Implications of earthquakes for the slab subduction dynamic process in Southeast Asia

Abstract

Earthquake geohazards that occur throughout the Borneo Block, especially in SW Borneo, cannot be reconciled within the classical earthquake mechanism and a uniform stress field, and unfulfilled earthquake forecast for many years. In this paper, we present a new inventory of 37 Borneo earthquakes, and focal mechanisms show that in NE Borneo earthquakes and aftershocks are dominated by NW-trending normal faults, in East Borneo earthquakes are controlled by the reactivation of NW-trending sinistral strike-slip faults, and the NE-trending thrusts acted as the main seismogenic faults in the SE Borneo seismicity zone. We calculated the Coulomb stress and observed the shallow faults exhibiting a high coefficient response to the Coulomb stress change and all these earthquakes under the Coulomb failure regime have decreased by the stress shadows or are triggered by dynamic stress increase and propagation. We performed a research using the horizontal GPS velocity displacements and vertical seismic sections and found that the micro-blocks convergence occurred here corresponding to the Coulomb stress distribution, and can best explain the earthquake mechanism within the “Borneo Block”. Additionally, the earthquakes in SW Borneo showing a concordant focal mechanism along the Red-River Fault-Tinjar Fault-Sumatra Trench, are deduced to have formed along the “Sunda Block” boundary. Finally, the micro-block boundaries determined from the heatflux map can be effective in describing the main and aftershocks distribution in SE Asia, and the deep-shallow coupling dynamic model is proposed to solve the stress loading for these crustal-scale earthquakes and the responses to plate convergence in SE Asia.