High-frequency seismic wave propagation beneath the Indian Shield, Himalayan Arc, Tibetan Plateau and surrounding regions: high uppermost mantle velocities and efficient Sn propagation beneath Tibet
High-frequency seismic wave propagation beneath the Indian Shield, Himalayan Arc, Tibetan Plateau and surrounding regions: high uppermost mantle velocities and efficient Sn propagation beneath Tibet
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DOI：
10.1111/j.1365-246x.1983.tb02826.x
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发表时间：
1983-03
影响因子：
2.8
通讯作者：
J. Ni;M. Barazangi
中科院分区：
文献类型：
--
作者：
J. Ni;M. Barazangi
摘要本文报道了在中亚、西藏和印度等几个地区的高频P_i、P_i、S、L_i波（0.5 ~ 2 Hz）和P_i、P_g、S_i波速度的区域传播特征。一个重要的结果是，S波在青藏高原大部分地区的上地幔中有效地传播。此外，在西藏的S，传输不受跨越许多自然地理和构造边界，如印度-藏布缝合线。这些观测结果与稳定大陆和屏蔽区的S传播观测结果相似。在稳定的塔里木盆地、沿着天山和喜马拉雅山脉以及印度地盾也观察到有效的S1传播。青藏高原北方（Chang Thang）的S_（1-x）强度衰减较强。这种强烈的衰减表明，在该地区下方的上地幔中存在低Q带。这一解释得到了最近在Chang Thang Chae广泛的第四纪到现代玄武岩火山活动的地质观测的支持。在塔里木盆地、印度地盾和沿着喜马拉雅山走向传播。L，也被观察到，虽然不太明显，为道路穿越天山，喀喇昆仑和帕米尔复杂的结构的大部分。L，是没有观察到的路径穿越青藏高原。在西藏的L_1传播无效区的南部边界位于印度-西藏缝合带附近。缺乏L，可以归因于西藏地壳内的衰减;然而，其他的可能性，包括在西藏的边缘结构不连续的散射是同样合理的。Pg和S是震中距小于4”的短周期WWSSN地震图上最显著的特征。确定喜马拉雅山地区的Pg视速度为6.0？0.2 km s-l.在青藏高原上地幔中至少有50%路径的P波和S波的视速度分别为8.42 π：0.10和4.73 π：0.06 km·s-1。这些速度与喜马拉雅山（Pi = 8.45 f 0.08 km s-1，Si = 4.74 + 0.05 km s-1）和印度地盾（Pi = 8.40 0.08 km s-1，Si = 4.69 k 0.04 km s-1）的速度十分相似。P、
Summary. This paper reports the regional propagation characteristics of high-frequhcy P,, P,, S, and L, waves (0.5 to 2Hz) and P,, Pg and S, velocities for several regions in Central Asia, Tibet and India. An important result is that S, waves propagate efficiently in the uppermost mantle beneath most of the Tibetan Plateau. Also, S, transmission in Tibet is not affected by crossing many physiographic and tectonic boundaries, such as the Indus-Tsangpo suture. These observations are similar to observations of S, propagation in stable continental and shield regions. Efficient S, propagation is also observed across the stable Tarim Basin, along the Tien Shan and Himalayan Mountains and across the Indian Shield. S, is strongly attenuated across the northern Tibetan Plateau (Chang Thang terrane). Such strong attenuation suggests the existence of a low-Q zone in the uppermost mantle beneath that region. This interpretation is supported by recent geological observations of widespread Quaternary to Recent basaltic volcanism in the Chang Thang terrane. L, propagates efficiently across the Tarim Basin, the Indian Shield and along the strike of the Himalayan Mountains. L, is also observed, although less pronounced, for paths crossing large portions of the complicated structures of Tien Shan, Karakoram and Pamir. L, is not observed for paths crossing the Tibetan Plateau. The southern boundary of the region of inefficient L, propagation in Tibet lies in the vicinity of the Indus-Tsangpo suture zone. The lack of L, can be attributed to attenuation within the Tibetan crust; however, other possibilities including scattering by structural discontinuities at the margins of Tibet are equally plausible. Pg and S, are the most prominent features on most short-period WWSSN seismograms at epicentral distances less than about 4". Apparent Pg velocity determined for the area of the Himalayan Mountains is 6.0 ? 0.2 km s-l. Apparent velocities of P, and S, waves that have at least 50 per cent of their paths in the uppermost mantle beneath the Tibetan Plateau are 8.42 It: 0.10 and 4.73 f 0.06 km s-', respectively. These velocities are quite similar to those determined for the Himalayan Mountains (P, = 8.45 f 0.08 km s-I, S, = 4.74 _+ 0.05 km s-') and the Indian Shield (P, = 8.40 0.08 km s-', S, = 4.69 k 0.04 km s-'). P,