Focal mechanism and seismogenic structure of the Yongning M_S4.6 earthquake on 20 November 2012

The Yongning M_S4.6 earthquake on November 20, 2012 is relocated by using the absolute positioning method (Hypo2000), and distribution of aftershocks is also given. In order to investigate the seismogenic structure of the earthquake, focal mechanism and depth of the earthquake are inverted by using CAP method. The inversion result shows that the Yongning earthquake is of dextral strike-slip faulting with a small amount of thrust component, and the moment magnitude is M_W4.3. The best double couple solution is 11°/74°/171° for the nodal plane Ⅰ,and 103°/81°/16° for the nodal plane Ⅱ. The estimated focal depth is about 8 km. The earthquake epicenter, focal mechanism solution and cross sections along the focal depth suggest that the earthquake is likely to occur on the secondary fault in the western Yinchuan buried fault zone.