IRIS Summer Undergraduate Internship Program
2005 Project Descriptions |
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Daniel
Bowman
dbowman@macalester.edu
Institution: Macalester College
Major: Geology
Graduation: Spring 2008
The Endeavour segment of the Juan de Fuca Ridge is the
site of vigorous seafloor hydrothermal venting, high levels of seismicity,
and a melt lens located 2.5 km beneath the sea floor. A network of seafloor
seismometers has been recording local seismicity at Endeavour since August
2003 as part of an experiment to study the links between seismic deformation
and thermal, chemical, and biological variations associated with the hydrothermal
vents. More than 12,000 earthquakes were recorded during the first year
of operation. Approximately 3000 of these have been roughly located in
the region beneath the hydrothermal vent fields and above the melt lens.
We are using absolute and relative relocation methods to image the fine-scale
spatial distribution of this seismicity in order to understand the tectonic,
magmatic, and hydrothermal processes operating beneath the seafloor in
this area. Our project is in collaboration with the University of Oregon,
where Jonathan Parker, another IRIS intern, is analyzing the source mechanisms
of these earthquakes. |
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Scott
Burdick
sburdick@purdue.edu
Instituion: Purdue University
Major: Applied Physics In Geophysics and Mathematics
Graduation: May, 2006
The Sierra Nevada Earthscope Project (SNEP) is designed
to determine the topography of the root of the northern and central Sierra
Nevada range and ascertain how far the Moho discontinuity discovered in
the southern Sierras continues to the north. To that end, the project
is to deploy a closely-spaced array of fifty broadband seismometers. The
new information obtained from this array will aid in the understanding
of the process by which the root of the range is foundering and to what
extent the foundering is occurring. The broadband data allows for a receiver
function study of the area underlying the Sierra Nevadas. Using the technique
of iterative deconvolution in the time domain, radial and tangential receiver
functions have been made with the early data from SNEP and with data from
many of California’s plural broadband arrays surrounding the study
area. These receiver functions illuminate deep crustal structure by way
of locating interfaces between zones of different velocity, and may be
stacked into backazimuthal bins to create a two-dimensional map of subsurface
structure. |
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Monica
Guerra
mguerra@mines.edu
Institution: Colorado School of Mines
Major: Geophysics
Graduation: May, 2006
The Calaveras Fault is a right-lateral strike-slip fault
that is a portion of the San Andreas Fault System in Northern California.
The actively creeping fault, surrounded by nearby dormant fault splays,
is of interest to geoscientists and residence of the quaint town of Hollister,
CA, located apporoximately 160 km SE of San Fransisco, CA. The right-lateral
slip has created offset curbs and swells in the asphalt pavement streets
and sidewalks, leaning houses, offset fences and west-facing fault scarps.
My project involved working in collaboration with the United States Geological
Survey of Menlo Park, CA and Catherine Snelson at the University of Nevada,
Las Vegas. High-resolution seismic refraction data was acquired along
a 156 m long profile located in Dunne Memorial Park, Hollister, CA. Processing
involved developing a seismic reflection cross-section in Promax and creating
a velocity model subsurface image.
In addition to this project I was able to assist in a magnetic survey
over an evaporite karst development in the Southern Virgin Mountains,
Nevada. I was also involved in acquisition of several high-resolution
seismic studies with the USGS, Menlo Park, CA, including the Los Trancos
Open Preserve Project researched by another IRIS intern, Sandra Saldana
of UNLV.
My experiences as an IRIS intern provided many opportunities to apply
academics to a career oriented atmosphere. Furthermore, I have developed
valuable connections with highly respectable persons in the geosciences
including graduate students, post doc students, professors, and geoscientists
in industry. |
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Tara Mayeau
tmayeau@nmt.edu
Institution: New Mexico Institute of Mining and Technology
Major: Earth Scienc w/ Geophysics Option
Graduation: May, 2006
I used digital broadband seismograms from the FLED PASSCAL
array to examine the thickness of the transition zone beneath the northern
Pacific plate using the SS precursor phases S410S and S660S.
The thickness of the transition zone between 410 and 660 km depth is a
possible indicator of lateral temperature variations in the mantle. The
Clapyron slopes of the 410 km and 660 km phase changes should cause the
transition zone to thin in regions of high temperature and thicker in
cooler areas. The differential travel times of phases reflecting off of
the 660 km discontinuities can yield estimates of transition zone thickness
and indicate the temperature variations that may occur near subducted
slabs or in regions of mantle upwelling. This study examined SS precursor
phases, specifically S410S and S660S, recorded by the Florida-to-Edmonton
(FLED) Array, which was in operation between May 2001 and September 2002,
and neighboring US stations.
The traces from earthquakes with strong SS arrivals were binned by the
location of the SS bounce point, and the bins stacked into vespagrams
using the MATLAB-based MATSEIS program. Records were first rotated into
transverse components, converted to displacements, and had the instrument
responses removed. A considerable amount of time went into understanding
and adapting the many parameters (filtering, stacking, visualizing, etc.)
that went into constructing the vespagrams (slowness slant stacks). Differential
travel times between S410S and S660S could be measured directly from the
vespagrams and inverted for transition zone thickness, with appropriate
corrections applied for lateral SH velocity variations within the mantle.
There were a half-dozen earthquakes in the western Pacific that yielded
good data. The results will be interpreted during the fall, and presented
at the Fall AGU meeting in San Francisco.
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Kristin Pape
kmpape@bsu.edu
Institution: Ball State University
Major: Geology and GIS
Graduation: December, 2005
The Puget Sound area of the Pacific Northwest is tectonically
characterized by the southward dipping Seattle fault zone and the northward
dipping Tacoma fault zone. These two faults lie in an area of transpression
caused by the northward motion of the Oregon Coastal Range toward the
static North American Plate. The area is also under strain from the Cascadia
Subduction Zone between the Juan de Fuca Plate and the North American
Plate. These combined factors lead to potential for very large magnitude
earthquakes.
For my project, we imaged the east-west Tacoma fault zone northwest of
Tacoma, Washington across the Kitsap peninsula, the Carr and Case Inlets,
Vashon Island and the Tacoma Narrows. We acquired four north-south seismic
reflection lines in Mason, Pierce and Kitsap Counties using a 180 channel
seismic system with 5 meter source and receiver spacing. The four lines
covered approximately 26 kilometers and were located based on USGS marine
profiles and LIDAR imaging of fault scarps . My daily responsibilities
during the field work included making sure that the cable and geophones
were deployed, operating the seismic source, and marking the locations
of each shot and geophone. The seismic source was a hydraulically lifted
500 pound hammer with rubber bands that helped to increase the energy.
In addition, I spent some time monitoring the three seismographs that
were collecting our data and collecting GPS points for each source location
to be used to create the geometry of the lines. I also had the opportunity
to interact with different volunteers throughout the field work. I provided
instructions for their assistance and informed them of the geology of
the area and the goals of the project.
After completing the field work, we returned to Boise where we could begin
to process the data. While I am helping process data from all of the lines,
I am concentrating on a 9.2 kilometer line that is the eastern most line
in our study area. This line extends a marine profile that hypothetically
terminated immediately south of the Tacoma fault zone. I am hoping that
this line can tell us if the Tacoma fault extends through the entire area
and help define the character of the fault and its relationship to other
structural features in the area.. Overall, our main goal is to obtain
a better understanding of the geometry involved with the Tacoma fault
zone and thereby help with the understanding of the earthquake hazards
in the area. |
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Jonathan
Parker
joparker@mines.edu
Institution: Colorado School of Mines
Major: Geophysics
Graduation: May, 2007
The Keck proto-NEPTUNE project initiates the first long-term
study of the relations between seismic activity, hydrothermal fluxes,
and seafloor microbiological life at Earth’s mid-ocean ridges. A
central part of this study is characterizing the patterns of seismic activity
that occur within and near a site of vigorous seafloor hydrothermal activity.
Scientists from the University of Oregon and the University of Washington
are collaborating on this study, which is providing research opportunities
for undergraduates at both institutions.
My study involves analyzing earthquakes from a network of eight ocean-bottom
seismometers located near the hydrothermal vent fields on the Endeavour
segment of Juan de Fuca ridge. My principal goal is to determine focal
mechanisms of micro earthquakes that occur beneath the vent fields and
in the vicinity of the axial magma chamber. The results of my work will
be integrated with that of another IRIS intern at UW (Daniel Bowman),
who is working on methods to constrain hypocentral parameters. Together,
our research will define the temporal and spatial patterns of seismogenic
deformation and provide insights to the interactions between faulting
and hydrothermal circulation beneath the Endeavour vent fields. To achieve
these goals I am developing semi-automated computer algorithms to determine
focal mechanisms. A focal mechanism indicates the style of faulting, for
example normal or thrust, and the orientation of possible fault planes.
I will be working with two methods. The first is the standard approach
of using P wave first motions plotted on a focal sphere. While we expect
this method to yield some constraints on the style of faulting, it is
likely to work for only the best-recorded events. The second method I
will use employs a combination of S-to-P amplitude ratios and first motion
data. There is debate as to whether the use of S-to-P amplitude ratios
improves the quality and accuracy of the estimated focal mechanisms; a
bonus of this study will be to give some insight into this debate.
Given the large number of earthquakes that have been recorded by our seismic
array, the initial challenge will be to integrate several computational
tool sets in a manner that is easy and efficient to use. Once we have
a working set of tools, the methods will be applied. It is at this stage
of the research that I will have to evaluate the robustness of these different
methods and subsequently interpret the results in the context of processes
occurring within the vicinity of the Endeavour hydrothermal field. |
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Amanda
Thomas
gtg873q@mail.gatech.edu
Institution: Georgia Institute of Technology
Major: Civil/Environmental Engineering
Graduation: Spring 2007
The Sierra Nevada Earthscope Project (SNEP) began with
the installation of an array of approximately 50 broadband seismometers
spanning the Sierra Nevada mountain range in late spring and summer of
2005. During their 30-month deployment the SNEP stations will continuously
collect passive seismic data from the Sierra region. This data is quickly
reviewed to identify any problems with seismometers or equipment functionality.
Initial analysis of teleseismic P-wave arrival times reveals interesting
evidence regarding the mechanism causing the Moho to "disappear"
within the western Sierra. Recent converted wave images of the Western
Sierra have revealed a region in the western Sierra where the Moho conversion
is very weak or absent. This has been interpreted as the result of a downward
pointing cusp on the Moho,. produced by viscous drag from the foundering
of the mafic Sierran lower crustal root between 3 and 5 million years
ago. However, initial examination of the new teleseismic travel times
from the SNEP stations deployed within the Western Sierra reveal earlier
P-wave arrivals above the "missing" Moho than in the surrounding
area. These P-arrivals appear to be inconsistent with concept of the downward
cusp on the Moho: if there were a thicker crust where the Moho is "missing"
then the P-wave arrivals in that area should be later than in surrounding
areas. Future research efforts will seek to verify this initial impression
and reconcile the converted wave and travel time datasets. |
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Sandra
Saldana-Farkas
ssaldana@physics.unlv.edu
Institution: University of Nevada, Las Vegas
Major: Applied Physics
Graduation: June, 2007
While working with Dr. Rufus Catchings of the United States
Geological Survey, I have been involved with several projects. One of
which I will present at the American Geophysical Union Conference in December.
This project involves high resolution seismic studies of a portion of
the main fault trace of San Andreas fault system as it runs through the
Los Trancos Open Space Preserve located in the hills just above the city
of Palo Alto in Northern California. During the course of this project,
I assisted with the collection of the seismic data, produced a seismic
reflection cross section using Promax and ran inversions to produce a
velocity model. This project has vastly increased my knowledge of seismic
processing as it pertains to reflection and refraction and the physical
theory therein. I have also learned to process seismic data in various
software mediums which has broadened both my scope of understanding and
has allowed me to make direct application to research that is being conducted
at my home university. |
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Christina
Viviano
cviviano@mail.colgate.edu
Institution: Colgate University
Major: Astrogeophysics
Graduation: May, 2006
The goal of this project is to further seismic research
and earthquake risk assessment in Colorado. The Rocky Mountain Front PASSCAL
experiment required the installation of 33 broadband seismic stations
spread across the state of Colorado. Acquired in 1992, approximately six
months of data from these stations will be used to calculate earthquake
epicenters and magnitude. UNIX program dbpick and the Antelope dbloc2
program will be used to assist in the picking of earthquake arrivals and
determining the location of their epicenters. From this information, a
catalog for local earthquakes will be established. Care will be taken
to filter out other measured events from the catalog, such as local mine
blasts. After magnitude is calculated, magnitude-frequency curves will
be developed in order to look at seismicity recurrence and determining
the sensitivity of the Colorado station array to smaller magnitude earthquakes.
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