recent ets results in nw washington tremor locations and migration during last four ets events...
Post on 15-Jan-2016
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Recent ETS results in NW Washington
Tremor Locations and Migration during last four ETS eventsLocked Zone relative to Tremor LocationInter ETS Tremor Swarms:
Adds up to nearly as much as ETS tremorGutenberg-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 interfaceDown-dip limit of tremor coincides with down-dip limit of low-velocity zone
below plate interface (CAFE result)
Creager, Wech, Vidale, Sweet, Ghosh, Melbourne, Houston and Abers
Tremor Migration for
four ETS events
Wech, Creager and Melbourne, JGR, submitted
Tremor and Slip summed over 4 ETS events
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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
Creagerand Wech
Tremor Swarm Duration vs Length
Slope=1/2
Slope=1/3
Slope=1
Creager and Wech
An hour of LFEs
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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.
La Rocca, Science, next week
Checking location by cross-correlation of horizontal with vertical across 5-minute windows
S-P timeZero lag
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La Rocca, Science, 2009
Checking location thriceS-P time Beam (rainbow)
and envelope (green stars)
LaRocca et al., Science, 2009
Schematic interpretation of receiver function results.
Abers, MacKenzie, Rondenay, Zhang, Wech, Creager, submitted, Geology
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ETSEvery15
months
Creager & Wech
*
BS Array
Inter ETS Tremor
Feb 2007 to April 2008
some patches repeat up to 5
times
Creager and Wech
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84 sensors in a km2,Caught 8 days with light tremor last March, then 17 days of heavy tremor passing directly underneath last May
Time (days)
UW dense array pilot study
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1 km