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Analysis for the seismotectonics of the 2016 MS6.4 Menyuan earthquake

May 16, 2017

An MS6.4 earthquake occurred in Menyuan County, Haibei Prefecture, Qinghai Province (China) on January 21, 2016, with a moderate strong earthquake following in the area on August 26, 1986. A recent research revealed the seismogenic structure of the 2016 Menyuan earthquake.

The study of the relevant thesis entitled "Activity of the Lenglongling fault system and seismotectonics of the 2016 MS 6.4 Menyuan earthquake", published in the recent 2017 SCIENCE CHINA Earth Sciences. The researcher named as Han Zhijun serves as a communications author, who is from Institute of Geology, China Earthquake Administration. The researchers have carried on the analysis of the activity of the Lenglongling fault system and the structural environment of the Menyuan earthquake, and revealed that the Northern Lenglongling fault was a more suitable seismogenic structure for the MS6.4 Menyuan earthquake.

The 2016 MS6.4 Menyuan earthquake occurred near the the Lenglongling fault. The earthquake epicenter was distant from the Minle-Damaying and Huangcheng-Shuangta faults, eastern of the Northern Qilian Shan fault zone. A near northwest-striking rupture plane intersects the two faults at a certain angle. The focal mechanism solution shows that this was a thrust-type earthquake, slightly different from the strike-slip movement with a thrust component of the LLLF. Understanding the tectonic environment of the moderate-strong earthquake is of great theoretical and practical significance in evaluating future earthquake risks in the Lenglongling area and determining key areas for future earthquake mitigation.

Field geological mapping, tectonic geomorphology analysis, trench excavation and 14C dating reveal that (1) the LLLF has been obviously active since the Holocene, and may behave with characteristic slip behavior and produce MW 7.3-7.5 earthquakes; (2) the LLLF appears as a flower structure in terms of structure style, and dips NNE at a steep angle; and (3) the most recent earthquake event occurred after 1815-1065 a BP. An associated fault, the Northern Lenglongling fault (NLLLF), is located at the northwestern end of the LLLF. Consequently, the NLLLF was continually subject to tectonic pushing effects from the left-lateral shear at the end of the LLLF, and, accordingly, it bent and rotated outward tectonically. Subsequently, the fault deviated from the dominant rupture azimuth and activity weakened. In the late Quaternary, it behaved as a thrust fault with no obvious deformation at the surface. This is indicated by the arc shape, with a micro-protrusion northeastward, and no geologic or geomorphic signs of surface rupturing since the late Quaternary. However, such faults could still rupture at depth, producing moderate-strong earthquakes. The geometric and kinematic properties of the NLLLF are in good agreement with the occurrence and kinematic properties of nodal plane 2, and with the distribution characteristics of the aftershocks and seismic intensity. Therefore, the NLLLF is a more suitable seismogenic structure for the MS 6.4 Menyuan earthquake. In addition, the thrust movement of the NLLLF accommodates subsequent movement of the LLLF. During the historical evolution of the NLLLF, the LLLF and the NLLLF have affected the local topography through tectonic uplift.

The result of the research will help to understand the characteristics of the structural environment of the 2016 Menyuan earquake. It is not only significant to understand the activity of the Lenglongling fault, but also to reveal features of the seismogenic structure of the moderate-strong earthquake.
This research was funded by the Special Project on Earthquake Research (Grant No. 201408023), and Fundamental Research Funds in Institute of Crustal Dynamics, China Earthquake Administration (Grant No. ZDJ2015-16).

See the article: Guo P, Han Z J, An Y F, Jiang W L, Mao Z B, Feng W. 2017. Activity of the Lenglongling fault system and seismotectonics of the 2016 MS6.4 Menyuan earthquake. Science China Earth Sciences, doi: 10.1007/s11430-016-9007-2

Science China Press

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