37-7 What Can Shear Wave Splitting (SWS) Analysis Tell Us About Mt. Spurr’s 2004-6 Unrest Episode?

Session: Geoscience Research Poster Showcase by 2YC and 4YCU Undergraduate Students

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Between 2004 and 2006, Mount Spurr, Alaska, experienced unusual volcanic unrest that included the formation of an ice cauldron within the summit vent, episodic development of a roiling summit lake, debris flows, increased fumarolic activity, and expansion of exposed steaming rock. Although this unrest did not culminate in an eruption, its surface manifestations indicated substantial changes within the volcanic system. Examining such non-eruptive unrest contributes to the development of a broader shear-wave splitting reference framework that may ultimately help distinguish signals preceding eruptions from those associated with unrest that subsides without eruption.

We applied shear-wave splitting analysis to local earthquakes recorded by four three-component seismic stations surrounding Mount Spurr between 2004 and 2006. Of 1,515 event-station pairs from 989 unique earthquakes within the shear-wave window, 511 produced acceptable splitting measurements used in the final interpretation. Fast polarization directions and delay times were highly variable and showed no systematic temporal or depth-dependent trends. In contrast, apparent percent anisotropy varied strongly with earthquake depth. Shallow earthquakes exhibited a broad range of values, including the highest apparent anisotropy observed in the dataset, whereas earthquakes originating at greater depths consistently produced low apparent anisotropy throughout the unrest period.

These results indicate that anisotropy was not distributed uniformly throughout the full crustal volume sampled by the ray paths. The contrast between shallow and deep events is consistent with a relatively localized shallow anisotropic region whose contribution becomes proportionally smaller along longer ray paths passing through more weakly anisotropic crust. This study demonstrates how shear-wave splitting measurements from non-eruptive unrest can contribute to comparative assessments of subsurface volcanic processes. This work was conducted as part of the Geo-Launchpad internship program, supported by the NSF NGF operated by EarthScope Consortium.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-21480

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