Ophiolites, synthetic seismograms, and ocean crustal structure: 1. Comparison of ocean bottom seismometer data and synthetic seismograms for the Bay of Islands ophiolite

Abstract

A series of synthetic Seismograms based on the Bay of Islands ophiolite data are compared with ocean bottom seismometer seismic refraction observations which sample 60‐m.y. crust in the northeastern Pacific. The general agreement between the synthetics for the ophiolite and the observations support the idea that some ophiolites are representative of normal ocean crust. This support extends to similarities in complex second arrivals in the synthetics and observations which often are not used in the interpretation of marine seismic data. The use of the ophiolite model also allows us to show how the interpretation of seismic data is affected by experimental design and interpretation procedures; as the sampling density increases and as more phases in the observations are accounted for, the velocity‐depth model more closely approaches that found for the ophiolite. The results of this modeling support sharper P velocity transitions within the crust than are found in young (<12‐m.y. age) oceanic crust. The need for a thin (approximately 1 km thick) P low‐velocity zone at the base of the crust is interpreted as support for serpentinization at the crust‐mantle boundary; serpentinization of the ultramafic component in the Bay of Islands ophiolite, therefore, may include a small preemplacement component.