S Wave Anelastic Attenuation of Shallow Sediments in Mainland China
S Wave Anelastic Attenuation of Shallow Sediments in Mainland China
复制标题
中国大陆浅层沉积物的S波滞弹性衰减
DOI：
10.1029/2020ea001348
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发表时间：
2020-10-01
影响因子：
3.1
通讯作者：
Li, Zhiwei
中科院分区：
文献类型：
--
作者：
Tian, Wen;Li, Zhiwei
频率相关的滞弹性衰减是在反演地震数据时必须考虑的事实。中国大陆地震频发的大型沉积盆地的浅层衰减特征尚不清楚，这阻碍了强地面运动的研究。分布在这些地区的钻孔地震仪提供了关于浅层结构的信息。本文利用近震钻孔地震记录中的直达波和地表反射波相，计算了中国大陆浅层沉积物中S波的平均滞弹性衰减。根据103个钻孔台站记录的地震记录，应用多时间窗分析方法，估计了钻孔地震计上方浅层沉积物的衰减值和岩性。我们认为，Q（S）（-1）值通常从1 Hz时的0.04-0.50下降到10 Hz时的0.01-0.05。我们得到了衰减，速度和深度之间的经验关系，并发现，以上和以下的深度为400米的衰减的主导机制可能是不同的，由于沉积物的成分和规模。通过分析时差变化和Q（S）（-1）差异，对某些钻孔深度和相应的V-s值进行了校正。简明语言总结地震波在介质中传播时，能量会因内部摩擦和沿传播路径沿着的不均匀散射而消散。衰减是地球介质的一个重要特征。强衰减对强地面运动的预测有重要影响，特别是对于沉积盆地。此外，与速度相比，衰减对由应力引起的岩石性质的变化更敏感。因此，了解中国大陆浅层沉积物的衰减是很重要的，中国大陆具有高地震活动性。通过发展地震台网，在中国建立了100多个钻孔台站。依靠这些地下台站记录的地震图，通过应用稳健可靠的分析方法，估计了钻孔地震计上方浅层沉积物的衰减和速度值以及岩性。我们还得到了衰减，速度和深度之间的经验关系。这些结果对强地面运动的预测是非常有用的。本研究采用的方法也可用于其他沉积盆地滞弹性衰减的评价。
Frequency-dependent anelastic attenuation is a fact that must be considered when inverting seismic data. The shallow attenuation characteristics of large sedimentary basins with frequent earthquakes in mainland China are still unclear, which hinders the study of strong ground motion. Borehole seismometers distributed in these areas provide information on shallow structures. In this study, the direct and surface-reflected phases in local earthquake borehole seismograms were extracted to calculate the average S wave anelastic attenuation of shallow sediments in mainland China. Relying on the seismograms recorded by 103 borehole stations, the attenuation values and lithologies of the shallow sediments above the borehole seismometers were estimated by applying a multi-time window analysis method. We suggested that the Q(S)(-1) values generally decrease from 0.04-0.50 at 1 Hz to 0.01-0.05 at 10 Hz. We obtained the empirical relationships among attenuation, velocity, and depth and found that the dominant mechanisms for attenuation above and below a depth of 400 m could be different due to sediment compositions and scales. Certain borehole depths and corresponding V-s values were corrected by analyzing the time difference variation and the Q(S)(-1) distinction.Plain Language Summary The energy of seismic waves propagating through a medium will dissipate due to internal friction and non-uniform scattering along the propagation path. Attenuation is an important feature of Earth's media. Strong attenuation has a significant influence on predictions of strong ground motion, especially for sedimentary basins. Moreover, compared to velocity, attenuation is more sensitive to changes in rock properties caused by stress. Therefore, it is important to understand the attenuation of shallow sediments in mainland China, which has high seismicity.More than 100 borehole stations have been established through the development of a seismic network in China. Relying on the seismograms recorded by these underground stations, the attenuation and velocity values and lithologies of the shallow sediments above the borehole seismometers were estimated by applying a robust and reliable analysis method. We also obtained the empirical relationships among attenuation, velocity, and depth. These results can be most useful in the prediction of strong ground motion. The method adopted in this study will also be useful for the evaluation of anelastic attenuation in other sedimentary basins.