远震P波振幅层析成像新方法及其在确定中国地区LAB二维结构中的应用

In this proposal, the three dimensional structure of Q value in the crust and upper mantle will be inverted by the tomography method using amplitude and period data of teleseismic body wave in the Annual Bulletin of Chinese Earthquakes. These data were only used to determine magnitude mb and mB, and amount to more than 1.6 million from 1985 to 2010.There are many attenuation information in these data, however that have never been dug out. We will develope a tomography method to obtain Q value from these amplitude data. The method not only improve the utilization of the history data, but also is able to obtain high resolution image because of huge quantity data. LAB is the boundary of lithosphere and asthenosphere, which can not be accurately determined by tradtional method (temperature field modeling, MT, seismological method). Receiver function of S wave is able to get LAB, but application of this method is not widespread because of lacking enough data. However, Q value is very sensitive to anomaly with high temperature or fluid, so it is efficient to identify asthenosphere near melt-out. we hope to accurately image two dimensional LAB in China by high resolution Q value tomogarphy method. This research is able to provide efficient constrain to the geodynamics of movement, collision and subduction of lithosphere plates drifted on the asthenosphere.

本申请计划利用中国地震年报中仅用来测定远震体波震级（mb、mB）的振幅周期数据，研究中国及周边地区上地幔三维Q值结构。该数据数量巨大，仅1985~2010年就有超过160万条之多，其中含有丰富的介质衰减信息，但从未被提取利用，本申请将发展一套适合该数据的振幅层析成像方法来研究Q值，这不仅有效提高了历史数据的利用率，而且因为采用巨量的数据而能够获得高分辨率的图像。 LAB是岩石圈和软流圈之间的边界，传统的方法（温度场模拟，大地电磁，地震学方法等）给出的区间都比较宽泛，近年来的S波接收函数能够给出较准确的LAB，但尚未能大范围应用。Q值对高温或含流体丰富的异常体比较敏感，能够有效识别接近熔融状态的软流圈，本申请希望能够通过高分辨率Q值成像方法较准确地获取中国地区二维LAB深度信息。这对认识漂流在软流圈之上的岩石圈板块的运动、碰撞、俯冲等动力学问题具有非常重要的意义。

本项目利用中国地震年报中仅用来测定远震体波震级（mb、mB）的振幅周期数据，研究了中国及周边地区上地幔三维Q值结构。该数据数量巨大，1985~2016年就有超过230万条之多，本项目充分利用了这些历史数据。本项目因此发展一套适合该数据的振幅层析成像方法来研究Q值，这不仅有效提高了历史数据的利用率，而且因为采用巨量的数据而能够获得高分辨率的图像。层析成像结果表明，中国东西部Q值具有明显的差异，同时在不同深度上Q值的也不相同。总体上在150到400公里范围内呈现高Q值异常，这可能西太平洋向中国大陆下方俯冲以及印度大陆向青藏高原下方的碰撞俯冲有关。总之，三维Q值研究对认识中国岩石圈板块的运动、碰撞、俯冲等动力学问题具有非常重要的意义。