Eight Days in Bhuj: Field Report Bearing on Surface Rupture and Genesis of the 26 January 2001 Earthquake in India

Abstract

The Mw 7.6 Bhuj (Republic Day) earthquake in India occurred in the morning of 26 January 2001, resulting in nearly 20,000 deaths. The event occurred away from a plate boundary and is a possible analog to intraplate earthquakes such as those of the New Madrid and Charleston regions of the eastern United States. We visited the epicentral area for eight days between 11 and 18 February. The purpose of our visit was to characterize surface ruptures associated with the earthquake, examine the region for evidence of longer-term tectonic activity, and place the location and mechanism of the earthquake into the context of the regional geology. We report here observations and impressions arising from our brief visit, with the aim of documenting our efforts to record surface rupture as well as providing a starting point for field investigations by others that may follow. Toward that end, we also draw on published literature that came to our attention subsequent to our return. The USGS National Earthquake Information Center places the epicenter of the Bhuj earthquake in northwestern India at 23.40°N latitude and 70.32°E longitude. The epicenter sits within a zone of diffuse seismicity that extends southeastward and into the Indian Plate from the Eurasian, Arabian, and Indian Plate triple junction, which is located near the city of Karachi, Pakistan (Figure 1). The Bhuj earthquake may reflect reactivation of older structures. Plate tectonic reconstructions show that the Indian subcontinent split from the larger supercontinent of Pangaea during Permian to Triassic (Biswas, 1982) and migrated north through equatorial latitudes until colliding with the Asian continent in the Eocene (Figure 2A). The process of rifting is of some import to understanding the setting of the Bhuj earthquake. The break-up of continents and continental drift is initiated by the formation of multilimbed rifts that …