Understanding the massive M 7.7 Mentawai Earthquake

The Pulau Pagai Selatan, Sumatra earthquake of October 25, 2010 occurred as a result of thrust faulting on or near the subduction interface plate boundary between the Australia and Sunda plates.

At the location of this earthquake, the Australia Plate move north-northeast with respect to the Sunda plate at a velocity of approximately 57-69 mm/yr.
On the basis of the currently available fault mechanism information and earthquake depth it is likely that this earthquake occurred along the plate interface.
The subduction zone adjacent to the region of this event last slipped during the Mw 8.5 and 7.9 earthquakes of September 2007, and today’s event appears to have occurred near the rupture zones of those earthquakes.

Map Austrlia and Sunda plates - courtesy olehnielsen.dk

Today’s earthquake is the latest in a sequence of large ruptures along the Sunda megathrust, including :
– a M 9.1 earthquake that ruptured to within 800 km north of this earthquake in 2004;
– a M 8.6 700 km to the north between Nias and Simeulue in 2005;
– a M 7.5 300 km to the north near Padang in 2009.
– a Mw 8.7-8.9 rupture in 1797
– a Mw 8.9-9.1 earthquake in 1833
(text : courtesy USGS)

 

2010 Mentawai earthquake

 

2009 South Sumatra earthquake

2007 South Sumatra earthquake

2007 South Sumatra earthquake

2004 Sumatra - Andaman Islands - Banda Aceh earthquake

Overview page with all the articles we wrote on this dramatic earthquake / tsunami

Latest news page 4

Latest news page 3

Latest news page 2

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Understanding the Vanuatu M 7.3 earthquake

Which are Nature’s triggers for the massive Vanuatu earthquake from August 10,2010 ?

Courtesy : Wikipedia and USGS

Courtesy : Wikipedia and USGS

In plate tectonics, a convergent boundary also known as a destructive plate boundary (because of subduction), is an actively deforming region where two (or more) tectonic plates or fragments of lithosphere move toward one another and collide.
A
s a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near convergent boundaries.
When two plates move towards one another, they form either a subduction zone.
This depends on the nature of the plates involved. In a subduction zone, the subducting plate, which is normally a plate with oceanic crust, moves beneath the other plate, which can be made of either oceanic or continental crust.

When two plates with oceanic crust converge they typically create an island arc as one plate is subducted below the other. The arc is formed from volcanoes which erupt through the overriding plate as the descending plate melts below it.
The arc shape occurs because of the spherical surface of the earth (nick the peel of an orange with a knife and note the arc formed by the straight-edge of the knife).

A deep undersea trench is located in front of such arcs where the descending slab dips downward, such as the Mariana trench near the Mariana Islands. Other good examples of this type of plate convergence would be Japan and the Aleutian Islands in Alaska.
The Vanuatu trench near the island of Efate can be seen very clearly on the satellite maps below.
When both of the plates are made of oceanic crust, convergence is associated with island arcs such as the Solomon Islands.


Main source text and graphics :  Wikipedia

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