A wave equation migration method for receiver function imaging: 1. Theory

摘要

A wave equation-based poststack depth migration method is proposed to image the Earth's internal structure using teleseismic receiver functions. By utilizing a frequency wave number domain one-way phase screen propagator for wave field extrapolation in the migration scheme, common conversion point (CCP) stacked receiver functions are backward propagated to construct a subsurface structural image. The phase screen propagator migration method takes into account the effects of diffraction, scattering, and travel time alternation caused by lateral heterogeneities, and therefore it is particularly useful for imaging complex structures and deep discontinuities overlain by strong shallow anomalies. 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 model features. Influences of several factors on the image quality of the poststack migration are further investigated, including interstation spacing, noise level of the data, velocity model used in migration, and earthquake distribution (incident direction of source fields). On the basis of the sampling theorem and previous statistic results, we discuss the relation of spatial resolution and signal-to-noise ratio of the migrated image with the frequency of the data, surface station spacing and number of receiver functions used in stacking. We show that both CCP stacking and poststack migration of receiver functions need to be designed in a target-oriented way for reliable and efficient imaging. Our results also suggest that careful consideration of earthquake source distribution is necessary in designing seismic experiments aimed at imaging steeply dipping structures.