Seismotectonics of Mindoro, Philippines

• Slab dipping angles steepen with upwards propagation southeasterly in NW Mindoro.
• Intermediate-depth earthquakes exhibit down-dip T axes caused by negative buoyancy.
• South of Central Mindoro broadly distributes strike–slip shallow earthquakes.
• Rifting of the Macolod Corridor extending southwestward to NW Mindoro

Mindoro Island is located where the Palawan Continental Block indented into the Philippine Mobile Belt during the Early Miocene and where the Manila Trench terminates, having ceased convergence due to collision. The seismotectonics of Mindoro are crucial to understanding the processes of arc-continent collision and slab dynamic responses of convergence cessation. This study was conducted using data from both the EHB and Global Centroid Moment Tensor catalogues. It is shown that following the southeasterly reduction of convergence rates from the Manila Trench offshore NW Mindoro to onshore SW Mindoro, the slab dipping angles steepen, were initiated at depth (~ 200 km) and propagate upwards. The horizontal distances of the trench and slab, as measured from the Wadati–Benioff zone at 200 km depth, also reduce in a southeasterly direction. Observations of intermediate-depth earthquakes that exhibit predominantly down-dip extensional stress patterns attest that the steepening of slab dipping angles is due to the negative buoyancy of the slab. In contrast, a broad region covered by central and south Mindoro, the Romblon group, and NW Panay, is characterized by a sporadic distribution of shallow earthquakes of mostly strike-slip type. Among these, the significantly sized events (Mw > 5.5) tend to distribute around the borders suggesting that the region roughly acts as a unit block, moving or rotating coherently. Events in the vicinity of the Wawa–Mamburao valley exhibiting normal faulting of NW–SE horizontal extension suggest rifting of the Macolod Corridor extending southwestward to NW Mindoro.