Discussion of the seismogenic structure of the 1901 M 6¾ Nyemo earthquake

Abstract

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.

Keywords

• 1901 nyemo earthquake
• seismogenic structure
• yadong-gulu rift
• panggang graben