Fault rupture through the residential suburban neighborhood of Browns Valley in Napa caused extensive damage that is still being repaired, and fault afterslip is confounding repair work by residents. Patches need to be re-patched as the fault continues to creep. FEMA commissioned USGS to forecast the afterslip, a challenging task never before needed for any other earthquake in world history. The USGS used a variety of field observations including alinement array and GPS surveys, InSAR and UAVSAR data to develop a new quantitative new system for characterizing fault afterslip hazard, intended for practical application by residents and the City of Napa building officials to help guide decisions, for example in the design of repair work solutions by structural engineers. Over twenty homes along the fault rupture are expected to experience an additional 5 to 15 cm of fault afterslip during the next three years; an additional one hundred homes are expected to experience up to 5 cm of additional fault afterslip during the next three years. These amounts and rates of afterslip, although they do not pose a life safety concern, certainly are enough to potentially require repeated repair jobs over many years if not accounted for early in the repair design process.
Ken Hudnut is a Geophysicist for the Earthquake Science Center of the United States Geological Survey (since 1992) and a Visiting Associate in Geophysics on the faculty of the California Institute of Technology (since 1997) in Pasadena, California. He recently led the fault afterslip forecast for the South Napa earthquake for FEMA. To better understand earthquakes and faults, he incorporates real-time GPS into the ShakeAlert earthquake early warning system for the west coast of the US, and innovates systems for airborne imagery of active faults. From 2009-2012, he coordinated all USGS Earthquake Program work in Southern California and served as chair of the statewide California Integrated Seismic Network. He has served multiple terms on the boards of the Southern California Earthquake Center and UNAVCO. He recently conducted field studies after the earthquakes in Haiti and Baja California, Mexico and provided expertise to investigate damaging earthquakes in China. He led the earthquake source design for the ShakeOut scenario, a M 7.8 on the southern San Andreas fault, and has directly advised the Governor of California on the ‘Big One’ and the statewide earthquake threat. He received his Ph.D. (in Geology) from Columbia in 1989, and his A.B. (high honors in Earth Sciences) from Dartmouth in 1983.
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