Ryan Gold’s Research
Ph.D. (University of
Title: Is the Holocene slip rate along the Altyn Tagh Fault10
mm/yr, 30 mm/yr, or both?
Project Description: For my doctoral research, I propose to measure the Holocene slip rate along the sinistral Altyn Tagh Fault. Previous work on this fault system has produced two contradictory slip rates, with GPS and paleoseismic studies indicating a rate of ~10 mm/y, whereas geomorphic reconstructions indicate a rate of ~30mm/y. A noticeable data gap, from2 to 6 ka, separates the datasets and leads me to ask, is the Holocene slip rate along the central Altyn Tagh Fault 10 mm/y, 30 mm/y, or did it drop from~30 mm/y to ~10 mm/y between 2 and 6 ka? To distinguish between these scenarios, I propose to reconstruct and date displaced fluvial terrace risers. At selected sites, I plan to:
(1) Conduct detailed geomorphic mapping,
(2) Make high resolution topographic measurements of displaced geomorphic markers using a total station and real-time kinematic GPS system, and
(3) Date
samples collected from the displaced surfaces using AMS analysis of radiocarbon
(14C) and terrestrial cosmogenic radionuclides (10Be).
Altyn Tagh Fault (modified from Cowgill et al., 2004)
Project Significance: The active, left lateral Altyn Tagh Fault extends 1200 km along the northwestern margin of the Tibetan Plateau and is a first-order structure within the Indo-Asian collision. Determining the Holocene slip rate along the Altyn Tagh Fault is important for three reasons.
(1) The fault’s slip rate is thought to be an important criterion for distinguishing between two mutually exclusive views of continental deformation. One view contends that continents deform heterogeneously by breaking into microplates and predicts a high (~30mm/yr) slip rate. In contrast, the opposing view holds that continents deform homogenously as continua and predicts a low (~10 mm/yr) slip rate.
(2) If the Holocene slip rate has varied along the Altyn Tagh Fault at the 2-6 ka time interval, then a detailed record of this change in fault slip rate will add an important observational constraint on models that attempt to describe this type of behavior. Recent attempts at modeling this type of secular variation in fault slip rate have focused on conjugate strike-slip fault interaction and rheological heterogeneities such as a weak seismogenic layer.
(3)Constraining
the Holocene slip rate along the Altyn Tagh Fault is important is to address
the seismic risk to growing population centers, north of the Altyn Tagh Fault.
The largest of these cities include Qiemo, Huatugo, Aksai, and Dunhuang.
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M.S. (
Title: Application of trishear
fault-propagation folding to active reverse faults: examples from the Dalong Fault,
Project Description: I have investigated the active, ~50°dipping,Dalong reverse fault system. This ~40
km-long fault system forms part of the Aksai restraining stepover along the
active, left-slip Altyn Tagh Fault in northwestern
Synthetic trishear fold generated with Fault/Fold
v.5.0.
Project Significance: Determining
accurate fault slip rates at 1 ka to 1 Ma timescales requires well-constrained
palinspastic reconstructions of dateable geomorphic and/or geologic markers.
Although general kinematic models have been developed to simultaneously
reconstruct both bedrock (e.g. bedding and fault attitudes) and neotectonic
markers (e.g. strath terraces) along active strike-slip and thrust faults, it
is not clear if these models can also account for deformation along steeply
dipping (>45°) reverse faults. Through my analysis, I have extended the
trishear model of fault-related folding to active reverse faults, and find that
to a first-order, this model matches bedrock and neotectonic data along the
Dalong Fault. This work indicates
that an important implication of active trishear fault-propagation folding is
that terrace deformation extends for over 1 km on either side of the fault
trace. Thus, to accurately measure
the total magnitude of vertical separation between matching terraces in the
hanging wall and footwall, terrace profiles across active reverse faults must
extend 1-2 km to either side of this zone of deformation.
Downloadable version of M.S. Thesis in PDF format (7.2 MB
(or)
Visit the Journal of Structural Geology and
download a copy of the paper that came from this study (v. 28, no. 2,
pg.209-219)
B.A. (
Title: A comparative study of
aerial photographs and LIDAR imagery for landslide detection in the Puget Sound,
Washington.
Project Description: Landslides in western Washington cause millions of dollars in damage each year. Accurate and precise remote sensing techniques are a necessary first step in creating useful landslide inventories for future land use planning and engineering mitigation decisions. Both aerial photos and LIDAR (LIght Distance and Ranging) imagery were evaluated and compared on the basis of the accuracy of landslide location and the precision of landslide boundary definition for an eight-kilometer stretch of heavily forested coast along Hood Canal, Kitsap County, Washington, an area which is characterized by numerous slides occurring in Pleistocene glacial and non-glacial sediments. Independent landslide inventories were developed from each remote sensing dataset and were followed by field observations of approximately half of the identified slides. A geologic map and complete landslide inventory for the eight-kilometer stretch of coast was created. In the southern reaches of the field area, a thick unit of pre-Vashon gravel (Qpgo) comprises the basal unit, overlain by Vashon advance outwash (Qgas), in turn overlain by Vashon till (Qgt) which mantles the upper plateau throughout the field area. Landsliding in this area is characterized by shallow, colluvial slides. In the northern reaches of the field area, non-glacial sediments including stratified silts and clays comprise the basal unit which is overlain by advance outwash and till from the Vashon Stade. The non-glacial sediments act as an aquatard, increasing pore-water pressures in the sediments above, and resulting in large-scale, deep-seated landslides.
Example
of a landslide identified on LIDAR imagery.
Project Significance: Results suggest that the two remote sensing methods
(LIDAR and photogrammetry) yield similar results for the identification of
landslides. However, other factors
such as the type of sliding, precision of slide boundary definition, vegetation,
cost, imagery availability, and user efficiency show varied results. Photogrammetry is effective for
locating small, shallow slides occurring along coastal bluffs as well as
larger, deep-seated slides, costs only $25/mi2 to fly, works well
when vegetation cues indicate recent sliding, and is available throughout
Washington State in multi-year intervals.
LIDAR imagery is highly effective for precisely defining landslide
boundaries where the laser return from the ground is good, is efficient in the
field and office, is easier to interpret than aerial photographs, and is highly
manipulatable with respect to shadows and vertical exaggeration. Results from this comparison suggest
that both methods have strengths and weaknesses with regard to generating
landslide inventories and that the best approach is to use both methods in a
complementary fashion.
Downloadable version of B.A. Whitman Thesis in PDF format (21.1
MB) (or)
Visit the Division of Geology and Earth
Resources webpage (Washington State Department of Natural Resources) and
download a version of the thesis there (OFR 2004-6).
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