青藏高原东北缘远震P波走时层析成像研究

利用青藏高原东北缘地区固定地震台网2010年4月至2015年3月期间记录的远震事件，采用多道波形互相关方法（Multi-Channel Cross-Correlation）拾取了10697个有效P波相对走时残差数据，进而采用FMTT （Fast Marching Teleseismic Tomography）方法获得了青藏高原东北缘上地幔400 km深度范围内的P波速度结构，结果显示：秦祁地块下面存在深达70 km的高速异常，阻断了青藏高原块体中下地壳低速层向东北方向的延伸；40~140 km深度范围内，四川西南部存在一个低速区，该低速区穿过龙门山断裂带进入到四川盆地内部；祁连山造山带东部低速异常区从地壳一直延伸到上地幔400 km处，表明这里可能存在一个上地幔到地壳间的热流通道；松潘-甘孜地块分布大面积的低速异常区，而鄂尔多斯地块西南缘相对速度较高，这与青藏高原为软块体、介质密度低和鄂尔多斯块体为硬块体、介质密度高相吻合.

Traveltime tomography using teleseismic P wave in the northeastern Tibetan plateau

In this paper, the teleseismic waveforms recorded by permanent networks in northeastern Tibetan plateau from Apr. 2010 to Mar. 2015 are used for P wave tomography. We picked 10697 P wave relative traveltime residuals by Multi-Channel Cross-Correlation method and then we get the P wave velocity structure of upper mantle beneath NE Tibet by Fast Marching Teleseismic Tomography (FMTT). The results reveal that a high velocity anomaly extends to 70 km depth beneath the Qinling-Qilian Block. The result shows that the lower crustal channel flow model is not suitable for the whole NE Tibet; an obvious low-velocity is located at the region beneath Qilian Orogen from crust down to 400km, which suggests that there may exist a hot flow channel in the upper mantle and the crust. A large area in Songpan-Garzê block is low velocity anomaly and this is consistent with low density Tibetan plateau. The velocity of Ordos block is high, and it is consistent with high density Ordos block.