Post on 03-Jun-2018
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Geomorphology and Earthscope:
Landscape evolution in the service of geodynamics
Eric KirbyPenn State University
Earthscope Science Planning Workshop
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Tectonic Geomorphology Records of deformation over
103- 106yrs
Bridges geologic andgeodetic timescales Provides information on
spatial wavelength, rates,and historyof topographicchange
Lithospheric deformation at intermediate timescales 2 Approaches:
Displaced debris-flow levee in Panamint Valley
Landforms as markers of deformation
Invert topography for rock uplift
Stolar et al., 2006
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I. Landforms as markers of fault slip
Enabled by newtechnologies LiDAR Geochronology:
(cosmogenic and OSL)- access timescales
between 10 - 200 ka
Bridges geologic andgeodetic timescales
Patterns/rates ofstrain release throughtime
How wide are faults? LiDAR (ALSM) shaded relief of debris-flow - Panamint Valley
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Pace of deformation in western US Geologic studies
reveal variationsin fault slip overtimescales longerthan seismic cycle
Examples from: Southern CA Eastern CA
PBO Geodetic network
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Alternating periods of fault activity
Bennett et al., 2004
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Diffuse dextral shear in eastern CA
T. Dixon
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Transient loading during seismic cluster?
Oskin et al., 2008 - Geology
Dolan et al., 2007 - Geology
Does strain hardening drive alternating periods of activity and quiescence?
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Continued investment is warrantedLiDAR coverage of active faults
R. Malservisi and M. Hackl - data from PBO, USGS, SOPAC, SCEC
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II. Invert topography for rock uplift
Landscape reliefadjusts such thaterosion rate balancesdifferential uplift ofrock
Timescales ~105- 106yr Depend on length
scale of system
What measure oftopography?
Ahnert, 1970
Montgomery and Brandon, 2002
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II Invert topography for rock uplift Relief is scale-dependent
measure that convolveslandscape process-domains
Most relief in activemountain belts on channelnetwork
Channels also governlandscape response tochanges in tectonics,climate
Liwu River, Taiwan
0
3.5 km
30 km
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Tectonic Geomorphology Primer
High erosion rate
Low erosion rate
S=ksA
"#
Duvall, Kirby and Burbank, 2004
Blue ~ 6 mm/yrRed ~ 14 mm/yrOrange ~ 2- 14 mm/yr
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What do we know?
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What do we know?
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Transient Channel Response
Vkp =Uf
1n (Uf "Ui)
Uf1n "Ui
1n
Vkp =Uf
knickpoint
High U
Low U
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Whats in it for you?
Data of Kirby et al., 2003
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Whats in it for you?
Data of Kirby et al., 2003
Joint inversion of InSAR and GPS - Shen et al., 2009
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Whats in it for you?
Kirby et al., in prep
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Whats in it for you?
Kirby et al., in prep
100-200 m/My
600-1200 m/My
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II. Future Directions
Linkages between mantle buoyancy and topography: Vigorous small-scale convection? Removal and/or hydration of mantle lithosphere Edge convection vs. warming of heterogeneous lithosphere
3%
2
1
0
1
2
3
P-wave
fast
slow
B. Schmandt and G. Humphreys
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The challenge
Long wavelength and (relatively) slow rates Subtle signals in landscape Long response timescales
Require interdisciplinary approach combining landscape analysis withproxies for erosion and paleoelevation
W. Ouimet and E. Kirby
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Karlstrom and CREST Working Group, in prep
The opportunity
Rates and spatial scales of topographic change can helpdistinguish processes generating buoyancy (lithosphericheating vs edge convection)
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The opportunity
And hold potential for constraining wavelength ofdeformation
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The opportunity
Uplift history provides bounds on timescale and densitystructure associated with small-scale convection (e.g.,Molnar and Jones, 2004)
Zandt et al., 2004
Stock et al., 2005
Sierra Wallowa Mtns
~2 km uplift
post-CRB
(Hales et al.)
-2 -1 0 1 2% Vp
Schmandt and Humphreys
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II. Future Directions
Persistence of topography in Appalachians: Slow degradation of relict topography?
Paul Bierman et al., Peter Zeitler, Jim Spotila
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Take-home The evolution oflandscape topography
encodes informationabout the pace andwavelength oflithospheric
deformation
History is key Cross-fertilization
among geodynamics,earth structure,geology, climate, andlandscape