Plate dynamics at the Cascadia subduction zone:  What is assumed, why that is lacking, and how to ad...
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Plate dynamics at the Cascadia subduction zone: What is assumed, why that is lacking, and how to address it. Dave Chadwell Scripps Institution of Oceanography. What is assumed (I):.

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Dave Chadwell Scripps Institution of Oceanography

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Dave chadwell scripps institution of oceanography

Plate dynamics at the Cascadia subduction zone: What is assumed, why that is lacking, and how to address it.

Dave Chadwell

Scripps Institution of Oceanography


What is assumed i

What is assumed (I):

We assume convergence at Cascadia Subduction Zone is defined by Euler pole motion between North America and Juan de Fuca.

NA_JdF = NA_PA + PA_JdF

NA_PA from present-day GPS

PA_JdF from 0.78 geomagentic reversal

In this approach there is no present-day

measurement of JdF plate motion.


Dave chadwell scripps institution of oceanography

What is assumed (II):

Question: Where is the locked zone?

Approach: Observe elastic strain with geodetics, assume convergence rate,

assume thrust fault geometry, then solve for the lock zone:

elastic strain = f(convergence rate, fault geometry, lock zone)


Dave chadwell scripps institution of oceanography

Why that is lacking (I):

A = D+C+E

Observe horizontal seafloor motion with centimeter resolution by combing GPS with precision underwater acoustics: GPS-Acoustics.

Seafloor motion vectors in same frame as GPS allows direct comparison to land-GPS vectors and other seafloor vectors separated by 100s km.

e.g., (Gagnon, Chadwell, Norabuena Nature, March 2005)


Dave chadwell scripps institution of oceanography

What that is lacking (II):

Significant deformation (~ 20 mm/yr : white arrow) of JdF plate in direction opposite to convergence.


Dave chadwell scripps institution of oceanography

Why that is lacking (III):

PROPOSED MECHANISM: Plate forces

create region near yield point offshore

central Oregon (Wang et al., 1997), add

backstop of Siletzia basalt and asperity

(Trehu et al.).

OBSERVATIONS:

*GPS-A observation

*onshore vertical (Weldon)

*faults in forearc (Goldfinger)


Dave chadwell scripps institution of oceanography

How to address it:

Can address along-strike and across-strike

deformation by establishing new

GPS-Acoustic sites using either:

1) ship-based measurements

2) buoy-based GEOCE system under

development at SIO. ORION?


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