stress thresholds static and dynamic effects reservoirs
TRANSCRIPT
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.