The Philippine Institute of Volcanology and Seismology recorded a Magnitude 6.1 Earthquake at a depth of 26.9 km about 21 km off the coast of Sarangani Province on Mindanao Island, Philippines, slightly after 8.20 am local time on Wednesday 16 December 2020 (slightly after 11.20 pm on Tuesday 15 December, GMT). There are no reports of any damage or casualties associated with this event, but it was widely felt across southern Mindanao.
The geology of the central Philippines is Complex. The west of Mindanao
Island is located on the Banda (or Sunda) Microplate, and the east on
the Philippine Plate, which is being subducted beneath the Sunda (or
Banda) Microplate along the central part of the island. Immediately to
the east of the Island the Pacific Plate is being subducted along the
Philippine Trench, and passes beneath eastern Mindanao as it sinks into
the Earth. This is not a smooth process, an the plates constantly stick
together then break apart again as the pressure builds up, resulting in
Earthquakes.
Subduction beneath the Philippines. Yves Descatoire/Singapore Earth Observatory.
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