Soft sediment deformation features in Dauki Fault region: evidence of paleoearthquakes, Shillong Plateau, NE India

Praveen B Gawali,B V Lakshmi

doi:10.1007/s12665-022-10168-4

Abstract

The northeastern region (NER) of India has several complex regional geological structures, out of which the Dauki fault (DF) is a prominent one. The E–W trending reverse DF, which is inferred to go through the southern margin of Shillong Plateau (SP), has played major role in the regional deformation of the adjoining areas and was believed to be active during the Late Quaternary time. Previous paleoseismological studies conducted on the eastern and western part of the DF, Bangladesh, revealed that the fault ruptured in AD 849–920 and AD 1548, respectively. However, there were no studies on the DF from southern side of the SP, India. For the first time, from Indian side, soft sediment deformation structures (SSDS) are reported from five trenches in and around the DF zone, SP. Close to the Dauki village, five trenches in the eastern part of the DF, SP, show micro faulting, sand dykes, disturbed strata, and water escape structures. The detailed investigation of SSDS indicates that the origin of deformation is seismic trigger. The 14C AMS dating of deformation structures generated by earthquakes suggests three seismic events occurred between 130 and 920 year BP, 5415 to 9140 year BP, and at about 4285 year BP. This study confirms that DF is indeed active, at least, since the mid-Holocene. More trenching and dating of seismically induced deformation features are needed to accurately calculate the recurrence interval of significant earthquakes that can strike the fast-expanding urban areas in India and Bangladesh.

Highlights

Paleoseismology was originated in the late nineteenth century, but the modern paleoseismology formed at the end of the 1970s
(1) Trenching carried in meizoseismal areas of 1548, 1897 and 1923 large earthquakes occurred in areas contiguous to the Dauki fault (DF) unraveled seismites at 5 locations wherein the geological and geomorphological terrain is quite complex
(2) The soft sediment deformation structures (SSDS) features identified in and around DF region contained micro fault, sand dykes, detached blocks suspended in sand, water escape structures and pinch-swell features formed through liquefaction of alluvial sediment during strong ground shaking

Summary

Introduction

Paleoseismology was originated in the late nineteenth century, but the modern paleoseismology formed at the end of the 1970s. The goal of paleoseismological studies is to characterise the location, size, and frequency of strong earthquakes that have occurred in the recent geological past as a way to better understand both short-term and long-term seismic hazards. This geological information complements historical records of significant seismic events, and offers a more complete picture of seismic hazards and fault behaviour. The information about past seismic activity can be inferred from the soft-sediment deformational structures (SSDS) in the late quaternary geologic record (Allen, 1975). A direct relationship between earthquake occurrence and the resulting deformation of the sediments has been invoked by various workers (Sims 1973, 1975; Sieh 1978; Hempton and Dewey 1983; Talwani and Schewer 2001; Jayangondaperumal et al 2008)

Objectives

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Discussion

Conclusion