Seismicity rate immediately before and after mainshock rupture from high-frequency waveforms in Japan

Zhigang Peng (1, 2) , John E. Vidale (1) , Miaki Ishii (3) , A. Helmstetter (4)

1 IGPP - Institute of Geophysics and Planetary Physics [Los Angeles]
2 School of Earth and Atmospheric Sciences [Atlanta]
3 EPS - Department of Earth and Planetary Sciences [Cambridge, USA]
4 LGIT - Laboratoire de Géophysique Interne et Tectonophysique

We analyze seismicity rate immediately before and after 82 mainshocks with the magnitudes ranging from 3 to 5 using waveforms recorded by the Hi-net borehole array in Japan. By scrutinizing high-frequency signals, we detect ~5 times as many aftershocks in the first 200 s as in the Japan Meteorological Agency catalogue. After correcting for the changing completeness level immediately after the mainshock, the aftershock rate shows a crossover from a slower decay with an Omori's law exponent p = 0.58±0.08 between 20 and 900 s after the mainshock, to a faster decay with p = 0.92±0.04 after 900 s. The foreshock seismicity rate follows an inverse Omori's law with p = 0.73±0.07 from several tens of days up to several hundred seconds before the mainshock. The seismicity rate in the 200 s immediately before the mainshock appears steady with p = 0.36±0.45. These observations can be explained by the epidemic-type aftershock sequence (ETAS) model, and the rate-and-state model for a heterogeneous stress field on the mainshock rupture plane. Alternatively, non-seismic stress changes near the source region, such as episodic aseismic slip, or pore fluid pressure fluctuations, may be invoked to explain the observation of small p values immediately before and after the mainshock.

Domaines: Géophysique [physics.geo-ph]

Zhigang Peng, John E. Vidale, Miaki Ishii, A. Helmstetter. Seismicity rate immediately before and after mainshock rupture from high-frequency waveforms in Japan. Journal of Geophysical Research, 2007, 112, pp.B03306. ⟨10.1029/2006JB004386⟩. ⟨hal-00195470⟩