Strong ground motion in the Kathmandu Valley during the 2015 Gorkha, Nepal, earthquake
Strong ground motion in the Kathmandu Valley during the 2015 Gorkha, Nepal, earthquake
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DOI：
10.1186/s40623-016-0383-7
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发表时间：
2016-01-26
影响因子：
3
通讯作者：
Sasatani, Tsutomu
中科院分区：
文献类型：
--
作者：
Takai, Nobuo;Shigefuji, Michiko;Sasatani, Tsutomu
2015年4月25日，尼泊尔中部喜马拉雅主逆冲断层沿线发生7.8级大地震。它是由印度板块在欧亚板块下方的碰撞造成的。震中位于加德满都西北80公里处的Gorkha地区附近，破裂从震中地区向东传播，穿过充满沉积物的加德满都山谷。这一事件造成8000多人死亡，大部分发生在加德满都和邻近地区。在这场毁灭性的地震中，我们在加德满都山谷的四个观测点(一个岩石点和三个沉积点)成功地观测到了强烈的地面运动。当观测到的峰值地震动加速度值小于利用地面运动预测方程得到的预测值时，观测到的峰值地面速度值略大于预测值。在岩石现场观测到的地面速度(KTP)显示出简单的速度脉冲，导致与永久构造偏移相关的单调阶跃位移。在沉积地点观测到的垂直地面速度与在岩石地点观测到的脉冲运动相同。相反，由于山谷响应，在三个沉积点观测到的水平地面速度和加速度具有较长的持续时间和明显的长周期振荡。水平谷响应的特征是放大幅度大(约10)，振荡时间延长。然而，它们的振荡的主要周期和包络形状在不同的地点是不同的，表明了一个复杂的盆地结构。最后，在速度反应谱的基础上，我们表明沉积场地上的水平长周期振动具有足够的破坏力来破坏自振周期为3~5个S的高层建筑。
On 25 April 2015, a large earthquake of Mw 7.8 occurred along the Main Himalayan Thrust fault in central Nepal. It was caused by a collision of the Indian Plate beneath the Eurasian Plate. The epicenter was near the Gorkha region, 80 km northwest of Kathmandu, and the rupture propagated toward east from the epicentral region passing through the sediment-filled Kathmandu Valley. This event resulted in over 8000 fatalities, mostly in Kathmandu and the adjacent districts. We succeeded in observing strong ground motions at our four observation sites (one rock site and three sedimentary sites) in the Kathmandu Valley during this devastating earthquake. While the observed peak ground acceleration values were smaller than the predicted ones that were derived from the use of a ground motion prediction equation, the observed peak ground velocity values were slightly larger than the predicted ones. The ground velocities observed at the rock site (KTP) showed a simple velocity pulse, resulting in monotonic-step displacements associated with the permanent tectonic offset. The vertical ground velocities observed at the sedimentary sites had the same pulse motions that were observed at the rock site. In contrast, the horizontal ground velocities as well as accelerations observed at three sedimentary sites showed long duration with conspicuous long-period oscillations, due to the valley response. The horizontal valley response was characterized by large amplification (about 10) and prolonged oscillations. However, the predominant period and envelope shape of their oscillations differed from site to site, indicating a complicated basin structure. Finally, on the basis of the velocity response spectra, we show that the horizontal long-period oscillations on the sedimentary sites had enough destructive power to damage high-rise buildings with natural periods of 3 to 5 s.