Deterministic seismic hazard and landslide hazard zonation of Arunachal Pradesh

This paper presents a seismically induced landslide hazard assessment for the state of Arunachal Pradesh, India, based on GIS techniques. A comprehensive earthquake catalog was prepared with data from various sources like USGS, ISC, etc., within a rectangular enclosure having a distance of 500 km in four cardinal directions from the Arunachal Pradesh state boundary. The catalog was homogenized in a unified moment magnitude scale. The earthquake data were collected for a period ranging from the 1500s to the year 2020. The earthquakes having a magnitude >= 4 are considered for this study as they are mainly responsible for inducing enough horizontal movement along the slopes for landslides. Considering the linear source model, the deterministic seismic hazard analysis was performed to estimate peak horizontal acceleration (PHA) at the bedrock level. The log-likelihood method was employed to decide the most efficient and reliable ground motion prediction equation (GMPE) for the Arunachal Pradesh region. Then peak ground acceleration (PGA) values generated at the surface due to the shaking of bedrock were calculated using a non-linear site amplification (considering the soil nature as B-type NHERP classification). The PGA values were considered to induce driving force on slopes, thus causing a landslide. The topographical slope map of Arunachal Pradesh was developed from CARTOSAT Digital Elevation Model Data (30m resolution). The study region was divided into 50 x 50 m(2) grids. The seismically induced landslide hazard assessment was performed using Newmark's methodology using PGA values and slope angles at the center of each grid. The critical factor of safety necessary to counter the landslide for corresponding PGA values was determined, and its spatial variation in the state is presented as contour maps. For any grid point in the study region, if the in-situ (available) static factor of safety is higher than the static factor of safety necessary to counter the landslide as predicted in the current study, that slope is regarded to be safe.