Geology topics

Robin Matoza

Publications and source records attributed to Robin Matoza.

5 recordsLinked to original sources

USGS2026

Bulk location and source mechanisms of repetitive long-period seismicity at Mount St. Helens in July 2005

The 2004–2008 eruption of Mount St. Helens exemplified the practical challenges of processing high seismic event rates and data volumes. This protracted multi-year eruptive sequence was accompanied by a near-continuous occurrence of long-period (LP, 0.5–5 Hz) seismicity, but network-based picks and locations have previously been performed for only a relatively small subset of the overall seismicity, and full-waveform source–mechanism inversions have previously been performed for just two event types during the eruption. We present a new workflow for the bulk detection, cluster picking, 3-D location, and full-waveform source–mechanism inversion of repetitive LP volcanic seismicity recorded by a local broadband seismic network. Our emphasis is on methods that: exploit waveform similarity (multiplets) commonly observed for volcanic LP seismicity swarms; can take into account 3-D topographic and velocity structure heterogeneity typical of volcanoes; can process high event rates with relatively low analyst burden; and do not require a priori catalogue picks or known waveform templates. We develop and illustrate the workflow using data from Mount St. Helens from 2005 June 29 to July 31, a time-window characterized by high-rate LP seismicity, including numerous lower amplitude small LPs, and for which relatively dense seismic network coverage is available. Approximately 40 per cent of seismicity (20 561 events out of 52 141 triggers) during 2005 June 29 to July 31 is repetitive enough to be grouped into 17 multiplets of at least 300 events. We present 3-D locations of the 17 multiplets, representing 20 076 events having picks from at least eight stations, along with full-waveform source mechanism inversions of the 17 separate multiplet stacks. Collectively, our seismic 3-D hypocentre distributions for 2005 June 29 to July 31 are compatible with sources around the margins of the upper conduit section that is associated with plug solidification. All location results indicate compact seismicity clusters, with the 17 multiplets spatially connected and collectively located at shallow depth, approximately ~ 775 m depth beneath the 1980s crater floor and directly beneath, or immediately adjacent to, the extruding dacite spine. The full-waveform source–mechanism inversions for the 17 multiplets generally indicate mechanisms dominated by volumetric components consistent with subhorizontal cracks along with minor contributions from subvertical cracks. The overall picture is that of a stack or plexus of subhorizontal cracks located at shallow depth beneath the extruding dacite spines, consistent with subhorizontal hydrofractures extending from the conduit margins into the surrounding wall rock; minor subvertical crack components of the mechanisms could possibly arise from surfaces parallel to the conduit wall, such as within the damage halo associated with degassing pathways.

Washington↗

USGS2025

Commentary on paper by Matoza et al. (2021): Catalog revision to a common depth datum

We present a revision and update to the high-precision relocated seismicity catalog presented by Matoza et al. (2021, https://doi.org/10.1029/2020ea001253 ) for the Island of Hawai'i from 1986 to 2018. The starting catalog of hypocenters (input data), on which the study by Matoza et al. (2021, https://doi.org/10.1029/2020ea001253 ) was based, contained an inconsistent depth datum for events before and after 00:00 UT, 29 December 2017. Here we present a recomputed version of the catalog using a consistent reference depth. We corrected the starting catalog to a common depth datum (all events now use the model depth reference datum) and re-ran the entire workflow as described in the paper by Matoza et al. (2021, https://doi.org/10.1029/2020ea001253 ). This included pairing, cross-correlating, and relocating all seismic events again based on the updated starting catalog. We consider 347,446 events representing 32 years of seismicity on and around the island from 1986 to 2018. We now successfully relocate 299,966 (86%) events using ∼2.53 billion differential times ( P and S ) from ∼194 million similar-event pairs, derived from cross-correlations between ∼887 million event pairs total, a significant increase from our original analysis. The resolution of fine-scale seismicity features is improved and the median depth of shallow events (<5 km) under Kaluapele (Kīlauea summit caldera) in 2018 is shifted 926 m deeper as a result of the change. The interpretations and other major conclusions in the paper by Matoza et al. (2021, https://doi.org/10.1029/2020ea001253 ) are unchanged.

Earth and Space Science↗

USGS2023

Back-azimuth estimation of air-to-ground coupled infrasound from transverse coherence minimization

We present the transverse coherence minimization method (TCM)—an approach to estimate the back-azimuth of infrasound signals that are recorded on an infrasound microphone and a colocated three-component seismometer. Accurate back-azimuth information is important for a variety of monitoring efforts, but it is currently only available for infrasound arrays and for seismoacoustic sensor pairs separated by 10 s of meters. Our TCM method allows for the analysis of colocated sensor pairs, sensors located within a few meters of each other, which may extend the capabilities of existing seismoacoustic networks and supplement operating infrasound arrays. This approach minimizes the coherence of the transverse component of seismic displacement with the infrasound wave to estimate the infrasound back-azimuth. After developing an analytical model, we investigate seismoacoustic signals from the August 2012 Humming Roadrunner experiment and the 26 May 2021 eruption of Great Sitkin Volcano, Alaska, U.S.A., at the ranges of 6.5–185 km from the source. We discuss back-azimuth estimates and potential sources of deviation (1°–15°), such as local terrain effects or deviation from common analytical models. This practical method complements existing seismoacoustic tools and may be suitable for routine application to signals of interest.

The Seismic Record↗

USGS2020

Co-eruptive tremor from Bogoslof volcano: Seismic wavefield composition at regional distances

We analyze seismic tremor recorded during eruptive activity over the course of the 2016–2017 eruption of Bogoslof volcano, Alaska. Only regional recordings of the tremor wavefield exist for Bogoslof, making it a challenge to place the recordings in context with other eruptions that are normally captured by local seismic data. We apply a technique of time-frequency polarization analysis to three-component seismic data to reveal the wavefield composition of Bogoslof eruption tremor. We find that at regional distances, the tremor is dominated by P-waves in the band from 1.5 to 10 Hz. Using this information, along with an enriched Bogoslof earthquake catalog, we obtain estimates of average reduced displacement ( D R ) for eruption tremor during 25 of the 70 Bogoslof events. D R reaches as high as approximately 40 cm 2 for two of the major events, similar to other VEI~3 eruptions in Alaska. Overall, average reduced displacement displays a weak correlation to plume height during the first half of the 9-month-long eruption sequence, with a few notable exceptions. The two events with the highest D R values also generated measurable eruption tremor at very-long-periods (VLP) between 0.05 and 0.15 Hz.

Alaska↗

USGS2017

Seismic equivalents of volcanic jet scaling laws and multipoles in acoustics

We establish analogies between equivalent source theory in seismology (moment-tensor and single-force sources) and acoustics (monopoles, dipoles and quadrupoles) in the context of volcanic eruption signals. Although infrasound (acoustic waves < 20 Hz) from volcanic eruptions may be more complex than a simple monopole, dipole or quadrupole assumption, these elementary acoustic sources are a logical place to begin exploring relations with seismic sources. By considering the radiated power of a harmonic force source at the surface of an elastic half-space, we show that a volcanic jet or plume modelled as a seismic force has similar scaling with respect to eruption parameters (e.g. exit velocity and vent area) as an acoustic dipole. We support this by demonstrating, from first principles, a fundamental relationship that ties together explosion, torque and force sources in seismology and highlights the underlying dipole nature of seismic forces. This forges a connection between the multipole expansion of equivalent sources in acoustics and the use of forces and moments as equivalent sources in seismology. We further show that volcanic infrasound monopole and quadrupole sources exhibit scalings similar to seismicity radiated by volume injection and moment sources, respectively. We describe a scaling theory for seismic tremor during volcanic eruptions that agrees with observations showing a linear relation between radiated power of tremor and eruption rate. Volcanic tremor over the first 17 hr of the 2016 eruption at Pavlof Volcano, Alaska, obeyed the linear relation. Subsequent tremor during the main phase of the eruption did not obey the linear relation and demonstrates that volcanic eruption tremor can exhibit other scalings even during the same eruption.

Geophysical Journal International↗