Reinterpretation of the seattle uplift washington as a passive roof duplex
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Reinterpretation of the Seattle uplift, Washington, as a passive roof duplex. Tom Brocher, Rick Blakely, and Ray Wells U.S. Geological Survey Menlo Park, California. What’s a passive roof duplex?. One sided fold (monocline). A modified fault-bend

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Reinterpretation of the seattle uplift washington as a passive roof duplex l.jpg

Reinterpretation of the Seattle uplift, Washington, as a passive roof duplex

Tom Brocher, Rick Blakely, and Ray Wells

U.S. Geological Survey

Menlo Park, California


What s a passive roof duplex l.jpg
What’s a passive roof duplex? passive roof duplex

One

sided

fold

(monocline)

A modified

fault-bend

fold, sometimes called a triangle wedge or a triangle zone

Wedge

tip


The old model l.jpg
The Old Model passive roof duplex

Tacoma

Seattle

Folds

Seattle fault

Slip at depth

A fault-propagation fold


Hazards posed by old model l.jpg
Hazards Posed by passive roof duplex Old Model

Seismic energy directed toward Seattle

Seismic waves amplified by Seattle basin

Shallow faulting

M 7.6-7.7 estimated

Seattle

Slip at depth

Seattle fault

Slip at depth


Problems with old model l.jpg
Problems with Old Model passive roof duplex

North-dipping thrust faults not explained

2) Tacoma fault zone not incorporated

3) Shallow folding not convincingly explained

4) Seattle monocline not recognized as evidence for a wedge

5) Coseismic uplift data not well predicted


The new model l.jpg
The New Model passive roof duplex

M6.4

M6.7?

M7.2

Shallow slip, multiple sources


Depth in miles to the main faults l.jpg
Depth in miles to the main faults passive roof duplex

Seattle

Seattle fault

Tacoma fault


Seattle fault zone l.jpg

Seattle fault zone passive roof duplex

You are here

Seattle

fault

zone


Seattle fault zone9 l.jpg

Seattle fault zone passive roof duplex

Blake Island


Seattle fault zone ad 900 l.jpg

Seattle fault zone - AD 900 passive roof duplex

Blake Island

M6.4

M7.2


Folding along seattle fault lake washington l.jpg
Folding along Seattle fault - passive roof duplexLake Washington

Johnson et al. (1999)


Passive roof thrusts l.jpg

Passive roof thrusts passive roof duplex

Passive roof thrusts only slip when the master floor thrusts slip - they do not represent independent seismic sources. Paleo slip on them tells us about slip on the master floor thrusts.


Other wedges pakistan l.jpg
Other wedges (Pakistan) passive roof duplex

Banks and Warburton (1986)


Summary of new model l.jpg
Summary of New Model passive roof duplex

  • Seattle and Tacoma faults are blind thrusts

  • Both faults overlain by shallow roof thrusts

  • Leading edge (wedge tip) of Seattle fault moved northward to northern end of Elliott Bay

  • Directivity, basin amplification remain important

  • Tilting and folding are integral and important in a narrow band south of the wedge tip

  • Shallow north-dipping thrust faulting is passive

  • Deformation in Seattle basin


The end l.jpg
The End passive roof duplex

BSSA in review, [email protected]


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