Geology as a proxy for Vs30-based seismic site characterization, a case study of northern Pakistan

Earthquakes, with their unpredictable and devastating nature, have resulted in large damages worldwide. Seismic site characterization maps (SSCMs) are frequently and effectively used to demarcate the locations that are prone to amplified seismic response. The time-averaged shear wave velocity of top 30 m of earth surface (Vs30) is effectively used as a parameter to evaluate seismic amplification. Northern Pakistan is one of the most seismically active region in the world with 2005 Kashmir earthquake as the most devastating natural disaster. However, for most of the country, the seismic site characterization maps are not available. Geological units and topographic slope are used as proxies for Vs30-based SSCMs around the world and in northern Pakistan. However, the studies in northern Pakistan are lacking field-based validation of the estimated Vs30 and hence the proxy-based SSCMs might be unrealistic. The aim of this study is to correlate instrument-based Vs30 measurements with geological units and remote sensing-derived topographic slope to develop a more realistic SSCM for the study area, located in the seismically active northern Pakistan. Geology of the study area has significant impact on the estimated Vs30 and hence is used as a proxy for SSCM. The developed SSCM shall assist in developing earthquake mitigation strategies in the region