马尼拉俯冲带的地震层析成像研究

基于国际地震中心的P波走时数据和层析成像反演方法，获得了具有较高分辨率的马尼拉俯冲带的深部速度模型.结果表明，（1）高速的南海俯冲板片沿马尼拉俯冲带的俯冲形态随纬度发生变化，在14°N和16°N之间，板片俯冲角度较大，俯冲深度可达400~500 km，在17°N附近，俯冲板片角度和深度较南部变小，而在18°N附近，俯冲板片以近垂直角度俯冲到地幔转换带;（2）17°N和18°N之间俯冲角度的变化意味着南海板片发生了撕裂;（3）在14°N附近，南海板片由300 km以上的近垂直俯冲转为200~300 km深度的近水平展布，与震源分布存在较大的差异，表明南海板片发生了撕裂，并且导致410 km间断面抬升.根据成像结果计算的不同位置南海板片的俯冲长度和时间表明，南海板片俯冲之前的面积为现今面积的两倍，14°N最先开始发生俯冲，并由南向北扩展.

P-wave seismic tomography of the Manila subduction zone

The P-wave velocity perturbation images beneath the Manila Subduction zone are generated by utilizing P-wave arrival times from International Seismological Centre (1960-2008) and the seismic tomographic inversion method. The data set is comprised by 12582 high-quality P-wave arrival times from 1372 regional earthquakes and 14799 travel-time residuals from 2129 teleseismic events. The results show that the shape of the subducted South China Sea slab (SCSs) represented by high velocity anomalies changes with latitudes.From 14°N to 16°N, the subduction angle and depth are both larger than that at 17°N, whereas the SCSs is subducted to the mantle transition zone at a nearly vertical angle at 18°N.The different subduction angles from 17°N to 18°N suggest the slab tearing in the SCSs which turns from nearly-vertical above 300 km depth to horizontal at 200~300 km depth at 14°N, much different from the distribution of seismic sources, also suggesting the possible slab tearing in the SCSs and the elevation of the 410 km discontinuity.The subduction length and time of SCSs calculated by the tomographic results at different latitudes suggest that the area of the original SCSs was about twice that its present range, and the subduction of the SCSs started at 14°N and propagated from south to north.