Kinematics and Dynamics of Western U' S' Deformation

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Kinematics and Dynamics of Western U. S.
Deformation
EarthScope Basin Range Workshop Lake Tahoe,
CA 22 June 2004

• Wayne Thatcher
• U. S. Geological Survey
• Menlo Park, CA 94025, USA

Thanks to Bill Hammond Marleen Nyst, and to
Rob McCaffrey for Sharing Results
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Applied Forces Rheology Determine Basin Range
Deformation
Forces Rheology
Deformation
(F)
(?)
eij(x, y)

• USArray Dynamic Modeling

• PBO Eq Geology

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Present-Day Western US Deformation?
Thatcher (2003)
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Sierra Nevada
Colorado Plateau
1992-2002
Granlibakken Lodge
Hammond Thatcher (2004)
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Southwest U. S. Block Model GPS Sites
McCaffrey, 2003
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Thatcher (2003)
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Hammond Thatcher (2004)
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Plate Boundary Observatory (PBO) BR GPS Network
High precision permanent continuous GPS
stations -160 new sites - completion by
2007 120 sites in dense profiles
-ultra-precise fault slip rates in a few
regions 40 sites 200 km spacing -sparser
regional coverage Detection of episodic
transient deformation
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USGS-NASAPre-EarthScopeCampaign GPS Networks

• 350 new sites established since 1999
• Complemented by other campaign continuous sites
• Velocity field to 1 mm/yr precision throughout
  western USA by 2007 (when PBO network fully
  installed)
• Can use PBO CGPS to focus on transient
  deformation very low strain rate faults

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Applied Forces Rheology Determine Basin Range
Deformation
Forces Rheology
Deformation
(F)
(?)
eij(x, y)

• USArray Dynamic Modeling

• PBO Eq Geology

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External Plate Driving Resisting Forces
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Internal Forces due to Density Gradients

• Lateral gradients in thickness density generate
  internal stresses
• -crust mantle lithosphere---GPE
• -asthenosphere---dynamic topography
• (plumes, tacos,.)

• USArray tomography can map constrain

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Western U. S. Geoid, GPE Faults
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Kinematics Dynamics of Deformation
Forces Rheology
Deformation
(F)
(?)
eij(x, y)

• USArray Dynamic Modeling

• PBO Eq Geology

?
?
?
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Background--Charge to Speakers

• Organizing Committee requests speakers address
  Grand Challenges
•  We naturally expect your comments will be
  related to your expertise, but do not intend to
  restrict you in any way
• Such guidelines naturally inviteGrand
  Pontification
• Instead of grand challenge, Ill focus on an
  achievable EarthScope goal
• Quantitatively determine rates and spatial
  distribution of present-day crustal strain and
  understand forces driving this deformation

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Velocity Field Interpretation
Hammond Thatcher (2004)
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Select NE Nevada Basin and Range
Hammond Thatcher (2004)
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Velocities Predicted by Best Euler Pole
Hammond Thatcher (2004)
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Velocities wrt NE Nevada Microplate
Hammond Thatcher (2004)
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Hammond Thatcher (2004)
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Hammond Thatcher (2004)
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• Anatolia moves westward due to Arabia-Eurasia
  collision at Caucasus
• Extension in Aegean Turkey and Greece due to
  retreat of Hellenic Trench

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Probabilistic Seismic Hazard Analysis
Historical Large Earthquakes Recurrence
Statistics Active Faults
Probabilistic Strong Ground Motion Maps
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Aegean Seismic Hazard Spatially Uniform
European Seismological Commission (2003)
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GPS Velocities Relative to Eurasia
Nyst Thatcher (2003)
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GPS-Based Rigid Microplate Model
Nyst Thatcher (2003)
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GPS Model Suggests Seismic Hazard Focused Near
Microplate Boundaries
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What Kind of Microplates are These Anyway?
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Questions

• Is continental microplate viewpoint even valid?
• -We think so, but welcome criticism
• If so, is microplate description useful?
• -Yes, it can be applied to seismic hazard
  assessment
• Can it be applied over geologic time, as in
  ocean basins?
• -Topic for another talk, initial results
  promising

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LESSONS from AEGEAN WORK

• Seismicity and active faults widely distributed
• However, continental microplate model provides
  good match to Aegean GPS data, suggesting major
  deformation (and hazard) is much more localized
• GPS data microplate models should be useful
  for improving probabilistic earthquake hazard
  assessment