Page 12: of Marine Technology Magazine (April 2006)

news squiggles you think of when someone men- tions seismography," said Dr. Uri ten Brink of the USGS Coastal and Marine Science

Center.

According to ten Brink, many of the

Aleutian volcanoes are located on small islands that greatly restrict the geometry and aperture of AVO's seismographic net- works. Location of seismic stations is often further restricted by strong noise generated by ocean waves, which masks the seismic signal. The noise is often amplified by the unconsolidated pyroclastic deposits (loose fragmented pieces of rock that may be min- erals, crystals or glass that are ejected from a vent) that frequently make up the flanks of many Aleutian arc volcanoes. The limited extent of many of the AVO's seismographic networks often restricts the accuracy of earthquake hypocenter determination and frequently precludes the detection and tracking of volcano induced seismicity in the mid to lower earth's crust. "The use of Ocean Bottom Seismometers will allow AVO to improve the data collect- ing locations of volcano related seismicity, and better the determination of the vol- cano's internal structure. These improve- ments will further our understanding of the subsurface components of the magmatic system and the processes that proceed and lead to eruptions," said ten Brink.

As the cutter approached Augustine

Island the volcano was in full view and the crew could easily see the steam coming from the top of the mount. Ash deposits colored the peak alluding to recent erup- tions. The Coast Guard has put in place a one-mile safety zone off Augustine Island for maritime traffic. "It was so clear, really beautiful," said

Loreaux, operations officer on the cutter

Roanoke Island. "You could see the recent activity at the top." Long flows of pyroclas- tic rock and debris were visible, especially along the north side of the volcano.

As they neared the first OBS location the scientists filed out on deck and readied the

OBS for deployment. Using the vessel's crane the OBS was raised over the water. A scientist pulled a line connected to a quick release hook and the yellow instrument vanished beneath the water. The Coast

Guard deck supervisor radioed up to the

Seaman Josiah Goetz, the Quartermaster of

Science team members, assisted by cutter

Roanoke Island's crew, ready an OBS to be hooked to the crane, hoisted over the side and dropped to the ocean floor. (Photo courtesy of U.S. Coast Guard cutter

Roanoke Island.) 12 MTR April 2006

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