Himalayan Surface Rupture in the 1934 Bihar-Nepal M8.3 Earthquake - Did It or Didn't It, and Does It Matter?

Session: Alpine-Himalayan Alpide Shallow Earthquakes and the Current and the Future Hazard Assessments
Type: Oral
Date: 4/30/2020
Time: 01:30 PM
Room: 215 + 220
Description: 

One month after the great 1934 Mw=8.3 Bihar-Nepal earthquake, geologist John Auden traversed the Siwalik foothills specifically to search for a surface rupture. He found none. In contrast, Sapkota et al (2013) claim surface rupture occurred ~40 km west of his traverse. Wesnousky et al., (2018), however, demonstrate that no surface rupture or 1934 fault scarp exists at that location. Subsequently Rizza et al., (2019), who characterize this absence of surface rupture or scarp as "an alternative interpretation", propose that ~10 km closer to Auden's transect a 5 to 8 m surface scarp was emplaced that has now been eroded. Although it is possible Auden crossed this putative >5-m-high scarp four times without noticing it, we consider it unlikely. Particularly because villagers with whom he discussed earthquake effects near the MFT (landslides and impounded lakes), made no mention of vertical offsets of their land. Auden's accounts support the notion that the 1934 earthquake was a blind thrust similar to those symptomatic of the southward advance of the Himalaya evident in seismic profiles. It is also possible that the termination pulse of a blind thrust may have been responsible for the widespread liquefaction and lateral spreading associated with the earthquake in Bihar.

The absence of a surface rupture would confirm that not only are earthquakes similar to the Mw7.8 Nepal earthquake missing from the paleoseismic record, so too are earthquakes greater than Mw= 8.3. With an unknown number of great earthquakes missing from paleoseismic findings (more than 24 trenches), the estimated current slip potential may be too high in locations where no recent great earthquake has occurred. Although, with a few exceptions, the entire Main Frontal fault appears to have segmentally ruptured between 1100 and 1600, it is possible that the slip potential of apparently unruptured segments (Bilham, 2019) may require downward revision.

Presenting Author: Roger Bilham

Authors