| 柴达木盆地东部地震地面运动放大效应 |
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| 引用本文： | 黄妍,陈彦阳,王彦宾.柴达木盆地东部地震地面运动放大效应[J].西北地震学报,2017,39(3):534-544. |
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| 作者姓名： | 黄妍 陈彦阳 王彦宾 |
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| 作者单位： | 北京大学地球与空间科学学院地球物理学系, 北京 100871,北京大学地球与空间科学学院地球物理学系, 北京 100871,北京大学地球与空间科学学院地球物理学系, 北京 100871 |
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| 基金项目： | 国家自然科学基金项目（41374046） |
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| 摘 要： | 柴达木盆地是青藏高原东北部大型断陷山间盆地,该地区的流动观测记录了2008年11月10日发生于大柴旦附近的M_W6.3地震。和附近的基岩上的记录相比,盆地内部的记录显示出非常显著的地面运动放大效应,表现为峰值速度的增大、持续时间的延长,其呈现出长持续时间的后续震相。傅里叶频谱分析表明盆地内部显著的后续震相的频率和直达波相比较低,地面质点运动轨迹图显示后续震相为面波运动特征。为了解释地面运动的差异,构建二维模型,通过交错网格高阶有限差分方法计算了地震波在盆地内部的传播过程,结果显示盆地内部低速层的存在造成直达波的放大以及多次反射与转换,盆地边缘结构造成的波的相干叠加产生了强烈的次生面波,其低频、大振幅、长持续时间的特征是盆地内部地面运动放大的主要原因。
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| 关 键 词： | 柴达木盆地 地震地面运动 沉积盆地 地震波传播 数值计算 |
| 收稿时间： | 2016/5/10 0:00:00 |
Amplification Effect of Seismic Ground Motion at the Eastern Part of Qaidam Basin |
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| HUANG Yan,CHEN Yan-yang and WANG Yan-bin.Amplification Effect of Seismic Ground Motion at the Eastern Part of Qaidam Basin[J].Northwestern Seismological Journal,2017,39(3):534-544. |
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| Authors: | HUANG Yan CHEN Yan-yang and WANG Yan-bin |
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| Institution: | Department of Geophysics, School of Earth and Space Sciences, Peking University, Beijing 100871, China,Department of Geophysics, School of Earth and Space Sciences, Peking University, Beijing 100871, China and Department of Geophysics, School of Earth and Space Sciences, Peking University, Beijing 100871, China |
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| Abstract: | Qaidam Basin is located at the Northeastern margin of Qinghai-Tibet plateau, which is the largest basin on the plateau. The thickness of the Quaternary and Tertiary sediments in the basin vary laterally and reach a maximum of 3,000 m and 8,000 m, respectively. The temporary seismic stations deployed by the INDEPTH IV project recorded three component seismograms of the November 10, 2008 Dachaidan MW6.3 earthquake, which occurred at the margin of Qaidam Basin. Analysis of seismograms at two stations, namely H01 and H02, which have similar epicentral distance and azimuth, show a significant difference. Station H01 is located at the bedrock around the basin and the H02 station is located inside the basin on the Quaternary sediments. Compared with the records at the H01 station, those at the H02 station show significant amplitude amplification, obvious duration extension, and very strong later phases. The amplification of the peak ground velocity reaches 2-3 times, and that for the later phases reaches up to 6 times. Fourier amplitude spectrum analysis for the seismograms show similar frequency range for the two stations. However, the later phases have a lower and concentrated frequency range. Horizontal ground particle motion at the H02 station for the later phases exhibit typical elliptical ground motion, which suggests that the later phases are surface waves. To investigate the mechanism of the ground motion amplification and strong later phases, two 2-dimensional (2D) cross sections through the hypocenter and two stations are constructed. Seismic wave propagation inside the two 2D models are calculated with the fourth-order staggered grid finite difference method. The size of the models is 210 km by 50 km. The model is discretized into 1,000 and 500 grids in the horizontal and vertical direction, respectively. Two-dimensional double-couple line sources are used in the modeling and the dominated period of the source time function is 1.5 s. Modeling results are analyzed with wavefield snapshots and synthetic seismograms. They show that the existence of a low-velocity sedimentary layer in the basin causes amplification of direct waves because of the changes of propagation direction in the basin. Multiple reflections and conversions occurred after the direct waves in the basin. At the edge of the basin, surface waves with large amplitude and low propagation velocity were generated by constructive interference between direct waves and their reflections and conversions. Comparing the observed and synthetic seismograms at the H01 and H02 stations show very similar characteristics. This suggests the existence of the low-velocity layer inside the basin caused the significant difference of observed ground motion at the H01 and H02 stations. The amplification of amplitude of direct waves at the H02 station resulted from the variation of propagation direction in the basin. Seismic phases between the direct waves represent their multiple reflections and conversions in the sedimentary layer. The large amplitude later phases with longer duration are surface waves generated at the basin edge by constructive interference between the direct waves and their reflections and conversions. Results of this study provide new observational examples for seismic ground motion amplification in the sedimentary basin and their possible mechanisms from numerical modeling. |
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| Keywords: | Qaidam basin seismic ground motion sedimentary basin seismic wave propagation numerical modeling |
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