Subthrust Seismic Mapping with the WARP Method

Jannis Makris and Richard G. Boyce

The Wide Aperture Reflection Profiling (WARP) technique has successfully imaged complex subthrust geometries in western Greece and in northern Oregon. Exploration in both areas has been hampered by the failure of conventional CDP seismic to penetrate the surface cover of volcanics or high velocity limestones. Using large offsets (30-40 km) and recording post critical reflections, the structural configuration and velocity distributions have been accurately mapped.

Two WARP seismic profiles were recorded to explore a basin in north-central Oregon. Interpretation reveals this basin was subjected to compression which thrust basement rocks over the sedimentary sequences, contradicting previous tectonic models. Rugged topography formed by the thick Columbia River Basalts did not affect seismic data quality.

Three WARP profiles were acquired in western Greece crossing from onshore to offshore. Utilizing both ocean bottom and land based SEDIS 2 recorders, excellent data was recorded in spite of the rough topography caused by high velocity limestones on the surface. Inversion and modelling of the wide angle reflections defines, for the first time, the thrust geometry of the western Hellenides, as well as thicknesses of the limestones and Triassic evaporites beneath the thrust. Due to the 170 km line lengths and efficient energy propagation, the boundary between continental and oceanic crust has also been mapped.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California