New Scientist-in-Charge at the Alaska Volcano Observatory plus 1 more

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Title: USGS Newsroom

New Scientist-in-Charge at the Alaska Volcano Observatory plus 1 more

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New Scientist-in-Charge at the Alaska Volcano Observatory

Posted: 04 Apr 2016 11:00 AM PDT

Summary: USGS geologist Michelle Coombs has been appointed Scientist-In-Charge of the Alaska Volcano Observatory. ANCHORAGE, Alaska — The U.S. Geological Survey is pleased to announce the selection of Dr. Michelle Coombs as the next Scientist-in-Charge of the Alaska Volcano Observatory, a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys. Coombs succeeds John Power, who served as AVO SIC for the past five years and will now rotate to an AVO staff geophysicist position. 

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Contact Information:

Yvette Gillies ( Phone: 907-786-7039 ); Leslie  Gordon ( Phone: 650-329-4006 );

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USGS geologist Michelle Coombs has been appointed Scientist-In-Charge of the Alaska Volcano Observatory.

ANCHORAGE, Alaska — The U.S. Geological Survey is pleased to announce the selection of Dr. Michelle Coombs as the next Scientist-in-Charge of the Alaska Volcano Observatory, a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys. Coombs succeeds John Power, who served as AVO SIC for the past five years and will now rotate to an AVO staff geophysicist position. 

“Michelle brings an especially strong research background in volcano geology in addition to her eruption response work. She also has strong ties to Alaska, starting with her graduate work in Katmai and her Ph.D. from the University of Alaska Fairbanks. We are lucky to have her come into the SIC position,” said Tom Murray, Director of the USGS Volcano Science Center, which oversees the five U.S. volcano observatories. 

Following her time as an undergraduate student at Williams College in Massachusetts, Coombs traveled northwest to study at the University of Alaska Fairbanks. Her interest in volcanoes drew her to study the causes behind the 1953-1968 eruptions of the Southwest Trident Volcano in Katmai National Park.

After receiving her doctorate in geology in 2001, she began a postdoctoral position with the USGS in Menlo Park, California. There, she studied landslide hazards and evolution of Hawaiian volcanoes until 2004 when she returned to Alaska to join AVO. 

As a research geologist at AVO, Coombs participated in the responses to the 2006 and 2009 eruptions of Augustine and Redoubt in Alaska’s Cook Inlet. She has also studied the evolution and hazards of volcanoes along the expanse of Alaska’s Aleutian arc, from Semisopochnoi and other western islands, to Hayes Volcano in the easternmost arc, near Anchorage. 

Alaska is a volcanically active region, experiencing one to two eruptions per year. As SIC at AVO, Coombs will have a prominent role in communicating these hazards to the public. 

“I wish to thank John Power for his guidance as AVO SIC these past five plus years. During his tenure he effectively dealt with the serious complications of threatened and real government shutdowns and a budget sequestration. Throughout he kept AVO functioning at a high level and moving forward,” said Murray. 

Rodgers Creek Fault Traced through Santa Rosa

Posted: 04 Apr 2016 10:00 AM PDT

Summary: For the first time, scientists at the U.S. Geological Survey have mapped the active surface trace of the Rodgers Creek Fault through the central part of the northern California city of Santa Rosa. Urban development has, until now, obscured its exact location. Knowing where the fault reaches the ground surface and the total width of the zone of faulting are important for assessing the hazard from surface rupture in a large earthquake.

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Contact Information:

Susan  Garcia ( Phone: 650-346-0998 ); Leslie  Gordon ( Phone: 650-329-4006 );

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For the first time, scientists at the U.S. Geological Survey have mapped the active surface trace of the Rodgers Creek Fault through the central part of the northern California city of Santa Rosa. Urban development has, until now, obscured its exact location. Knowing where the fault reaches the ground surface and the total width of the zone of faulting are important for assessing the hazard from surface rupture in a large earthquake.

“We used detailed topographic imagery from airborne lidar and subsurface imaging from high-resolution geophysical surveys to trace the fault through Santa Rosa,” said USGS geologist Suzanne Hecker, lead author of the study.

The zone of faulting at the surface is broader and covers an area that extends farther east than previously assumed, which means the surface-rupture hazard is more widespread than previously thought. There are subtle fault “scarps” (the vertical scars left on the landscape from fault motion) on the gently-sloping floodplain of Santa Rosa Creek, on which the city is built, that define a surface depression that is one-quarter-mile wide by one-mile long.

Scientists also discovered, through analysis of gravity and magnetic data, an especially dense, magnetic body of rock below the ground surface on the east side of the scarp-defined depression. This dense, magnetic body of rock appears to be in contact with the east side of the Rodgers Creek Fault, and its northern end is associated with concentrations of small earthquakes, mainly aftershocks from the 1969 magnitude 5.6 and 5.7 Santa Rosa earthquakes. The pattern of surface faulting and earthquake activity may be an _expression_ of deformation resulting from intensified frictional resistance where the fault abuts the dense, magnetic body of rock at depth. 

On the basis of the lidar and geophysical observations, and preliminary data from previous studies suggesting a change in the rate of surface creep on the fault in the vicinity of Santa Rosa, USGS scientists speculate that the dense, magnetic body of rock may be a stuck patch, or “asperity,” on the fault, where stress concentrates. A large earthquake on the Rodgers Creek Fault that ruptures through the proposed asperity has the potential to intensely shake the sedimentary basin beneath Santa Rosa. This basin is already known, from an earlier study of the damaging 1969 Santa Rosa and 1906 San Francisco earthquakes, to amplify shaking at the ground surface. The Rodgers Creek Fault is thought to be among the most likely faults to produce the next large earthquake in the Bay Area. 

A pre-publication version of the full report “Detailed Mapping And Rupture Implications Of The 1-Km Releasing Bend In The Rodgers Creek Fault At Santa Rosa, Northern California,” is available online in the Bulletin of the Seismological Society of America.

Google Earth image of central Santa Rosa (dated 24 October 2009) showing the surface trace of the Rodgers Creek Fault (red lines) and the inferred location of the fault prior to this study (orange dotted line). Yellow lines on either side of the fault are the boundaries of the lidar survey.

Shaded relief image of the Santa Rosa area showing active faults (black lines) and the detailed rupture pattern of the Rodgers CreekFault where it crosses central Santa Rosa (in red). The orange, bean-shaped area represents the dense, magnetic body of rock on the east side of the fault beneath Santa Rosa. This body of rock may be largely responsible for the pattern of surface faulting and may influence the distribution of small earthquakes (white and blue circles, blue for 1969 aftershocks) and the occurrence of the damaging 1969 earthquakes (approximately located by blue stars).