Seismic P-wave tomography in eastern Tibet: Formation of the rifts

为更好学习在裂缝和深结构之间的关系，在东方西藏下面的详细 P 波浪速度结构从由 51 个便携式的车站记录的 169 个 teleseismic 事件用 4767 到达时间被建模。在通过模型的水平片，一个突出的低速度的异例从表面在裂缝下面被检测到 250 km 的深度；这在垂直的片延长到 400 km 的深度。这个低速度的异例作为上面的披风 upwelling 被解释。做的观察为纵贯的 trending 裂缝的形成提供地震证据。低速度的异例的东方，一个清楚的高速度的异例在 40 和 200 km 的深度之间被发现。由于它的浅深度，我们建议它从古老的大陆人闭合而非印度板由材料组成。从 250 ～ 400 km 的深度，一个高速度的异例出现到 Jiali 差错的南方。这个异例可以对应于在喜玛拉雅的块下面从表面分开了的印度板的北边。我们建议印度板 underthrusts 不在东方西藏比 Jiali 差错推进。

For better studying the relationship between the rifts and deep structure, a detailed P-wave velocity structure under eastern Tibet has been modeled using 4767 arrival times from 169 teleseismic events recorded by 51 portable stations. In horizontal slices through the model, a prominent low-velocity anomaly was detected under the rifts from the surface to a depth of -250 km; this extends to a depth of -400 km in the vertical slice. This low-velocity anomaly is interpreted as an upper mantle upwelling. The observations made provide seismic evidence for the formation of north-south trending rifts. East of the low-velocity anomaly, a clear high-velocity anomaly is found between depths of 40 and 200 km. Due to its shallow depth, we suggest that it consists of materials from an ancient continental closure rather than the Indian Plate. From depths of 250 to 400 km, a high-velocity anomaly appears to the south of the Jiali Fault. This anomaly may correspond to the northern edge of the Indian Plate that detached from the surface under the Himalayan block. We suggest that the Indian Plate underthrusts no further than the Jiali Fault in eastern Tibet.