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Investigating the Elastic Response of Geologically Complex Systems Using Numerical Methods

Kali Allison ('12 HMC); Mentor: Linda Reinen

Abstract: As part of an NSF CCLI grant, I spent four weeks helping to develop and test two educational modules designed to help Structural Geology students use numerical methods to investigate the elastic response in physically complex systems. The first module investigates the stresses created by an opening crack and their implications for further crack growth. The second module evaluates the stresses created by movement on a transform fault. Both modules use POLY3D, a three-dimensional boundary-element code developed at Stanford University. The program allows users to create models of geological phenomena (such as cracks and faults) and to compute the displacement and stresses in the surrounding material, including ground surface displacements. I created the answer key for the first module, which has been submitted for review. For the second module, I tested trial problems and created an Excel spreadsheet to relate the numerical solution to published analytical solutions.
Funding provided by NSF (LR); Pomona College Geology Faculty Research Fund (LR)

GIS Mapping to Benefit Spatial Analysis of New Zealand Tectonics

Adam Long ('13); Callie Sendek ('12 SCR); Roxanne Degens ('12 PZ); Lee Finley-Blasi; Eric Grosfils; Mentor: Linda Reinen

Abstract: New Zealand’s modern-day geology reflects its location on an active tectonic margin. As part of a project investigating the tectonic history of New Zealand (see Sendek et al. abstract), we created a digital basemap of the central part of the North Island including the five sample locations near Port Waikato, a coastal 20 exposure of the Murihiku Terrane, and two sites in the Taupiri Range located on the boundary between the Murihiku and Waipapa Terranes. During the four weeks of this project, we used ArcGIS to create an accurate digital basemap of the geology of the area to enable precise spatial analysis of paleomagnetic and field data. Map data sources included published geologic maps, satellite images, and Professor Reinen’s field notes. Future work on this map could include analyzing rock outcrops visible in satellite imagery to identify distribution of deformation in the Murihiku Terrane.
Funding provided by Pomona College SURP (AL); Pomona College Geology Faculty Research Fund (LR)

Paleomagnetic Analysis of Metamorphosed Sediments in the Murihiku Terrane, North Island, New Zealand

Callie Sendek ('12 SCR); Adam Long ('13); Roxanne Degens ('12 PZ); Dan Hikuroa*; Lee Finley-Blasi; Adam Curry ('10); Mentors: Linda Reinen, Ami Radunskaya
*University of Auckland, Auckland, NZ

Abstract: Murihiku Terrane of New Zealand is comprised of folded and faulted metamorphosed volcanic sediments. Previous paleomagnetic studies of the terrane have proposed a postdepositional magnetic overprint. Our study was performed on oriented blocks from four sampling locations at Port Waikato (see Long, et al. abstract). 28 one-inch diameter cores were drilled in the blocks and subsampled to 73 one-inch long specimens for paleomagnetic analyses. Specimens were demag-netized with step-wise alternating magnetic fields of up to 18 steps ranging from 0 to 100 mT. The directions cluster well within each sample site; however, the site means show significant scatter. Our results are consistent with those of previous studies, and suggest that the Port Waikato region has experienced a magnetic overprint or has been heavily affected by the geocentric axial dipole. We are currently investigating relationships between grain size, magnetic intensity, and the charact-eristics of the magnetic remanence directions within the samples.
Funding provided by Pomona College SURP (AL); Pomona College Geology Faculty Research Fund (LR)

Research at Pomona