Hosted/Tsunami_Hazard_Line (FeatureServer)

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Tsunami_Hazard_Line (0)

Description: Abstract: Produced collectively by tsunami modelers, geologic hazard mapping scientists, and emergency planning specialists from the California Geological Survey, the California Governor’s Office of Emergency Services, the Tsunami Research Center at the University of Southern California, and AECOM Technical Services. The Tsunami Hazard areas are developed for all populated areas at risk to tsunamis in California and represent a combination of the maximum considered tsunamis for each area. Local agencies, organizations, and other stakeholders assisted the State in the development of the hazard area as they will be used for evacuation planning at the community level.Data was projected by SanGIS to California NAD 83 State Plane.Tsunami modeling is performed by AECOM Technical Services and the University of Southern California funded through the California Governor’s Office of Emergency Services by the National Tsunami Hazard Mitigation Program and through FEMA. Recent tsunami modeling uses probabilistic tsunami hazard analysis to compute tsunami waves from sources from around the Pacific Ocean and results in inundation models that are associated with different probabilities of exceedance over time. The tsunami modeling process allows for wave evolution over a variable bathymetry and topography used for inundation mapping. The California Geological Survey, Seismic Hazards Program, Tsunami Unit selected the 975-year average return period tsunami model, with a 5% probability of exceedance in 50 years, as abasis for the minimum hazard level; this minimum hazard level, along with a suite of maximum credible events, helped define the extent for inundation mapping.For the probabilistic modeling the bathymetric/topographic data that are used in the tsunami models consist of a series of nested elevation grids. Deep ocean modeling is prepared using SRTM30+ bathymetric data (30 arc-second resolution). National Centers for Environmental Information coastal digital elevation models with a 1/3 arc-second (~10-meters) resolution and a “Mean High Water” vertical datum is used as the near-shore grids since these data represent a more conservative sea level for the intended use of the tsunami modeling and mapping. In order to enhance the 10-meter resolution inundation data, we use higher-resolution digital topographic data (e.g., 1-meter resolution LiDAR digital elevation models) to refine the location of the maximum inundation area. The location of the inundation area is refined by using digital imagery (e.g. recent National Agriculture Imagery Program imagery) and digital terrain data on a GIS platform with consideration given to historic inundation information. This information is verified, where possible, with workshops and fieldwork coordinated with local county personnel.Data from the California Geological Survey (CGS) Tsunami Inundation Maps for Emergency Planning {2009} and the enhanced high resolution mapping of the 975 year return period probabilistic tsunami inundation model results are initially used as a minimum spatial constraint for the placement of the Tsunami Hazard Area. Guidance from local stakeholders, including emergency managers, first responders, and subject matter experts is used to help advise CGS on the placement of the final hazard area in places that would help the public and government safely evacuate during a tsunami event. The accuracy of the hazard area shown on these maps and in these data is/are subject to limitations in the accuracy and completeness of the mapping conducted by the California Geological Survey. While an attempt has been made to define a maximum tsunami hazard extent at any location along the coastline, it remains possible that the actual Tsunami Hazard Area may be greater as required by the local agencies.

Service Item Id: fc0b591a03d84fa4a058b0b53bbf9b78

Copyright Text: California Geological Survey, Seismic Hazards Program, Tsunami Unit

Spatial Reference: 102646 (2230)

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