Effects of the heterogeneous subducting plate on seismicity: Constraints from b-values in the Andaman–Sumatra–Java subduction zone

Abstract

The Andaman–Sumatra–Java subduction zone is characterized by significant spatial variations in subducting plate age, subduction velocity, and slab bending. With (i) the uplifting controlled by the Ninety East Ridge in the north, (ii) trench eroding affected by the Roo Rise in the south, and (iii) the highly deformed Warton Basin in front of the trench cut through by a series of strike-slip faults, the entire subducting plate exhibits strong spatial heterogeneity. In this paper, we investigated the effect of the heterogeneous subducting plate on seismicity based on the comparison between the spatial variations in the b-value of the Gutenberg-Richer Law and in the tectonic features of the subducting oceanic plate. We used the International Seismological Centre, EHB Bulletin (ISC-EHB) from 1970 to 2013 to conduct a detailed study of b-value spatial variations in the Andaman–Sumatra–Java subduction zone. Via the inter-comparison of tectonic factors, we found that the subduction zone was tectonically segmented. There are good positive correlations between b-value and subducting plate age in two tectonic domains after removing the influence of local tectonic irregularities, which implies that the subducting plate density generally controls the stress and coupling between the plates. The subduction of local tectonic irregularities, such as the fracture zones and seamounts, has significantly affected seismicity, which prevents the occurrence of large earthquakes and causes the b-value to rise. In addition, the anomalous tectonic environments, such as the spreading center, and the thrust fault zones, could also impact spatial variations of the b-value. Therefore, seismicity in subduction zones is a result of the combined impacts of complex tectonic features. Understanding and clarifying the mechanisms of these tectonic features in relation to b-values can help us to better assess seismic risk in subduction zones.