HR: 14:40h
AN: S13E-05    [Abstracts]
TI: Scaling Relation of Seismic Nucleation Estimated from Slow Initial Phase
AU: * Ito, S
EM: s.ito@aist.go.jp
AF: Natl Inst of AIST, Tsukuba Central 7,1-1-1 Higashi, Tsukuba, 3058567 Japan
AU: Ito, H
EM: hisao.itou@aist.go.jp
AF: Natl Inst of AIST, Tsukuba Central 7,1-1-1 Higashi, Tsukuba, 3058567 Japan
AB: Synthetic seismogram expected from the slip dependent friction law isthe slow initial phase; convex downward seismograms seen in aroundfirst P-arrivals of velocity seismograms. The scaling law expectedfrom the slip dependent friction law was suggested, but it has notbeen confirmed with the slow initial phase. In this study, we showthat the scaling law expected from the slip dependent friction law isvalid with the slow initial phase.At first, we obtained moment rate functions by deconvolution with causalattenuation operators. Next, we estimated stress drop and seismicmoment released during unstable, accelerating phase in slip dependentrelationship, and obtained them for 28 earthquakes of which moment rangeis $1 \times 10^{10} \mbox{Nm}$ to $1 \times 10^{13} \mbox{Nm}$.Finally, we evaluated fault dimension of unstable, accelerating phase;the critical size $2L_c$ of the nucleation zone and the critical slipdisplacement $D_c$ with theoretical relation by Ohnaka (2000). Both thecritical size $2L_c$ of the nucleation zone and the critical slipdisplacement $D_c$ are proportional to power of 1/3 of seismic moment,and it can explain the theoretical formula proposed by Ohnaka (2000).Our results suggest that the rupture process of earthquakes is subjectto the slip dependent law because the relationship between the criticalsize $2L_c$ of the nucleation zone and the critical slip displacement$D_c$ and the seismic moment is consistent with scaling law expectedfrom the slip dependent law. The results of this study obtained withthe slow initial phase is consistent with the results with the seismicnucleation phase by Ellsworth and Beroza (1995). This means that theslow initial phase and the seismic nucleation phase is the samephenomenon in the macro scale. However, the results with the seismicnucleation phase are relatively more perturbed than that with the slowinitial phase. This difference can be interpreted as quality or varietyof data. Nevertheless, it is possible that the seismic nucleation phaseis produced by inhomogeneous distribution of asperities on a faultplane.
DE: 7260 Theory and modeling
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting