HR: 1340h
AN: S33B-1311    [Abstracts]
TI: Ionosphere Responses to Large Earthquakes of Different Focal Mechanisms: Case Study of 1994, 2006 and 2007 Kuril Islands Earthquakes
AU: * Astafyeva, E
EM: elliada@mail.sci.hokudai.ac.jp
AF: Dept. Natural History Sci., Hokkaido Univ., N10 W8, Kita-ku, Sapporo, 060-0810, Japan
AU: Heki, K
EM: heki@mail.sci.hokudai.ac.jp
AF: Dept. Natural History Sci., Hokkaido Univ., N10 W8, Kita-ku, Sapporo, 060-0810, Japan
AB: Using GPS TEC measurements we studied ionosphere response to the Kuril Islands Earthquakes of 04 October 1994, 15 November 2006 and 13 January 2007 (all M>8.0). High spatial resolution of the Japanese dense GPS array (GEONET) allowed us to analyze dynamical characteristics of the propagation of the observed coseismic ionospheric disturbances (CID) in detail. The CID appeared ~10-15 minutes after the main shock and manifested themselves as 'positive' and 'negative' N-waves in TEC series with the amplitude of 0.6-1.0 TEC units. The CID were found to propagate with a spherically-similar wavefronts outward from the epicenters with the velocity of about of 800-1000 m/s that correspond to the sound speed at the height of the F-layer of the ionosphere. Then, at distances 500-600 km from the epicenter the propagation velocity increased to ~4 km/sec. This suggests that the TEC signals of the secondary acoustic waves excited by the Rayleigh surface waves became dominant as the subionospheric points went farther from the epicenter. Another important point is the dependence of the shape of TEC response on the type of fault that ruptured in the earthquake. The three earthquakes are of different types. The 2006 earthquake was a low-angle thrust event and the 2007 one was a normal fault event in the outer rise of the trench. Their coseismic movements are characterized as crustal uplift and subsidence, respectively. The 1994 earthquake occurred in the subducting Pacific Plate slab as a high-angle (~50 deg) reverse faulting resulting in both surface uplift and subsidence of comparable size. TEC response to a reverse faulting is known to show a 'positive' N-wave – a typical compression-rarefaction wave, and this was the case for the 2006 event. On the other hand, normal faulting seems to cause a 'negative' N-wave, the negative TEC changes appear first, and this was the case for the 2007 outer rise earthquake. The TEC response to the October 1994 earthquake was a 'complex' one, i.e. it contains the two types of N-waves excited at the uplifted and subsided parts, and either one becomes dominant depending on the azimuth of subionospheric points relative to the epicenter.
DE: 1243 Space geodetic surveys
DE: 2435 Ionospheric disturbances
DE: 2483 Wave/particle interactions (7867)
DE: 2487 Wave propagation (0689, 3285, 4275, 4455, 6934)
DE: 7209 Earthquake dynamics (1242)
SC: Seismology [S]
MN: 2007 Fall Meeting