Variations in the Kinematics of Deformation in the Vicinity of the Catastrophic Sumatra Earthquake

Аннотация

The Great Andaman–Sumatra earthquake (GASE) on December 26, 2004, with magnitude M_w of 9.2, occurred in the Indian Ocean near the northwestern coast of Sumatra Island at a depth of 30 km and is the third-largest earthquake of the historical world seismic observations. The surface rupture of 1200–1600 km provoked a right-lateral strike-slip fault at a distance of 15 m along the subduction zone of the Indian Plate beneath the Sunda arc in the west of the Southeast Asia (Melanesia) and the Burma Plate (part of the larger Eurasian Plate) in the north. It is suggested that such a strong event should be reflected in variations in the long-term type of seismotectonic deformation (STD) in its vicinity. The aim of this work is the search for these deformations. The STD type in the GASE spatial-temporal vicinity is estimated on the basis of a set of focal mechanisms of earthquakes with M_w ≥ 5 published in the ISC catalog. The long-term estimations of the STD type are consistent with current ideas on the character of collision of tectonic plates in the western part of the Sunda arc and support the geological ideas on near-horizontal compression (shortening) across the arc in the nearest vicinity of the earthquake epicenter. At the same time, variations in the STD type are noticeable in comparison with long-term estimations in different periods relative to the time of the GASE. These variations can be explained by the change in the kinematics of deformation at different stages of evolution of the deformation process in the spatial-temporal vicinity of the strongest seismic catastrophe. In a control sample to the south of the territory studied (without rupture during the earthquake), the type of STD underwent no noticeable changes during the entire period considered.