Task 4: Small Magnitude Scaling

In the last few years, there have been a large number of ground motion recordings for low-magnitude events in California from broadband instruments and Tri-net stations used in the ShakeMap program. Preliminary analysis of a limited subset of these recordings have indicated that the NGA West models over-predict low magnitude ground motions. This preliminary analysis has also suggested that small magnitude ground motions in southern California might be higher, on average, than ground motions in northern California. This task will collect these low-magnitude California recordings, process these recordings consistent with the current NGA database, compile the required metadata, compare the ground motions with the existing NGA West models, and modify the low-magnitude scaling characteristics of the NGA West models incorporating any regional differences between southern and northern California as required. For the purpose of this task, we limit an upper bound magnitude 6.0 for the collection and analysis of “low magnitude” earthquakes.