Geophysics and Seismology

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    Dataset: Ocean-bottom P and S arrival waveform dataset from the Alaska Amphibious Community Seismic Experiment, 2018-19
    Barcheck, Grace (2023-11)
    This archive contains an earthquake waveform dataset and corresponding metadata generated from offshore seismic data collected in 2018-19 as part of the Alaska Amphibious Community Seismic Experiment (AACSE) (Ruppert et al., 2022, SRL; Barcheck et al., 2020, SRL; Abers et al., 2019, EOS). AACSE was deployed May 2018 through August 2019, and the experiment collected seismic data both on- and off-shore along a stretch of the Alaska-Aleutian subduction zone near the Alaska Peninsula. The Alaska Earthquake Center created the authoritative, analyst-checked earthquake catalog for the experiment (Ruppert et al., 2022). Waveforms are cut out relative to the analyst-checked P and S picks, for all events within 350 km epicentral distance. Data are from ocean-bottom seismometers and collocated hydrophones only; no land data are included. Datasets are intended to be used for machine learning training with seismic data.
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    Data from: Active normal faulting, diking, and doming above the rapidly inflating Laguna del Maule volcanic field, Chile imaged with CHIRP, magnetic, and focal mechanism data
    Peterson, Dana; Garibaldi, Nicolas; Keranen, Katie; Tikoff, Basil; Miller, Craig; Lara, Luis E.; Tassara, Andres; Thurber, Clifford; Lanza, Federica (2020)
    Data in support of the following research: The Laguna del Maule volcanic field (LdMVF) in Chile, a rapidly inflating silicic volcanic system without historical eruption, is intersected by active regional faults. The LdMVF provides an opportunity to observe how faults influence, accommodate, or are driven by an actively deforming large silicic system. Here we use Compressed High Intensity Radar Pulse (CHIRP) acoustic reflection data to map the fault network in sediments captured within the eponymous lake at the LdMVF, and combine our fault maps with the volcanic history, earthquake locations, focal mechanisms, and lacustrine magnetic data to interpret how faults and magmatism interact. Our seismic data image dominantly dip-slip faults forming grabens within the lake, subparallel to regional faults. No indications exist in the seismic data to suggest that fault patterns were created by the volcanic system, either ring or radial faults. Fault strikes interpreted from seismic and magnetic data are consistent with mapped dike and fault orientations on land. We therefore interpret that active faults at the LdMVF are tectonic rather than volcanic in origin, forming a transtensional zone that hosts the magmatic system. However, vertical motion along a NS-striking fault near the center of uplift suggests trapdoor-style faulting above the volcanic center in which tectonic faults are reactivated to accommodate magmatic inflation and overlying deformation. Magnetic anomalies follow regional faults, suggesting that faults also provide migration pathways. Depositional patterns indicate a prior episode of uplift followed by quiescence, indicating that significant magmatically related uplift at the LdMVF can occur without an associated major eruption.
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    Data from: Shear velocity structure from ambient noise and teleseismic surface wave tomography in the Cascades around Mount St. Helens
    Crosbie, Kayla J; Abers, Geoffrey A; Mann, Michael Everett; Janiszewski, Helen A; Creager, Kenneth C; Ulberg, Carl; Moran, Seth C (2019)
    Mount St. Helens (MSH) lies in the forearc of the Cascades where conditions should be too cold for volcanism. To better understand thermal conditions and magma pathways beneath MSH, data from a dense broadband array are used to produce high-resolution tomographic images of the crust and upper mantle. Rayleigh-wave phase-velocity maps and three-dimensional images of shear velocity (Vs), generated from ambient noise and earthquake surface waves, show that west of MSH the mid-lower crust is anomalously fast (3.95 ± 0.1 km/s), overlying an anomalously slow uppermost mantle (4.0-4.2 km/s). This combination renders the forearc Moho weak to invisible, with crustal velocity variations being a primary cause; fast crust is necessary to explain the absent Moho. Comparison with predicted rock velocities indicates that the fast crust likely consists of gabbros and basalts of the Siletzia terrane, an accreted oceanic plateau. East of MSH where magmatism is abundant, mid-lower crust Vs is low (3.45-3.6 km/s), consistent with hot and potentially partly molten crust of more intermediate to felsic composition. This crust overlies mantle with more typical wavespeeds, producing a strong Moho. The sharp boundary in crust and mantle Vs within a few km of the MSH edifice correlates with a sharp boundary from low heat flow in the forearc to high arc heat flow, and demonstrates that the crustal terrane boundary here couples with thermal structure to focus lateral melt transport from the lower crust westward to arc volcanoes. This dataset supports the research described here.
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    Synthetic data from: Enhanced resolution of the subducting plate interface in Central Alaska from autocorrelation of local earthquake coda
    Kim, Doyeon; Keranen, Katie; Abers, Geoff; Brown, Larry (2018)
    This dataset supports the following research: Subducting plates below 10‐km depth are primarily imaged using phases from teleseismic earthquakes at frequencies dominantly below 1 Hz, resulting in low‐resolution images compared to fault zone thickness. Here we image the plate boundary zone in Alaska using scattered body wave arrivals in local earthquake coda to produce a higher‐resolution image of the slab. An autocorrelation method successfully extracts coherent arrivals from the local earthquake signals. Our autocorrelation results image interfaces associated with the subducting oceanic plate at higher resolution than our teleseismic receiver functions, with increased coherence and sharper boundaries. Our results provide one of the first coherent structural images of the seismogenic zone using scattered local body waves. Amplitudes suggest that seismic wave speed decreases with increasing depth within the low‐velocity zone, supporting lithologic rather than purely overpressure models for the zone in our region. Similar methodologies using dense stations could provide higher‐resolution images to characterize crustal and uppermost mantle boundaries globally.