RUPTURE DIRECTIVITY AND SHORT-PERIOD SPECTRAL LEVEL OF MODERATE-SIZED INTRASLAB AND INTERPLATE EARTHQUAKES OFF THE COAST OF FUKUSHIMA PREFECTURE; [福島県沖の中規模スラブ内地震とプレート境界地震の破壊伝播効果と短周期レベル]

We estimated rupture directions and directivity effects of moderate-sized intraslab and interplate earthquakes off coast of Fukushima prefecture using S-net, K-NET and KiK-net records. Source spectral ratio of each earthquake to a reference earthquake observed at the same station is modeled by using the dependency of amplitude in the frequency higher than corner frequencies on azimuths assuming unilateral rupture. All four intraslab earthquakes are estimated to rupture to updip which is the direction to west toward land. Therefore, their short-period spectral level estimated using only KiK-net records are much larger than those estimated using records at all stations. © 2022 Architectural Institute of Japan. All rights reserved.