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
By means of the hypocenter distribution and focal mechanism of Wuding Ms=6.5 earthquake sequence occurred in1995. the space orientation and activity characteristics of focal fault of Wuding earthquake have been studie...By means of the hypocenter distribution and focal mechanism of Wuding Ms=6.5 earthquake sequence occurred in1995. the space orientation and activity characteristics of focal fault of Wuding earthquake have been studied fromthe three-dimensional space-time process. The results indicate that the focal fault of Wuding earthquake is a subsurface, NWW-trending, upright and right-lateral strike slip fault which is consistent with the intensity distributionin foe meizoseisfnal region. Although the large-scale NS-trending Tanglang-Yimen active fault passes through theearthquake region. it is irrelevant to the Ms=6.5 Wuding main earthquake. Since the relationship between thestrong earthquake and the shallow geological active fault can not be determined, the crustal deep structure shouldbe studied. The method proposed in the paper can be used to distinguish the focal fault in the deep crust.展开更多
Earthquake focal mechanism solutions provide the basic information about the present-day regional tectonics stress distribution, which controls the activities of crustal faults. Therefore, continued efforts for updati...Earthquake focal mechanism solutions provide the basic information about the present-day regional tectonics stress distribution, which controls the activities of crustal faults. Therefore, continued efforts for updating the database of earthquake focal mechanism solutions are quite valuable and important.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By means of the hypocenter distribution and focal mechanism of Wuding Ms=6.5 earthquake sequence occurred in1995. the space orientation and activity characteristics of focal fault of Wuding earthquake have been studied fromthe three-dimensional space-time process. The results indicate that the focal fault of Wuding earthquake is a subsurface, NWW-trending, upright and right-lateral strike slip fault which is consistent with the intensity distributionin foe meizoseisfnal region. Although the large-scale NS-trending Tanglang-Yimen active fault passes through theearthquake region. it is irrelevant to the Ms=6.5 Wuding main earthquake. Since the relationship between thestrong earthquake and the shallow geological active fault can not be determined, the crustal deep structure shouldbe studied. The method proposed in the paper can be used to distinguish the focal fault in the deep crust.
基金National Natural Science Foundation of China (40125011 and 00410785).
文摘Earthquake focal mechanism solutions provide the basic information about the present-day regional tectonics stress distribution, which controls the activities of crustal faults. Therefore, continued efforts for updating the database of earthquake focal mechanism solutions are quite valuable and important.
