A Specific Earthquake Processing Workflow for Studying Long‐Lived, Explosive Volcanic Eruptions With Application to the 2008 Okmok Volcano, Alaska, Eruption

Abstract

The rupture of rocks, as manifested by earthquakes, is an intrinsic part of volcanic eruptions. The seismic waves of earthquakes are the most readily observable aspect of rock failure and fluid flow during large scale eruptions. Seismicity is one of the most common precursors of eruptions and it often continues after an eruption ends. But what happens in between? How do the earthquakes progress during an eruption? These questions have been studied at length for effusive eruptions, but have been hampered by detection limits during sustained, large-scale explosive eruptions. Explosive eruptions are generally characterized by high-noise seismic wavefields produced by strong seismic tremor, explosions, collapses, and many other sources of seismic excitation, causing the surviving, on-scale seismograms in the near-field (<20 km) to be covered with continuous waves that obscure the signals of individual earthquakes, particularly the low magnitude ones.Our goal is to create a high-resolution earthquake catalog in near-field (i.e., high-noise environment) records during an extended explosive eruption to better understand co-eruptive earthquake dynamics. To accomplish this, we developed a specific seismic processing workflow that detects, associates, locates, relocates, computes local magnitudes, and finally classifies events in a binary way: volcano-tectonic earthquakes (VTs) or long-period

Trapdoor Fault Activation: A Step Toward Caldera Collapse at Sierra Negra, Galápagos, Ecuador

“…One key data set needed to discriminate between these two cases of exponential ground deformation would be the spatial distribution of earthquake hypocenters. Deflating reservoirs during eruptions tend not to have a clear alignment of hypocenters next to faults (e.g., Garza‐Giron et al., 2023; Ohlendorf et al., 2014), while in collapsing calderas the seismicity is located next to the normal ring‐faults and can increase in response to episodic caldera collapses controlled by fault friction (Gudmundsson et al., 2016). Unfortunately, there are few cases of eruptions with large ground deformation (>1 m), and with accurate hypocenter locations that can differentiate between earthquakes related to caldera ring‐fault activation or magma migration.…”

Earthquakes Record Cycles of Opening and Closing in the Enhanced Seismic Catalog of the 2008 Okmok Volcano, Alaska, Eruption

“…We discuss the creation of the enhanced seismic catalog in our complementary paper (Garza‐Girón et al., 2023). This high‐resolution catalog was built using continuous seismic waveform records from seven broad‐band and 16 short‐period instruments of the AVO and the Alaska Earthquake Center (AEC) networks (Figure 1) and multiple earthquake detection algorithms in tandem.…”

“…The distribution of percentage of energy below the 5 Hz threshold is bimodal, suggesting that the catalog is predominantly composed of two classes of events. Further details, including a discussion of uncertainties, are available in Garza‐Girón et al., 2023).…”

“…However, seismicity during long‐lived, explosive eruptions is practically invisible because of the extreme noise levels of the eruption itself. In a companion paper, we have set out a workflow to solve the detection problem utilizing modern earthquake detection methods (Garza‐Girón et al., 2023). As we showed in that paper, we can use a combination of traditional, machine learning and template matching approaches to expand the co‐eruptive seismic catalog of the 2008 Okmok Volcano eruption by about a factor of 10.…”

Recent advances in earthquake seismology using machine learning

“…Scotto di Uccio et al ( 2022) reported that a similar waveform search using FAST potentially complements events not detected using DL-based methods, although they achieved the best performance using a templatematching technique based on a template catalog developed using a DL-based method. The FAST algorithm has been used for induced earthquakes due to hydraulic fracturing and wastewater injection (Yoon et al 2017), induced earthquakes in gas fields (Scala et al 2022), swarms (Festa et al 2021), foreshocks (Yoon et al 2019b), and volcano seismicity (Garza-Girón et al 2023).…”