Relocation of the mainshock and aftershock sequences of M S7.0 Sichuan Lushan earthquake

Abstract

The mainshock of April 20, 2013 Sichuan Lushan M S 7.0 earthquake was relocated using a 3-D velocity model. Double difference algorithm was applied to relocate aftershock sequences of Lushan earthquake. The locations of 2405 aftershocks were determined. The location errors in E-W, N-S and U-D direction were 0.30, 0.29 and 0.59 km on average, respectively. The location of the mainshock is 102.983°E, 30.291°N and the focal depth is 17.6 km. The relocation results show that the aftershocks spread approximately 35 km in length and 16 km in width. The dominant distribution of the focal depth ranges from 10 to 20 km. A few earthquakes occurred in the shallow crust. Focal depth profiles show fault planes dip to the northwest, manifested itself as a listric thrust fault. The dip angle is steep in the shallow crust and gentle in the deep crust. Although the epicenters of aftershocks distributed mainly along both sides of the Shuangshi-Dachuan fault, the seismogenic fault may be a blind thrust fault on the eastern side of the Shuangshi-Dachuan fault. Earthquake relocation results reveal that there is a southeastward tilt aftershock belt intersecting with the seismogenic fault with y-shape. We speculate it is a back thrust fault that often appears in a thrust fault system. Lushan earthquake triggered the seismic activity of the back thrust fault.Lushan earthquake, aftershock sequence, earthquake location, double difference location, Longmenshan fault Citation:Fang L H, Wu J P, Wang W L, et al. Relocation of the mainshock and aftershock sequences of Ms7.0

Space Geodetic Observations and Modeling of 2016 Mw 5.9 Menyuan Earthquake: Implications on Seismogenic Tectonic Motion

“…The thrust propagation along the updip rift would have caused breaking of the shallow part of the fault, resulting in coseismic surface uplift [30]. Using the double-difference relocation algorithm, 647 aftershocks were relocated within 60 h of the main shock [31]. The aftershocks occurred along the maximum regional slip, and the aftershocks take on a shovel-shaped structure at a depth of 7-15 km ( Figure 6).…”

A more accurate relocation of the 2013 M s7.0 Lushan, Sichuan, China, earthquake sequence, and the seismogenic structure analysis

“…To date, significant differences exist among relocated hypocenter depths of the Lushan mainshock: from the near-real-time reports of 13 and 17 km by the China S e i s m i c N e t w o r k C e n t e r a n d E a r t h q u a k e Administration of Sichuan Province, respectively; to 17.4 km by , using HypoDD; to 24 km (http://www.cea-igp.ac.cn/tpxw/266810.shtml), 18 km (Du et al 2013;Liu et al 2013b), 16±2 km (Xie et al 2013), and 14-15 km , from moment tensor inversions (the CAP method; Zhu and Helmberger 1996); to 12-15 km from rupture process inversions (Liu et al 2013a;Wang et al 2013a;). Using our combined location technique, we also relocated the 2013 M s 7.0 Lushan mainshock.…”

“…A small number of minor events in the Lushan sequence are located at depths of 0-6 km, with a distribution suggesting that the three NEtrending faults with surface traces running through or passing close to the aftershock area are confined to the upper Mesozoic sedimentary cover, making them independent of the deeper thrust faults that ruptured during the mainshock. Therefore, the 2013 M s 7.0 Lushan earthquake was a blind thrust fault generated on active thrust faults within the basement of the southwestern Longmenshan fault zone, with an upper limit estimationstudies targeting the rupture process and focal mechanism solutions of the Lushan earthquake sequence have also illustrated that the Lushan mainshock occurred on a NE-trending thrust fault (Du et al 2013;Han et al 2014;Liu et al 2013b;Lü et al 2013;Wang et al 2013a;Xie et al 2013;Zeng et al 2013;Zhao et al 2013). A field survey immediately following the mainshock has verified that no tectonically controlled surface coseismic rupture was produced during the mainshock, leading to the conclusion that the Lushan earthquake occurred on a typical blind reverse-fault .…”

Deep structure beneath the southwestern section of the Longmenshan fault zone and seimogenetic context of the 4.20 Lushan M S7.0 earthquake

“…Rose diagrams show electric strike. Relocation of main shock and aftershock sequences of M W 7.9 Wenchuan earthquake [23], Relocation of main shock and aftershock sequences of M S 7.0 Sichuan Lushan earthquake [24]. extends to the northeast and joins the WMf.…”