Paleoseismic evidence of a giant medieval earthquake in the eastern Himalaya

Abstract

We present here the results of a paleoseismic investigation carried across a ~10 m high fault scarp at Panijhora village, West Bengal in northeastern India. Accelerator Mass Spectrometer analyzed 14C radiocarbon age constraints from six detrital charcoal samples ranging between 1688 B.C. and A.D. 1152 are consistent with the great medieval earthquake of A.D. 1255 that is interpreted to have produced a minimum observed fault slip of ~5 m in the trench exposure. Recalibration of radiocarbon ages from previous studies at Harmutty, Nameri, and Marha in the eastern Himalaya using Bayesian statistical analyses further substantiates the possibility that the A.D. 1255 earthquake might have ruptured the Himalayan front over a length of ~800 km from ~85.87° to 93.76°E longitudes.

Overestimation of the earthquake hazard along the Himalaya: constraints in bracketing of medieval earthquakes from paleoseismic studies

“…The results of all the trench at Panijhora, Chalsa, Nameri, and Harmutty in Darjeeling Himalaya suggested that paleo-earthquake in this region postdate 1152 AD, but before 1378 AD, assigning 1255 AD event to be a mega event that ruptured the entire 800 km Himalayan arc (Kumar et al 2010;Mishra et al 2016) (Fig. 3).…”

“…Assuming the 30° dip of HFT as indicated by seismic reflection data, and radiocarbon ages from the displaced surfaces suggest 13.8 ± 3.6 mm/year of slip rate on HFT (Wesnousky et al 1999). Malik et al 2008Malik et al , 2010aMalik et al , b, 2015Malik et al , 2016Mishra et al 2016;Sapkota et al 2013;Yule et al 2006;Vassallo et al 2015) at the frontal and the hinterland faults of Himalaya Discontinuous scarplets of the Mohand Thrust which is a segment of HFT have displaced Quaternary alluvium at Rampur Ganda and at Lal Dang located ~24 km south and ~50 km southeast of Dehra Dun, respectively. The charcoal sample recovered from the faulted youngest unit from Rampur Ganda trench suggested that the recent event occurred around 1319-1380 and 1310-1442 AD (Fig.…”

“…With the motive to refine surface rupture data of the past earthquakes and filling the gaps of the historical archives in the northeast Himalaya, several trenches have been excavated across the discontinuous scarps along HFT (Kumar et al 2010;Mishra et al 2016). The results of all the trench at Panijhora, Chalsa, Nameri, and Harmutty in Darjeeling Himalaya suggested that paleo-earthquake in this region postdate 1152 AD, but before 1378 AD, assigning 1255 AD event to be a mega event that ruptured the entire 800 km Himalayan arc (Kumar et al 2010;Mishra et al 2016) (Fig.…”

“…In the last few decades, several paleo-seismological investigation has been carried out along the active HFT which has provided significant data to understand the occurrence of large magnitude earthquakes in the Himalayan region (Wesnousky et al 1999;Malik and Nakata 2003;Lavé et al 2005;Malik et al 2008Malik et al , 2010aMalik et al , b, 2015Malik et al , 2016Kumar and Mahajan 2001;Kumar et al 2006Kumar et al , 2010Kumahara and Jayangondaperumal 2013;Sapkota et al 2013;Yule et al 2006;Bollinger et al 2014Bollinger et al , 2016Jayangondaperumal et al 2016;Mishra et al 2016). However, there exist constraints in terms of their period of occurrence and in determining the extent of surface rupture.…”

“…1a, 3). Succession of earthquakes along these Himalayan zones from historical archives of (Oldham 1883;Iyengar et al 1999;Pant 2002;Ambraseys and Douglas 2004) and the paleo-seismological data including timing, displacement of the latest event, and slip rates from the trench studies has been compiled (Bollinger et al 2014Gavillot et al 2016;Jayangondaperumal et al 2016;Kumar and Mahajan 2001;Kumar et al 2006Kumar et al , 2010Kumahara and Jayangondaperumal 2013;Kondo et al 2008;Lavé et al 2005;Meigs et al 2012, Madden et al 2011Malik and Nakata 2003;Malik et al 2008Malik et al , 2010aMalik et al , b, 2015Malik et al , 2016Mishra et al 2016;Sapkota et al 2013;Yule et al 2006;Vassallo et al 2015). An attempt has been made to highlight the problems of bracketing the ages and assigning a specific event to the surface ruptures along the Himalayan front, where other earthquake events with similar time frame could be fitted.…”