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Recent ETS results in NW Washington

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

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  1. 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)

  2. Tremor Migration for four ETS events Wech, Creager and Melbourne, JGR, submitted

  3. Tremor and Slip summed over 4 ETS events

  4. 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

  5. ETS vs inter-ETS tremor Wech, Creager and Melbourne; JGR, submitted

  6. 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

  7. Tremor Swarm Duration vs Length Slope=1/3 Slope=1 Slope=1/2 Creager and Wech

  8. An hour of LFEs

  9. 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.

  10. Checking location by cross-correlation of horizontal with vertical across 5-minute windows Zero lag S-P time La Rocca, Science, next week

  11. Checking location thrice Beam (rainbow) and envelope (green stars) S-P time La Rocca, Science, 2009

  12. LaRocca et al., Science, 2009

  13. Schematic interpretation of receiver function results.

  14. Abers, MacKenzie, Rondenay, Zhang, Wech, Creager, submitted, Geology

  15. Every 15 months ETS BS Array * Creager & Wech

  16. Inter ETS Tremor Feb 2007 to April 2008some patches repeat up to 5 times Creager and Wech

  17. 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)

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