1995年兵庫県南部地震による西宮・大阪地域の震害と地盤構造 Damage Caused by the 1995 Hyogo-ken Nanbu Earthquake and the Geologic Structure of Nishinomiya and the Osaka area
The 1995 Hyogo-ken Nanbu Earthquake caused serious damage in the Hanshin and Awaji areas. Ground failures, such as liquefaction and gravity slides widely occurred in coastal zones and inland areas. Many of these areas include man-made land.<br>The areas that sustained the most serious liquefaction damage were reclaimed lands along the margin of the Osaka Bay, including Port-Island and Rokko-Island. Comparison between old and new topographical maps shows that wide areas damaged by liquefaction correspond to man-made land reclaimed since the Edo Era (about 1680). In particular, land reclaimed since 1945 under-went major subsidence settling up to about 50cm.<br>In the inland parts of Nishinomiya City and the surrounding area, some sites of liquefaction, lateral spreading, and ground subsidence damage were confirmed. These sites are recent alluvial valleys and man-made lands created by reclaiming irrigation ponds. Many public and educational institutions are built on reclaimed ponds. Many of these buildings which are specified as places of refuge at times of disaster were damaged and did not serve their purpose.<br>Some slopes on hilly lands collapsed under this earthquake's shock and gravity. Many of these slope failures occurred in residential areas built on filled alluvial valleys. At Nikawa-yurino-cho Town in Nishinomiya City, a big slope failure occurred behind the residential area and killed 34 people. This man-made slope has about a 20°dip. The natural terrace cliffs and slopes of granitic rocks around this area are steeper than this slope, but this slope was the weakest one in the earthquake. These man-made lands, like coastal reclaimed land, are filled with loose sandy materials and have a high ground water table.<br>The Osaka area, including Amagasaki, Itami, Toyonaka, Osaka, and Sakai cities and located 30 to 50km east of the epicenter, was widely damaged by liquefaction and the intense ground motion. Liquefaction damage in the inland area occurred along the old river channel. The old channels were also filled up with loose materials and have a high ground water table due to permeation of surface water.<br>Damage to houses in the Osaka area was concentrated along the margin of the basin divided by faults. In the uplifted side area, damage was slight. This distribution of damage suggests that the seismic waves were amplified and focused by the Quaternary layer and its geologic structure in the Osaka Plain.
第四紀研究 35(3), 179-188, 1996-07-31
Japan Association for Quaternary Research