Andaman-Sumatra island arc: III. Time evolution of seismogenic activation of the arc since the beginning of the 21st century

Abstract

The spatiotemporal evolution of the intense burst in seismogenesis within the Andaman-Sumatra island arc in 2000–2010 is analyzed. The onset of seismogenic activation was marked by two strong (MS ∼ 7.9, MS ∼ 7.8) quakes that occurred in the lithosphere of the South Sumatra region on June 4, 2000 and by the strongest (MW = 7.3) earthquake of July 25, 2004 that took place in the lower part of the focal zone. These seismic events were the foreshocks of the main episode of seismogenic activation of the island arc—the catastrophic earthquake of December 26, 2004, with its source near the northern coast of Sumatra. The large shocks (MS ∼ 7.7–8.4) that occurred from March 28, 2005 to October 25, 2010 between the source of the Sumatran earthquake and epicentral zone of the foreshocks of June 4, 2000, are the aftershocks of the Sumatran event. The spatiotemporal evolution of seismogenic activation of the Andaman-Sumatra island arc at the beginning of the 21st century is compared to the seismogenic activation of the Kuril-Kamchatka arc in the middle of the 20th century. The positions, geological conditions, and focal parameters of the strongest Sumatran earthquakes of 2000–2010 are determined. The interpretation of the sources relies on the (1) complex analysis of all the manifestations of the earthquakes of 2000–2010 and (2) the established regularities of the occurrence of the earthquakes in the island arcs. The sources of the earthquakes of 2005–2010 are the steep longitudinal (trending along the arc) reverse faults of a backthrust type, which have a bedding depth of about a few dozen kilometers. The reverse-fault sources of the earthquakes of March 28, 2005, September 12, 2007 (11:10 UT), and October 10, 2010 are located in the zone of the Outer Range, and the earthquakes of September 12, 2007 (23:49 UT) fall in the Mentawai Trough. The strike-slip reverse fault, which cuts the island arc, is likely to be the focal mechanism of the earthquake of June 4, 2000. The sources of the events of March 28, 2005 and September 12, 2007 did not coincide with the sources of the historical devastating earthquakes of 1861 and 1833, respectively. The system of seismic sources in the form of a series of subparallel arc-parallel steep reverse faults off the western coast of Sumatra is similar to the system of seismic sources in the Kuril-Kamchatka island arc.