1,209 earthquakes occurred in Xianyou,Fujian from August 4,2010 to October 4,2013.The largest earthquake was M L5. 0 on September 4,2013. In order to study the Xianyou earthquake sequence and understand the causative structure and stress field of Xianyou,the focal mechanism solutions of six earthquakes( M L> 3. 5) in the Xianyou earthquake sequence are calculated using the broadband digital data of the Fujian Seismic Network with the seismic moment tensor inverse method. The results show that the focal faults of the six earthquakes are similar,which are all strike-slip faults striking to the northwest with high dip angles. The direction of the principal compressive stress axes is near SN,which is different from the stress field of Fujian region. The Xianyou earthquake sequence may have been induced by the stress adjustment after the impoundment of Jinzhong reservoir.
Ⅰ. Beijing Subway Line 10 Accident On March 28, 2007, six people were buried by a cave-in at Suzhoujie Station on Line 10 of the Beijing Subway. The fatalities were caused when the unit in charge of construction failed to implement a timely evacuation after a construction accident took place. (See Beijing Youth, April 1, 2007)……
The paper inverts the focal mechanism solutions of the Yutian M_S7. 3 main shock,foreshocks and M_S≥3. 5 aftershocks by using the CAP method,based on the broadband waveforms recorded by the Xinjiang and Tibet Digital Seismic Networks. The results show that the M_S7. 3 strong earthquake is of strike-slip type with a normal faulting component,and combined with the analysis of focal structure and the aftershock distribution,the nodal plane I with strike 241°,dip 90° and rake- 22° is considered to be the seismogenic fault plane of the main shock. The direction of P-axis for the main shock is 194°,close to the near NS direction of the principal stress P-axis of historical strong earthquakes in this region. The focal mechanism solution of the M_S5. 4 foreshock has a good consistency with that of the main shock. Among the 18 aftershocks,10 are of strike-slip type,6 are of normal faulting type and 2 are of thrust type. 70% of the aftershocks in the sequence have a focal mechanism with P-axis in the near-NS direction. The focal depths of this M_S7. 3 earthquake sequences are distributed in the range of 5km- 28 km,with the majority in the depth range of 15km- 20 km,slightly deeper than the depth of 10 km of the main shock as calculated.
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