- Copyright © 2003 Society of Exploration Geophysicists
Seismic profiling across the ocean-land transition is a known challenge that requires a combination of data collection techniques. Seismic acquisition may require the use of swamp buggies, bay cables, ocean bottom hydrophones or seismometers, and/or marine air guns. The onshore-offshore seismic profiling technique, which uses moderate-to-widely spaced land instruments to record densely spaced marine air-gun sources, undershoots the coastline to provide detailed images of subsurface regions that cannot be seen in either marine or land profiles. Intermediate to wide-angle raypath geometries are common in this technique. Useful analysis methods include arrival-time velocity tomography or wide-angle prestack migration, neither of which is based on vertical-incidence raypaths.
The creation of the IRIS PASSCAL pool of portable seismic recorders accelerated an era of investigations of continental crust using this onshore-offshore seismic profiling technique. During the past decade, the crustal seismology community based primarily in Europe and North America has used this method to improve our understanding of the 3D structure of passive and active continental margins, ocean-continent subduction zone and arc systems, and plate boundaries situated near coastlines. Recent targets include the Baltic shield, conjugate margins on both sides of the mid-Atlantic spreading system, subducting slabs at Cascadia and the Andes, the Mendocino triple junction, the San Andreas strike-slip plate boundary, and as we report here, the Pacific/Indo-Australian transpressional plate boundary in southern New Zealand.
This latter plate boundary, which has often been compared to the Big Bend of the San Andreas fault in southern California, is an example of extremely active strike-slip translation and continent-continent convergence with one of the fastest present-day exhumation and erosion rates (8–10 mm/yr) in the world. Unlike the San Andreas fault, this southern New Zealand plate boundary has suppressed levels of modern seismicity which suggest either long recurrence rates for strong episodic earthquakes or a larger role …