| 講演要旨(和文) | | 2011年3月11日に発生した東北地方太平洋沖地震（Mw9.0）の余震観測を茨城県中部の東茨城台地で実施した．本震の断層面からの距離が近く、東茨城台地のやや南方に位置する鉾田（K-NETのIBR013）では、最大速度で70cm/sを超える強震動が観測された．そこで本観測では、K-NETなどの定常観測点が配備されていない地点を対象として東茨城台地及びその周辺地域に計1５の余震観測点を配置し、当該地域に於ける地震動の空間分布を把握することを目的とした．また、得られた地震記録の解析（地震動コーダを用いたH/Vスペクトル比）と連続微動記録の解析（地震波干渉法を適用した相間法）を通じて、当該地域の地下構造を理解することに努めた．地震動コーダのH/Vスペクトル比と連続微動記録から得られた微動の群速度の各観測点での傾向は特に太平洋沿岸から筑波山地に対してよく調和し、既存の地質情報とも一致した． |
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| | 講演要旨(英文) | | We performed the aftershock observation of off the Pacific Coast of Tohoku Earthquake (Mw9.0, March 11/2011) in the East Ibaraki Plateau of the middle part of Ibaraki Prefecture. Strong ground motions larger than the maximum velocity of 70 cm/sec were observed at Hokota (IBR013 of K-NET) located in the south from the East Ibaraki Plateau, due to a short distance from the fault plate of the main shock. In the observation, therefore, we distributed 15 stations in and around the East Ibaraki Plateau where the permanent observation stations such as K-NET have not been installed, to understand spatial distributions of earthquake ground motions in this area. We also aimed to understand the underground structures, by both analyses of H/V spectral ratios of Coda waves for earthquake recordings and cross-correlations using the seismic interferometry method for continuous microtremors recordings. The tendency of H/V spectral ratios of Coda waves and group velocities of microtremors was matched well, especially for the area from the seacoast of Pacific to the Tsukuba Mountains. Also, these results were in good agreements with the existent geological data. |
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