| 2018年2月6日花莲M_W6.4地震近场地震动方向性效应 |
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| 引用本文： | 安昭,谢俊举,李小军,温增平.2018年2月6日花莲M_W6.4地震近场地震动方向性效应[J].地球物理学报,2019,62(12):4658-4672. |
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| 作者姓名： | 安昭 谢俊举 李小军 温增平 |
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| 作者单位： | 1. 中国地震局地球物理研究所, 北京 100081;2. 中国地震风险与保险实验室, 北京 100081;3. 北京工业大学建筑工程学院, 北京 100124 |
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| 基金项目： | 国家重点研发计划（2017YFC1500405），国家自然基金项目（51578513，51639006，51738001）资助. |
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| 摘 要： | 利用中国台湾省内222个强震动台站以及Palert地震预警系统520个台站所观测的三分量加速度记录,研究此次花莲M_W6.4地震近场强地震动空间分布和衰减特征,将观测结果与美国NGA-West2地震动经验预测模型进行对比,揭示此次台湾花莲地震近场地震动的长周期特点,基于回归残差分析研究地震动峰值加速度(PGA)、峰值速度(PGV)和不同周期地震动的空间分布差异,定量考察近场地震动的方向性效应.研究结果表明:(1)整体上此次地震的近场PGV观测值和周期1.0s以上的长周期加速度谱值与美国NGA-West2地震动预测模型结果接近,PGA观测值和周期小于1.0s的加速度反应谱略低于预测模型结果.从空间分布来看,周期1.0s以上的长周期地震动在断层的不同方位有系统性差异,在破裂传播前方(震中西南方位),周期大于1.0s时的反应谱明显高于美国NGA-West2地震动经验预测模型,在破裂传播后方(震中东北方位),周期大于1.0s时的反应谱低于经验预测模型,表明此次地震近场地震动具有显著的方向性效应.(2)破裂传播的方向性效应主要影响周期超过1.0s的长周期,而对PGA以及周期小于1.0s的短周期地震动影响较弱.在破裂传播前方,周期1.0～10.0s的加速度反应谱值被增强到整体观测平均水平的1.16～1.52倍;在破裂传播后方,周期1.0～10.0s的加速度反应谱值被减弱到整体观测平均水平的0.36～0.70倍.(3)此次地震破裂方向性效应的影响表现出明显的窄带效应,破裂方向性的影响(包括破裂传播前方的增强作用和破裂传播后方的减弱作用)在周期T=3.0s时达到最大,在该周期破裂传播前方的增强系数为1.52,破裂传播后方的减弱系数为0.36.从周期T=3.0s到10.0s,破裂方向性效应的影响随周期增大总体上呈减弱趋势,这与2016年日本熊本M_W7.0地震破裂方向性效应的影响特点显著不同.
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| 关 键 词： | 花莲地震 长周期 近断层地震动 方向性效应 空间分布 |
| 收稿时间： | 2018-09-30 |
Directivity effects on strong ground motion from the February 6, 2018 MW6.4 Hualien earthquake |
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| AN Zhao,XIE JunJu,LI XiaoJun,WEN ZengPing.Directivity effects on strong ground motion from the February 6, 2018 MW6.4 Hualien earthquake[J].Chinese Journal of Geophysics,2019,62(12):4658-4672. |
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| Authors: | AN Zhao XIE JunJu LI XiaoJun WEN ZengPing |
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| Institution: | 1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China;2. China Earthquake Hazard and Insurance Research Laboratory, Beijing 100081, China;3. College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100124, China |
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| Abstract: | Using three-component acceleration records from 222 strong motion stations of Taiwan province, China and 520 stations of Palert Earthquake Early Warning System, we investigate spatial variability and attenuation characteristics of observed near-field strong ground motion during the Hualien MW6.4 earthquake, and compare the observation with NGA-West2 prediction models. We reveal the characteristics of long-period motions during this event and quantitatively analyze the directional effects on strong motion based on residual analysis. Following conclusion can be made based on our study:(1) overall observations at PGV and long-period spectral accelerations above period 1.0 s show good coincidence with the NGA-West2 prediction models, while the PGA observations and acceleration response spectra below period 1.0 s are slightly lower than those of the prediction models. Long-period motions above period 1.0 s are systematically biased by the azimuth in terms of spatial distribution. In the rupture forward (South-west of epicenter), observed spectral accelerations above period 1.0 s are much higher than the NGA-West2 prediction models, while lower than the NGA-West2 prediction models in the backward (North-east of epicenter). (2) The rupture directivity mainly affects the long-period motions above period 1.0 s and the effects on PGA and short-period motions are relatively weak. The ground motions right ahead of the rupture forward at period 1.0~10.0 s are strongly amplified and are 1.16~1.52 times of the average level. Observed ground motions in the backward at period 1.0~10.0 s are reduced to 0.36~0.70 times of the average level. (3)The rupture directivity during the Hualien earthquake shows clear narrow-band effect. The influence of the rupture directivity including the amplification effects in the forward and de-amplification effects in the backward reaches its maximum values at the period T=3.0 s. The maximum amplification and de-amplification coefficients are 1.52 and 0.36 respectively. From the period 3.0 s to 10.0 s, the influence of rupture directivity gradually weakens with the increase of period on the whole, which is significantly different from the characteristics of the rupture directivity effects during the 2016 Kumamoto MW7.0 earthquake in Japan. |
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| Keywords: | Hualien earthquake Long-period Near-fault ground motion Directivity Spatial distribution |
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