Lenglongling Fault Research Articles

Gravity variations before the Menyuan Ms6.4 earthquake

In order to study the relationship between gravity variation and Menyuan Ms6.4 earthquake, gravity variation characteristics in mid-eastern of Qilian Mountain were analyzed based on the 2012–2015 relative gravity datasets. The results indicated that the gravity changes in mid-eastern of Qilian Mountain increased gradually, while gravity changes around Menyuan remarkably. Besides, great positive-negative gravity changing gradients appeared along the Lenglongling Fault which was located at the north of Menyuan, and the 2016 Menyuan Ms6.4 earthquake occurred near the junction of positive and negative gravity changes.

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

Determining the relationship between crustal movement and faulting in thrust belts is essential for understanding the growth of geological structures and addressing the proposed models of a potential earthquake hazard. A Mw 5.9 earthquake occurred on 21 January 2016 in Menyuan, NE Qinghai Tibetan plateau. We combined satellite interferometry from Sentinel-1A Terrain Observation with Progressive Scans (TOPS) images, historical earthquake records, aftershock relocations and geological data to determine fault seismogenic structural geometry and its relationship with the Lenglongling faults. The results indicate that the reverse slip of the 2016 earthquake is distributed on a southwest dipping shovel-shaped fault segment. The main shock rupture was initiated at the deeper part of the fault plane. The focal mechanism of the 2016 earthquake is quite different from that of a previous Ms 6.5 earthquake which occurred in 1986. Both earthquakes occurred at the two ends of a secondary fault. Joint analysis of the 1986 and 2016 earthquakes and aftershocks distribution of the 2016 event reveals an intense connection with the tectonic deformation of the Lenglongling faults. Both earthquakes resulted from the left-lateral strike-slip of the Lenglongling fault zone and showed distinct focal mechanism characteristics. Under the shearing influence, the normal component is formed at the releasing bend of the western end of the secondary fault for the left-order alignment of the fault zone, while the thrust component is formed at the restraining bend of the east end for the right-order alignment of the fault zone. Seismic activity of this region suggests that the left-lateral strike-slip of the Lenglongling fault zone plays a significant role in adjustment of the tectonic deformation in the NE Tibetan plateau.

SEISMOGENIC MECHANISM OF THE 21 JANUARY 2016 MENYUAN, QINGHAI MS6.4 EARTHQUAKE

AbstractOn 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.