雷琼火山与华夏块体的远震P波走时成像

利用广东及邻省的地震台网共94个地震台站记录的2009—2015年的256个远震波形数据,采用基于波形互相关的自适应迭代技术获得了18968个可靠的P波相对走时残差数据,进而应用FMTT(Fast Marching Teleseismic Tomography)地震层析成像方法确定了雷琼火山与华夏块体深至450km的三维P波速度结构.结果显示,雷琼火山下方100~450km深度显示明显低速异常,该低速异常随深度增加向华夏块体下方扩展.研究认为该低速异常由海南地幔柱热物质上涌造成,雷琼火山为板内热点火山,这与已有体波成像及接收函数成像等结果一致.根据该低速异常的整体特征,推测海南地幔柱向北东方向倾斜,并可延伸至450km以下.华夏块体下方的低速异常,可能是由海南地幔柱热物质上涌过程中不断向北东方向侵蚀而造成.结果同时显示研究区大陆至海域的岩石圈厚度可能具有由厚变薄的过渡特征.

Teleseismic P-wave traveltime tomography for the Leiqiong volcano and Cathaysia block

We obtained 18968 reliable P wave relative traveltime residuals by adaptive stacking technique based on waveform cross-correlation of 256 distant earthquake records. The teleseismic waveform data were recorded by 94 permanent seismic stations belonging to seismic networks of Guangdong and neighboring provinces. The P wave velocity structure beneath the Leiqiong volcano and Cathaysia block down to 450 km depth was determined by the Fast Marching Teleseismic Tomography (FMTT). The results show an obvious low-velocity anomaly beneath the Leiqiong volcano from 100 km to 450 km depth. This low-velocity anomaly extends to the Cathaysia block with depth increasing. It is suggested that this low-velocity anomaly is caused by the upwelling of thermal materials of the Hainan plume, and the Leiqiong volcano is an intraplate hot spot, which is consistent with previous results of body-wave tomography and receiver function studies. It is also inferred that the Hainan plume dips to the northeast and probably extends to 450 km depth from the pattern of the low-velocity anomalies. The low-velocity anomalies beneath the Cathaysia block is likely produced by the northeastward erosion of upwelling hot materials of the Hainan plume. The results may also imply that the lithospheric thickness of the study area tends to be thinner from the land to the sea.