Geology
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)