Relocation of the April 2017 Batangas, Philippines, earthquake sequence, with tectonic implications

Abstract

The 2017 M_w 5.9 Batangas earthquake occurred on a location abutting the Macolod Corridor (MC) to the NE and above the steeply dipping slab of subducted South China Sea lithosphere to the SW. While the spatial distribution of the 2017 Batangas earthquake sequence provides a constraint on the scope of MC’s geothermal activity, the focal mechanisms are associated with the states of stress in MC. Here, we relocated the 2017 Batangas sequence using data from two seismic network which cover the region of the NW Mindoro and Southern Luzon. Upon employing the HypoDD algorithm, we retrieve a compact distribution within the Batangas Bay, which in turn suggests that the Balayan Bay to the north remains aseismic and is within the scope of geothermally impact area by MC. In addition, the 2017 Batangas earthquake and the 1994 Mindoro Earthquake share similar focal mechanisms that exhibit an E-W extension in the region of SW Luzon, which differs from a few leftlateral moderate earthquakes to the east at 121.5°E on the Sibuyan Verde Passage Fault. Together with the results of 3D numerical modeling on coeval subduction of oceanic and continental lithospheres and P-wave tomography in the region from previous studies, we incline to explain the regional E-W extension in SW Luzon as induced by the toroidal asthenospheric flow and the mechanisms of MC formation as originated by the overriding-plate stretching. Both are incipiently driven by the collision of the Palawan Continental Block into the Philippine Mobile Belt and the subsequent detachment of the South China Sea slab beneath central Mindoro.

Key points

• The 2017 Batangas earthquakes distributed within the Batangas Bay after relocation

• SW Luzon exhibits EW tensions revealed by earthquake mechanisms and the MC rifting

• The regional tension may incipiently be driven by subduction/collision of the PCB