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用波形相关法精确地测定了在世界各地发生的87个6级以上地震的P波, PP波和Pdiff波的503个走时数据。记录这些地震波形的是新建于西太平洋地区的海洋半球地震观测网。我们利用这些高精度的走时数据研究了地幔体波的走时残差的范围及地幔非均匀性的强度。结果表明,P波、PP波和Pdiff波的走时残差最大分别为9 s ,11 s和15 s ,这为地幔层析成像反演中应该使用的体波走时残差数据的范围提供了重要信息。超出这一范围的走时残差数据不应该用于反演中,以免歪曲成像结果。我们发现,当震中距小于40°时,P波走时残差的范围为-6到+9 s。而对于40°到99°之间的震中距,P波走时残差的范围为-3到+5s。由于震中距越大,P波穿透地幔越深,我们这一结果提供了直接和确凿的证据,表明上地幔和地幔转换带中的横向非均匀性的强度要远胜于下地幔。我们精确测量的Pdiff波的走时数据表明,在地幔底部存在显著的低速异常,可能与地幔热柱或者超级地幔柱有关。我们使用了一个最新的三维全球层析成像模型来解释这些体波走时数据的空间变化。
Waveform correlation method was used to accurately measure 503 travel time data of P wave, PP wave and Pdiff wave of 87 earthquakes of magnitude 6 or higher occurring in various parts of the world. The seismic waveforms recorded for these are the newly built ocean hemispherical seismic networks in the western Pacific. We use these high-precision travel-time data to study the range of traveltime residuals and the intensity of the mantle heterogeneity of the mantle waves. The results show that the maximum travel time residuals of P wave, PP wave and Pdiff wave are 9 s, 11 s and 15 s, respectively, which provide important data for the range of residual wave velocity of body wave travel to be used in mantle tomography inversion information. Traveltime residual data beyond this range should not be used in inversion to avoid distorting imaging results. We found that when the epicentral distance is less than 40 °, the P-wave travel time residuals range from -6 to +9 s. For epicentral distances between 40 ° and 99 °, the range of P-wave travel-time residuals is -3 to + 5s. Since the greater the epicenter distance, the deeper the P wave penetrates the mantle, and our results provide both direct and conclusive evidence that the lateral inhomogeneities in the upper mantle and mantle transitions are stronger than the lower mantle. The traveltime data of the Pdiff waves we measured accurately shows that there is a significant low-velocity anomaly at the bottom of the mantle, which may be related to the hot mantle plumes or the super mantle plumes. We use a state-of-the-art 3D global tomography model to account for the spatial variation of these B wave travel times.