Using ShakeMap and ShakeCast to Prioritize Post-Earthquake Dam Inspections

The use of ShakeMap in conjunction with the U. S. Geological Survey (USGS) ShakeCast software provides an effective means to notify engineering and field inspection staff of the occurrence of a potentially damaging earthquake and its potential impact at all dam locations around the State of California. The ShakeCast software automatically downloads a ShakeMap immediately after it is generated, and evaluates whether selected sites have experienced ground motions exceeding predefined threshold levels. ShakeCast automatically sends a customizable notification to identified individuals via e-mail, PDA, or cell phone apprising them of the results. Instrumental Intensity, based on a combined regression of recorded peak acceleration and velocity amplitudes, is our chosen threshold parameter because it better indicates damage potential than PGA alone. In the absence of custom threshold values determined by engineering analysis, we have selected Instrumental Intensity 5 as the "damage possible" threshold and Instrumental Intensity 8 as the "damage likely" threshold. The latter was selected because a significant percentage of dams that experienced Instrumental Intensity 8 and greater in the Loma Prieta and Northridge earthquakes, were damaged.