Abstract
Abstract The 2004 Mid Niigata Prefecture earthquake (37.289°N, 138.870°E, 13.1 km, MJMA 6.8; JMA), also known as the 2004 Niigata Prefecture Chuetsu earthquake, was a thrust type earthquake that occurred on October 23, 2004 at 17:56 (JST). Strong ground motions of PGA 800-1700 cm/s2 and PGV 60-130 cm/s were observed at stations located immediately above the source region. We deduced the rupture process of this earthquake with a multi-time-window linear waveform inversion procedure. We used near-fault strong ground motion data observed at nine K-NET and KiK-net stations within 50 km from the epicenter. In order to obtain appropriate Green’s functions for the waveform inversion, we constructed two velocity structure models for stations on the hanging wall and one structure model for stations on the footwall. The estimated total slip distribution contains three asperities: (a) around the hypocenter, (b) in the upper-middle section of the fault plane, and (c) southwest of the hypocenter. The maximum slip is 3.8 m at the hypocenter and the total seismic moment is 1.2 × 1019 Nm, which corresponds to Mw=6.7. The moment rate functions in asperities (a) and (c) have a short rise time, while those in asperity (b) have a longer rise time.
Highlights
On October 23, 2004 at 17:56 (JST), the 2004 Mid Niigata Prefecture earthquake (MJMA 6.8; Japan Meteorological Agency) struck mid-Niigata Prefecture, central Japan
We review the characteristics of the strong ground motions observed by K-NET (Kinoshita, 1998) and KiK-net (Aoi et al, 2000) during the 2004 Mid Niigata Prefecture earthquake and estimate the rupture process by waveform inversion analysis
We found a large discrepancy between the observations and synthetic seismograms for aftershocks in the case of NIG019 on the hanging wall
Summary
On October 23, 2004 at 17:56 (JST), the 2004 Mid Niigata Prefecture earthquake (MJMA 6.8; Japan Meteorological Agency) struck mid-Niigata Prefecture, central Japan. Strong motions of several dozen to more than one hundred cm/s were observed mainly at stations on the northwest side of the causative fault, where deep basins exist (e.g., Kobayashi et al, 1991; Yanagisawa et al, 1986). A large, brief pulse commonly appears at the stations on the northwest side Such pulses which recorded at south stations of the northwest side (e.g., NIG022) arrived a few seconds later than the expected direct S-wave arrival from the hypocenter. At the north stations (e.g., NIG019), such pulses arrived on time expected as arrival time from the hypocenter These delays do not appear in the aftershock records, and the delays are longer than expected from the thickness and S-wave velocity of the sediments beneath the stations. This implies that the delays are not caused by the subsurface structure
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