Crustal structure in regions bordering Pacific Ocean

Tectonic patterns of various circum-Pacific regions have many remarkable similarities and some puzzling differences. Consistent patterns of vulcanism and seismicity are well known, and recent geologic and geochronologic studies indicate surprisingly similar geologic histories of geosynclinal accumulation and Plutonism in many regions, particularly along the Pacific margin of the Americas. Similarly, dominant strike-slip faulting parallel with the oceanic margins is being found as a consistent pattern in an increasing number of circum- Pacific areas, although the two areas where documentation is best, California and southern New Zealand, are definitely atypical in other important respects, such as the absence of abundant vulcanism and deep-focus earthquakes. Active strike-slip faulting is primarily right-handed in the Americas from Alaska through Chile but applicability of this sense of displacement to the Asiatic margin is a subject of controversy. Available geologic evidence from this region does not agree with seismological studies of earthquake first motions, and reconciliation of conclusions from the two approaches remains a major problem in the understanding of circum-Pacific tectonics.