Observations from multiple seiche load induced transient strains constrain the upper crustal magma reservoir beneath Yellowstone Caldera.
Abstract
The Yellowstone Volcanic field is characterized by significant hydrothermal activity, ground deformation, and seismicity centered on the 640 ka Yellowstone Caldera (YSC). Continued monitoring and characterization of the Earth's crust beneath the YSC and of the magma reservoir is important for the evaluation of hazard in the region. Multiple periodic strain events induced by large (>7 cm) sudden-onset long period standing waves (seiche waves) in Yellowstone Lake (YSL), can be observed on five borehole strainmeters (BSM) of UNAVCO's Plate Boundary Observatory, two near ( 100 m) and 3 distant ( 20 km) from the shores of YSL. These episodic strain events onset abruptly and persist a few hours up to day(s) and have a remarkably consistent period ( 78 minutes). We measure the horizontal strain components (areal strain ɛa, differential strain ɛd, and engineering strain ɛs) induced by six of these seiche load events, observed between August 2014 - September 2015 on the BSMs. Observed peak-to-peak amplitudes of ɛa during these events range from 6 - 20 ns and 4 - 9 ns at BSMs near and distant from YSL respectively. We evaluate YSC subsurface properties by comparing observed strain amplitude values to predicted values of a modeled strain field in the YSC due to a seiche wave load in YSL. The 3-D model is composed of an elastic layer underlain by a viscoelastic half-space, analogous to a layer of partial melt within the YSC subsurface relaxing stresses imposed at the surface, loaded at the surface with a vertical tractions representing the true shape of the fundamental (longest-period) peak-to-trough seiche wave of YSL. Modeled strain fields with varying values of melt depth, melt viscosity, and country rock rigidity are compared. Preliminary results from the six observed strain events suggest that the depth to the upper limits of the magma reservoir or body of partial melt in the YSC subsurface is no shallower than 6km, independent of, and consistent with seismic tomography studies.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.G33A1081G
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITYDE: 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITYDE: 1294 Instruments and techniques;
- GEODESY AND GRAVITYDE: 8419 Volcano monitoring;
- VOLCANOLOGY