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Do Earthquakes Rupture Through Releasing Bends in the Western Nepal Fault System?

Knowledge of potential seismic sources in the upper-plate of Western Nepal is limited. Recent studies of the Western Nepal Fault System (WNFS), an oblique-dextral-slip system of splay faults, expand the known fault geometry and segmentation based on the mapping of the tectonic geomorphology and documentation of offset landforms. The WNFS trends along the northern bifurcation (PT2-N) of the physiographic transition between the Lesser and the Greater Himalaya (PT2). It contains a large, greater than 100 km wide, right-stepover between the primary NW-SE-oriented Talphi-Tripurakot fault segments and the Bari Gad fault. These segments are connected by ~N-S oriented faults, such as the Jang la Oblique and the Dhorpatan fault segments. To investigate the rupture extents of large, surface-rupturing earthquakes, we seek to characterize the earthquake history of the WNFS. We conducted paleoseismic investigations at three sites on the fault system in Fall 2021. The three trenches dug revealed previously undocumented earthquakes and begin to help establish whether ruptures on this fault system are not hindered by bends in the fault traces. At Puphal Phedi at least four events were exposed in each trench, five events were exposed at our Naya Ban trench and at Bhujekhung, at least two were exposed. Previous results from the trenches dug in 2019 also demonstrate the occurrence of multiple Late Holocene earthquakes. Overall, our results provide important constraints for seismic hazards which we will implement into regional seismic hazard models. This will improve risk mitigation and resilience development in the High Himalayas of Western Nepal as well as inform models of the connectivity between ruptures of the Main Frontal Thrust and the WNFS.

Session: Advances in Earthquake Geology: Spatiotemporal Variations in Fault Behavior From Geology and Geodesy II

Type: Oral

Room: Cedar

Date: 4/22/2022

Presentation Time: 05:30 PM Pacific

Presenting Author: Elizabeth Curtiss

Student Presenter: Yes

Additional Authors