Monday, 12 March 2012

1995 Kobe Quake

January 17, 1995, M 7.2

The Southern Hyogo Prefecture Earthquake occurred on the Rokko-Awajishima fault zone that stretches from the Hanshin area of southern Hyogo Prefecture to Awajishima Island. During this earthquake, seismic intensity 6 in JMA scale was observed at the Kobe Marine Observatory and the Sumoto Weather Station. Field investigation have shown, however, that an area from part of the Awajishima Island to Kobe and Takarazuka corresponded to a seismic intensity of 7 in JMA scale. Seismic intensity 5 in JMA scale was observed in Kyoto, Hikone, and Toyooka, while ground motion corresponding to a seismic intensity of 5 in JMA scale was observed in Osaka, depending on the ground conditions (Fig.7-13, Fig.7-14). In addition to many wooden houses and concrete buildings, rail and highway lines collapsed, including those for expressways and the Shinkansen. The damage was extremely severe, totaling 6,427 dead and missing, more than 40,000 injured, more than 110,000 houses completely collapsed, and 285 fires (as of December 26, 1996) (Fig.7-15). The earthquake occurred in the early morning; thus, many of the deaths were the result of collapsing houses or fires. Harbor facilities were also damaged as a result of liquefaction, and the rains after the earthquake caused landslides as well as other damage. The damage caused by this earthquake is referred to as the Great Hanshin-Awaji Earthquake Disaster.

Slipping of the earth's surface at the Nojima fault (Nozima fault) on Awajishima Island resulted from this earthquake (Fig.7-16). The southeastern side of Nojima fault rose a maximum of 1.4 m to the northwest, and slipped a maximum of 2.1 m to the southwest. Observation of crustal deformations during this earthquake show that the area surrounding the focal region was compressed in an east-west direction and that the southeastern side of the Nojima fault rose to the northwest (Fig.7-17). It was also determined that the northwest side of the focal region rose to the southeast in the Hanshin area, in contrast to the uplift on Awajishima Island. These deformation suggest that the area was subjected to compression in an east-west direction. This is in rough conformity with the topography of the area and previously known crustal movements. No large-scale movement occurred in the Hanshin area, however. It is difficult to believe that the Rokko Mountain (Rokko Santi) area was formed by repeated earthquakes of the same type as the Southern Hyogo Prefecture Earthquake, so we must conclude a different type of earthquake was responsible for the formation of this area. For example, it has been suggested Linkthat the 1596 Keicho Fushimi Earthquake (M 7 1/2) might be this type of event.

Many felt and unfelt aftershocks occurred after the Southern Hyogo Prefecture Earthquake. This aftershock activity gradually diminished, with the largest aftershock (M 5.4) occurring about two hours after the main shock (Fig.7-18, Fig.7-19).

A Special Measures Law on Earthquake Disaster Prevention was promulgated after the occurrence of this earthquake, and the Headquarters for Earthquake Research Promotion was established.

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