A Wave Equation Migration Method for Receiver Function Imaging

A wave equation based poststack depth migration method is proposed to image the crustal and upper mantle structures using teleseismic receiver functions. By utilizing a frequency-wavenumber domain one-way phase-screen propagator for wavefield extrapolation in the migration scheme, the common conversion point (CCP) stacked receiver functions are backward propagated to construct the subsurface structural images. Synthetic experiments demonstrate the validity of the migration method for a variety of laterally heterogeneous models. The migrated images show considerable improvement over the CCP images in recovering the structural features. The phase-screen propagator migration method proves to be particularly useful for imaging complex structures and deep discontinuities overlain by strong shallow anomalies, because of its capability of handling lateral velocity variations. Influences of several factors on the image quality of the poststack migration are further investigated, including inter-station spacing, noise level of the data, velocity model used in migration, and earthquake distribution (incident direction of source fields). Theoretical derivation and numerical results suggest that both the CCP stacking and the poststack migration of receiver functions need to be designed in a target-oriented way for reliable and efficient imaging, and special consideration on earthquake distribution is particularly required in designing seismic experiments if structures of large dips are present. The proposed wav equation migration scheme is applied to image the Earth's internal structures using a number of dense field data sets collected at many seismic arrays in Asia. The constructed images reveal several interesting subsurface structures of the study regions and synthetic tests indicate that those subsurface features are well resolved by the seismic data. Significant improvements of the image quality demonstrate the great potential and flexibility of the proposed migration method for imaging the Earth's internal structures using seismic data collected in the future dense passive seismic arrays, such as the USArray.