Recent Surface Ruptures of the Western Nepal Fault System: Active Oblique-Slip in the High Himalaya from Talphi to Tripurakot
Abstract
Megathrust ruptures typically dominate the seismic hazards of convergent plate boundaries; however, upper plate faults and splay faults often present poorly constrained contributions to regional hazards. Furthermore, as illustrated by the April 2015 Nepal earthquake, even large earthquakes may not produce a surface rupture on the source fault, highlighting the potential for ambiguities when seeking to attribute major pre-instrumental earthquakes to their source. To contribute to fault-based paleoearthquake chronologies within the High Himalaya, we conducted a series of reconnaissance paleoseismic investigations along the Western Nepal fault system (WNFS). This fault system is an oblique-right slip series of faults that appears to extend from the Karakoram fault in the northwest to the Main Frontal Thrust in the southeast. The portion of the WNFS between Talphi to Tripurakot exhibits youthful tectonic geomorphology along the fault trace, including prominent uphill-facing scarps and offset terraces and alluvial fans. We targeted three sites for paleoseismic investigations along this transect, the Kilahannechaur site near Talphi, the Leti site near Leti Lagna, and the Tripurakot roadcut site in Tripurakot. Excavations and exposures at each site exhibit evidence for faulting of late Holocene deposits, with the Tripurakot roadcut providing the clearest constraints on the most recent earthquake. At that site, possible agriculturally reworked sediments are juxtaposed against sheared bedrock, and these in turn are overlain by agricultural sediments and cobbles. Additional sites along this transect exhibit surficial evidence for late Holocene surface ruptures and are promising for future paleoearthquake investigations. The evidence for recent earthquakes along this 60 km long transect demonstrates that this portion of the WNFS is an active seismogenic structure, and supports the interpretation that this system accommodates the transfer of strain from the Main Frontal Thrust to the Karakoram fault.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMT054.0004B
- Keywords:
-
- 1209 Tectonic deformation;
- GEODESY AND GRAVITY;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8036 Paleoseismology;
- STRUCTURAL GEOLOGY;
- 8107 Continental neotectonics;
- TECTONOPHYSICS