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SUCCESSFUL SONNE CRUISE RESULTS ENHANCED BY EARTHQUAKE The German research vessel Sonne came into port in Astoria, Oreg., on May 22, after completing seismic studies of earthquake hazards posed by the subduction zone off Washington and Oregon. Co-chief scientist Mike Fisher (the other co-chief was Ernst Flueh of GEOMAR, Germany) was disappointed that strong currents in the Columbia River forced the Sonne to be pulled into the dock stern-first by a tugboat, thus preventing a more triumphant entry. But Mike had little else to complain about, reporting "spectacular success" for the cruise. Generally good weather allowed data collection on all but 3 days of the 5-week cruise. As Mike reported to Steve Bohlen, "Thanks to a highly skilled and motivated German-American crew we achieved nearly everything we had proposed to do. We have multichannel seismic lines that show the downgoing oceanic plate 120 km eastward from the trench. Using these data...with detailed, wide-angle information, Im confident that we will make decisive statements about the earthquake environment of the subduction zone." Tom Parsons led an onshore crew that set up and maintained three east-west lines of seismometers to extend the Sonne results across western Washington. Additional data were contributed by cooperators Anne Trehu of Oregon State University, who ran two lines of seismometers in northern Oregon, and Steve Malone of the University of Washington, who maintains a permanent network of seismometers around northern Washington. An unexpected bonus was a magnitude 5.4 earthquake centered east of Seattle that occurred on May 2 and was recorded by seismometers on- and offshore. Data from the earthquake and its aftershocks may sharpen the picture of the downgoing oceanic plate. In addition to getting good data, the project team also had good luck with equipment and logistics: Out of 22 ocean-bottom seismometers (OBSs), only one was lost; two others were snagged by fishermen and eventually returned. At the end of the cruise, the USGS equipment was cleared from the Sonne in less than 24 hours, amazing the ships captain and the co-chief scientist Flueh. The Germans were also amazed by Dave Scholl. As Mike reported to Steve Bohlen, "[The Germans] knew of his world-class status as a scientist, but they were unprepared for a 65-year-old, Herr Professor Doktor who relishes getting his hands dirty. Most German scientists with his credentials pass time sipping coffee with the captain. In contrast, Dave made every streamer and airgun party, activities we dubbed "deck sports." He cheerfully wrapped miles of tape around wires, tugged on airgun hoses, and hustled everywhere to toss in his muscle....Dave definitely leads from the front." Another part of Mikes report to Bohlen reveals just how far-reaching were the Sonnes effects: "Steve Lewis (ex-USGS, now SRI) said that Navy, submarine, sound arrays near Kamchatka were picking up odd noise from near Oregon and Washington. Steve impressed the Navy types by guessing correctly that the odd sounds were low- frequency bursts every 20 seconds. He explained that he knew all about the Sonne because he had friends onboard." Now begins the task of processing and interpreting the data, which will take a couple of years. Eventually the results will be used by scientists, planners, government officials, and others to assess and mitigate earthquake hazards in densely populated areas of the Pacific Northwest. Geologic evidence suggests that a future earthquake there may be as large as magnitude 9.
Staff information imported from InfoBank
Mike Fisher (USGS Western Region) - Chief Scientist
Ernst Flueh (Geomar, Germany) - Chief Scientist |
