The Version 4.0 update incorporates several important changes:
ARS Online V4.0 obtains response spectrum data for different return periods using the USGS applications program interface (API). ARS Online applies near-fault adjustment factors as required by Caltrans Seismic Design Criteria (SDC) V2.1. Any inconsistencies in the base response spectrum (i.e. without near-fault adjustment factors applied) between ARS Online and the USGS Hazard Toolbox are due to inconsistencies between the different USGS hazard platforms themselves and not due to additional calculations performed by ARS Online. Caltrans has studied the differences between USGS platforms and found them to be too small to affect engineering design. Caltrans considers all hazard data from the USGS equally valid, regardless of the platform used.
To improve website performance, USGS 2008 hazard results are no longer provided. Version 3.1 supports USGS 2014 hazard information only.
Caltrans ARS Online was recently updated to satisfy two objectives:
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.
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.
If you have a general question or if ARS Online is not working correctly please contact Tom Shantz at thomas.shantz@dot.ca.gov.
This website is fully dependent on hazard information provided by the USGS Earthquake Hazards Program. Caltrans is highly appreciative of their critical work.