ARS Online Information

ARS Online updated to Version 3.1

To improve website performance, USGS 2008 hazard results are no longer provided. Version 3.1 supports USGS 2014 hazard information only.

Version 4.0 is coming soon!

ARS Online V4.0 will be released in the Fall of 2023. Key features include support for USGS 2018 hazard data and a Google Maps interface for site selection.

ARS Online updated to Version 3.0

Caltrans ARS Online was recently updated to satisfy two objectives:

  • Conform to Caltrans Web Accessibility for All (CWAA) requirements
  • Comply with Caltrans Seismic Design Criteria (SDC) Version 2.0
  • All external Caltrans websites must be CWAA compliant by Jan 1, 2020. Due to very limited development time, ARS Online V3.0 employs a very basic interface. This interface will be updated in the future to enhance functionality.

    Caltrans SDC 2.0 was adopted September 1, 2019. A major change in SDC 2.0 is the construction of the Design Spectrum . Previously, the Design Spectrum was constructed using the envelope of probabilistic and deterministic spectra. For SDC 2.0, the Design Spectrum is based on the USGS 975 year uniform hazard spectrum only. Effective December 1, 2019, the USGS hazard spectrum is based on the 2014 National Hazard Map per memorandum from the State Bridge Engineer. The updated Design Spectrum continues the use of near fault adjustment factors and basin amplification factors. The only change to these factors is the use of the Campbell-Bozorgnia (2014) and Chiou-Youngs (2014) basin amplification factors, updated from their 2008 models.

    Is ARS Online V2.3 still available?

    No. Version 2.3 has been removed from Caltrans servers.


    Caltrans' near fault adjustment factor is dependent on the site to source distance. For probabilistic analysis, the mean site-source distance is used based on a hazard deaggregation performed at 1s spectral period. This site-source distance represents the default value used in the ARS Online V3.0 calculation. The user can specify a different site-source distance.

    ARS Online V3.0 also reports a mean magnitude. This value is not used in the ground motion calculation. The mean magnitude is included to support simplified liquefaction analysis and is obtained from a hazard deaggregation performed at PGA.

    Error reporting and questions

    If you have a general question or if ARS Online is not working correctly please contact Tom Shantz at

    Kudos to the USGS Earthquake Hazards Program!

    This website is fully dependent on hazard information provided by the USGS Earthquake Hazards Program. Caltrans is highly appreciative of their critical work.