yunnan and its adjacent regions.展开更多
Jiashi and its surrounding areas are composed of many structural zones. Using the focal mechanism solutions of 59 moderately strong earthquakes in Jiashi and its surrounding areas, and combining these with the calcula...Jiashi and its surrounding areas are composed of many structural zones. Using the focal mechanism solutions of 59 moderately strong earthquakes in Jiashi and its surrounding areas, and combining these with the calculation results of system cluster and stress field inversion, we analyzed the evolvement characteristics of the stress field for different times and different regions. The results were as follows: The earthquakes in Jiashi are mainly strike-slip. However, those of the Kalpin block are mainly reverse events, showing an obvious thrusting. The regional characteristics are different from other areas. The direction of the regional principal stress field is near NS. However, under different tectonic backgrounds, the directions of the stress fields are different. The direction of the principal compress stress is near NS in the Kashi-Wuqia area. But before and after the 3 earthquakes with M7.0, dynamic evolution from NW to NS and then to NE with time process was observed. The Kalpin block has been dominated by a consistent stress field in the NW direction for a long time. However, the direction of the stress field of the Jiashi region is NE. Since 1996, the direction of the regional stress field has changed obviously. The direction of the P axis was deflected towards the NE, and the plunge angle increased. The result shows clearly the regional characteristics and variation of the distribution pattern of the stress field in different tectonic environments.展开更多
At 19:33 p.m on September 27, 2003, an earthquake with M7.9 occurred in the Russia-Mongolia-China boundary Region. It was strongly felt in the Altay region of Xinjiang. The losses caused by the earthquake was 76 milli...At 19:33 p.m on September 27, 2003, an earthquake with M7.9 occurred in the Russia-Mongolia-China boundary Region. It was strongly felt in the Altay region of Xinjiang. The losses caused by the earthquake was 76 million yuan (RMB). Some information about the earthquake was outlined, including basic parameters, focal mechanism, evaluation of earthquake disaster losses and so on. The satellite remote sensing information worked initial analysis for deformation of ground and failure phenomenon.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.81272495)the Natural Science Foundation of Tianjin,China(Grant No.16JC2DJC32200)
文摘Recently, the phase compensation technique has allowed the ultrasound to propagate through the skull and focus into the brain. However, the temperature evolution during treatment is hard to control to achieve effective treatment and avoid over-high temperature. Proposed in this paper is a method to modulate the temperature distribution in the focal region. It superimposes two signals which focus on two preset different targets with a certain distance. Then the temperature distribution is modulated by changing triggering time delay and amplitudes of the two signals. The simulation model is established based on an 82-element transducer and computed tomography (CT) data of a volunteer's head. A finite- difference time-domain (FDTD) method is used to calculate the temperature distributions. The results show that when the distances between the two targets respectively are 7.5-12.5 mm on the acoustic axis and 2.0-3.0 mm in the direction perpendicular to the acoustic axis, a focal region with a uniform temperature distribution (64-65 ℃) can be created. Moreover, the volume of the focal region formed by one irradiation can be adjusted (26.8-266.7 mm3) along with the uniform temperature distribution. This method may ensure the safety and efficacy of HIFU brain tumor therapy.
文摘A method estimating the stress level in the focal region of an earthquake is proposed here. Taking the 2001 M=8.1 Western Kunlun Mountain Pass earthquake as an example, we estimate its stress level in the focal region before and after it by this method. The results show that the stress level in the focal region just prior to the initiation of this event is approximately 6.3-8 MPa, and about 5-6.7 MPa remained in the focal region after its occurrence. The stress in the focal region decreased by roughly twenty percent after this event.
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.
文摘There are put forward in this paper the principle of using artificial neural networks to determine the featureswhich reflect seismotectonics and seismicity of the potential focal regions and the method to divide quantitativelythe potential focal regions. The calculation of the actual data of North China area shows that it may fully reveal the relations between the potential focal regions and their controling characteristics by the method, of which the principle is concise and convenient to apply, the calculated results reasonable, the division in a meticulous way and the achievement practicable.
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.
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.
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 corresponding 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 structures. 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.
文摘An earthquake with magnitude 6.6 occurred on November 16,1983 in the Kaoiki,Hawii.The hierarchical clustering analyses were made by stages for the focal mechanism solutions of 74 earthquakes with M≥3.0 in this area from 1977 to 1985,it was found that each type of focal mechanism is roughly with invariable percentage,and that the strike-slip events including the mainshock,which did not appear in other stages,occurred in the stage around M=6.6 mainshock.The dominant types in the other stages were depressed in the period around the mainshock. This is a believable precursor phenomena.orientation of the principal axes of stress field was inversed by fitting slip vector based on the focal mechanisms in the different periods.The results show that the stress field around the main shock with M=6.6 was more stable,its maximum and minimum principal axes is nearly horizontal in EW and NS direction respectively,the middle one is nearly vertical.The middle principal axis of stress field in the other periods appeared to be horizontal and the corresponding seismic rupture horizontally slip with a small dip.The significant difference between the stress field of source region in the period around the strong shock and that in the other periods shows that the seismogeny and occurrence of the strong shock were controlled by the variation of stress field.The characteristic environment factors of Kaoiki region and its effects were discussed.
基金jointly sponsored by “The Ground Motion Attenuation Relationship Based on Seismology and Its Practicability” of the National Natural Science Foundation of China(51178434)“With Digital Ride Network Small Earthquake Records to Establish Regional Strong Ground Motion Attenuation Relations”from the National Natural Science Foundation of China(51478443)“Based on the Regional Parameters of Mixed Ground Motion Attenuation Relationship”from the National Natural Science Foundation of China(51678540)
文摘Small earthquake data from the Pishan MS6.5 aftershocks is collected by the Xinjiang Regional Digital Seismic Observation Network.Five parameters of the focal region are obtained by micro genetic inversion:stress dropΔσof 75.95 bars,quality factor parameters Q0of 186.33 andηof 0.26,geometric attenuation parameters R1of 72.18km and R2of 139.70km.We calculate the Fourier spectrum and combine it with the random phase spectrum to get the ground motion time history,and build the strong motion acceleration attenuation relationship.The strong ground motion acceleration attenuation of the Pishan area is thus obtained.Because of the insufficiency of strong ground motion records,we added the records from the Wuqia MS6.9 earthquake on October 5,2008,the Akto MS6.2 earthquake on October 6,2008,and the Lop MS6.0 earthquake on March 9,2012 to the data.The comparison of the calculation results and the empirical attenuation relationships with strong ground motion records reveal that the strong motion data of Pishan and Lop earthquakes is higher than the empirical attenuation relationships.The Wuqia MS6.9 earthquake strong motion data is consistent with Yu Yanxiangs(2013)short axis result,and lower than the present result.
基金Scientific and Technological Key Project of Yunnan Province (2001NG46)
文摘On the basis of about 300 earthquake wave forms observed in the Shidian MS=5.9 sequences on April 12, 2001 recorded in Kunming Digital Seismic Network, the spectra of shear wave have been used to estimate the focal parameters of these earthquake sequences. The results show that within the magnitude range of 1.5~5.3, the seis-mic moments are 1010~1016 N?m, the corner frequencies are 0.2~0.8 Hz, radii of the focal rupture are 200~2 500 m and the stress drops are 0.1×105~20×105Pa. Through the statistical analyses of variation of corner frequency fc and stress drop ?σ with time, it is discovered that the average corner frequency of the foreshock sequences is obviously lower than that of the aftershock sequences. Contrarily, the average stress drops ?σ of the foreshock sequences are clearly higher than that of the aftershocks. It is considered that these variation characteristics of av-erage corner frequency and stress drops before and after the main shock have index significance to the precursory information before a strong earthquake. The higher stress drops for the foreshock sequences show that the higher shear stresses have been stored in the area of main shock. After the main shock, most of the stresses have been released, so the aftershock sequences show a rupture process of lower stresses.
基金sponsored by the “Major Scientific and Technical Project of Science and Technology Department of Inner Mongolia in 2016 (Strong Earthquake Track in the Short Stage and Integration Innovation of Stereoscopic Observation Technology in Space and Ground)”
文摘We selected the 103 M_L≥2. 5 earthquake waveform data from the Inner Mongolia-Ningxia border during 2009-2015,which was recorded by the Inner Mongolia Digital Seismic Networks and used the simplex method, Hyposat method, double difference location method,and deterministic method (PTD) for the determination of focal depth,and compared the results. The CAP moment tensor inversion method is used to determine the focal depths of the Alxa Left Banner M5. 8 and M4. 2 earthquakes. The final results of the focal depth by the deterministic method (PTD) and the double difference location method fit well with the tectonic characteristics of the Inner Mongolia-Ningxia border area,but those of the simplex method and the Hyposat method do not. The average depth of the Inner Mongolia-Ningxia border seismic tectonic zone is 13. 32 ± 8 km.
基金sponsored by the important projects of Yunnan Province,entitled"The regularity of strong earthquake activities and the plate margindynamic mechanism on the eastern margin of the Qinghai-Tibet plateau"(2010CC006)"Study on relationship between evolutionary dynamics of geophysical and geochemistry field and strong seismic activity in Yunnan"(JCYB200806015)
文摘In this paper, using focal mechanism solutions of moderate-strong earthquakes in Yunnan and its adjacent areas, and based on the statistical analysis of the parameters of focal mechanism solutions, we discussed in detail the earthquake fault types and the characteristics of the modern tectonic stress field in the Yunnan region. The results show that most moderate-strong earthquakes occurring in the Yunnan region are of the strike-slip type, amounting to 80% of the total. Normal faulting and normal with strike-slip and reverse and reverse with strike-slip earthquakes is almost equivalent in proportion, about 8% each. The tectonic stress field of the Yunnan region is near-horizontal, and the dips of earthquake fault planes are large. There are three main dynamic sources acting on the Yunnan region: one is the NE, NNE and NNW-directed acting force from Myanmar, Laos and Vietnam; the second is the SE-SSE directed force from the Sichuan and Sichuan-Yunnan rhombus block and the third is the NW-NNW directed force from the South China block. These three acting forces have controlled the faulting behavior of the main faults and the characteristics of strong earthquake activity of Yunnan and its adjacent regions.
基金The research was jointly sponsored by the State Key Science and Technology Development and Research Program of the 10th Five-Year Plan ( Grant No. 2001BA601B010303)the project of Science and Technology Department of Xinjiang Uygur Autonomous Region (Grant No.200333116) .
文摘Jiashi and its surrounding areas are composed of many structural zones. Using the focal mechanism solutions of 59 moderately strong earthquakes in Jiashi and its surrounding areas, and combining these with the calculation results of system cluster and stress field inversion, we analyzed the evolvement characteristics of the stress field for different times and different regions. The results were as follows: The earthquakes in Jiashi are mainly strike-slip. However, those of the Kalpin block are mainly reverse events, showing an obvious thrusting. The regional characteristics are different from other areas. The direction of the regional principal stress field is near NS. However, under different tectonic backgrounds, the directions of the stress fields are different. The direction of the principal compress stress is near NS in the Kashi-Wuqia area. But before and after the 3 earthquakes with M7.0, dynamic evolution from NW to NS and then to NE with time process was observed. The Kalpin block has been dominated by a consistent stress field in the NW direction for a long time. However, the direction of the stress field of the Jiashi region is NE. Since 1996, the direction of the regional stress field has changed obviously. The direction of the P axis was deflected towards the NE, and the plunge angle increased. The result shows clearly the regional characteristics and variation of the distribution pattern of the stress field in different tectonic environments.
文摘At 19:33 p.m on September 27, 2003, an earthquake with M7.9 occurred in the Russia-Mongolia-China boundary Region. It was strongly felt in the Altay region of Xinjiang. The losses caused by the earthquake was 76 million yuan (RMB). Some information about the earthquake was outlined, including basic parameters, focal mechanism, evaluation of earthquake disaster losses and so on. The satellite remote sensing information worked initial analysis for deformation of ground and failure phenomenon.