Summary of triggering of non-volcanic tremor in Cascadia

Justin Rubinstein Justin Rubinstein

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Tremor is Modulated by Love WavesTremor is Modulated by Love Waves

How things work*Love

waves

Earthquake in Alaska

Tremor Modulated by Stress AmplitudeTremor Modulated by Stress Amplitude

Rubinstein et al, 2007

Rubinstein et al, submitted

Does Amplitude Control Triggering?

Rubinstein et al, 2009

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Peng et al, submitted

Does Amplitude Control Triggering

in Parkfield?

Peng et al, in prep

Does Amplitude Control Triggering

in Taiwan?

Tremor correlates with tides

Shelly et al., (2007)Shelly et al., (2007)

Recordings of 3 ETS episodesRecordings of 3 ETS episodes

Tremor“Noise”

Tremor spectra for the 5 arraysTremor spectra for the 5 arrays

Rubinstein et al, 2008

Amplitude variation with 12.4-hr periodAmplitude variation with 12.4-hr period

12.4-hr tides 30% effect24-hr probably similar magnitude

Summary & ConclusionsSummary & Conclusions

• Tremor is triggered by very small dynamic Tremor is triggered by very small dynamic stresses from teleseismic EQs (10s of KPa)stresses from teleseismic EQs (10s of KPa)

• Tremor is modulated by the very small stresses Tremor is modulated by the very small stresses of the earth and ocean tides (~10KPa)of the earth and ocean tides (~10KPa)

• Ambient stress ~10Ambient stress ~1055 times stronger times stronger

• Tremor is occurring on faults that are very Tremor is occurring on faults that are very close to failureclose to failure– Fluids? Low Friction? Just Close to Failure?Fluids? Low Friction? Just Close to Failure?

Triggered Tremor = ETS TremorTriggered Tremor = ETS Tremor

Tremor vs aligned 12.4-hr bumpsTremor vs aligned 12.4-hr bumps

Array SO for 2004

PA for 2005

BS for 2007