Abstract

The source rupture process of the 1964 Niigata earthquake (MJMA 7.5), Japan, is inferred in detail from regional strong-motion data recorded with low-gain mechanical displacement seismographs. A fault-plane model with high-angle dipping to the west is assumed as a result of reinvestigating the aftershock distribution, and the thickness of the fault zone is determined from recent high-resolution seismicity in the source region. To develop appropriate Green’s functions, a one-dimensional velocity structure model for each station is constructed by modeling the waveforms from recent small earthquakes in the source region. A multiple-time-window technique is applied to invert the observed waveforms for the spatial and temporal slip distribution. The obtained source model indicates large slips mainly in the northern part of the fault plane and secondary slips in the vicinity of the hypocenter and slightly expanding to the south. The total moment release reached forumla (Mw 7.6) and the rupture velocity of the first time-window sweep was 1.5 km/s. The static stress drop was estimated to be 8.9 MPa by assuming a circular fault model. The crustal deformation estimated from the slip distribution agrees well with the tsunami-generating area, the sea-bottom movement, and the uplift measurement at Awashima Island, located above the fault plane.

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