Sedimentary records of liquefaction from central Kerala (southwestern India), as earthquake indicators in a cratonic area

Far from the plate boundaries, the seismogenic zones within the cratonic areas of Indian land mass had remained largely undetected. The moderate earthquakes in such areas have proved to be hugely damaging because of their infrequency and consequent lack of societal preparedness. As the subtle geological expressions of tectonism make identifying hazardous zones in cratonic areas difficult, it is important to develop locally appropriate geological criteria to isolate potential seismic source zones. Although seismically induced liquefaction preserved in the sedimentary sections is useful as an earthquake proxy, its scope remains underestimated in cratonic regions. Here we offer a field-based methodological approach to mapping liquefaction features from such an area, located south of the Bharathapuzha River in the southwestern part of the Indian craton. We used the field data to constrain the near-field earthquake potential. The earthquake-induced soil liquefaction, in the form of sand dikes and sills, was identified within an area of roughly 100 km², and the available data suggest two episodes of liquefaction – the one between 2.0 ka and 2.5 ka, and a later event around 0.78 ka BP. The spatial distribution and the dimension of the soil liquefaction features, in an area known for the occasional spurt in minor earthquakes in recent times, are suggestive of a potential seismic source in the region that can generate earthquakes of moment magnitudes (M_w) ranging from 5.5 to 6.5. Thus the present observation is a vital input for constraining the region’s seismic hazard and the methodology developed here can be used in other areas of unknown potential.