IRIS Summer Undergraduate Internship Program
2004 Project Descriptions

Briana Agar
briana.agar@colorado.edu
Institution: University of Colorado, Boulder
Major: Geology
Graduation: December, 2004

This summer Briana Agar (geology senior at CU, Boulder) is working at theU.S. Geological Survey in Menlo Park, California with geologist Michael Rymer on a seismic imaging study of the San Andreas fault zone in northern California. They will be collecting data from several seismic lines in the Point Arena area, about 90 miles northwest of San Francisco, and near where the San Andreas fault extends northward into the Pacific Ocean. This area has several secondary thrust faults that are a part of the greater San Andreas fault zone. Data will be gathered along two to three high-resolution reflection/refraction lines across these thrust faults to better understand the location and style of deformation within the fault zone. The project also includes a seismic line northeast of the other lines that will further reveal the interaction of other thrust faults and the San Andreas fault at depths of 3,000 to 5,000 feet below the ground surface.

Justin Brown
jrbrown5@wisc.edu
Instituion: University of Wisconsin
Major: Geology & Geophysics
Graduation: May, 2006

Seismic Analysis and Double Difference Tomography of Aleutian Arc Volcanoes

Our study focuses on the seismic analysis of microearthquakes since the 1992 eruption of Mount Spurr. We use the bispectrum verified cross correlation program BCSEIS (Du and Thurber 2004) in order to improve the quality of seismic studies at volcanoes using double difference softwares. The results are carefully applied using hypoDD (Waldhauser and Ellsworth, 2000) for relocation analysis and tomoDD (Zhang and Thurber, 2004) for a tomography assessment.

Margaret Kroehler
mekroe@wm.edu
Institution: College of William and Mary
Major: Geology
Graduation: May, 2005

In April-May 2004 University of Texas Institute for Geophysics researchers acquired onshore-offshore seismic reflection and refraction data in the SE Caribbean. At this location the Leeward Antilles Arc is currently accreting to the South American continent in northern Venezuela; accretion of island arc material is thought to play a primary role in the continental growth. The study focuses on changes in the processes and geometries of arc-continent collision from western Venezuela (arc collision initiated ~50 Ma) to eastern Venezuela (arc collision initiated ~15 Ma) to Trinidad/Tobago (no arc collision). They acquired ~6000 km of seismic reflection profiles, ~180 ocean bottom seismometer recordings, and ~1200 onshore seismometer recordings. This study is in collaboration with colleagues at Rice University. For my part in this project, I am processing and interpreting a subset of the offshore seismic reflection and refraction data in this new dataset.

Kelly Grijalva
kag16@stanford.edu
Institution: Stanford University
Major: Geophysics
Graduation: June, 2005

This summer, I am working with the High Resolution Reflection/Refraction Seismic Imaging Team, which is part of the Earthquakes Hazards Team at the U. S. Geological Survey. I have been primarily working on a seismic imaging project of Point Arena, California. The object of the project is to better understand the deformation and extent of the San Andreas Fault zone on the northern segment of the fault. We completed four different seismic profiles in the Point Arena area, in order to image anticlines, synclines and secondary faults in the region surrounding the San Andreas Fault. The profile that I am focusing on consists of a 600 meter, northeast-southwest trending line, located about 2.5 miles northwest of the city of Point Arena. My profile crosses a syncline and at least one secondary thrust fault. I participated in the data collection in the field, where we used both a BETSY™ Seisgun and a sledge hammer to generate the seismic sources. The data was recorded by a linear array of two Geometrics Strataview RX 60 seismographs, with each seismograph containing 60 active channels. Back at the U. S. Geological Survey, I have been learning how to process and interpret the data we collected in the field.

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