The USGS tracks non-earthquake seismic events here: https://earthquake.usgs.gov/earthquakes/search/.

This market resolves to YES if there is a ≥4.4 magnitude non-earthquake seismic event that occurs by April 1, 2024, according to the USGS. The event can be anywhere in the world. In the past, non-earthquake seismic events that have had this magnitude include volcanic eruptions, explosions, nuclear explosions, mine collapses, quarry blasts, rock bursts, and "other events."