ESS Mailing Address
Phone: 206-685-2803, 543-6626
Fax: 206-543-0489 (shared)
Research Groups: Seismology and Tectonics
Areas of Interest:
Seismology, inverse theory, tectonic tremor, volcanoes
Ph.D., Earth Sciences, University of California, San Diego, 1984
Current Research Interests:
My research has focused focus exploring dynamical processes within the Earth's deep interior by probing the Earth using seismic waves. Most recently I have been analyzing tremor signals in an attempt to understand slow slip along plate boundaries.
Slow Slip and Tremor
Slip along some subduction plate boundaries, down dip of megathrust earthquakes, occurs episodically during discrete slow-slip events. The slip is observed geodetically and is accompanied by low-amplitude tremor that is observed seismically. We are teasing out the secrets of this process by analyzing tremor on our 187-station Array of Arrays and other data sets. We are systematically detecting and locating tremor throughout Cascadia. The resulting epicenters of nearly 100,000 five-minute windows of tremor cluster in space and time into several hundred tremor swarms. The largest swarms correlate with geodetically observed slip and we infer that the smaller ones correspond to slip that is below current geodetic detection levels. The inferred slip events exhibit the same Gutenberg-Richter logarithmic frequency-magnitude relation as earthquakes with a b-value of 1. Smaller, more frequent slip events occur down dip, transferring stress up dip to the region containing the largest (moment magnitude 6.8) events. During the largest events, tremor migrates 10km/day along strike, with occasional reversals in direction at 10 times that rate and more frequent streaks that zip parallel to relative plate motion 100 times faster. We are also analyzing strong correlations between tremor amplitude and tidal stresses, Low-Frequency Earthquakes embedded in tremor that repeat one hundred times per day, as well as the fine structure of the subducting plate using tremor recorded at the arrays.
Previous Research Interests that I might get back to: (see my homepage for details):
Inner-Core Anisotropy and Rotation
Imaging discontinuities in the mantle
Seismic Imaging of Subducting Slabs
3-D Modeling of Slab Deformation
Wech, A. G. and K. C. Creager, 2011, A continuum of stress, strength and slip in the Cascadia transition zone, Nature GeoSci..,4, 1-5, doi:10.1038/ngeo121. Wech, A. G., K. C. Creager, H. Houston, and J. E. Vidale, 2010, An earthquake-like magnitude-frequency distribution of slow slip in northern Cascadia, Geophys. Res. Lett., doi:10.1029/2010GL044881, 1-5. Ghosh, A, J. E. Vidale, J. R. Sweet, K. C. Creager, A. G. Wech, H. Houston, and E. E. Brodsky, 2010, Rapid, continuous streaking of tremor in Cascadia, Geochem., Geophys., Geosyst., 11, Q12010, doi:10.1029/2010GC00330. Wech, A. G., K. C. Creager and T. I. Melbourne, 2009, Seismic and geodetic constraints on Cascadia slow slip, J. Geophys. Res., 114, B10316, doi:10.1029/2008JB006090, 1-9. La Rocca, M., K. C. Creager, D. Galluzzo, S. D. Malone, J. E. Vidale, J. R. Sweet, and A. G. Wech, 2009, Cascadia tremor located near plate interface constrained by S minus P wave times, Science, 323, 620-623, doi:10.1126/science.116711. Creager, K. C., 1999, Large-scale variations in inner core anisotropy, J. Geophys. Res., 104, 23127-23139.