Abstract
A 1° -square (12,363 km 3) area of the eastern Pacific Ocean centered on 21° 30′N and 126° 30′W (PAC 5) was surveyed in orthogonal grid fashion in order to provide geophysical data from which to select optimum sites for IPOD drilling. Interpretation of the magnetic anomalies in the survey area suggests that either asymmetric seafloor spreading occurred there or that a former spreading center migrated approximately 200 km to the west. Seismic-reflection and -refraction profiles show the survey area to be typically oceanic in structure. In places, thick accumulations of acoustically reverberant material fill depressions in oceanic basement (layer 2B), attesting to some process of modification of oceanic crust by sedimentation and (or) volcanic flows.
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