TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 56 (No. 2), pp. 87-93, 2004

Source processes of the foreshock, mainshock and largest aftershock in the 2003 Miyagi-ken Hokubu, Japan, earthquake sequence

Kazuhito Hikima1,2 and Kazuki Koketsu1

1Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
2OYO Corporation, 2-61-5 Toro-cho, Kita-ku, City of Saitama, Saitama 331-0804, Japan

(Received October 28, 2003; Revised January 27, 2004; Accepted February 5, 2004)

Abstract: The waveform inversions for the 2003 Miyagi-ken Hokubu earthquake sequence were performed using strong-motion records to determine the source processes. We carried out the inversions for the foreshock (M5.6), the mainshock (M6.4) and the largest aftershock (M5.5), respectively. The strong-motion waveforms observed at 10 stations from KiK-net and K-NET within about 70 km epicentral distance were used. The mainshock is composed of two subplanes dipping toward west. The strike direction of the south subplane is NE-SW and that of the north subplane is almost N-S. The fault plane of the foreshock is almost the same as that of the south subplane of the mainshock, but the strike direction of the largest aftershock is NW-SE. The asperities of the three earthquakes are not overlapped strongly each other and it is considered that this earthquake sequence is a result of seismic activity on a reverse fault, which is curved along strike, with time lags. The shallow asperity of the mainshock may result in specific distributions of damage and high accelerations.
Key words: Source process, waveform inversion, strong motion, earthquake sequence.

Corresponding author E-mail: hikima@eri.u-tokyo.ac.jp

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