報告書番号

N13007

タイトル（和文）

物理探査・室内試験に基づく2004年留萌支庁南部の地震によるK-NET港町観測点 (HKD020)の基盤地震動とサイト特性評価

タイトル（英文）

Estimation of basement earthquake motion and site characteristics at HKD020 during the 2004 Rumoi earthquake based on geophysical exploration and laboratory tests

概要 （図表や脚注は「報告書全文」に掲載しております）

2004年12月14日午後2時56分頃に発生した北海道留萌支庁南部を震源とする地震（M6.1, 深さ9 km）では，震央距離8.6 kmのK-NET港町観測点（以下，HKD020地点と称す）で最大加速度1127 cm/s2（最大速度約74cm/s）を観測した．この地震でのHKD020地点における高加速度，高速度の地表観測記録に対するサイト特性の影響を明らかにするため，当該地点にて物理探査と地盤の室内試験を実施した．物理探査としてはボーリング孔を用いたPS検層，室内試験については強震時のサイト特性に影響を及ぼす地盤の非線形特性（動的変形特性）の測定を現地にて採取した地盤試料に対して行った．本報告書は，現状までに得られた調査・試験結果，およびそれらの結果に基づき実施した基盤地震動の推計とサイト特性の影響評価についての検討結果について，速報的にとりまとめたものである．

概要 （英文）

During the 2004 Rumoi earthquake (M6.1, Depth 9km), earthquake ground motion with the peak ground acceleration (PGA) of 1,127 cm/s/s and the peak ground velocity (PGV) of 74 cm/s was recorded at HKD020 (K-NET by NIED). In order to clarify the effect of site amplification factor induced subsurface structure and nonlinear dynamic property of soils on such a very high-level acceleration by moderate-size earthquake, we conducted PS-logging ranging from surface to GL-300m and laboratory test of soils (< GL-6m) at HKD020. A new subsurface model for earthquake ground-motion estimation at HKD020 was constructed based on PS-logging data and previous surface wave dispersion curve. The basement earthquake motion at HKD020 during the 2004 Rumoi earthquake was estimated by 1D equivalent linearized method using the new subsurface model and dynamic property of soils. The PGA of the estimated basement earthquake motion was 585 cm/s2 that was approximately 50 percent smaller than the surface observed record. In contrast, the PGV was 62 cm/s that was only approximately 20 percent smaller than the surface observed record. These results demonstrated that the high-level acceleration recorded at HKD020 during the 2004 Rumoi earthquake is considered to be strongly affected by site factor due to soil nonlinearity.

報告者

キーワード