Reflection imaging from crust to core

Abstract:

In the Earth's crust and mantle there are plenty quite sharp discontinuities in material properties. These material contrasts lead to reflections of seismic waves. Detailed images of the contrasts could be made by applying reflection imaging. Thus far, however, reflection imaging of the deep Earth has been restricted to isolated depth ranges, for which sufficient source-receiver reflection paths could be found. Rarely there is a dense sampling of both sources and receivers in the same region, which allows consistent illumination of reflectors over a large depth range. We do create such dataset by applying seismic interferometry to ScS reverberations measured over Japan. The earthquake responses are detected with the Hi-net high-sensitivity accelerometers (tiltmeters) network operated by the NIED. Large-magnitude earthquakes nearby Japan generate a clear ScS phase that is observed over the entire island arc. For deep earthquakes, additionally ScS reverberations can be observed from interfaces ranging from the lithosphere to the mantle transition zone, and all the way to the D'' region. We apply seismic interferometry to a multitude of these ScS arrivals and reverberations. Doing so, the responses are retrieved as if there were shear-wave sources at all Hi-net stations and the resulting reflections were measured at the same stations. We migrate the zero-offset (co-located source and receiver) reflection responses to a reflectivity image. The main features on this image are the Moho, the topography of the 410 and 660 discontinuities and the reflectors delineating low- and high-velocity zones above the core-mantle boundary.