The Miyagi-Ken-Oki Earthquake on the 12th of June, 1978 causes severe disaster in Sendai and its vicinity, and it gives many lessons on safety of residential site in and around city. Destroyed houses amount more than 700, and many other structures are broken. Most of them are in the alluvial plain or in the hill-land where newly-built housing estates have rapidly expanded. While originally built-up area of Sendai on the river terrace has little disaster. The characteristics of the disaster in the alluvial plain and the hill-land are as follows,
Alluvial plain
The damages or the acceleration of the earthquake motion are closely related to the microtopography or the thickness of uppermost clayey deposits. Each topography, such as beach ridge, natural levee, back marsh etc. has certain range of the accelaration estimated by overturning of gravestones (Fig. 2). Due to strong motion, many houses are destroyed, and most of them are concentrated on the artificial ground which have been formed on back marsh or abandoned channel (Fig. 6). In addition to such subsoil condition, the damages depend on house type. Houses with big and heavy roof, such as traditional Japanese farmers' house, sustain grater damages than small houses.
Hill-land
Around Sendai, housing estates have been developed since 1960', modifying natural land form. These residential estates can be classified into three types, according to the extent and mode of modification of land form (Fig. 8). In the “A-type” housing estates, many cracks are observed along the boundary between artificial fill and cut. Damages of houses, water and gas pipes or other structures appear intensively along the cracks (Fig. 10). In the “C-type”, many cracks arise on artificial retaining walls, causing disastrous failures at places. The damage differs from estate to estate according to the above mentioned modification types, and the variance of the degree of the damages are explained by the difference in the distribution of the acceleration estimated by overturning furnitures (Fig. 12).
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