An archaoseismological investigation of the footprints of human resilience to seismic shaking from the alluvial plains of Gujarat, Western India

Abstract

The town of Vadnagar, located on a prominent geomorphic surface ∼ Gujarat Alluvial Plains (GAP) of western India, presents unabetted human occupation for the last 2754 years. An integrated archaeoseismological study (involving tectonogeomorphology, geophysical and geoarchaeological investigation) in the Cambay basin led to the identification of a previously un-noticed the reverse splay fault for the first time with the evidence of the surface rupture in the GAP region. The present study based on electrical resistivity tomography (ERT) and previous investigation of magnetotulleric geophysical surveys in the vicinity, demonstrates it to be the ruptured splay of the East Margin Cambay Basin Fault. The timing of the event is constrained ∼1200–2000 years Before Present (BP) using optical dating, whereas archaeological findings briefs it around 9th – 10th Century CE. Additionally, based on the various empirical relationships between magnitude and maximum displacement of 1.6 m observed in the trench, the magnitude of the event was constrained at M_w 7 ± 0.3. In addition to this, our investigation in the vicinity of the site reveals the tectono-geomorphic expressions of the identified Vadnagar Fault and associated archaeological seismic deformations (i.e. collapsed structures, tilted, and rotated wall fragments) along the hanging wall. The presence of timber-bondings in masonry walls (1st – 4th century CE) suggests earthquake resistant structural know-how in Vadnagar as one of the oldest in Asia. We invite more in-depth scrutiny by seismologists and geologists for assessing the realistic hazard of GAP in light of this new seismic source and the human resilience to earthquakes.