Deterministic maximum peak bedrock acceleration maps for Utah (MP 02-11)
By: M. W. Halling, J. R. Keaton, L. R. Anderson, and W. Kohler
Maximum ground motion maps for the State of Utah were prepared for the Utah Department of Transportation to provide context for probabilistic ground motion maps. Deterministic procedures were used to prepare maps of both horizontal and vertical maximum peak bedrock acceleration.
Spatial data on Quaternary faults and folds inside Utah and within 100 km of Utah's border were collected from available sources. Where fault dip was uncertain, ground motion was modeled with the faults dipping both directions. Mean and 84th percentile Maximum Considered Earthquake (MCE) magnitudes were assigned to each fault based on fault rupture length and slip type using the relationships by Wells and Coppersmith (1994). Spatial earthquake-source data were managed and displayed using ArcView GIS.
Three recently developed ground motion attenuation relationships were considered, one of which is specific to extensional tectonic regimes, such as that found in Utah, and the others for comparison purposes. Mean and 84th percentile peak horizontal and vertical bedrock accelerations were calculated for the entire state for mean MCE magnitudes at points on a 1-km grid. The 1-km grid acceleration calculations were made with the Spatial Analyst extension to ArcView GIS. Contours of peak horizontal and vertical bedrock acceleration were interpolated from the grid values to prepare the maps.
The need for the deterministic ground motion map was based on observations that probabilistic values in some locations exceed deterministic values, and slip-rate data needed for probabilistic analyses typically are poor for Utah faults. The deterministic maps produced by this research provide the first systematic assessment of maximum peak bedrock accelerations for the State of Utah. Future research building on these maps could be maps of maximum bedrock spectral accelerations for selected fundamental periods, as well as the incorporation of soil or site effects where that information is available.
Pages: 57 p.
Media Type: Paper Publication and CD-ROM