A Study on Characteristics of Strong Ground Motions from the 2003 Tokachi-oki Earthquake

2003年十胜大地震强地震动特征研究

• 批准号: 16310120
• 负责人: SASATANI Tsutomu
• 金额: $ 6.66万
• 依托单位: HOKKAIDO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2004
• 资助国家: 日本
• 起止时间: 2004 至 2006
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-16310120/
• 关键词: 2003 Tokachi-oki Earthquake; Long-period seismic wave; Non-linear soil response; Velocity response; Source effect; Propagation path effect; Basin surface wave; attenuation relationship; 地下構造調査; 最大地動速度; 微動アレー観測; 非線形地震応答; 最大地動加速度; 計測震度; 速度応答スペ

The 2003 Tokachi-oki earthquake, a great interplate earthquake (Mw8.3), is the first M8 class earthquake in Japan since the dense strong-motion networks such as the K-NET and KiK-net have been deployed. We examine spatial distributions of velocity responses (damping factor h=0.05) with various natural periods for this earthquake by using the dense strong-motion network data. The short-period (T=0.1sec; T=natural period) velocity response distribution shows a typical feature for subduction-zone earthquakes; the high response values are observed along the Pacific coast of north Japan. This feature is explained by the S-wave attenuation structure beneath north Japan; that is, the path effect. On the other hand, the long-period (T=20sec) velocity response distribution shows a peculiar feature: at comparable distance, the response values in the northern part of the epicenter are higher than those in the south-western part. This peculiar feature is mainly explained by the source effect; the radiation pattern of long-period Rayleigh waves.We find various types of the site effects. A remarkable one is excitation of long-period basin surface-waves at large plains with thick sedimentary layers. The other remarkable one is nonlinear site response. We find mild nonlinear site response at a soft soil site located on flood plain deposits; the nonlinearity is confirmed by comparing the transfer functions for weak and strong motions using the downhole array data. The distinctive nonlinearity is also observed at a not-so-soft soil site located on reclaimed land during the largest aftershock; the accelerogram shows a spiky waveform.

2003年的德立树大地震（Mw8.3级）是自部署密集强震台网（K-NET）和KiK-net等强震台网以来，日本发生的第一次M8级地震。利用密集强震台网资料，研究了该地震不同自然周期的速度响应（阻尼因子h=0.05）的空间分布。短周期（T=0.1s， T=自然周期）速度响应分布是俯冲带地震的典型特征；在日本北部太平洋沿岸观测到高响应值。这种特征可以用日本北部的s波衰减结构来解释；这就是路径效应。另一方面，长周期（T=20sec）速度响应分布表现出一个奇特的特征：在相当距离下，震中北部的响应值高于西南部。这种奇特的特征主要是由源效应来解释的；长周期瑞利波的辐射模式。我们发现了不同类型的场地效应。其中最显著的是在厚沉积层的大平原上对长周期盆地表面波的激发。另一个值得注意的是非线性场地响应。在河漫滩沉积物上的软土场地上发现了轻微的非线性场地响应；利用井下阵列数据对比弱运动和强运动的传递函数，证实了非线性。在最大的余震期间，位于填海土地上的非软土场地也观察到明显的非线性；加速度图显示出尖尖的波形。