Seismic Tremor at Brothers Volcano: A Comparative Case Study

D.R. Bohnenstiehl¹*, P.W. Monigle¹, R.P. Dziak², J.H. Haxel² & H. Matsumoto²

Corresponding author: drbohnen@ncsu.edu
¹Department of Marine, Earth and Atmospheric Science, NC State University, Raleigh NC 27695
²Oregon State University, NOAA Cooperative Institute for Marine Resources Studies, Newport, OR 97365

Spectral cross-correlation methods are used to detect mono- and poly-chromatic tremor sources recorded at a set of three ocean bottom hydrophones (OBH’s) deployed in the caldera of Brothers Volcano within the Kermadec Arc. The data span a period of seven months. As reported by Dziak et al. [2008], these signals are not coherent between closely space (<2 km) stations, suggesting that they are sourced from multiple sites within the upper crust. Tremor activity is clustered during times of increasing tidally induced extension, with relative quiescence observed during times of compression. This suggests that fluid and gas pressures build up during the compressive strain period, when cracks are closed, and are released as the strain field reverses and cracks open. Consistent with this model, we observed that the typically louder poly-chromatic signals occur preferentially in the period immediate after the tidally-modulated strain field moves from compression to extension.

Keywords:
Seismic tremor, fluid flow, tidal processes, hydrology

Contributions to Integration and Synthesis:
Shallow, fluid-driven tremor signals have been reported along both the Juan de Fuca Ridge near Axial Volcano [Tolstoy et al., 2002] and within 9°50’N Integrated Study Site [Monigle et al., in review]. At 9°50’N, where they have been studied in detail during a period of 41-months, tremor also is tidally modulated. However, unlike Brothers Volcano, different stations show distinct temporal relationships with respect to the tidal strain field, with activity at some stations being dominant during periods of extension and others during times of compression. Comparing observations between ridge crest sites and other submarine environments provides and important opportunity to understand the mechanics of tremor generation and the hydrology of the shallow subsurface at both locations.

References:
Dziak, R.P., et al. Observations of regional seismicity and local harmonic tremor at Brothers volcano, south Kermadec arc, using and ocean bottom hydrophone array, J. Geophys. Res., 113, 2008.
Monigle et al., Seismic Tremor at the 9°50'N East Pacific Rise Eruption Site, in review, G-cubed 2009.
Tolstoy et al., Breathing of the seafloor: Tidal correlations of seismicity at Axial Volcano, Geology 30, 503-506, 2002.