Research

North Canterbury Fold and Thrust Belt, New Zealand

New Zealand Terraces

The North Canterbury fold and thrust belt (NCFTB) of New Zealand is a region of young, actively growing, basement-involved fault-propagation folds. The fold belt is developing as part of a complex plate boundary transition region in the northeastern part of New Zealand's South Island. Fold growth has uplifted marine terraces along the coast, which act as markers of deformation over time. The region, therefore, is a good place to investigate a number of questions including the kinematics of fault-propagation folding, the relationship between structural geology and geomorphology, and the role of the NCFTB in accommodating plate boundary deformation. This region was the setting for my Ph.D. dissertation research, supervised by Don Fisher at Penn State. My work here has involved dating marine terraces, modeling fold kinematics and fault geometry, using marine terraces and the patterns of uplift rates that they record to constrain fold kinematic models and calculate fault slip rates, and constructing a balanced cross section across the NCFTB to estimate the total shortening that it has accommodated. I have made substantial use of my InvertTrishear program in my New Zealand work, and the problems that I have encountered there have influenced development of the program.

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Inverse Modeling of Fault-Related Folds

Trishear Fold

Kinematic models of fault-related folding are a valuable tool in structural geology and are widely used to predict subsurface fold structure and reconstruct structural histories. These methods find applications in seismic hazard assessment, resource exploration, and tectonic studies. The models produced by typical forward modeling workflows are, however, not unique. Data inversion methods such as Markov chain Monte Carlo simulations provide the means to both find the model that best fits a given dataset and calculate uncertainty in model parameters. Rather than providing a single result, such stochastic methods can provide an ensemble of possible models. Although widely used in fields such as geophysics, data inversion methodologies have not seen widespread use in structural geology. In this work, I aim to develop, test, and apply tools to facilite data inversion and the use of stochastic methods in modeling fault-related folds. A primary aspect of this research has been the development of the InvertTrishear program for inverse modeling of trishear fault-propagation folds using Markov chain Monte Carlo methods.

In my current postdoctoral research, I am working on two inverse modeling projects. In one, I am applying the Ensemble Kalman Filter to restoration of complex, three-dimensional structural models. In the other, I am fitting elastic boundary element models to data and comparing the results to trishear models.

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Subduction Interface Processes and Earthquake b-values

This project aims to investigate the role of fault-healing by silica redistribution in controlling earthquake dynamics at subduction zones. My role in the project has primarily involved the analysis of earthquake frequency-magnitude relationships (b-values) at different subduction margins and investigations of the relationship between b-value and temperature.

An important part of this project is the development of the Mefisto program for modeling subduction zone behavior, which is led by John Hooker at Penn State. The program is available for download here: Mefisto

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Geophysical Imaging of the Critical Zone

This was my previous postdoc project, supervised by Andrew Nyblade and Sue Brantley at Penn State. The primary goal of my work was to use ambient noise seismology to look for changes in seismic velocity in the shallow subsurface at the Susquehanna Shale Hills Critical Zone observatory in Pennsylvania. This method uses the small vibrations caused by cars, wind, or other processes -- rather than seismic waves generated by earthquakes or deliberate human-made sources -- to measure seismic velocities in the Earth. While we originally aimed to observe the movement of water in the critical zone over time, we found that the strongest time-varying signals in the ambient noise related to temperature changes, with water playing only a secondary role. We also conducted electrical resistivity surveys at Shale Hills, which more clearly revealed water flow paths and changes over time and provided evidence of the role of geologic structure in controlling flow paths and electrical anisotropy.

The ambient noise project complemented traditional seismic refraction surveys, and I assisted with interpreting this data as well. These studies revealed the depths of rock weathering and porosity generation at Shale Hills and showed that the "bowtie" pattern of weathering expected from previous studies does not occur at Shale Hills.

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Marcellus Shale

The Marcellus shale of the Appalachian Basin is a major gas-producing unit in Pennsylvania and surrounding states. Hydraulic fracturing ("fracking") has allowed this valuable resource to be exploited but has also become a source of envirnomental concern. I have contributed structural modeling and analysis to a study on a site of aquifer contamination near a shale gas well, and I am currently working on a model of another site. I have also worked to map the depth and thickness of the Marcellus and Utica shales and the depth to basement in Pennsylvania.

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Thermal Models of Rifting

This project aims to investigate the possible pressure-temperature-time paths of rocks in extensional settings. In particular, this will provide insight into the metamorphic conditions of rocks in the middle and lower crust. Modeling consists of a finite-difference model of heat flow in regions of pure and simple shear extension. No publications yet; I am working with Andrew Smye of Penn State, but the project is in its early stages.

Shimanto Belt, Japan

In this project, we dated motion on faults in the Shimanto Belt accretionary complex of Shikoku, Southwest Japan, using K-Ar dating.

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