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Summary The matched-filter technique is an effective way to detect repeats, or near-repeats, of a seismic source, but prior identification of an event from that source to use as a template is required. We propose a recursive matched-filter approach to systematically explore earthquake swarms, here applied to a swarm of volcanic long-period seismicity beneath Mount Sidley in Antarctica. We start with a single visually chosen template event with a high signal-to-noise ratio. We then extend our template database by selecting new templates to use in a subsequent matched-filter search from the newly detected set of events, allowing us to recursively expand the number of templates. We demonstrate that each iteration of the matched-filter search progressively extends the spatial coverage of our set of templates away from the original template event. In such a way, our proposed method overcomes the matched-filter search’s strictest constraint: that an event must already be identified to detect other similar events. Our recursive matched-filtering approach is well suited for the systematic exploration of earthquake swarms in both volcanic and tectonic contexts. 

Abstract How faulting processes lead to a large earthquake is a fundamental question in seismology. To better constrain this pre‐seismic stage, we create a dense seismic catalog via template matching to analyze the precursory phase of the Mw 6.1 L’Aquila earthquake that occurred in central Italy in 2009. We estimate several physical parameters in time, such as the coefficient of variation, the seismic moment release, the effective stress drop, and analyze spatio‐temporal patterns to study the evolution of the sequence and the earthquake interactions. We observe that the precursory phase experiences multiple accelerations of the seismicity rate that we divide into two main sequences with different signatures and features: the first part exhibits weak earthquake interactions, quasi‐continuous moment release, slow spatial migration patterns, and a lower effective stress drop, pointing to aseismic processes. The second sequence exhibits strong temporal clustering, fast seismicity expansion, and a larger effective stress drop typical of a stress transfer process. We interpret the differences in seismicity behaviors between the two sequences as distinct physical mechanisms that are controlled by different physical properties of the fault system. We conclude that the L’Aquila earthquake is preceded by a complex preparation, made up of different physical processes over different time scales on faults with different physical properties.