HR: 1340h
AN: S13D-1093    [Abstracts]
TI: Temporal Changes of Seismic Structure Around Iwate Volcano as Inferred From Waveform Correlation Analysis of Multiplet Earthquakes
AU: * Yamawaki, T
EM: yamawaki@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science Tohoku University, Aoba Aramaki Aoba, Sendai, 980-8578 Japan
AU: Nishimura, T
EM: nishi@zisin.geophys.tohoku.ac.jp
AF: Graduate School of Science Tohoku University, Aoba Aramaki Aoba, Sendai, 980-8578 Japan
AU: Hamaguchi, H
EM: hamaguti@cello.ocn.ne.jp
AF: Graduate School of Science Tohoku University, Aoba Aramaki Aoba, Sendai, 980-8578 Japan
AB: Temporal change of crustal structure around Iwate volcano, northeastern Japan, for the period from 1995 to 2002 is investigated by examining waveform similarity in P- and S-waves of multiplet earthquakes occurring at the subducting Pacific Plate boundary. We analyze seventy-three groups of multiplets consisting of 2 to 20 events whose epicentral distances range from 80 to 260 km and magnitudes from 2.1 to 4.5. These multiplets are recorded at 30 stations within approximately 80 km from the summit of Iwate volcano. We calculate cross-correlation coefficients of P- and S-waves for each pair of multiplets belonging to the same group. Totally, 1142 pairs are analyzed. We first band-pass filter each waveform from 4 to 8 Hz and align them at P-wave onset. The cross-correlation coefficients of P- and S-waves are calculated for 5-second time window starting at onset time of each phase. The spatial distribution of the coefficient is examined by averaging the cross-correlation coefficients at each station. At most stations far from Iwate volcano, the averaged coefficients of S-waves are estimated to be from 0.95 to 0.97. On the other hand, two stations, IKG and GNB, located close to the west of the volcano show smaller average of 0.85 and 0.91, respectively. These stations are located close to active volcanic pressure sources detected by geodetic measurements. We further examine temporal changes in S-wave by aligning the cross-correlation coefficients for multiplet pairs with an occurrence interval of 6 to 18 months. The results show that no significant temporal change is observed at most of stations located far from the volcano. However, it is found that the coefficients at IKG and GNB remarkably decreased from 1998 during which significant volcanic activity was observed and an M6.1 earthquake took place at the southwest of the volcano. As the volcanic activity slowly subsided from 2000, the coefficients gradually become large. These changes are well correlated in time with activities of Iwate volcano. Since changes in cross-correlation of P-waves are smaller compared with those of S-waves, the crustal structure changed its property properties sensitive to S-waves, such as rigidity, related to magmatic and/or seismic activity in and around the volcano.
DE: 7280 Volcano seismology (8419)
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
SC: Seismology [S]
MN: 2004 AGU Fall Meeting