RESESS 2006

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The UCAR SOARS class of 2006.

RESESS successfully completed its second summer program in 2006 with three interns and their mentors. This year students did research on visualization of GPS signals, computer modeling of complex geology in Pakistan, and field work to study the break up of Africa in the East African rift zone. Miriam Garcia, Stephen Hernández, and Lennox Thompson will present the results of their summer research at the fall SACNAS national meeting in Tampa, Florida. [See abstracts below.]

2006 RESESS protégés (L to R): Lennox Thompson, Stephen Hernández, and Miriam Garcia.

In its fledgling years, RESESS operates in partnership with the well-established SOARS (Significant Opportunities in Atmospheric Research and Science) internship program at UCAR (University Corporation for Atmospheric Research). Stephen and his fellow protégés participated in SOARS-sponsored leadership orientation, team-building exercises, seminars, and writing workshops. These students form a core learning community from which they draw upon for peer support and shared experiences. RESESS aims to strengthen the presence of underrepresented groups within the solid earth sciences and increase the completion of master's and PhD degrees by these groups in the field.

Miriam Garcia was a first-year protégé and had just finished some undergraduate research during her junior year at the University of Texas at El Paso. Miriam joined the research team of Roger Bilham in the Department of Geological Sciences at the University of Colorado. PhD student Walter Szeliga was her direct supervisor and taught Miriam the necessary software package to conduct some computer modeling of an area of Pakistan that has experienced several significant earthquakes in the 1900's. The modeling attempted to decipher whether the 1931 Mach earthquake was caused primarily by compression of the Indian Plate into the Eurasian Plate or by a west-dipping thrust fault which created the Bolan Pass fold. [See abstract below.]

Stephen Hernández who had just completed his junior year at the University of Texas at El Paso returned to Boulder for his second year as a RESESS protégé. Stephen had an unusual project this year. He worked with David Phillips of UNAVCO to learn processing of high precision GPS data during the regular summer RESESS program and then accompanied Dr. Eric Calais of Purdue University on a field season in Tanzania to obtain GPS data in a small portion of the East African Rift. A crew of scientists, a UNAVCO field engineer, and students from the U.S. joined Tanzanian scientists and support staff for three weeks of installing short term GPS instrumentation. Stephen's abstract explains that the exact direction and distribution of strain across the East African Rift plate boundary zone remains a mystery due to inadequate data and analysis of the rift. After returning from Africa, Stephen continues to work on taking the raw data from the summer field work and refining it to obtain extremely precise GPS data points which will be used to determine the amount and direction of crustal movement in the field area. [See abstract below.]

Lennox Thompson from Coppin State University in Baltimore, Maryland is a computer science and mathematics major participating in RESESS for the first time. Professor Penny Axelrad of the Department of Aerospace Engineering at University of Colorado was Lennox's science mentor in his study on how visualizing how objects in the environment interrupt satellite signals that are transmitted to GPS antennas. This interruption causes distortion to the signal resulting in inaccurate measurements called multipath error. By using specialized software to create a detailed three-dimensional map of proposed GPS locations, people installing GPS stations can find the optimum position for the station. [See abstract below.]

Students interested in applying for the 2007 RESESS program should submit an application before February 1, 2007. The application form is available at (http://resess.unavco.org/application/application.html).

Modeling of vertical deformation associated with the 1931 Mach earthquake, Pakistan

The Kirthar Range in western Pakistan is the result of east-west compression caused by the indentation of the Indian Plate into the Eurasian Plate. The 1931 Mw 7.3 Mach earthquake resulted in 65 cm of local uplift on a leveling line through the Bolan Pass in the northern Kirthar Range. Previous studies modeled the fault as an east-dipping blind thrust with a top depth of 4 km and a bottom depth of 35 km, yet geologic cross-sections illustrated a blind wedge thrust system verging to the east with a horizontal décollement at 8 km. Extensive simulations of slip on this inferred structure suggested that this subsurface geometry could not be responsible for slip in the Mach earthquake. A west-dipping thrust was also considered a viable fault, as it was geologically capable of producing the anticlinal fold seen at the Bolan Pass. Forward elastic-modeling methods applied to the west-dipping thrust showed that the earthquake could not have occurred on a simple fault of this form either. A new approach, merging the wedge and west-dipping geometries may ultimately explain what happened in the 1931 earthquake sequence. Understanding fault constraints in Bolan Pass will give insight into correlations between the Mach earthquake and other seismic events during the 1930s.

Continental breakup on the East African Rift

Although the East African Rift (EAR) is often cited as the premier example of incipient rifting, the shear size and oft times inaccessibility of the rift have limited the analysis and interpretation for accurate determination of the physical processes controlling the deformation of the Earth's crust. Existing geodetic data are wholly inadequate to address the direction and distribution of extensional strain along and across this incipient plate boundary zone. A new five-year project with three Global Positioning System (GPS) campaigns (in years 1, 3, and 5) distributed across Tanzania will help us obtain interpretable results with a total extension rate across the EAR on the order of 5 mm yr-1. GPS measurements in the EAR are critical to finally establish the kinematic framework of rifting. New GPS measurements spanning the Western and Eastern rifts in Tanzania, combined with the distant data on the surrounding plates, will provide the kinematics of deformation across and along the length of the EAR. In particular, they will allow us to test and further refine the counter clockwise rotation model of the Tanzanian craton suggested by the very scarce geodetic data currently available. GPS measurements will also provide strain distribution across and along the Western and Eastern rifts. In addition to horizontal motions, GPS measurements will provide vertical displacements, critical to test for present-day uplift of the African plateau predicted from the African Superplume upwelling. Using the GAMIT/GLOBK suite of GPS processing software, we present a new, preliminary determination of the horizontal velocities in the EAR at Tanzanian latitudes.

A new approach to Global Positioning System (GPS) multipath visualization

Multipath is a condition where the transmitted radio signal is reflected by physical features or structures, creating multiple reflections of the same signal arriving at the receiver at different times. The result is degradation in signal strength of the transmitted signal from the satellite to the Global Positioning System (GPS) antenna. Multipath occurs when transmitted signals do not go directly to the GPS antenna, but rather arrive from different parts of the environment. These additional reflected signals cause distortion of the direct signal to GPS antennas, but proper positioning can minimize multipath error. Reception of bounced signals at the antenna causes erroneous data from the GPS receiver, which results in inaccurate measurement of position. The GPS receiver has trouble distinguishing between reflected signals from direct signals and that is one of the problems multipath produces. To minimize the multipath error, positioning the GPS antenna from a location that is less susceptible to multipath can help the receiver accept amplified signals. Furthermore, a MATLAB simulation was developed previously that predicts multipath based on site analysis data to generate the plot of vectors on a Digital Terrain Model (DTM). This work produces a three-dimensional plot of ray paths when signals are being transmitted from a satellite. This ray path visualization enables a user to properly position a GPS antenna to minimize the multipath error.

Photo credits: Carlye Calvin of UCAR Communications.