Juliet Crider, Western Washington University
Current Research
Research at erupting volcanoes has shown that high surface temperatures, gas
emissions, and geodetic and
seismic unrest are signatures of magmatic activity at depth. Few studies
have correlated such geophysical
and geochemical measurements at non-erupting volcanoes. We
are investigating the relationship
between volcano degassing and magmatic activity by collecting gas samples
and geodetic measurements
at Mount Baker volcano, Washington. The volcano has shown no signs of
historical seismic unrest, yet
actively emits both carbon dioxide and hydrogen sulfide at rates similar to
other volcanoes where
intrusions have been inferred from seismicity. Mt. Baker has also shown
persistently high helium isotope
ratios, another suggestion of magma at shallow depths. By combining both
geophysical and geochemical
observations, we expect better resolution of the magmatic system than could
be achieved with geodesy or
gas measurements independently. Mount Baker is of additional interest
because of an unexplained
increase in gas emissions and thermal activity that occurred in 1975. The
goals of this study are to (1)
characterize the patterns of gravity change and surface deformation at a
quiescent, degassing, subduction
zone volcano, (2) evaluate the relationship between gas emission and
geodetic changes over time, and (3)
use the combined gas, thermal, and geodetic datasets to infer magmatic
processes at depth.
Collaborators: Mike Poland, USGS-HVO; Glyn-Williams-Jones, Simon Fraser
University;
Kristin Hill, Brendan Hodge, Kurt Parker (all WWU)
The goal of this study is to define an initial state against which to gage
late Miocene changes in surface
and peak elevation in the North Cascades. We are investigating the
paleotopography of the
Okanogan Range, the eastern border of the North Cascades. This range is
located in a region that is
central to competing hypotheses concerning the topographic condition of the
North Cascades prior to late
Miocene orogenesis. Distinguishing between these hypotheses has important
implications for unraveling
the timing and cause of orogenesis in the North Cascades, and has
implications for the relative importance
of climatic vs. tectonic causes of orogenesis in the North American
Cordillera as a whole.
We will investigate the exhumation history and paleotopography of the
Okanogan Range using apatite
(U-Th)/He low-temperature thermochronology, GIS-assisted Eocene surface
reconstruction, and thermal
modeling of landscape evolution scenarios. Topographic relief serves as a
proxy for the minimum
elevation of peaks within the range. Paleotopography calculated via
thermochronology will be compared
to the relief preserved in erosional remnants of Eocene volcanics scattered
throughout the range. The
refined elevation history of the Okanogan Range will then be used to
evaluate the contribution of erosion
and consequent flexural isostatic peak uplift to the production of high
peaks in the Cascades.
Collaborators: Owen Callahan, WWU; Peter Reiners, Yale
The 1872 earthquake is the largest known crustal earthquake in the Pacific
Northwest, with an estimated magnitude exceeding most recent damaging U.S.
earthquakes. The fault that produced the 1872 earthquake is not known, nor
has a record of earlier events been produced. Recent work on the precise
relocation of modern earthquakes traces a blind thrust in the presumed 1872
epicentral region, and our preliminary mapping hints at
deformation of glacial terraces along the Columbia River. Surface exposure
dates of the Columbia River terraces (determined using cosmogenic isotopes)
have the potential to deliver rates of deformation over the 1872 blind
thrust. Ground-shaking in the epicentral region likely disturbed lake
sediments. Sediment cores from Lake Chelan and vicinity may document
deformation related to the 1872 event and could hold evidence for earlier
large earthquakes.
Collaborators:Justin Brooks, WWU; John Stone, UW
Discontinuities in space (rock) and time (processes) dominate the generation
and evolution of bedrock fault scarps. In this set of studies, students and
I have documented near-tip deformation for near surface-breaking normal
faults in basalts of the high lava plains in Oregon and Washington. We use
a boundary element model to evaluate parameters that influence the shape of
near-tip folds, and find that folds are likely produced by vertical
propagation of a blind fault, rather than lateral propagation alone. The
rate and style of degradation these scarps depends not only on time but also
the spacing of discontinuities in the rock. We are exploring the
possibility that large toppled basalt columns may serve as
strong motion sensors for paleo earthquakes.
Collaborators: Kelsay Davis, Ian White (both at WWU)
The Canyonlands graben system in southeastern Utah has been called a "natural laboratory" for the study of extensional faulting. A high rate of extension has produced a fault pattern in a short time, and is on-going; consequently, relevant structures visible at the surface have not been lost to erosion. Important details of this "natural experiment" remain unquantified. Precise
measurement of the rate and direction of extension -- and how that direction and rate may vary spatially -- will permit rigorous interpretation of the field data and provide crucial constraints for modeling.
We have measured the on-going deformation at Canyonlands via three approaches at different scales of observation: 1) evaluating the rate and spatial variation in vertical deformation using interferometric synthetic aperture radar (InSAR); 2) determining the rate and direction of horizontal extension along two orthogonal traverses
across the Canyonlands using GPS; and 3) monitoring the contribution of individual faults directly.
This work was supported by a 5-year grant from the NSF Tectonics Program.
Collaborators:
Susan Owen, JPL/USC;
Scott Marsic, USC
The mechanical interaction of normal faults plays a significant role in the organization of faults into fault systems. This work investigates perturbations in the local stress field around normal faults via numerical experiments using the boundary element method. The modeling is motivated by field study of Miocene normal-fault scarps in the northern Basin and Range province of Oregon, and results yield insight into the distribution of aftershocks of the 1993 Klamath Falls, Oregon, earthquake sequence.
My general research interests include: crustal extension (ancient and
active), fault mechanics and the dynamics of faulting, earthquake
triggering, tectonic geomorphology, and (recently) crustal deformation
related to volcanic activity. Currently active, funded projects are
described in these pages. These projects are part of a larger effort to characterize
the processes of deformation associated with active tectonics, including
faulting, folding and earthquakes.
The research activities described above illustrate the breadth of my
research: the study of individual faults and folds; the growth of faults in
geographically extensive fault systems; interaction between active volcanoes
and active faults; deformation in unique tectonic environments (e.g.
salt-driven extension); and the geomorphic expression of earthquakes. I
collaborate with students, colleagues here at Western, and colleagues at
other universities, in national research labs, and in industry. Several
past and current projects address problems of societal concern: damaging earthquakes in
Washington and Oregon, the geologic stability of the proposed federal
nuclear waste repository at Yucca Mountain, and current activity at Mt.
Baker volcano. The projects are linked by an approach that seeks to uncover
the mechanics of the systems, to investigate how faults work, and to build
understanding that is fundamental and therefore applicable to a broad range
of geologic problems.
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