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