Journal of Natural Disaster Science

RELATION BETWEEN SEISMIC OBSERVATIONS AND THE FAULT COMPLEXITY OF THE 1995 HYOGOKEN-NAMBU EARTHQUAKE

Kiyoshi YOMOGIDA
Department of Earth and Planetary Systems Science, Faculty of Science, University of Hiroshima, Higashi-Hiroshima 739, Japan
and
Takashi NAKATA
Department of Geography, Faculty of Letters, University of Hiroshima, Higashi-Hiroshima 739, Japan

(Received 23 February 1995 and in revised form 8 May, 1995)

Abstract

We investigated how surface fault breaks are related to seismic records of the 1995 Hyogoken-nambu earthquake. Distinct surface fault breaks present along the Nojima fault in northwestern Awaji Island have a total length of nearly 9 km and a maximum right-lateral slip of l.9 m. The aftershock distribution agrees well with both this fault trace and minor surface breaks seen in the northern tip of Awaji Island and near Suma-ura Park in the west of Kobe. The straight and long fault slips in Awaji Island account for a subevent of large moment release retrieved by teleseismic studies in contrast to the small moment release in Kobe for which no large surface faultings are reported. Broadband P wave seismograms in Japan are consistent with simple bilateral fault ruptures from the epicenter near the Akashi Strait, and the part of the waveforms corresponding to the rupture along the Nojima fault agrees with the observed fault-slip distribution of a horizontal scale of less than 1 km. High-frequency seismic-wave radiation in Kobe may be due to complex faultings as represented by the collection of small cracks partly observed on the surface.

Key words

surface faulting, aftershock distribution, local broadband seismogram, slip distribution, fault complexity