The Yishu fault zone (YSFZ) is the most active fault in eastern China, and it is the location of an M 8.5 earthquake that occurred in 1668. However, topography and landforms in this area have been greatly altered by human activity during the previous three to four decades, which makes assessment of past earthquakes difficult. We therefore used a set of remote sensing images captured in the 1960s to evaluate the single‐event and multievent cumulative offsets of streams along the fault. The local landforms have preserved the Holocene seismic offsets well despite the moderately humid climate in which the local landforms have evolved rapidly. Geomorphic markers associated with 401 systematically dextrally offset streams were analyzed and measured. These offset markers are considered to record seismic rupture processes. Cumulative offset probability densities were analyzed according to slip distributions along various subsections of the YSFZ. Four strong paleoearthquakes in addition to the 1668 earthquake were revealed by offset density peaks within the YSFZ, a finding that differs from those of previous studies. The average offset of the 1668 event is approximately 9 m. The cumulative offsets of the other four paleoseismic events are essentially multiples of the latest event. A single event ruptured more than 200 km of discontinuous fault traces. The similarity of the previous five earthquakes implies that rupturing of the YSFZ has followed a characteristic slip model during the Holocene, with a right‐lateral slip rate of 2.2–2.6 mm/yr. We expect that the YSFZ is not due for another large earthquake for several thousand years.

The Lenglongling fault located in the northeast margin of the Tibetan Plateau plays an important role in accommodating the tectonic deformation of the Tibetan Plateau relative to the Gobi-Ala Shan platform to the north and the North China craton to the east. However, little is known about the fault due to a lack of previous research. In this study we use terrestrial light detection and ranging (LiDAR) data combined with high-resolution remote sensing images to survey offset landforms in the east part of the Lenglongling fault. Microtopographic analysis of well-preserved offset terraces, gullies, ridges, and pluvial fans in the highland environment allows evaluation of single-event slip and multievent cumulative slip.Our study provides an important assessment of the horizontal offset associated with the latest earthquake and four paleoearthquakes that were identified from a series of offset bedrock terraces by constructing a morphotectonic evolution model. Terrestrial LiDAR data indicate that the east Lenglongling fault follows a characteristic slip model. The single-event slip of this section is ~9.4 m; 7-8 paleoearthquakes are thought to have occurred during the Holocene, and a left-lateral strike-slip rate of 6.6 ± 0.3 mm/yr is estimated.Combining the slip rate and the single-event slip distribution, we determine a mean recurrence interval of 1430 ± 140 yr for past earthquakes along the east Lenglongling fault. This result is similar to that of the adjacent Gulang fault, but differs slightly from those of other adjacent faults, which may mean that the Lenglongling and Gulang faults compose an integral fault zone. The large number of millennial recurrent active faults in this region heightens the risk of future seismic activity in the northeast Tibetan Plateau.

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Abstract: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.