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Merging Event Catalogs Using Agglomerative Hierarchical Clustering
SANDIA NATIONAL LABS LIVERMORE CA
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Many agencies construct catalogs of the hundreds of seismic events that occur daily around the world. The Ground-Based Nuclear Explosion Monitoring Research and Development GNEMRD program merges these catalogs together into a composite catalog containing multiple descriptions of the same seismic event, one from each catalog of interest. The merging process requires associating seismic events in individual catalogs herein called origins, that are independent estimates of the same seismic event. In this paper we describe application of classical cluster analysis techniques that provide a straightforward and robust solution to this merging problem. The resulting algorithm is much simpler to tune than the rule-based methodology used by EvLoader, which is the application currently used to merge catalogs in the GNEMRD program. For this study, we used a simple agglomerative hierarchical clustering technique to create clusters of similar origins where the various origins in a cluster represent different estimates of the seismic parameters of the same actual seismic event. Similarity between origins is calculated using a difference measure based on latitude, longitude, depth, time, and catalog author. Uncertainty in locations is accounted for by dividing distances between origins and differences in origin time by uncertainty estimates from the catalogs. To enforce the assumption that each catalog contains only a single origin for each event, origins from the same catalog are assigned infinite difference, regardless of other parameter values.
APPROVED FOR PUBLIC RELEASE