资源环境科技发展态势分析平台

Interpreting core-related body wave traveltimes is challenging for seismologists because Earth's heterogeneities are averaged over thousands of kilometers and the sparsity of earthquake measurements makes these heterogeneities difficult to localize. We show how the ambient seismic wave field can be used to overcome these limitations. We present a regional-scale analysis of core-mantle boundary reflections (ScS) under Mexico. We show that body wave arrivals (i.e., P and ScS) are retrieved from higher-order cross correlations (C-3), a technique that provides a more uniform and controlled source distribution using the scattered waves of the coda of classical ambient field cross correlations (C-1). Then, we extract ScS traveltimes along a dense linear array in Mexico and find that lithospheric lateral heterogeneity, such as the subducting Cocos slab beneath Mexico, may have a strong impact on ScS traveltimes. In parallel, we show that lateral heterogeneity such as a possible ultralow velocity zone (ULVZ) near the core-mantle boundary might also affect, although to a lesser extent, the traveltime anomalies. Our results and interpretation are supported through numerical simulations that account for slab and ULVZ properties.