Hayward Fault: Bay Area Earthquake Scenarios

Bay Area Earthquake Scenarios

M6.7 Southern
Hayward Fault

In order to help with response and recovery planning, several "scenario" studies for earthquakes on the Hayward fault have been developed over the years. The California Geological Survey (formerly known as the California Division of Mines and Geology) has published scenario earthquake studies for most major California faults. Their 1987 study of the Hayward fault assumed a magnitude 7.5 earthquake with an offset averaging 2.3 meters (5 feet) for a 100 km segment of the fault. This study estimated that between 1,500-4,500 people would be killed in this event, depending on the time of day. In 1996, EERI published a report on a scenario earthquake of magnitude 7 on the Hayward fault. This study estimated that the earthquake would rupture 50 km with an average slip of 2 meters.

M6.5 Northern
Hayward Fault

As part of the 2003 Probability Study, the USGS has developed new earthquake scenarios for 34 possible future earthquakes in the San Francisco Bay Area, 6 of which involve portions of the Hayward and Rodgers Creek fault systems. The scenarios - length and location of rupture and event size - were used to predict the level of ground shaking from the earthquake using ShakeMap. ShakeMaps are normally produced within 5-8 minutes after an earthquake, to show the distribution of strong ground shaking, based on observations from seismometers. However, ShakeMap can also be used as a predictive tool, given a description of the scenario event.

M6.9 Northern &
Southern Hayward

While the ShakeMaps provide a general sense of the expected shaking, these maps do not include several important effects. In any large earthquake, the direction of rupture will strongly influence the ground shaking. The effect of directivity will strongly amplify motions in the direction of rupture. For example, if the scenario event on the Southern Hayward fault begins in Fremont and ruptures toward Berkeley, the shaking in Berkeley will be much stronger than if the earthquake starts in Berkeley and ruptures toward Fremont - for the same magnitude earthquake. Second, although the ShakeMaps do include the effect of surface soils, they do not include the effects of 3-dimensional wave propagation. Such effects will be very important in the deep basins of the Bay Area.

Earthquake scenarios can be extremely useful for planning. Many Bay Area agencies can draw upon these scenarios to plan response and recovery activities and for earthquake exercises and drills. UC Berkeley is using the Northern Hayward Fault M6.5 as the basis for their Quake2003 drill this year. The new scenarios include GIS shape files that can be used in damage and loss estimation programs such as HAZUS. More information about the scenarios is available from the USGS. The list of scenarios events for the Hayward and Rodgers Creek faults is below:

The Association of Bay Area Governments has used the new USGS scenarios to update their predictions of the impact on housing, lifelines, and other critical resources. A sampling of the reports from ABAG are below:

References

Earthquake Engineering Research Institute, Scenario for a Magnitude 7.0 Earthquake on the Hayward Fault, EERI, Oakland, CA, 109pp., paperback, 1996.
Steinbrugge K. et al., Earthquake Planning Scenario for a Magnitude 7.5 Earthquake on the Hayward Fault in the San Francisco Bay Area, CDMG Special Publication 78, 1987.
Toppozada T. et al., Planning Scenario for a Major Earthquake on the Rodgers Creek Fault in the Northern San Francisco Bay Area, CDMG Special Publication 112, 1994.

Hayward Fault
Home

Overview

Maps &
Tours

Monitoring &
Research

Seismicity &
Earthquake Potential

Hazards &
Preparedness