Magnitude 5.7 Earthquake off the coast of Surigao del Sur, Philippines.

The Philippine Institute of Volcanology and Seismology recorded a Magnitude 5.7 Earthquake at a depth of 14 km slightly off the coast of Hinatuan in Surigao del Sur Province on Mindanao Island, Philippines, slightly before 2.10 pm local time (slightly before 6.10 am GMT) on Friday 31 July 2020. There are no reports of any damage or casualties associated with this event, but it was widely felt across eastern Mindanao.

The location of the 31 July 2020 Surigao del Sur Earthquake. USGS.

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.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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Landslides and flooding kill five as Tropical Depression Basyang sweeps across the Philippines.

Five people, including three children, have died, three more have been injured and several more are missing after Tropical Depression Basyang (or Sanba) swept across the Philippines on Tuesday 13 February 2018, triggering a series of landslip and flooding events. All of the known deaths have been linked to landslips that hit two villages in Surigao del Sur Province on Mindanao Island. In the first event Irene Lamela Benguilo, 25, and her two children died in a landslide that hit the village of Gamuton, in the second Jay Conjurado, 10, and another, as yet unnamed person, died in a landslide that hit the village of Babuyan.

 Rescue workers in Gamuton, Surigao del Sur Province, the Philippines, following a landslide on 13 February 2018. Roselyn Coronel/PTV.

Tropical storms are caused by the warming effect of the Sun over tropical seas. As the air warms it expands, causing a drop in air pressure, and rises, causing air from outside the area to rush in to replace it. If this happens over a sufficiently wide area then the inrushing winds will be affected by centrifugal forces caused by the Earth's rotation (the Coriolis effect). This means that winds will be deflected clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere, eventually creating a large, rotating Tropical Storm. They have different names in different parts of the world, with those in the northwest Atlantic being referred to as hurricanes.

The path and strength of Tropocal Depression Basyang. Thick line indicates the past path of the storm (till 6.00 pm GMT on Tuesday 13 February 2018), while the thin line indicates the predicted future path of the storm, and the dotted circles the margin of error at six and twelve hours ahead. Colour indicated the severity of the storm. Tropical Storm Risk.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

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Magnitude 4.8 Earthquake on Mindanao Island, Philippines.

The United States Geological Survey recorded a Magnitude 4.8 Earthquake at a depth of 10.1 km, 14 km to the southeast of the city of Tandag in Surigao del Sur Province on Mindanao Island in the Philippines, slightly after 10.20 am local time (slightly after 2.10 am GMT) on Sunday 12 January 2014. There are no reports of any damage or injuries relating to this event, though it was felt across much of the east of the province.

The approximate location of the 12 January 2013 Surigao del Sur Earthquake. Google Maps.

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.

See also Magnitude 7.1 Earthquake on Bohol Island, the Philippines, Magnitude 4.8 Earthquake on Mindanao Island, the Philippines, Magnitude 5.0 Earthquake on Mindanao Island, the Philippines, Five people killed by eruption on Mount Mayon, the Philippines and Earthquake off Mindanao Island in the Philippines.

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