青藏高原地区的p波走时与上地幔结构

TRAVEL TIME OF P-WAVE AND UPPER MANTLE STRUCTURE IN THE QINGHAI-XIZANG PLATEAU REGION

摘要:

本文利用天然地震资料,研究了青藏高原及其邻区的P波走时特征。从2°到26°的走时可以近似用三段直线来描述,视速度在10°和19°附近有明显的变化。推断的上地慢结构表明:高原上地慢顶部属于岩石层范畴,P波速度为8.11±0.04公里/秒:腾冲地区存在低速层,其速度为7.59±0.09公里/秒,深度在40公里至170公里之间;"20°间断面"的深度在450~500公里,界面下的速度约为9.9公里/秒;从M界面至"20°间断面"之间的P波速度是随深度的增加而增加的。此外,还对本文结果的构造物理意义进行讨论。

Abstract:

Using the data of natural earthquakes, we have studied the characteristics of P-wave travel time in Qinghai-Xizang plateau and its vicinity. From 2° to 26°, travel time of p-wave could be approximately described by three sections of straight line, there are remarkable changes for apparent velocities near 10 and 19° Inferred upper mantle structure shows:
(1)The P-wave velocity in the uppermost part of the mantle beneath the plateau is 8.11±0.04 km/sec;
(2)In the Tengchong(腾冲)district, there exists a low-velocity layer with a p-wave velocity of 7.59±0.09km/sec. The depth of the low velocity layer is between 40km and 170km;
(3)The depth of "20° discontinuity" is 450-500km, and the P wave velocity beneath it is about 9.9km/sec;
(4)P-wave velocities increase, with depth from Moho towards "20± discontinuity".
Besides, we have discussed the tectonophysical implications of the results in this paper.