Regional phases in continental and oceanic environments

The very different crustal thicknesses between continental and oceanic crust lead to the establishment of distinct styles of regional seismic wavefield. Observations and numerical simulations of events near subduction zones in Japan allow a direct comparison of seismic wave propagation in oceanic and continental structures. The thick zone of lower seismic velocities in the continental crust acts to trap S-wave energy in particular and generates crustally guided phases such as Pg, Lg. In the oceanic environment there is no efficient S-wave trapping and crustal energy progressively leaks into the mantle. Reverberations in the crust and the water above help to sustain the amplitude of the mantle arrivals Pn, Sn to large distances.