SEISMOGENIC MECHANISM OF THE 21 JANUARY 2016 MENYUAN, QINGHAI M S 6.4 EARTHQUAKE

On January 21, 2016, an MS6.4 earthquake occurred in Menyuan county, Qinghai province. Field investigations suggest that the long axis of the elliptical affected area is N120°-140°E. Comparative interpretations of high resolution remote sensing images before and after the shock show more than 23 sites of landslides and collapses, which are more distributed in the north of epicenter than in the south, extending in NNW overall. As the Lenglong Ling fault (LLF) is dominated by horizontal movement from high resolution remote images and field observation, it should not be responsible for this event of pure thrusting. North of the Lenglong Ling fault, there is a fault striking in 140°, which is north-dipping on the surface according to high resolution remote sensing, similar to the nodal plane I of focal mechanism solutions from deferent institutes. The long axis' direction of the overall distribution of aftershocks has also a difference of 20° with LLF, while almost parallel to the fault on its north. Thus, we infer that this fault is most likely the seismogenic structure of the Menyuan earthquake. Integrating the characteristics of aftershock distribution at depth, main shock focal mechanism solutions, geometric distribution and activity of the seismogenic fault on surface, in combination with the magnetotelluric sounding and related geophysical data around the earthquake zone, a cartoon model of the seismogenic mechanism is established. We speculate this earthquake is one of the events occurring during the pushing growth process of the Tibetan Plateau blocks in NE direction following the 2008 MS7.4 and 2014 MS7.3 earthquakes in Yutian, Xinjiang.