2000 Oct. Tottori-Ken Seibu earthquake Last updated 15/Oct/2000

Rupture Process of the 2000 Tottori-Ken Seibu Earthquake using Strong Ground Motion Data
Sekiguchi, H.* and T. Iwata**

* Geological Survey of Japan
** DPRI, Kyoto Univ.

We derived rupture process of the 2000 Tottori-Ken Seibu Earthquake, occurred at 13:30JST, 6th October, using K-net and KiK-net strong motion data.

We assumed a fault plane with strike N150E and dip 90deg. from CMT solution and aftershock distribution. Fault length and width are 33km and 21km. Subfault-size is 3x3km square. Totally, we use 11 (in length) x 7 (in width) numbers of subfaults. Fourteen K-net and KiK-net station data were used in
Fig. 1. Target velocity waveforms were integrated from acceleration with BPF of 0.1 to 1.0Hz. We used surface station data for KiK-net. For obtaining Green's function, we used the velocity structure that RCEP-DPRI Tottori observatory use for the hypocenter determination. Target waveforms are 15second window length of the S-wave portion from 1sec before S-wave onset. Rupture stating point is fixed to 35.2679N, 133.3527E, and 13.5km from information by RCEP-DPRI (RCEP-DPRI decideed the hypocenter depth at 13.4km. And we shifted it 0.1km for combenience to assume a fault model.) . Multi-window linear waveform ingersion method (Hartzell and Heaton, 1983) with spatio-temporal constraint (Sekiguchi et al., 2000) was used for the analysis. Slip history on each subfault is represented by six element source time functions with 1s duration succesively triggered at 0.5s interval. Rake angle constraint was between +45 and -45deg. Better source model was searched using mis-fit values and ABIC criterion among a bunch of solutions of the waveform inversions. Tentative best result is as follows.

In Fig. 2, final slip model is shown. Right is N150E direction. Rupture velocity of the first time window was selected to be 2.3km/s with radial propagation. Slips mainly occurred at the shallower part. Largest slip occurred SE direction from the epicenter with at most 3m left lateral slip. Little slip occurred near the starting point. In Fig. 3, time progression of rupture is shown. Main rupture in the shallower part occurred from 4 to 6 sec after the rupture starting. Comparison between observed (Black) and synthetic (Red) waveforms are shown in Fig. 4. Synthetics agree well the observations numbers indicated each wawveforms are maximum velocity in m/s. Moment release is 1.93X10**19N.m or Mw =6.8. Faster velocity model could give us relatively larger seismic moment release.
Following Somerville et al.(1999, SRL), Miyakoshi (personal communication) abstracted characteristic parameters of the source model. We show the relationships between seismic moments and slip area Fig. 5-1, average slipFig. 5-2, combined asperity areaFig. 5-3, and laegest asperity area Fig. 5-4.
Awknowledgement: We used K-net and KiK-net data. Dr. Miyakoshi estimated characterized parameter of slip model followed by Somerville et al.(1999).

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