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.