報告書番号

U93028

タイトル（和文）

１９９３年北海道南西沖地震被害調査報告

タイトル（英文）

CHARACTERISTICS AND DAMAGE INVESTIGATION OF THE 1993 HOKKAIDO NANSEI-OKI EARTHQUAKE

概要 （図表や脚注は「報告書全文」に掲載しております）

北海道南西沖地震（Ｍ７．８）では，奥尻島をはじめ，瀬棚町，大成町，長万部町等北海道南西部地域において，大津波や崖崩れ，液状化により，港湾施設，道路，木造家屋，トンネル，配電設備，水道施設などに甚大な被害を及ぼした。当所では，耐震，地質，水理，土質の専門家により，津波調査，余震観測調査，地盤や土木構造物の被害調査を行った。今回の地震は北海道日本海沿岸では最大規模のものであり，地震後に発生した津波は奥尻島で今世紀国内最大の痕跡高（約３０ｍ）を記録した。又，当所の余震観測により奥尻島の岩盤観測点で約１９０ｇａｌ（Ｍ６．５）の最大水平加速度を得た。地震被害の特徴としては，津波斜面崩壊，地盤の液状化により道路や港湾施設が大きな被害を受けた事や，過去に例の少ない礫混じりの火山性堆積物が液状化した事等があげられる。電力施設では，配電施設の被害があったが，早急や復旧がなされ大きな支障はなかった。

概要 （英文）

ON 12 JULY 1993,THE SOUTHERN PART OF HOKKAIDO AND ITS ADJACENT OKUSHIRI ISLAND WERE SHAKEN BY THE HOKKAIDO NANSEI-OKI EARTHQUAKE(MAGNITUDE 7.8)RESULTING IN GREAT GROUND DAMAGE INCLUDING LANDSLIDES AND LIQUEFACTION.THE TSUNAMI ACCOMPANYING THE EARTHQUAKE CAUSED HEAVY DAMAGE TO OKUSHIRI ISLAND AND THE WEST COAST OF HOKKAIDO.INVESTIGATION OF THE DAMAGE CAUSED BY THE EARTHQUAKE MOTION AND THE TSUNAMIAS WELL AS AFTERSHOCK OBSERVATION WERE CARRIED OUT BY A CRIEPI TEAM CONSISING OF EARTHQUAKE ENGINEERS,SOIL ENGINEERS,GEOLOGISTS AND COASTAL ENGINEERS.THE RESULTS SUGGEST THAT:(1)THE MAXMUM RUN-UP HEIGHT OF THE TSUNAMI WAS ABOUT 30M,WHICH WAS RECORDED AT THE OKUSHIRI ISLAND.THIS IS THE HIGHEST VALUE THIS CENTURY.(2)MAXIMUM AFTERSHOCK RECORD WITH A MAXIMUM ACCELERATION OF ABOUT 190 GAL WAS MEASURED BY CRIEPI S AFTERSHOCK OBSERVATION SYSTEM SET UP OKUSHIRI ISLAND.(3)MANY SLOPES FAILED BEHIND OKUSHIRI PORT.(4)MOST STRUCTURES DAMAGED BY ERTHQUAKE MOTION,SUCH AS ROADS AND HOUSES,WERE CONSTRUCTED ON SOFT ALLUVIAL DEPOSITS,SUCH AS AT OSHAMANABE TOWN,KITAHIYAMA TOWN,AND KUN-NUI TOWN.THE MAIN CAUSE MAY BE LIQUEFACTION OF LOOSE SAND DEPOSITS.(5)VOLCANIC COARSE-GRAINED SOIL LIQUEFIED OVER A WIDE RANGE AT AKAI-GAWA DISTRICT IN MORI TOWN NEAR LAKE OHNUMA RASULTING IN DIFFERENTIAL SETTLEMENT OF HOUSES.SINCE GRAVELLY-SOIL RARELY LIQUEFIES,FURTHER RESEARCH IS NEEDED TO INVESTIGATE GENERATION OF LIQUEFACTION IN GRAVELLY DEPOSITS.(6)AL THOUGH THERE WAS SOME DAMAGE TOELECTRIC POWER DISTRIBUTION FACILITIES,POWER WAS RESTORED PROMPTLY.

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