Increasing deployment of dense arrays has facilitated detailed structure
imaging for tectonic investigation, hazard assessment and resource
exploration. Strong velocity heterogeneity and topographic changes have
to be considered during passive source imaging. However, it is quite
challenging for ray-based methods, such as Kirchhoff migration or the
widely used teleseismic receiver function, to handle these problems. In
this study, we propose a 3-D passive source reverse time migration
strategy based on the spectral element method. It is realized by
decomposing the time reversal full elastic wavefield into
amplitude-preserved vector P and S wavefields by solving the
corresponding weak-form solutions, followed by a dot-product imaging
condition to get images for the subsurface structures. It enables us to
use regional 3-D migration velocity models and take topographic
variations into account, helping us to locate reflectors at more
accurate positions than traditional 1-D model-based methods, like
teleseismic receiver functions. Two synthetic tests are used to
demonstrate the advantages of the proposed method to handle topographic
variations and complex velocity heterogeneities. Furthermore,
applications to the Laramie array data using both teleseismic P and S
waves enable us to identify several south-dipping structures beneath the
Laramie basin in southeast Wyoming, which are interpreted as the
Cheyenne Belt suture zone and agree with, and improve upon previous
geological interpretations.