California Department of Transportation


About Caltrans ARS Online

This web-based tool calculates both deterministic and probabilistic acceleration response spectra for any location in California based on criteria provided in Appendix B of Caltrans Seismic Design Criteria.

The deterministic spectrum is determined as the average of median response spectra calculated using the Campbell-Bozorgnia (2008) and Chiou-Youngs (2008) ground motion prediction equations developed under the “Next Generation Attenuation” project coordinated through the PEER-Lifelines program. These equations are applied to all faults considered to be active in the last 750,000 years (late-Quaternary age) that are capable of producing a moment magnitude earthquake of 6.0 or greater. The probabilistic spectrum is obtained from the USGS (2008) National Hazard Map for 5% probability of exceedance in 50 years. Caltrans design spectrum is based on the larger of the deterministic and probabilistic spectral values. Both the deterministic and probabilistic spectra account for soil effects through incorporation of the parameter Vs30, the average shear wave velocity in the upper 30 meters of the soil profile.

The map layer of California faults was constructed at an approximate scale of 1:750,000 (1 inch = 12 miles). Use of the zoom tool can result in a detailed satellite image and fault overlay that gives the appearance of greater precision in mapped fault locations than there really is. Therefore this map is intended for use in ground motion evaluation and should not be used for project scale fault location. The user is referred to the Technical References section of this site for updates in fault information and map errata.

The Project Team

Xing Liu (
Tom Shantz(
Martha K Merriam(
Loren Turner (
Brian Chiou (

The GeoResearch Group
Division of Research & Innovation
5900 Folsom Blvd, MS-5, Sacramento CA, 95819

For questions or comments about this tool, please contact Tom Shantz by email or by phone at (916) 227-7245.

History of the Project

The development of Caltrans ARS Online was prompted by a larger effort to update the specification of seismic loading in Caltrans Seismic Design Criteria (SDC). The update had three primary thrusts:

Faced with the added complexity associated with applying the NGA ground motion prediction models as well as the adoption of probabilistic criteria to the creation of the design spectrum, the SDC update team launched an effort to develop a user friendly web based design tool for the development of design spectra that meet SDC criteria. Caltrans ARS Online is the product of those efforts.

    • Adoption of the latest source models. This led to the adoption, deletion, or relocation of many faults relative to the 1996 Caltrans Fault Map (Mualchin, 1996)
    • Adoption of recently developed Next Generation Attenuation (NGA) ground motion prediction models (Earthquake Spectra, Vol.24, No.1, Special Issue on the Next Generation Attenuation Project, February 2008)
    • Inclusion of a probabilistic component in the design spectrum specification.


This project has benefited greatly by the direct or indirect involvement of many individuals. The SDC update team was led by Mike Keever. The Geotechnical Services review/implementation team was led by Hector Valencia and John Bowman. Team members included Hossain Salimi, Reza Mahallati, Mahmoud Khojasteh, and Mark Yashinsky (Office of Earthquake Engineering). GIS support was provided by Ke Zhou. Management support was provided by Mark Willian and Tom Ostrom.

The earthquake source model is based primarily on the 2005 California Geological Survey (CGS) interim revision of the 1994 Jennings fault database with additions and modifications from the United States Geological Survey (USGS), CGS, United States Bureau of Reclamation (USBR), the Community Fault Model (CFM) by Harvard University and the Southern California Earthquake Center (SCEC), and many others. Revisions to the fault database are ongoing, sought through outside comments, and will be provided in a timely manner on the website. The project team thanks the CGS, in particular Bill Bryant and Chris Wills, for assistance and helpful suggestions.

The project team is very grateful to Steve Harmsen and Mark Petersen of the US Geological Survey, Golden, Colorado for providing the probabilistic hazard data used in Caltrans ARS Online. The team is also grateful to providers of the following information:

    • The Southern California model basin model (Z1.0 and Z2.5) implemented in Caltrans ARS Online based entirely on the Community Velocity Model (Version 4) developed by researchers at Harvard University and the Southern California Earthquake Center (SCEC).
    • The Northern California basin model implemented in Caltrans ARS Online based primarily on work by Cliff Thurber (University of Wisconsin – Madison) and Tom Brocher and Brad Aagard (US Geological Survey, Menlo Park, California).