HR: 09:00h
AN: U21C-04    [Abstracts]
TI: Constraints for the 2004 Sumatra Earthquake Source Process From Coseismic Ionospheric Disturbances Observed by GPS
AU: * Heki, K
EM: heki@ep.sci.hokudai.ac.jp
AF: Div. Earth Planet. Sci., Hokkaido Univ., N10 W8, Kita-ku, Sapporo, 060-0801 Japan
AU: Otsuka, Y
EM: otsuka@stelab.nagoya-u.ac.jp
AF: STE Lab., Nagoya Univ., Honohara 3-13, Toyokawa, 442-8507 Japan
AU: Choosakul, N
EM: cnwatthn@geo.sc.chula.ac.th
AF: Dept. Geology, Chulalongkorn Univ., Phayathai Road, Bangkok, 10330 Thailand
AU: Hemmakorn, N
U21C-04 AF: King Mongkut's Inst. Tech., Ladkrabang, Bangkok, 10520 Thailand
AU: Komolmis, T
U21C-04 AF: Chiang Mai Univ., Chiang Mai, Chiang Mai, 50200 Thailand
AU: Maruyama, T
EM: tmaru@nict.go.jp
AF: National Inst. Inform. Comm. Tech., 4-2-1 Nukui-kita, Koganei, 184-8795 Japan
AB: Coseismic ionospheric total electron content (TEC) perturbations, observable with Global Positioning System (GPS), are caused by the three kinds of atmospheric waves, i.e. (1) direct acoustic wave from the focal area, (2) gravity wave propagating obliquely upward, and (3) secondary acoustic wave excited by the Rayleigh surface wave. They have been detected for the 2003 Tokachi-oki, Japan (Heki and Ping, 2005), the 2001 Peru (Artru et al., 2005), and the 2002 Denali (Ducic et al., 2003) earthquakes, respectively, all with dense GPS arrays. They have different apparent propagation speeds, and the first one has a latitude-dependent directivity due to the Lorentz force. Here we demonstrate that observed coseismic ionospheric disturbances could constrain the source rupture process of the 2004 December Great Sumatra earthquake. After that earthquake, we observed two kinds of ionospheric perturbations, i.e. the surface wave induced perturbation detected by the Japanese GEONET, and those by direct acoustic waves detected by nine continuous GPS stations in Indonesia and Thailand. The latter disturbances amounted to a few TEC units, an order of magnitude larger than the 2003 Tokachi-oki case, and propagated by about 1 km/sec. Their apparent periods were 4-5 minutes or longer. We assumed linear distribution of point sources for acoustic wave generation along the fault from NW Sumatra to the Andaman Islands, and calculated TEC variation waveforms by simulating the acoustic wave propagation from individual sources to the intersections of line-of-sights and ionosphere through the atmosphere with height-dependent sound velocities, by ray-tracing. Then, we tried to reproduce the combined TEC perturbations similar to the observed ones, for several different satellite-receiver pairs, by optimizing the relative strengths of the linearly distributed point sources. The strongest sources were found near G. Nicobar Island, which is consistent with seismological studies and displacements of GPS stations. We found that ruptures in the northernmost segment, under the Andaman Islands, are indispensable to reproduce some of the observed TEC waveforms, suggesting that even the northernmost fault segment underwent movements slow enough to be overlooked by seismometers but fast enough to excite atmospheric acoustic waves.
DE: 1241 Satellite geodesy: technical issues (6994, 7969)
DE: 2435 Ionospheric disturbances
DE: 7215 Earthquake source observations (1240)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8122 Dynamics: gravity and tectonics
SC: Union [U]
MN: Fall Meeting 2005