Update of the Urban Seismic and Liquefaction Hazard Maps for Memphis and Shelby County, Tennessee: Liquefaction Probability Curves and 2015 Hazard Maps

In 2012-2013, Memphis urban seismic hazard maps were updated and expanded to all of Shelby County, Tennessee, from the original six 7.5' quadrangles in 2004. The 2013 revised Memphis urban seismic hazard maps used an updated 3D geologic model, which led to a significant increase in hazard. In 2014-2015, we revised the geotechnical aspects of the 2004 hazard maps and adopted the U.S. Geological Survey (USGS) National Seismic Hazard Mapping Project (NSHMP) 2014 hazard model. We generated revised probabilistic and scenario ground motion and liquefaction urban hazard maps for 12+ quadrangles covering Shelby Co. The resulting 2015 probabilistic Memphis urban hazard maps showed similar seismic hazard (within 10%) to the 2013 maps, but reduced seismic hazard for the scenario maps compared to the 2013 maps, due to decreased ground-motion predictions by the 2014 NSHMP attenuation model. By including details about local geological, geotechnical, and geophysical conditions, the new seismic hazard maps tend to show lower peak ground acceleration (PGA) hazard compared to the B/C boundary 2014 USGS NSHMP, whereas the 1.0 s hazard is higher compared to the USGS 2014 maps. The 2004 liquefaction probability curves were revised using additional geotechnical boring information and updated water table information. Liquefaction hazard changes are mainly in the predictions for loess and alluvium, which show reductions and increases, respectively, from the 2004 equivalent hazard maps, due to improved modeling of liquefaction response from our 2014-2015 study. A public and professional outreach workshop was held 28 July 2015 to raise public, business, and professional awareness of Memphis area earthquake hazards and to disseminate the revised urban hazard maps produced in 2015.