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75 <br /> <br />5.3.5 EARTHQUAKE SHAKING SCENARIOS <br /> <br />In addition to this effort, ABAG and USGS have developed several shaking scenario <br />maps that depict shaking intensity for specific, plausible earthquake scenarios with a <br />given magnitude on a fault. These maps show possible levels of ground shaking <br />throughout the Bay Area in a single likely earthquake, taking into consideration the <br />earthquake magnitude; rupture location and direction; and soil conditions <br />throughout the region. The scenarios that are most likely to cause strong shaking in <br />San Leandro are shown in Figures 5-7 and 5-8. The maps indicate that an earthquake <br />on the Hayward Fault has the greatest contribution to seismic hazard for San Leandro, <br />with an earthquake on the San Andreas Fault having additional contribution to <br />seismic hazard. <br /> <br />Scenario maps are helpful to model the expected shaking of an individual event, but <br />they do not depict the likelihood of the event occurring or whether it is the most <br />significant event for a particular location. A Probabilistic Seismic Hazard Assessment <br />(PSHA) Map incorporates the likelihood of ground shaking from all nearby fault <br />sources, and accounts for the frequency of each event. The PSHA Map in Figure 5-6 <br />illustrates the 10 percent or greater chance in a 50-year period that each location on <br />the map will exceed the MMI shown at least once. <br /> <br />In terms of risk characterization, it is equivalent to a 500-year flood. A 10 percent in <br />50 years hazard level was chosen as it most closely aligns to the levels of shaking used <br />in the current building code. Seismic hazard maps are not intended to be site-specific <br />but depict the general risk within neighborhoods and the relative risk from <br />community to community. <br /> <br />Events with strong shaking can still occur in areas with low probabilities shown in a <br />PSHA map. The area damaged by the 2014 South Napa Earthquake is one example of <br />a strong earthquake occurring in a location with lower risk probability than other <br />areas within the region. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />_______________________________________________________________________________________________ <br />12 Bryant, W.A., and Hart, E.W., (2007) <br />13 California Public Resources Code, Division 2, Geology, Mines and Mining, Chapter 7.5, Earthquake Fault Zoning, sections <br />2621-263 <br />14 ABAG, (2013). Modified Mercalli Intensity Scale <br />114