Intraplate seismicity and earthquake hazard in the Aravalli–Delhi Fold Belt, India

Abstract

The Aravalli–Delhi Fold Belt (ADFB) is one of three prominent ridges on the continental part of the Indian plate extending northward from central India and subducting beneath the Himalayan arc. Though it is seismogenic along its entire NE–SW structural trend, activity varies spatially with a noteworthy region of higher seismicity in the vicinity of Delhi. We analyse historical and modern instrumented seismicity. Using recomputed focal mechanisms for events such as the 1956 Bulandshahr earthquake, we found that the maximum principal stress (σ1) in this region is oriented in the N–S to NE–SW direction, similar to that in the neighbouring Garhwal–Kumaun Himalayas. Our analysis also indicates that the earthquakes along the ADFB occur on steep faults which are parallel or oblique to its NE–SW structural trend and that the entire crust appears to be seismically active as the earthquakes occur up to a depth of ~40 km. Within the better instrumented Delhi region, we observed a pattern in the average monthly frequency of earthquakes recorded that we speculate was modulated by monsoonal recharge of the local water table. The cause of seismicity in the AFDB is still a question for debate, pending better seismological and geodetic instrumentation, but we build on evolutionary models of the ADFB to suggest that seismicity is the consequence of the continued relative motion between the Bundelkhand and Marwar cratons in the northern Indian shield. The nature and causes of earthquakes in this region notwithstanding, the proximity of large cities such as Delhi, Jaipur and Udaipur to poorly-studied or unknown sources of seismic hazard is a concern and warrants further scientific and policy intervention.