Sonne International Cooperative Survey

Little is known about potential earthquake sources along the interplate decollement between North America and the Juan De Fuca plates. Hence the Sonne survey focuses on the decollement and the subduction zone. The regional lack of shallow (less than 30 km) seismicity along the decollement means that the geometry of the downgoing plate cannot be determined using the classical approach of mapping the Benioff zone using earthquake monitoring data. Deep-crustal, seismic reflection and refraction surveys are the prime, if not the only, tools that can be used to characterize the potential source zones for great earthquakes off Cascadia.

The German scientific community's interest in joining the USGS in the offshore Cascadia investigation arose largely through the influence of Roland Von Huene's leadership as Head of the Marine Geodynamics Department of GEOMAR, Christian-Albrechts University, Kiel, Germany. Rolie is also an emeritus scientist with WR Coastal and Marine Geology. Chief scientists of the study are Mike Fisher (USGS) and Ernst Flueh (GEOMAR). Both international (Canadians are involved too) and intranational cooperation between institutions is required to pull off such a technically challenging and necessarily expensive program. Only through cooperation in marine studies, which allows the resources of people, equipment, and money to be assembled, can large-scale, offshore earth science investigations be carried out. The two cruises of F.S. Sonne, one to the Cascadia margin, and the other to investigate marine cold-seep communities off Alaska, are case examples of what can be accomplished through cooperation in ocean margin research. someone, CO-MAR's presumption is that the "whole is greater than the sum of its parts". The Sonne departed San Francisco just a few days after the 90th anniversary of the 1906 earthquake.

Text and illustrations by Mike Fisher and Guy Cochrane