Observational Evidence of a Very‐Low‐Frequency Earthquake ( <i>M</i> _w 3.8) Leading to an Earthquake ( <i>M</i> _w 4.2): Minto Flats Strike‐Slip Fault Zone, Central Alaska

Abstract The physical conditions governing earthquake initiation are largely unknown, particularly in the minutes to seconds preceding rupture. While there is geodetic and seismic evidence of precursory activity in the hours to weeks prior to large earthquakes, the observational evidence immediately preceding the earthquake rupture is limited and controversial. Here we present evidence of a well‐recorded earthquake from the Minto Flats fault zone in central Alaska having 43 s of high‐frequency precursory signals. Within these signals was a M w 3.8 very‐low‐frequency earthquake (VLFE) on a dipping strike‐slip fault. The VLFE was followed by a M w 4.2 earthquake having the same focal mechanism as the VLFE. The distinct signals and the close similarity in focal mechanisms between the VLFE and the earthquake provide evidence for a slow‐to‐fast rupture transition during earthquake initiation.