Detecting Real Earthquakes Using Artificial Earthquakes: On the Use of Synthetic Waveforms in Matched‐Filter Earthquake Detection

Matched‐filters are an increasingly popular tool for earthquake detection, but their reliance on a priori knowledge of the targets of interest limits their application to regions with previously documented seismicity. We explore an extension to the matched‐filter method to detect earthquakes and low‐frequency earthquakes on local to regional scales. We show that it is possible to increase the number of detections compared with standard energy‐based methods, with low false‐detection rates, using suites of synthetic waveforms as templates. We apply this to a microearthquake swarm and an aftershock sequence, and to detect low‐frequency earthquakes. We also explore the sensitivity of detections to the synthetic source's location and focal mechanism. Source‐receiver geometry has a first‐order control on how sensitive matched‐filter detectors are to variations in source location and focal mechanism, and this likely applies to detections made using both synthetic and real templates. Plain Language Summary Matched‐filters measure the similarity between continuous waveforms and template waveforms. These filters provide an effective means of detecting scaled copies of the template in seismic data, often enabling the detection of small earthquakes in noisy data. This makes them an excellent tool for detecting earthquakes in noisy environments or during sequences of many earthquakes occurring in a short time. However, matched‐filters require a known waveform to look for and are therefore not useful when studying a new area with no prior information. This paper describes an extension to the matched‐filter method in which synthetic waveforms are used as template events. We show that even simple synthetics generated using a very naïve model of the Earth and the earthquake source are capable of detecting real seismicity. Key Points Synthetic waveforms are shown to detect real earthquakes in matched‐filter routines LFEs, aftershocks, and other seismicity can be detected with little a priori knowledge Matched‐filters with synthetic templates outperform energy‐based detection routines in some cases