The sumatra earthquake of December 26, 2004, as an event unrelated to the plate-tectonic process in the lithosphere

Abstract

The Sumatra (Indonesia) earthquake of December 26, 2004 (M w = 9.0−9.3), is among the strongest seismic events (occupying the second to fourth place) recorded in the epoch of instrumental seismological observations. In addition, this earthquake appears to be the first event of such a scale for which results of up-to-date high-precision geodetic measurements are available. Therefore, it is of particular interest for studies of geodynamics of mobile belts, seismogenic zones, and the Earth’s crust as a whole. The available geological, geophysical, and geodetic data for the Mediterranean-Caucasian segment of the Alpine-Himalayan mobile belt, the Greater Caucasus, and the Tajik depression suggest that the tectonic structure, geological zonality, seismicity, and present-day geodynamics of these structural elements of the Earth’s crust are controlled by the interaction of two different mechanisms of tectogenesis. First, this is the mechanism of independent self-development of the aforementioned structural elements and, first of all, the mobile belt as a whole; this mechanism acts through an intense increase in the volume and area of laminated rocks of the crust/lithosphere, apparently, due to the influx of additional mineral material supplied by an ascending flow of deep fluids. The second type of mechanisms is related to the external plate-tectonic action on the mobile belt and the other structural elements due to lateral movements of lithospheric plates. The joint analysis of geological, geodetic (GPS), and seismological data on the Sumatra earthquake area shows that these two mechanisms also act in the Indonesian part of the Alpine-Himalayan mobile belt. However, the Sumatra earthquake itself is a result of an independent (unrelated to plate tectonics) process in the mobile belt rather than the convergence of adjacent lithospheric plates.