Seismic monitoring on the East Pacific Rise at 9°50'N


This project continuous analysis of seismic data collected by ocean bottom seismometers (OBSs) deployed at the Ridge 2000 Integrated Study Site at 9°50'N on the East Pacific Rise from October 2003 through January 2007. The goal of this OBS experiment was to gain insight into the inner workings of fast spreading Mid Ocean Ridge (MOR) systems and to help better understand the linkages between geophysical, geochemical, and biological processes at the 9°50'N site. The OBS array recorded over 200,000 micro-earthquakes within a 4x4 km footprint, capturing the build up of seismicity leading to a sea floor eruption in January 2006.
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The erupted magma buried and damaged several instruments close to the ridge axis. Three OBSs survived the crisis. The photos below show OBSs trapped in magma and Alvin's operations to rescue the instruments some 2500 m below the sea surface. [Photos courtesy of Dan Fornari and the Alvin crew.]

Analysis of this worlwide unique data set reveal, among other findings, the build up of seismicity towards the eruption (Tolstoy et al. 2006), the triggering of earthquakes during peak extentional stresses (Stroup et al. 2007, 2009), the existence of along axis hydrothermal circulation cells (Tolstoy et al. 2008), stress conditions within the ciruculation cells (Bohnenstiehl et al. 2008), and the seismogenic processes associated with magma inflation and fluid circulation (Waldhauser et al. 2011).

For a 3D interactive high-resolution view of the seismicity recorded during the first deplyment click here.

The EPR data set represents a significant challenge for processing and analysis because of both the nature of the signals (earthquakes, tremor, whale calls, ocean noise, etc) and the tremendous number of earthquakes in close spatial and temporal proximity. We continue to work on new analysis tools that allow us to image a complete picture of seismicity and detect temporal changes in the velocity structure and seismogenic stress evolution during the various phases of eruption preparation.

Waldhauser, F. and M. Tolstoy, Seismogenic structure and processes associated with magma inflation and hydrothermal circulation beneath the East Pacific Rise at 9°50'N, Geochem. Geophys. Geosyst., 12, Q08T10, doi:10.1029/2011GC003568, 2011. [PDF]

Monigle, P., D.R. Bohnenstiehl, M. Tolstoy, and F. Waldhauser, Seismic tremor at the 9°50'N East Pacific Rise eruption site, Geochem. Geophys. Geosyst., 10, Q11T08, doi:10.1029/2009GC002561, 2009. [PDF]

Stroup, D.F., M. Tolstoy, T.J. Crone, A. Malinverno, D.R. Bohnenstiehl, and F. Waldhauser, Systematic along-axis tidal triggering of microearthquakes observed at 9°50'N East Pacific Rise, Geophys. Res. Lett., 36, L18302, doi:10.1029/2009GL039493, 2009. [PDF]

Dziak, R.P., D.R. Bohnenstiehl, H. Matsumoto, M.J. Fowler, J.H. Haxel, M. Tolstoy, and F. Waldhauser, The January 2006 seafloor-spreading event at 9°50'N, East Pacific Rise: Ridge dike intrusion and transform fault interactions from regional hydroacoustic data, Geochem. Geophys. Geosyst., 10, Q06T06, doi:10.1029/2009GC002388, 2009. [PDF]

Bohnenstiehl, D.R., F. Waldhauser, and M. Tolstoy, Frequency-magnitude distribution of microearthquakes beneath the 9°50'N region of the East Pacific Rise, October 2003 through April 2004, Geochem. Geophys. Geosyst., 9, Q10T03, doi:10.1029/2008GC002128, 2008. [PDF]

Lutz, R.A., T.M. Shank, G.W. Luther III, C. Vetriani, M. Tolstoy, D.B. Nuzzio, T.S. Moore, F. Waldhauser, M. Crespo-Medina, A.D. Chatziefthimiou, E.R. Annis, and A.J. Reed, Interrelationships between vent fluid chemistry, temperature, seismic activity, and biological community structure at a mussel-dominated, deep-sea hydrothermal vent along the East Pacific Rise, J. of Shellfish Research, 27 (1), 177-190, 2008. [PDF]

Tolstoy, M., F. Waldhauser, D.R. Bohnenstiehl, R.T. Weekly, and W.-Y. Kim, Seismic identification of along-axis hydrothermal flow on the East Pacific Rise, Nature, 451, 1920-1922, doi:10.1038/nature06424, 2008. [PDF]

Stroup, D.F., D.R. Bohnenstiehl, M. Tolstoy, F. Waldhauser, R.T. Weekly, Pulse of the seafloor: Tidal triggering of microearthquakes at 9°50'N East Pacific Rise, Geophys. Res. Lett., 34, L15301, doi:10.1029/2007GL030088, 2007. [PDF]

Tolstoy, M., J.P. Cowen, E.T. Baker, D.J. Fornari, K.H. Rubin, T.M. Shank, F. Waldhauser, D.R. Bohnenstiehl, D.W. Forsyth, R.C. Holmes, B. Love, M.R. Perfit, R.T. Weekly, S.A. Soule, B. Glazer, A sea-floor spreading event captured by seismometers, Science, 314, 1920-1922, 2006. [PDF]