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 along-strike 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 OR-CA 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 Surface Wave Crust

Structure

Body WaveMantle

Structure

Brudzinski & Allen, 2007

Arc volcanism

Schmidt et al., 2008