Imaging a plate boundary using double-sided onshore-offshore seismic profiling

摘要

Double-sided onshore-offshore experiments are needed in order to image the subsurface of a narrow land-mass. This method can be applied to landmasses whose widths are from 1 to 3-5+ times the depth of the imaging target (Okaya et al., 2002). For crustal profiling, this translates to 50-150+ km wide regions for thin to moderate crustal thickness as is often associated with islands or peninsulas. If the landmass is too wide, air-gun energy from one side will not reach the other coast and the onshore-offshore experiments off opposing coasts become decoupled. In Figure 10, we identify a number of narrow landmasses at plate boundaries that are amenable to double-sided onshore-offshore profiling. These sites are at islands or peninsulas for which seismic air-gun energy may propagate across most of its width from offshore either coastline. In addition, the limited width of the landmasses are insufficient to properly image the crust-mantle boundary using just land profiling; marine and onshore-offshore methods are necessary. The availability of portable instruments such as the IRIS PASSCAL pool and an air-gun ship such as the Ewing allow for these plate boundary regions to be seis-mically imaged with high spatial resolution using high-confidence modern tomographic and wide-angle imaging analysis methods.