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Stress changes along the Sunda trench following the
26 December 2004 Sumatra-Andaman and 28 March 2005 Nias earthquakes,
Geophysical Research Letters, vol. 33, L06309, Doi:10.1029/2005gl024558, 2006.
[Appendix animation (2.1 Mb)] [Printable article (680 kb)]
Fred F. Pollitz1, Paramesh Banerjee2, Roland Bürgmann3, Manabu Hashimoto4,
and Nithiwatthn Choosakul5
1 U.S. Geological Survey, Menlo Park, CA
2 Wadia Institute of Himalayan Geology, Dehra Dun, India
3 Department of Earth and Planetary Science, University of California,
Berkeley, California, USA.
4 Disaster Prevention Research Institute, Kyoto University, Kyoto,
Japan.
5 Department of Geology, Chulalongkorn University, Bangkok,
Thailand.
Non-technical summary: The magnitude 9.2 Sumatra earthquake of December 26, 2004 changed the stress in Earth's crust and at greater depth. Our experience with large earthquakes teaches us that such stress changes can trigger other large earthquakes in the vicinity of the mainshock.
Because of the great size and length of the December, 2004 rupture, which is estimated at about 1500 km, the triggering capability of this earthquake likely extends over a great distance. This is confirmed by the occurrence of the magnitude 8.6 Nias earthquake on March 28, 2005, about 160 km to the south of the December, 2004 epicenter.
An important question is: How will the impact on Earth's stress field evolve with time, and can it lead to future remote earthquake triggering? The net change in stress at a remote location from the mainshock is a combination of the static stress change (which occurs immediately at the time of the mainshock) and the postseismic stress change (which accumulates gradually over months and years after the mainshock). Viscoelastic relaxation of the hot, ductile rock in Earth's asthenosphere at 100 km depth and greater will help propagate the initially localized static stress changes to much greater distance. This idea was first tested along the active tectonic margin of western North America by Pollitz et al. (1998) using the magnitude 9.2 1964 Alaska earthquake and other large Pacific earthquakes. It has been recently considered by Pollitz et al. (2006) along the Sumatran megathrust for the combined Sumatra-Andaman + Nias earthquakes. Using the Pollitz et al. (1998) viscoelastic-relaxation model, they predict that initially low static stress values along the megathrust bordering central Sumatra should evolve to larger stress values over the next several years. Stress increases are predicted along the ruptures zones of great (M>8) earthquakes that occurred off central Sumatra in 1797 and 1833, each of which generated damaging tsunamis. The stress changes are judged important given that these regions are likely highly stressed from the background tectonic motions accumulated during the two centuries since these events occurred.
Figure caption. Rupture areas associated with known megathrust earthquakes along the Sumatra-Sunda trench. Gray planes are the coseismic rupture of the 26 December 2004 earthquake from Model M3 of Banerjee et al. [2005]. Indicated are the 0 and 50 km slab depth contours of Gudmundsson and Sambridge [1998]. Epicenters of M≥4.0 earthquakes from 29 March 2005 to 1 August 2005 from the NEIC catalog are superimposed. Selected GPS sites from four regional networks are indicated.
