Characteristics of Deep Long-Period Earthquakes at Alaska Volcanoes From 2005 to 2017

Deep long-period earthquakes (DLPs) are often detected near volcanoes from the crust down to the upper mantle. Exhibiting coincidence with volcanic eruptions, DLPs are recognized as potential precursors to volcanic activities yet their detection remains challenging. Meanwhile, their relation to volcanic activities and specific source mechanisms remains uncertain. In this study, we first classify earthquakes into volcano-tectonic (VTs) and long-period (LPs) earthquakes at 10 Alaska volcanoes automatically by the consistent differences in frequency index. The co-location of both VTs and DLPs implies that the differences in their frequency content mainly arise from source effects. We then analyze 12 years of continuous waveforms by template matching and detect 5,421 new DLPs. Few potential repeating DLPs are identified, indicating their source processes are primarily non-repetitive. Detections of mantle DLPs and positive correlations between DLPs and volume change rate in the magma reservoir support the involvement of magmatic activities in some DLP sources, though there is limited correlation in DLP depth distribution with magmatic water content and kinematic parameters of plate motion. In addition, since only ∼17% of DLP bursts correlate with eruptions, with ∼8% occurring simultaneously with VT bursts, this suggests that most DLP bursts at Alaska volcanoes are not directly linked to shallow volcanic unrest. Therefore, their significance as potential precursors requires cautious evaluation before operational use in eruption forecasting.