Chapter 1 of "Earthquake and Tsunami":

The Cause: moving geological plates

The Indo-Australian plate moves below the Eurasian plate at around 70 mm per year on average. Plates get locked and move very little for many years, even centuries, pressure builds up - and then is suddenly and unpredictably released in the form of a major earthquake. This happened on 26th December 2004 below Sumatra and the fault line between the Indo-Australian and the Eurasian plates.

The major plates often have smaller plates at their edges. These minor and micro- plates tend to move, more or less, in the same direction as the major plates they belong to. They are often the location of specially active geological fault lines.

Plate tectonics - major plates The speed and direction of subduction (i.e. of a plate moving below another) is shown in mm per year

Plate tectonics - minor and micro-plates __ Major plate boundaries _____ Minor and micro-plate boundaries 1 epicenter of 26 Dec 2004 quake 2 epicenter of 28 Mar 2005 quake   CIDZ = Central Indian Ocean Deformation Zone, the fault line between the two rather large "minor" Indian and Australian plates.

 

Active tectonic elements in the Sumatra-Nicobar-Andaman area. Faults: WAF - west Andaman fault SEU - Seuliman fault SFS - Sumatra fault system Vectors: AE - Australian plate in relation to Eurasian plate AB - Australian plate in relation to Burma plate BE - Burma plate in relation to Eurasian plate AT - Australian plate in rlation to alignment of the trench. The vectors show that subduction is taking place all along the trench at various angles

A tectonic map of the northeastern Indian Ocean (adapted from Curray J.R. 1991, "Possible greenschist metamorphism at the base of a 22 km sediment section, Bay of Bengal," Geology 19:1097-1100)

 

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Last changed 27 August 2006