Bay Area Tsunami
Inundation Maps Summary Information
These maps, produced by California Emergency Management Agency (CalEMA) and California Geological Survey (CGS), are intended for local jurisdictional, coastal evacuation planning uses only. These maps do not represent inundation from a single scenario event. They were created by combining inundation results for a suite of realistic local and distant earthquakes and hypothetical extreme undersea, near-shore landslides, representing the worst-case scenario at any given location. These maps show inundation for the entire Bay Area Oceanside and inner Bay coastline, except for the north Coast of Sonoma County. Modeling was performed by the NOAA/OES-funded USC Tsunami Research Group and the results were verified in the field to improve accuracy.
Bay Area Tsunami
Inundation Frequently Asked Questions
1. How are the new maps different from the old maps?
2. Why is this map intended for evacuation planning only?
This map does not represent inundation from a single scenario event. It was created by combining inundation results for an ensemble of source events affecting a given region (Table 1). For this reason, all of the inundation region in a particular area will not likely be inundated during a single tsunami event. Tsunamis are rare events; due to a lack of known occurrences in the historical record, this map includes no information about the probability of any tsunami affecting any area within a specific period of time.
3. What is the purpose of this map?
This tsunami inundation map was prepared to assist cities and counties in identifying their tsunami hazard. It is intended for local jurisdictional, coastal evacuation planning uses only. This map, and the information presented herein, is not a legal document and does not meet disclosure requirements for real estate transactions nor for any other regulatory purpose.
Please
refer to the following websites for additional information on the construction
and/or intended use of the tsunami inundation map:
State of California Emergency Management Agency, Earthquake and Tsunami Program
University of Southern
California – Tsunami Research Center
State
of California Geological Survey Tsunami Information
National Oceanic
and Atmospheric Agency Center for Tsunami Research (MOST model)
4. What earthquake sources were used to develop this map?
A suite of tsunami source events was selected for modeling, representing
realistic local and distant earthquakes and hypothetical extreme undersea,
near-shore landslides (Table 1). Local tsunami sources that were considered
include offshore reverse-thrust faults, restraining bends on strike-slip fault
zones and large submarine landslides capable of significant seafloor
displacement and tsunami generation. Distant tsunami sources that were considered
include great subduction zone events that are known to have occurred
historically (1960
Table 1: Tsunami Sources modeled for the San Francisco Bay Coastline
|
Sources |
Moment magnitude used in modeled event |
|
|
Local Sources |
|
- |
|
Rodgers Creek-Hayward Faults |
- |
|
|
San Gregorio Fault |
- |
|
|
Distant Sources |
Cascadia Subduction Zone - full rupture |
9.0 |
|
Central Aleutians Subduction Zone #1 |
8.9 |
|
|
Central Aleutians Subduction Zone #2 |
8.9 |
|
|
Central Aleutians Subduction Zone #3 |
9.2 |
|
|
Chile North Subduction Zone |
9.4 |
|
|
1960 |
9.3 |
|
|
1964 |
9.2 |
|
|
Japan Subduction Zone #2 |
8.8 |
|
|
Kuril Islands Subduction Zone #2 |
8.8 |
|
|
Kuril Islands Subduction Zone #3 |
8.8 |
|
|
Kuril Islands Subduction Zone #4 |
8.8 |
|
|
Marianas Subduction Zone |
8.6 |
|
5. How was this map prepared?
Initial tsunami modeling was performed by the University of Southern
California (USC)
The bathymetric/topographic data that were used in the tsunami models consist of a series of nested grids. Near-shore grids with a 3 arc-second (75- to 90-meters) resolution or higher, were adjusted to “Mean High Water” sea-level conditions, representing a conservative sea level for the intended use of the tsunami modeling and mapping.
In order to enhance the result from the 75- to 90-meter inundation grid data, a method was developed utilizing higher-resolution digital topographic data (3- to 10-meters resolution) that better defines the location of the maximum inundation line (U.S. Geological Survey, 1993; Intermap, 2003; NOAA, 2004). The location of the enhanced inundation line was determined by using digital imagery and terrain data on a GIS platform with consideration given to historic inundation information (Lander, et al., 1993). This information was verified, where possible, by field work coordinated with local county personnel.
The accuracy of the inundation line shown on these maps is subject to limitations in the accuracy and completeness of available terrain and tsunami source information, and the current understanding of tsunami generation and propagation phenomena as expressed in the models. Thus, although an attempt has been made to identify a credible upper bound to inundation at any location along the coastline, it remains possible that actual inundation could be greater in a major tsunami event.
6. What base map was used for this map?
Topographic base maps prepared by U.S. Geological Survey as part of the 7.5-minute Quadrangle Map Series (originally 1:24,000 scale). Tsunami inundation line boundaries may reflect updated digital orthophotographic and topographic data that can differ significantly from contours shown on the base map.
7. References:
Intermap Technologies, Inc., 2003, Intermap product handbook and quick start guide: Intermap NEXTmap document on 5-meter resolution data, 112 p.
Lander, J.F., Lockridge, P.A., and Kozuch, M.J., 1993, Tsunamis Affecting the West Coast of the United States 1806-1992: National Geophysical Data Center Key to Geophysical Record Documentation No. 29, NOAA, NESDIS, NGDC, 242 p.
National Atmospheric and Oceanic Administration (NOAA), 2004, Interferometric Synthetic Aperture Radar (IfSAR) Digital Elevation Models from GeoSAR platform (EarthData): 3-meter resolution data.
Titov, V.V., and Gonzalez, F.I., 1997, Implementation and Testing of the Method of Tsunami Splitting (MOST): NOAA Technical Memorandum ERL PMEL – 112, 11 p.
Titov, V.V., and Synolakis, C.E., 1998, Numerical modeling of tidal wave runup: Journal of Waterways, Port, Coastal and Ocean Engineering, ASCE, 124 (4), pp 157-171.
8. Disclaimer:
The California Emergency Management Agency (CalEMA), the University of Southern California (USC), and the California Geological Survey (CGS) make no representation or warranties regarding the accuracy of this inundation map nor the data from which the map was derived. Neither the State of California nor USC shall be liable under any circumstances for any direct, indirect, special, incidental or consequential damages with respect to any claim by any user or any third party on account of or arising from the use of this map.