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Recent ETS results in NW Washington. Creager, Wech, Vidale, Sweet, Ghosh, Melbourne, Houston and Abers. Tremor Locations and Migration during last four ETS events Locked Zone relative to Tremor Location Inter ETS Tremor Swarms: Adds up to nearly as much as ETS tremor
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Recent ETS results in NW Washington Creager, Wech, Vidale, Sweet, Ghosh, Melbourne, Houston and Abers Tremor Locations and Migration during last four ETS events Locked Zone relative to Tremor Location Inter ETS Tremor Swarms: Adds up to nearly as much as ETS tremor Gutenberg-Richter Power-Law Distribution N = A -0.6 = a10-0.9Mw L = A 1/n n = 2-3 Tremor depths beneath arrays are near plate interface based on S-P times from cross correlation 100 LFEs within 100 m of each other are on plate interface Down-dip limit of tremor coincides with down-dip limit of low-velocity zone below plate interface (CAFE result)
Tremor Migration for four ETS events Wech, Creager and Melbourne, JGR, submitted
2004, 2005, 2007 ETS • Sharp western boundary to tremor • Consistently 75 km from tremor to 40% locking • Crustal earthquakes stop at eastern tremor boundary • Tremor is most active over water
ETS vs inter-ETS tremor Wech, Creager and Melbourne; JGR, submitted
Gutenberg-Richter Power-Law Distributionof Tremor Swarms N = A * -0.6 log10N=a10-bMw b=0.9 if moment proportional to duration Creager and Wech
Tremor Swarm Duration vs Length Slope=1/3 Slope=1 Slope=1/2 Creager and Wech
LFEs locate ~20km east of BS array at depth of ~47km, which is the depth to the plate interface at that location. Individual LFE S-P times vary by no more than 0.03s, suggesting they all locate within several hundred meters of each other.
Checking location by cross-correlation of horizontal with vertical across 5-minute windows Zero lag S-P time La Rocca, Science, next week
Checking location thrice Beam (rainbow) and envelope (green stars) S-P time La Rocca, Science, 2009
Abers, MacKenzie, Rondenay, Zhang, Wech, Creager, submitted, Geology
Every 15 months ETS BS Array * Creager & Wech
Inter ETS Tremor Feb 2007 to April 2008some patches repeat up to 5 times Creager and Wech
UW dense array pilot study 84 sensors in a km2, Caught 8 days with light tremor last March, then 17 days of heavy tremor passing directly underneath last May 1 km Time (days)