A document by Yiyuan Zhong. Click on the document to view its contents.

A document by Kaiwen Wang. Click on the document to view its contents.

Deep long-period earthquakes (DLPs) are often detected near volcanoes from the crust down to the upper mantle. Exhibiting coincidence with some 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 Alaskan volcanoes by frequency index (FI). The consistent differences in FI distribution between LPs and VTs across volcanoes suggest it can be leveraged for automatic classification. Presence of both VTs and DLPs in some regions suggests frequency content differences mainly arise from source effect. We then analyze 12 years of continuous waveforms by template matching and detect 20,979 DLPs. No repeating DLPs are identified below the depth of 10 km except ~1% of DLPs at Spurr Volcano, indicating source processes of DLPs at Alaskan volcanoes 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, only ~12% of DLP bursts occur simultaneously with VT bursts, suggesting most DLP rate anomalies are not directly linked to shallow volcanic unrests. Finally, since on average only ~26% of DLP rate anomalies coincide with eruption episodes, it is still challenging to foretell eruptions uniquely based on DLP occurrences.

At some submarine volcanoes, the influx and output of magma vary over time producing years-to-decades-long cycles of inflation and deflation, which in turn cause pronounced physical changes in the overlying oceanic crust and the hydrothermal circulation hosted within. Permeability within the oceanic crust exerts primary control on seafloor fluid circulation and hence has important influences on the heat and chemical exchange between the earth's lithosphere and oceanic hydrosphere, as well as surface and subsurface biological communities. Despite its importance, permeability is one of the most poorly constrained hydrologic properties for most of the mid-ocean ridge system. In this study, harmonic analysis of a high-resolution, long-term time series of effluent temperature measured at a high-temperature hydrothermal vent on Axial Seamount yields time-varying estimates of the effective permeability within the hydrothermal upflow zone. Comparing the records of permeability and volcanic deformation during and after the April-May 2015 eruption at Axial suggests a decrease in upflow-zone permeability during co-eruptive deflation and an increase in permeability during post-eruption re-inflation from July 2015 to June 2019. Modeling of the three-dimensional strain field suggests that the temporal variations in effective upflow-zone permeability can be explained by closing and opening of hydrothermal pathways that accompany crustal compression and extension in relation to the volcano's deformation cycle.

Both volcano-tectonic (VTs) and deep long-period earthquakes (DLPs) have been documented at Akutan Volcano, Alaska and may reflect different active processes. In this study, we perform high-resolution earthquake detection, classification, and relocation using seismic data from 2005-2017 to investigate their relationship with underlying magmatic processes. We find that the 2,787 VTs and 787 DLPs are concentrated above and below the shallow magma reservoir respectively. The DLPs’ low-frequency content is likely a source instead of path effect considering its uniformity across stations. Both VT and DLP swarms occur preferentially during inflation episodes with no clear migration. However, the largest VT swarms occur during non-inflating periods, and only VT swarms contain repeating events. Therefore, we conclude that the VTs represent fault rupture triggered by magma/fluid movement or larger earthquakes, while the DLPs are directly related to unsteady magma movement through a complex pathway or represent slow fault ruptures triggered by magma movement.