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According to historical records, an M 6¾ earthquake occurred in Nyemo, Tibet on April 21, 1901 without any reports on its seismogenic structure yet. To sort out its seismogenic structure helps to understand the earthquake recurrence pattern of the Nyemo graben group (NGG) and to scientifically evaluate the future earthquake risk of surrounding areas. According to our results from the remote sensing interpretation and geological survey, a 30 km-long fault with a trend of nearly NW-NNW at the western boundary of the Panggang graben (PG), one of the NGG, is divided into north segment and south segment by the Penggang River. The north segment is characterized by significant linear features, with fault scarps developed, offsetting multistage river terraces and moraines. The recovered displacements show that the vertical offsets of Terrace T0, T1 and T2 are ~1.0 m, ~2.6 m and ~5.0 m, respectively. The south segment with obvious linear features develops along the Xiaqing River and extends to the north Nyemo County, with fault scarps developed, offsetting multi-stage alluvial fans. We found the offset Terrance T2 profile in northern Nyemo, indicating the extension of the fault. Through the magnitude recovery, we calculated the moment magnitude of the latest earthquake as about MW6.8 along the PG, which is consistent with the Nyemo earthquake. Inferred from the results of the satellite image interpretation, geological survey and magnitude recovery, the PG is likely the seismogenic structure of the Nyemo earthquake. Also based on historical seismic records, we consider that each graben in the NGG could independently generate moderate-strong earthquakes, and the earthquake recurrence pattern and the seismicity difference between the NGG and the north and south segments of the Yadong-Gulu rift need further study.

The location of the main boundary fault of the Yadong-Gulu Rift (YGR) shifts from the east side in the southern segment to the west side in the northern segment. The Nyemo Graben Group (NGG) connects the southern and northern segments of the YGR and provides clues for understanding the migration of boundary fault locations along the YGR. However, the NGG has received very little attention. In this study, we map the geometry of the Pabu normal fault, which is the boundary fault of the westernmost graben in the NGG, using high-resolution remote sensing images. We then utilized a digital elevation model (DEM) with a spatial resolution of 1 m. Morphometric parameters such as scarp height, width, and slope were obtained from elevation profiles in three typical deformation regions. Our results reveal a fault segment approximately 3 km long that links the southern and northern segments of the Pabu Fault. Each fault segment could be a major segment. Furthermore, based on regional tectonic activity, the Pabu Fault has the potential to produce an earthquake with a magnitude of around M 6.7. [ABSTRACT FROM AUTHOR]

The Yadong-Gulu Rift (YGR) is the longest and most prominent rift in southern Tibet. While 14 large historical earthquakes have occurred on the northern-central segment of the YGR, historical or paleoearthquake records along the southern segment remain poorly understood. The spatial discrepancy of large earthquakes has significant implications for assessing seismic hazards along the entire YGR. To address this knowledge gap, this study presents the paleoseismic events for the first time in the Nieru graben located along the southern segment of the YGR. The excavation of a paleoseismic trench reveals two Holocene earthquakes with calibrated radiocarbon dates constraining the timing of the two events to be after 4084-3954 cal yr BP. The paleoearthquake had a magnitude of M 7. The study shows that the southern segment of the YGR experienced strong paleoseismic events, except for the Relong graben. Considering the high present extension rate of the southern rifts and the magnitude of the paleoseismic events along the Nieru graben, the southern segment of the YGR holds the potential for producing large earthquakes. Furthermore, the ongoing tectonic deformation in the area, coupled with stress changes from large earthquakes on Himalayan thrust faults, may increase the likelihood of future rupture along the active faults in the Nieru graben. [ABSTRACT FROM AUTHOR]

Duoqing Co is a 60 km2 outflow lake in the N-trending Pagri graben, located at the southern end of the Yadong-Gulu rift in Tibet. The water in this lake suddenly disappeared between November 2015 and April 2016, closely following the Ms 8.1 (Mw 7.8) Nepal earthquake in April 2015. Both, geomorphological and remote sensing data indicate the existence of blind faults striking NNE along the east boundary of Duoqing Co lake. There were also several nearly NE-trending extensional cracks preserved in the dried lakebed, apparently formed in response to creeping deformation of the underlying rock. Based on field studies and analysis of meteorological and remote sensing data, it is suggested that this phenomenon cannot be explained by evaporation linked to climate change nor can it be related to human activity. Instead, it is considered that the lake water drained through the extensional cracks formed in the lakebed as it responded to the far-field effects of the 2015 Nepal earthquake. It is proposed that a shift in regional tectonics occurred as a result of the Nepal earthquake, causing a sharp increase in stress accumulation along the seismically locked Bhutan–Sikkim zone on the Main Himalayan Thrust (MHT) fault, which was accommodated by the extension of the Pagri graben in the southern Yadong-Gulu rift. It is believed that the crust may have reached a critical stress-state that resulted in strain hardening and brittle failure throughout the region along the Bhutan–Sikkim segment of the MHT. If so, considering the high potential for tectonic activity along the segment of the MHT, it may be worth paying attention to deformational changes and potential geomorphological precursors that might appear in the seismically locked Bhutan–Sikkim gap to predict future earthquakes. [ABSTRACT FROM AUTHOR]

The Yadong-Gulu rift is the largest active rift within the southern Tibet Plateau. Although tectonic characteristics and geodynamic implications of normal faulting have been widely discussed, precise constraints on the fault slip rates and their spatial distribution are still scarce to date, hindering full exploration of the deformation mechanism of active rifts in the southern Tibet. In this study, we integrated the interpretations of high-resolution satellites and unmanned aerial vehicle (UAV)-acquired images, and topography with the results of field surveys and radiocarbon dating to demonstrate the slip distribution along the Chongba Yumtso fault (CYF) bounding the northeastern sector of the Duoqing Co graben and then discussed their implications for the seismic risk and regional deformation. Since the late Pleistocene, the vertical slip rate and extension rate across the CYF are about 1.2 ± 0.1 and 1.7 (+0.7/−0.5) mm/a, respectively, and the average extension rate across the Yadong-Gulu rift zone is about 2.1 (+0.5/−0.6). According to the activity rate, plane size, basin-mountain height difference, and sediment thickness of the grabens in the southern segment of the rift zone, it is considered that the extension of the main boundary normal fault in the southern segment of the rift has the spatial variation characteristics of decreasing from south to north. According to the comparison of the total extension rate on different time scales, it is considered that the total extension rate of the rift zone in southern Tibet is approximately stable in different time periods, which is ~16 (+5/−4) mm/a. According to the active rate and historical seismic records of the Duoqing Co graben in the Yadong-Gulu Rift Valley, it is considered that the CYF has potential to produce earthquakes with Mw 6.6–7.4. • The E–W extension rate of Yadong-Gulu rift and whole southern Tibet are about 1.5-2.6 mm/a and 12-21mm/a respectively. • The extension rate along the boundary normal faults of the southern Yadong–Gulu rift displayed a northward decreasing. • The Duoqing Co graben has a high seismic risk in the future. [ABSTRACT FROM AUTHOR]