Seismic tomographic imaging of P wave velocity perturbation beneath Sumatra, Java, Malacca Strait, Peninsular Malaysia and Singapore

Abstract

P wave tomographic imaging of the crust down to a depth of 90 km is performed beneath the region encompassing Sumatra, Java, Malacca Strait, peninsular Malaysia and Singapore. Inversion is performed with 99,741 first-arrival p waves from 16,196 local and regional earthquakes occurred around the Sumatra Subduction Zone (SSZ) between 1964 and 2018. Tomographic results show low-velocity (low-V) anomalies that reflect both accretion and possibly, asthenospheric upwelling associated with subduction of the Australian Plate beneath Eurasia around the SSZ. The prominent low-V anomaly is thickest around the Conrad, extending beneath Straits of Malacca and parts of peninsular Malaysia, but disappears around the Moho in the region. Below the Moho, the subducting slab, represented by a high-velocity (high-V) anomaly, trends in the orientation of Sumatra. At these depths, the eastern shorelines of Sumatra, most parts of Malacca Strait and the west coast of peninsular Malaysia show varying degrees of positive velocity anomalies. We consider that asthenospheric upwelling around the SSZ may provide heat source for the 40 or more hot springs distributed north–south in peninsular Malaysia. Different east–west and north–south cross-sections reveal the subsurface anomalies at various parts of the region. The predominant low-V anomaly is less than 35 km in depth, but other low-V anomalies are deeper.