A Seismic Hazard Map Based on Geology and Shear‐wave Velocity in Rawalpindi–Islamabad, Pakistan

Abstract

AbstractThe ‘twin cities’ district of Rawalpindi–Islamabad is among the most endangered seismic regions in Pakistan, with the seismic hazard assessed (0.32 g) to intensity IX MMI for a 475‐year return period. A seismic hazard map for Rawalpindi–Islamabad is presented herein, based on 85 shear‐wave velocity (VS) profiles obtained through geophysical H/V measurements and from the geological map of the region. Relationships between the average top thirty‐meter shear‐wave velocities (VS30) and surficial geological units have been determined. The peak ground acceleration (PGA) maps for 150, 475 and 2475‐year return periods were converted into a seismic intensity map. Intensity increments for different soils were used to compute PGA values for 150, 475 and 2475‐year return periods. Sites located on softer ground experienced a higher degree of damage from moderate earthquakes. Due to the presence of soft clay or liquefiable soil and lateral spreading, a few locations may be classified as hybrid sites class C and D. This map is a critical step in facilitating code‐based site classification and seismic design throughout Rawalpindi–Islamabad. Although the seismic hazard map based on seismic intensities is no longer used in engineering geology, it is still important in seismological analysis and for civil protection purposes.