Sunday 30 September 2018

Thousands feared dead after Earthquake and tsunami hit Sulawesi.

832 people have now been confirmed dead and it is feared that the eventual total will reach into the thousands following an Earthquake on northern Sulawesi on Friday 28 September 2018, which triggered a tsunami. The event was recorded by the United States Geological Survey as a Magnitude 7.5 Earthquake at a depth of 10 km, roughly 78 km to north of the city of Palu, which occurred slightly after 6.00 pm local time (slightly after 10.00 am GMT), and was felt across the island of Sulawesi and on eastern parts of Borneo. The majority of the confirmed fatalities so far (821) have been in the city of Palu, but it is likely far more people have died in the Donggala Regency to the north of the city, where the Earthquake occurred and which was inundated by the tsunami after the event.

Debris in the streets of Palu, Sulawesi, following an Earthquake and tsunami on 28 September 2018. Haritsah Almudatsir/Jawa Pos.

The tectonic situation beneath Sulawesi is complex, as it is caught in the collisional zone between the Eurasian, Pacific and Australian Plates. The north of the island is located on a breakaway section of the Eurasian Plate, called the Sangihe Plate. To the east lies the remnant Molucca Sea Plate, which is being subducted beneath both the Sangihe Plate and the more easterly Halmahera Plate, leading to Earthquakes and volcanism on Sulawesi and the islands of the Sangihe Arc in the west and the islands of the Halmahera Arc in the east.

The approximate location of the 28 September 2018 Sulawesi Earthquake. USGS.

Earthquakes along subductive margins are particularly prone to causing tsunamis, since these often occur when the overlying plate has stuck to the underlying plate, being pulled out of shape by its movement.. Eventually the pressure builds up to far and the overlying plate snaps back, causing an Earthquake and a tsunami. 

Simplified graphic showing tsunami generation along a convergent margin.NASA/JPL/CalTech.

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.
See also...
Follow Sciency Thoughts on Facebook.