Surface Fault Ruptures Associated with the 1995 Hyogoken-Nanbu Earthquake.

Abstract

Distinctive ruptures of the surface faulting which generated the destructive 1995 Hyogoken-Nanbu Earthquake (Ms=7.2) appeared along the Nojima fault, an active fault on the northwestern coast of Awaji island, Japan. The surface fault ruptures in Awaji island extend southwestward continuously for about 9km from Easki near the epicenter to Toshima in Hokudan town, and caused prominent right-latearl offsets of 1.9m at maximum on roads, paddy dikes with vertical displacement of 1.2m at maximum, while no large surface faulting has been reported in Kobe where major damage and casualties have appeared. Most of the surface ruptures follow along the pre-existing active fault traces of the Nojima fault. The ruptures are generally arranged in left-stepping echelon, and local extensional and compressional jog forms such as trenches, mole tracks, buldges are sometimes related to changes in fault strikes. The earthquake fault seems to have propagated bilaterally northeastward and southwestward from the hypocenter in the Straits of Akashi near the major jog of the earthquake fault system. The source process of the earthquake deduced from the slip distribution along the earthquake fault in Awaji island well explains near-field P-waveforms of broad-band seismometers for early part in about 4 seconds. The later part of much larger amplitude should attribute to the northeast fault ruptures toward Kobe.

Minute Locating of Faulting beneath Kobe and the Waveform Inversion of the Source Process during the 1995 Hyogo-ken Nanbu, Japan, Earthquake Using Strong Ground Motion Records.

“…The large slips in the shallowest grids in the second subevent area are consistent with the surface breaks along the Nojima fault. Their rake angles are also consistent with the southeast-side up trend along the Nojima fault (Nakata and Yomogida, 1995). The rise time near the surface in the second subevent area is long (about 4s, see Fig.…”

Simultaneous Inversion of Geodetic and Strong Motion Data for the Source-Process of the Hyogo-ken Nanbu, Japan, Earthquake.

“…The arrow shows the slip direction and amplitude of the southeastern block relative to the northwestern block. surface rupture is observed on the Nojima fault (e.g., Nakata and Yomogida, 1995). Since few aftershocks occur along this fault (Fig.…”

Rupture Process of the Kobe, Japan, Earthquake of Jan. 17, 1995, Determined from Teleseismic Body Waves.

“…A surface rupture was observed over nearly 10 km of the Nojima Fault on Awaji Island, while no distinct surface fault was found near the Kobe area on the mainland (Nakata et al, 1995 tion is that the most heavily damaged zone in Kobe City is slightly shifted to the south from the aftershock zone (Shimamoto, 1995). The questions are:(1) Did the buried fault break as far NE as the Kobe area?…”

“…Then, assuming that the rupture velocity(v) is 3 km/s, rigidity(j) is 30 GPa, and aspect ratio(length/width) is 2, we estimated the fault area, dislocation, and stress drop for the individual subevents. The results are given in (Nakata et al, 1995).…”