Triggered and Induced Seismicity

Stress thresholds Static and dynamic effects

Reservoirs Fracking

Yes, and yes.

Static Triggering (ST) •  Faults movement increases

stress nearby –  Permanent ground

deformation –  Increase: RED

•  Example: 1992 Landers, CA –  Joshua Tree Foreshock –  Big Bear Aftershock –  1999 Hector Mine occurred

in lobe of increased static stress 7 years later

•  Numerous studies from a number of investigators (e.g., Stein, Toda, King, Parsons, Lin, etc.) –  Well documented and

accepted

King et al., 1994

Static Stress Transfer Useful for Understanding Complex Fault Systems

•  e.g. Modeling of Anatolian Fault failure from static stress transfer event after event

•  Is this the whole story about fault interactions?

Dynamic Triggering (DT) •  Remote earthquakes can trigger through the passage of seismic

waves, which cause transient stresses to act on remote faults •  Example:1992 Landers (Mw=7.4) Earthquake (Hill et al., 1994)

–  First accepted case •  1999 Hector Mine (Mw=7.1) also shows evidence

Gomberg et al., 2005

Triggering implies that you increase stress acting on pre-existing faults that are below their failure limits, and push them above the failure threshold.

Some regions have no prior activity, so were well below their failure limit and got pushed above. Then aftershocks of triggered events produce a persistent sequence, or cascade.

Simultaneous Dynamic Triggering Rayleigh Triggering Love Triggering

Small local earthquakes occur in the signal of the surface waves

Triggered earthquakes

Same Channel

Same Channel

Aftershocks of initial triggers, or response to changes?

Ubiquitous Nature of Dynamic Triggering

•  Surface waves from large events can trigger small earthquakes everywhere!

–  Independent of tectonic province

–  Not near active faults

Velasco et al. (2008)

Closely Study 15 Large (M>7.0) Mainshocks

•  All events –  Created by summing

detections –  Reduced time –  300 s windows

•  Occurs with timing of Love wave (t=0), followed by Rayleigh waves

•  Timing shows triggering begins with Love wave

•  Triggering falls off rapidly for the first 30 minutes

–  Continues for hours •  Dispersion complicates

timing interpretation

Velasco et al. (2008)

April 11, 2012 Mw 8.7 Appears to have activated global activity.

Because there are earthquakes occurring all the time, must look at change in activity.

Activity at Yellowstone within 6 hours of Denali EQ

Tohoku (M=9.0) Japan Earthquake 2011 Triggered US Earthquakes

Tohoku 2011 Triggered Tremor Triggered Earthquakes

Triggering Examples: Australia

•  Looked at 36 events –  11 showed

triggering Love wave triggers events

•  The orientation of the incoming waves is critical for triggering

Gonzalez-Huizar and Velasco (2011)

1992 Landers EQ •  Examine Dynamic Stress Changes on Possible Faults

–  Can use modeling results to determine which fault plane triggered

Taiwan – Triggered Non-Volcanic Tremor (NVT)

•  Surface waves trigger other type of phenomena

Peng and Chao (2008)

Rayleigh wave Triggers NVT

Taiwan: 2003 Hokkaido

Regional activation of events is clearest in regions with sparse background activity. But what causes delays? Initial small triggers?

Great (Mw > 8) shallow events from Dec. 2004-Mar. 2014

Last 9.0 yrs - 16 great shallow earthquakes: rate 1.8/yr; rate over preceding century 0.7/yr

2

1.8/yr  !  

Other ways to make earthquakes: Change pore water.

Adding water (or moving water) can change the effective normal stress acting on fault – moves Mohr circle toward or away from failure criterion.

Lake Meade Reservoir Behind Hoover Dam

Impounded reservoir changed water table, changes load on landscape. Activated many earthquakes where there had been none.

Locations of activated earthquake�events

Typical annual induced earthquakes at Geysers, CA, geothermal energy production with water injection and steam extraction.

Deep waster water injection to isolate very polluted water done in deep injection wells at depths to 2-10 km. Idea is to isolate the water from aquifers; faulting may compromise isolation.

Enhanced exploitation of oil reservoirs

Injection of Fraccing

Fracking makes small faults and�earthquakes. Controlled?

Some regions are particularly easy to trigger, including regions of deep waste water injection. These are zones triggered by 2011 Japan earthquake.

CO2 sequestration (pump into isolated reservoirs for long-term climate control), enhance oil extraction from existing reservoirs, etc.