HR: 0800h
AN: U51A-0004    [Abstracts]
TI: Imaging of the 2007 Pagai Earthquake with Back-Projection of the Hi-net Data
AU: * Ishii, M
EM: ishii@eps.harvard.edu
AF: Dept. Earth & Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, United States
AU: Kiser, E
EM: kiser@eps.harvard.edu
AF: Dept. Earth & Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, United States
AU: Klinger, Y
EM: klinger@ipgp.jussieu.fr
AF: Dept. Earth & Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, United States
AU: Klinger, Y
EM: klinger@ipgp.jussieu.fr
AF: Institut de Physique du Globe, Equipe de Tectonique -UMR7154, Boite 89, Paris, 75252, France
AU: Shearer, P M
EM: pshearer@ucsd.edu
AF: Institute of Geophysics & Planetary Physics, University of California, San Diego, IGPP 0225, La Jolla, CA 92093, United States
AB: The location and geometry of the 2007 September 12th Pagai earthquake in Sumatra are well suited for application of the back-projection method using the Japanese High-Sensitivity Seismograph Network (Hi-net) array. This technique allows imaging of the relative strength of high-frequency radiated energy as a function of space and time. The 2007 Pagai earthquake appears to have ruptured unilaterally at a nearly constant speed of about 2.9~km/s toward the northwest from the epicentre. The event lasts for about 100~seconds, and the estimated total rupture area is consistent with that expected for magnitude~8.4. The inferred rupture area also agrees well with the aftershock distribution except for a cluster of events around Sipora island. This sequence starts about a day after the magnitude~8.4 event, and includes an event with magnitude~7.0. A heightened level of seismicity in this region was also observed after the 2005 Simeulue-Nias earthquake. The locations of these events and the gap of seismicity between this cluster of events and the rupture area of the 2007 earthquake suggest that they may be two separate sequences. The rupture of the magnitude~8.4 Pagai earthquake starts at the northwest edge of the slip region of the 2000 magnitude~7.9 Enganno earthquake, and terminates near the southern boundary of the slip region of the 1797 earthquake. The 2007 event broke an area that had significant slip during the 1833 earthquake, but did not cover its entire extent. It is also in good agreement with locations of strong seismic coupling along Sumatra that have been obtained from paleoseismic and geodetic data. The series of large earthquakes in Enganno (2000, M~7.9), Sumatra-Andaman (2004, M~9.3), Simeulue-Nias (2005, M~8.6), and Pagai (2007, M~7.9) cover most of the area along the Sunda trench from -7°S to 15°N. However, there are two gaps, both in ruptured area and seismicity. One covers a region between the Pagai and Sipora islands which is thought to have broken twice during the 1797 and 1833 earthquakes. Another is an area northwest of Sipora island, with the last giant earthquake occurring in 1797.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Union [U]
MN: 2007 Fall Meeting