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A Catalog Search Algorithm for Interpreting Complex Sequences

Current EEW algorithms are continuously optimized to strive for both timely and accurate ground motion estimates while also avoiding false alarms. However, they may still create missed or false events for complicated earthquakes. We aim to develop an algorithm that is able to handle such complicated cases, specifically foreshock-mainshock pairs and swarm-like sequences. Our algorithm finds earthquake source parameter estimates by matching the incoming observed ground motion envelope with two other types of envelopes that are based on the Cua-Heaton (CH) GMPEs and a catalog of earthquake history. To ensure that optimal parameter estimates are not missed, the algorithm is split into two independent approaches that check each other’s results: (i) a grid search that finds the best-fitting CH envelopes and (ii) a catalog search of envelopes from past real earthquakes and synthetic ground motions. In this talk, we focus on the second approach.

While the grid search gives average results, the second approach of the algorithm, the catalog search, provides more station-specific results. Here, we look for similar envelopes from nearby events. We find that in many cases, the catalog search reduces both error and computation time of the estimates given by the grid search. To ensure the catalog search works adequately and can handle complicated cases, we extend the catalog to cover a large enough range of earthquakes. We accomplish this by using Brune’s scaling model to produce unavailable data of large earthquakes from data of smaller ones. Also, we generate foreshock-mainshock pairs to include in the extended catalog by taking different combinations of envelopes and time delays. The goal is to create a catalog of complex sequences.

The advantage of matching envelopes is that it helps visualize when an abrupt signal arrives, such as a second, larger earthquake. With these two approaches working together, we hope to achieve an EEW algorithm that will not miss arrivals of multiple events.

Presenting Author: Becky H. Roh

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