Recent%20Studies%20in%20Earthquakes

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Recent Studies in Earthquakes Slow and Fast Slip
Events How Could We Study Them??

• Kevin M. Brown
• kmbrown_at_ucsd.edu Scripps Institution of
  
• Oceanography, University of California,
  San Diego,
• La Jolla, CA 92093-0244, United States

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Experimental Investigation of a Transition
Between Stick-slip and Creep as Function of
Temperature, Slip-Rate, and Normal stress A
possible origin of slow slip events
Erica Mitchell, Kevin Brown, Yuri Fialko Scripps
Institution of Oceanography, UCSD
AGU - T16
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Effective Normal stress
Transitions to Unstable Behavior in 3D Phase Space
Complex Transition Zones
Temp
Fast
a
s
Strain rate
a
Slow
a - aseismic
s - seismic
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Slip Time lt 0.1sStress Drop 0.664MPaSlip
Velocity gtgt1mm/s
Novaculite T200C Normal Stress4MPa Forcing
Velocity10-4mm/s
T25C Normal Stress1MPa Forcing
Velocity10-2mm/s
Slip Time4.8s Stress Drop.01MPa Slip
Velocity2.5x10-4mm/s
1)
2)
Increasing Instability
T200C Normal Stress4MPa Forcing
Velocity10-5mm/s
Slip Time90s Stress Drop0.043MPa Slip
Velocity5.78x10-5mm/s
4)
3)
T500C Normal Stress8MPa Forcing
Velocity 10-3, 10-2, 3x10-2mm/s
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Onset of Melting
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Thermal
Change in physics with slip velocity
Peak
Fabric/ localization
Friction Coefficient
Residual
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Do Field Studies

• And Get Lucky!

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We already know the Nicoya area of Costa Rica is
dangerous (Mw 7.8, potentially tsunamogenic) and
interesting

• What is partial
• plate coupling??
• Geodetically coupled region does not appear to
  be related to smectite to illite transition (too
  cold)

Newman
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OBS, flowmeter box
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ACDP Current meter
Early micro-observatories
Remote chambers
Marine Hydrologic Instrumentation on a Cold Seep
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Nicoya
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Correlations Between Flow and Noise
Brown, Deshone Dorman, Schwartz, Tryon

• Correlation between noise and flow anomalies is
  clear.
• Sites show flow anomalies of differing signs.

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Seismic Noise Manifestations
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Comparison of wind and noise
A) Regional RMS noise average of 8
instruments B) Significant wave height off Costa
Rica from meteorology using Tolman's WaveWatchIII
program C) RMS records, and regional average
noise. Note that site 5 stands out
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See Dorman Poster
Tremor or Many Micro Earthquakes?
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Spectrogram of event 3 at site 3Record length is
12 hours
See Le Roy Dormans poster
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Spectrogram of event 3 at site 5Record length is
12 hours
See Le Roy Dormans poster- From duel frequency
studies-noise is similar too but not exactly like
Julian 1994 tremor
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Hydrologic Manifestations
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The finite element model Abacusa fully coupled
model (LaBonte,Brown, Fialko)
Costa Rica subduction zone geometry
oceanic plate
continental plate

• Numerical calculation of
• displacement
• pore pressure
• fluid flow
• (tilt and volumetric strain
• also possible)

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Flow patterns differ between Near/Far Field
Earthquake - Depth gt Rupture length
The finite element model Abacusa fully coupled
model (LaBonte, Brown, Fialko)
Near surface flow/pore pressure signals are a
combination of poro-elastic effects and
surface buckling/flexure effects
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Updip Propagating Slow Slip
c
c
c
1
0.5
0.05
flow rate
time
OUT FLOW AT SURFACE
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Downdip propagating slow slip
c
flow rate
c
c
0.5
1
0.05
time
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model
Flow rate (mm/day)
Days since event initiation
Down dip propagation, 0.4 Duration of slow
slip event 22days Site 2 is 6.5km distant from
trench
Maximum extent 0.5km-15km Max. prop. velocity
0.7km/day Min. dislocation distance 30cm
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Updip propagation
Downdip propagation
c
0.2
flow rate
c
0.5
time
1
c
flow rate
time
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• One Strategy for a Subduction Zone
• Earthquake Observatory
• Buoys- Marine Geodetics
• 2) Boreholes
• 3) Cables

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Locked to the trench
Locked to the trench
8
8
6
4
2
0
Stress episodically released near the toe
Note on land geodetic measurements are not
sensitive to offshore locking patterns only the
down dip limit!
Continuous marine geodetic measurements can
determine where the up dip limit lies and how it
stresses are released episodically
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• SeisCORK Concept
• for time lapse VSPs and offset VSPs
• - for monitoring micro-earthquake activity

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DYNASEISE Geodynamic and SeisCORK Observatories
in the Central America Subduction System, Costa
Rica
GEOCE Buoys
Kevin Brown, Ralph Stephen, Andrew Newman, Tom
Pettigrew, Bob Petit, Kirk McIntosh, Sue Bilek,
Nathan Bangs, LeRoy Dorman, Glen Spinelli, Susan
Schwartz, Pete Lafemina
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CRSZ-1
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Hilton Fischer, Brown
Gradient
He Ra numbers
Wedge mantle boundary
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GEOCE BUOY
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• An ORION-Type Observatory
• s
• Multiple Components
• Horizontal marine GPS
• (cm)
• Verticalseabed height changes
• (lt1cm) oceanographic
• variability (internal density and
• dynamic height changes
• Absolute sea height Buoy GPS
• Communications (acoustic and
• radio/satellite)

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GEOCE system

• 1) XYZ seabed displacement
• 2) Corrected for oceanic noise
• 3) Initial system engineering test is ongoing off
  SIO
• 4) Highest data retrieval rates will be obtained
  by line of sight wireless modem.
• 5) Really useful for slow slip and aseismic creep
  events

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Conclusion

• A very wide variety of methods and techniques are
  required to make progress!