Complex Rupture of the 2014 M s 6.6 Jinggu Earthquake Sequence in Yunnan Province Inferred from Double-Difference Relocation

To study the seismogenic structure of the 7 October 2014 M s 6.6 Jinggu earthquake, we use the cut-and-paste (CAP) method to obtain the focal mechanisms and depths of the mainshock and the two largest aftershocks with M s > 5. Then, we take advantage of waveform cross-correlations to obtain precise time difference data and apply the double-difference method to relocate the aftershocks between October 7 and December 31. We relocate 2076 earthquakes (approximately 73.6% of the total) with an average horizontal accuracy of approximately 150 m and a depth uncertainty of approximately 700 m. The M s 6.6 mainshock epicenter originated at 23.378°N, 100.475°E at a depth of 15.38 km. The Jinggu earthquake sequence exhibited a linearly concentrated distribution in the northwest–southeast direction with obvious segmentation features and, thus, it can be divided into four branches spatially and two stages temporally. The aftershocks first appeared around the M s 6.6 mainshock and then extended on either side of the mainshock along the NW–SE direction (the NW branch). The earthquake rupture direction experienced a slight clockwise deflection at the NW end and rotated clockwise by approximately 90° toward the SW (the NE branch) at the SE end. Then, the rupture propagated a short distance along the SW direction and rotated counterclockwise by approximately 90° into an SSE direction (the NNW branch). There is a small angle between the NW and NNW branches. The depths of the whole sequence with vertical dip angles were shallower toward the NW and deeper with two seismogenic layers toward the SE. According to the distributions of the earthquakes and nearby fractures, it is highly possible that the Jinggu earthquake sequence occurred along a hidden fracture section of the Wuliangshan fault in the NW direction. Moreover, we can confirm that the three large earthquakes all occurred along right-lateral strike-slip faults.