Tsunami scenario affecting California coastal communities (USGS SAFRR project)

Corrie Neighbors, University of California, Riverside

Summary
 

Los Angeles is known for earthquake, wildfire, and mass movement (mudslide) hazards, but less emphasis has been placed on preparing for tsunamis. Should a tsunami flow onto the southern California coastline it would affect thousands of residential homes and commercial structures and, most importantly, the Ports of Los Angeles and Long Beach. The SAFRR (Science Application for Risk Reduction) scenario was developed to better understand tsunami impacts to California coastal communities. The earthquake and resulting tsunami scenario is based on historic earthquake events in the Alaskan-Aleutian subduction zone that caused known inundation, or flooding, along the state's coastline. The earthquake source is approximately a Mw9 event, which produces tsunami wave heights up to 5m that arrive on the California coastline hours after the tsunami is generated. 

This case study and tsunami-genic scenario was motivated by the Tohoku-Oki earthquake and tsunami disaster and involved a large team of scientists – state and federal government agencies, academic institutions, and private consulting firms – to construct a realistic, worst-case scenario from historic data and modeling constraints. In addition to the geoscience, much work has gone into estimating the socio-economic and environmental impacts (e.g., hazardous debris in coastal waters and altered wildlife ecosystems) from this potential disaster. It is calculated that at least 1/3 of all boats in coastal harbors and ports will experience damage or sink and 1/2 of docks and piers will be damaged or destroyed during this scenario; overall, damage to coastal structures could be up to $8-billion statewide. 

Another aspect of the project is to increase awareness and preparedness in the state. Scientists worked with the Art Center College of Design in Pasadena to create a video narrative featuring Sue Nami (get it?!) to inform people about the dangers of tsunamis and how to react to offshore earthquakes and their corresponding tsunamis.

Individuals with expertise/responsibilities in the following areas have helped create the case study:

• Physics-based computer modelers (Earthquake and Tsunami)
• Geologists
• Emergency Response (Economic and engineering-based risk modelers)
• Public preparedness (Emergency drills and table top exercises)

Key teaching points:

• Science of offshore earthquakes and tsunamis
• Coastal hazards from tsunamis
  • time-dependent wave arrivals and corresponding height, i.e., the first wave may not be the biggest
  • wave arrival and height varies by shape and slope of the coastline
• Socio-economic damage dependent on geographic location of businesses and ports
• Appropriate actions for coastal communities when a tsunami-genic earthquake occurs

How this example is used in the classroom:
This real-world example is utilized when the tsunami hazard module is discussed in lecture.

References

The First Sue Nami – public service video describing tsunami awareness
http://vimeo.com/62595618

The SAFRR website with links to scenario reports and tsunami propagation video
http://www.usgs.gov/natural_hazards/safrr/projects/tsunamiscenario.asp

SAFRR scenario interactive WebGIS where tsunami flooding data can be investigated by California address or county.
https://www.usgs.gov/natural-hazards/science-application-risk-reduction/science/haywired-scenario?qt-science_center_objects=0#qt-science_center_objects