Oso Landslide Research Paves Way for Future Hazard Evaluations plus 1 more |
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Oso Landslide Research Paves Way for Future Hazard Evaluations Posted: 12 Jan 2015 09:00 AM PST
Summary: VANCOUVER, Wash. — The large landslide that occurred on March 22, 2014 near Oso, Washington was unusually mobile and destructive. The first published study from U.S. Geological Survey investigations of the Oso landslide (named the “SR530 Landslide” by Washington State) reveals that the potential for landslide liquefaction and high mobility are influenced by several factors, and the landslide process at Oso could have unfolded very differently (with much less destruction) if initial conditions had been only subtly different.
Contact Information: Carolyn Driedger ( Phone: 360-993-8907 ); Leslie Gordon ( Phone: 650-329-4006 ); VANCOUVER, Wash. — The large landslide that occurred on March 22, 2014 near Oso, Washington was unusually mobile and destructive. The first published study from U.S. Geological Survey investigations of the Oso landslide (named the “SR530 Landslide” by Washington State) reveals that the potential for landslide liquefaction and high mobility are influenced by several factors, and the landslide process at Oso could have unfolded very differently (with much less destruction) if initial conditions had been only subtly different. A major focus of the research reported this week is to understand the causes and effects of the landslide’s high mobility. High “mobility” implies high speeds and large areas of impact, which can be far from the landslide source area. Because high-mobility landslides overrun areas that are larger than normal, they present a significant challenge for landslide hazard evaluation. Understanding of the Oso event adds to the knowledge base that can be used to improve future hazard evaluations. Computer reconstructions of the landslide source-area geometry make use of high-resolution digital topographic (lidar) data, and they indicate that the Oso landslide involved about 8 million cubic meters (about 18 million tons, or almost 3 times the mass of the Great Pyramid of Giza) of material. The material consisted of sediments deposited by ancient glaciers and in streams and lakes near the margins of those glaciers. The landslide occurred after a long period of unusually wet weather. Prolonged wet weather increases groundwater pressures, which act to destabilize slopes by reducing frictional resistance between sediment particles. The slope that failed at Oso on March 22, 2014 had a long history of prior historical landslides at the site, but these had not exhibited exceptional mobility. The area overrun by the March 22 landslide was about 1.2 square kilometers (one-half square mile), mostly on the nearly flat floodplain of the North Fork Stillaguamish River. Additional areas were affected by upstream flooding along the river, which was partially dammed by the landslide. Eyewitness accounts and seismic energy radiated by the landslide indicate that slope failure occurred in two stages over the course of about 1 minute. During the second stage of slope failure, the landslide greatly accelerated, crossed the North Fork Stillaguamish River, and mobilized to form a high-speed debris avalanche. The leading edge of the wet debris avalanche probably acquired additional water as it crossed the North Fork Stillaguamish River. It transformed into a water-saturated debris flow (a fully liquefied slurry of quicksand-like material) that entrained and transported virtually all objects in its path. Field evidence and mathematical modeling indicate that the high mobility of the debris avalanche was caused by liquefaction at the base of the slide caused by pressures generated by the landslide itself. The physics of landslide liquefaction has been studied experimentally and is well understood, but the complex nature of natural geological materials complicates efforts to predict which landslides will liquefy and become highly mobile. Results from a suite of computer simulations indicate that the landslide’s liquefaction and high mobility were very sensitive to its initial porosity and water content. Landslide mobility may have been far less if the landslide material had been slightly denser and/or drier. Computer simulations that best fit field observations and seismological interpretations indicate that the fast-moving landslide crossed the entire 1-km-wide river floodplain in about one minute, implying an average speed of about 40 miles per hour. Maximum speeds were even higher. Only one individual landslide in U.S. history (an event in Mameyes, Puerto Rico in 1985 that killed at least 129) caused more fatalities than the 43 that occurred in the 2014 landslide near Oso. The full paper, “Landslide mobility and hazards: implications of the 2014 Oso disaster” by R.M. Iverson et al. is published in the journal, “Earth and Planetary Science Letters” and is freely available online.
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USGS Earthquake Science Center Welcomes New Director Posted: 12 Jan 2015 08:30 AM PST
Summary: The U.S. Geological Survey is pleased to announce the selection of Dr. Stephen Hickman to serve as the new director of the USGS Earthquake Science Center, headquartered in Menlo Park, California
Contact Information: Susan Garcia ( Phone: 650-346-0998 ); Donyelle Davis ( Phone: 626-202-2393 );
MENLO PARK, Calif. — The U.S. Geological Survey is pleased to announce the selection of Dr. Stephen Hickman to serve as the new director of the USGS Earthquake Science Center, headquartered in Menlo Park, California. Dr. Hickman succeeds Dr. Thomas Brocher, who served in the position for the past six years. “Steve Hickman’s decades of experience in the USGS as a research geophysicist will serve the Survey and the American people well as he embarks on his new leadership position,” said USGS Pacific Region director Mark Sogge. “He has led or participated in numerous scientific projects in the United States and abroad, and was co-principal investigator on the San Andreas Fault Observatory at Depth, a major component of the National Science Foundation's EarthScope facility. His extensive science and leadership skills will be invaluable as he guides the Center and works with our partners to address new scientific and technical challenges ahead.” Dr. Hickman’s research focuses on borehole and laboratory studies of the interaction between stress, fractures, and fluid flow in high-temperature geothermal systems and the physical and chemical processes controlling faulting and earthquake generation within active faults. “Working with partners in academia, other agencies and industry, the Earthquake Science Center has a proud history of combining world-class scientific research with long-term monitoring to assess earthquake hazards, both natural and human-induced. As center director, I am excited by the opportunity to work with center staff, USGS programs and external partners to strengthen these activities so the USGS can continue to provide the information needed to reduce the risks earthquakes pose to society and facilitate the safe development of conventional and renewable energy resources,” said Hickman. Hickman was a member of the USGS Geologic Division Scientific Strategy Team, chair of the Science Advisory Group for the International Continental Scientific Drilling Program, member of the Geologic Well Integrity Team during the Deepwater Horizon blowout and member of the Ocean Energy Safety Advisory Committee. Hickman received a bachelor’s degree in geology from Earlham College and a PhD in solid-earth geophysics from MIT. His accolades include the Superior Service and Meritorious Service Awards from the U.S. Department of Interior and the 2014 “Paul G. Silver Award for Outstanding Scientific Service” from the American Geophysical Union. Dr. Brocher said it has been a pleasure to serve as center director and to work with the USGS Earthquake Hazards, Volcano Hazards, and Energy Resources Programs. “I’ve enjoyed helping to guide the center’s research, hazard assessment, and monitoring activities to address the highest priorities of the USGS mission,” he said. “During that time we upgraded the seismic monitoring networks in the West Coast, tested a prototype earthquake early system, and investigated how to incorporate real-time GPS into earthquake early-warning systems.” Brocher said he looks forward to returning to work in the USGS Earthquake Science Center as a research geophysicist, where he will focus on improving and refining 3-D seismic velocity models that will be used to forecast strong ground motions in future earthquakes, as well as helping to assess earthquake hazards in the Pacific Northwest. |
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