Crustal shear-wave velocity structure beneath Sumatra from receiver function modeling

Abstract

We estimated the shear-wave velocity structure and Vp/Vs ratio of the crust beneath the Sumatra region by inverting stacked receiver functions from five three-component broadband seismic stations, located in diverse geologic setting, using a well known non-linear direct search approach, Neighborhood Algorithm (NA). Inversion results show significant variation of sediment layer thicknesses from 1km beneath the backarc basin (station BKNI and PMBI) to 3–7km beneath the coastal part of Sumatra region (station LHMI and MNAI) and Nias island (station GSI). Average sediment layer shear velocity (Vss) beneath all the stations is observed to be less (∼1.35km/s) and their corresponding Vp/Vs ratio is very high (∼2.2–3.0). Crustal thickness beneath Sumatra region varies between 27 and 35km, with exception of 19km beneath Nias island, with average crustal Vs ∼3.1–3.4km/s (Vp/Vs ∼1.8). It is well known that thick sediments with low Vs (and high Vp/Vs) amplify seismic waves even from a small-magnitude earthquake, which can cause huge damage in the zone. This study can provide the useful information of the crust for the Sumatra region. Since, Sumatra is an earthquake prone zone, which suffered the strong shaking of Great Andaman–Sumatra earthquake; this study can also be helpful for seismic hazard assessment.