Abstract:

In the paper,we use 296334 P_n rays from 27777 earthquakes recorded by 1354 seismic stations in the eastern Asia region,an area spanning from 15癗-60癗 and 60癊-145癊,to invert the P_n velocity structure of uppermost mantle and its lateral variations. We also discuss the tectonic implication of the lateral variation based on the P_n velocity structure. Inversion results show that the mean velocity of P_n is 8.03km/s in the eastern Asia region. The lateral variation spans from -0.42km/s to 0.41km/s. Two different tectonic regions can be identified according to distributions of P_n velocity and its lateral variation. In the region from the boundary of the Pacific plate to the east of 108癊,i.e.the eastern China,P_n velocity is relatively low. In the region located at west of 108癊,P_n velocity is high. The different distribution of P_n velocity is consistent to the regional geodynamic background. The dominant geodynamic effect is subduction of the Pacific plate in the eastern China and collision of the Indian Ocean plate in the western China. At the same time,P_n velocity is relatively low in active tectonic regions and high in the stable tectonic regions. The P_n velocity also shows negative correlation to the regional seismicity. The higher of the seismicity,the lower of the P_n velocity,and vice versa. The negative correlation indicates the relationship of lateral variation of P_n velocity and tectonic deformation with seismicity level. The region with low P_n velocity usually is a region with high tectonic deformation and intensive seismicity.

Key words: eastern Asia, P_n velocity, lateral variation, geodynamics

摘要：

以东亚地区(15°～60°N,60°～145°E)为研究区,通过多种资料渠道收集了研究区内27 777次地震在1 354个地震台站记录到的296 334条P_n波射线,反演了东亚地区上地幔顶部P_n速度结构及其横向变化,并进而探讨了P_n波速度结构横向变化的动力学意义。反演结果给出,东亚地区P_n波平均速度为8.03km/s。横向变化量从-0.42km/s至+0.41km/s。在研究区内,P_n速度和横向变化总体上呈现为东、西2个特征性分区。从太平洋板块边界到中国东部(大致为东经108°以东)为P_n速度偏低区,而东经108°以西为P_n速度偏高地区。这2个特征性差异分区分别与太平洋板块俯冲和印度洋板块碰撞挤压的动力学背景相一致。无论是东部地区还是西部地区,均显示活动构造区为P_n速度的相对低值异常区,而构造上稳定地区为P_n速度的高值异常区。并且在东、西部各自分区中,均呈现为地震活动水平与P_n速度之间成反向变化关系,显示了P_n速度横向变化与构造变形和地震活动强度的相关性,P_n速度的低值异常区往往是构造变形和强震活动活跃的地区。

关键词: 东亚地区, P_n波速度, 横向变化, 动力学背景