Transcript Bump and Grind

Real-time Monitoring of Slip
• Triangles: Tremor Activity
– Average envelope seismogram
amplitudes in tremor passband
– Active Tremor = black triangles
• Arrows: GPS Short-term Velocity
– 50-day GPS site velocities after
long-term velocity is removed
– Slow Slip = large arrows pointing
towards trench
January-February 2007
June-July-August 2007
April-May-June 2008
NVT Location Approach
• Filtered envelope waveforms
• STA/LTA to find NVT bursts
• Pick relative times of good
S/N arrivals
– By hand and/or automated
• 1D inversion for locations
• Analyze for patterns in
space and time
NVT Migration in Southern Cascadia
2005-2006: Hand-picked vs. Automated
NVT Migration Along All of Cascadia
2007-2008 (Automated)
• Still preliminary, but find long migrating episodes that
overlap in time despite being separated by >100 km
• Three 2007-2008 events are more interrelated alongstrike than all events in previous few years
NVT Locations So Far
• Still plenty of work for
us to do in the
northern half
• Beginning to see a
persistent gap at ORCA border
• NVT band primarily
between 30-40 km
slab contours
• Matches some aspects
of slab curvature
Integrating ETS with
Earth Structure and Geology
ETS Periodicity
Brudzinski & Allen, 2007
Surface Wave
Crust Structure
Body Wave
Mantle Structure
Arc volcanism
Schmidt et al., 2008