We are scheduled to acquire marine seismic reflection and refraction data in July 2003 at Hess Deep. Hess Deep is a location in the Pacific where crust created on the east flank of the East Pacific Rise is being ripped open by the westward propagating Galapagos Spreading Center. Submersible dives along the walls of the Hess Deep rift have been able to map the uppermost 2 km of the exposed oceanic crust over a lateral distance of tens of kilometers. This program will acquire seismic data on the plateau adjacent to the exposed walls at the rift, and we will attempt to make a direct link between the geologic and seismic structure of fast-spreading oceanic crust. A web page for the project can be found at: http://www.ig.utexas.edu/research/projects/hess_deep/
The student intern would arrive at UT prior to the cruise and would spend time learning about the geologic background of the Hess Deep region and the constraints on the seismic structure of fast-spreading crust. He/she would also start learning software packages for processing seismic reflection and refraction data. In July the student would serve as a watchstander on the 3-week cruise aboard the R/V Maurice Ewing, where he/she will gain knowledge about the acquisition and processing of marine seismic reflection (6-km streamer) and refraction (16 ocean bottom seismometers) data. In August the student will have an opportunity to process and interpret selected profiles from the dataset.

The USGS would welcome an undergraduate intern to participate in modeling the crustal structure of south coastal Los Angeles from USGS refraction and reflection data, and industry reflection and oil-test well data. The active Palos Verde and Newport-Inglewood faults traverse this region and remain earthquake threats to Los Angeles. This effort is part of a broader iniative on the part of the Southern California Earthquake Center (SCEC) and the USGS Earthquake Hazards program to study the California offshore Continental Borderland.
The student project would involve modeling refraction traveltimes and constraining models with reflection interfaces and oil-test well data, in conjunction with Shirley and myself. The project would also involve work with large data compilation and display programs, which contain the industry data. We anticipate collaboration with John Shaw, a SCEC participant at Harvard University, who has compiled an enormous dataset from Texaco.

We have just initiated Project COARSE (COnsortium for Arizona Reconnaissance Seismic Experiments), a collaboration between the University of Arizona , Arizona State University and the University of Texas in Austin to deploy 9 broadband stations in southern Arizona for one year.
The overall goals for this project are:
1. Measure crustal thickness, upper mantle velocity structure, mantle transition zone thickness variations, and seismic anisotropy parameters across a SW-NE oriented Colorado Plateau-Basin and Range transect in southern Arizona. This region is currently the most seismically undersampled portion of the western US.
2. Investigate the crustal anisotropy structure of major metamorphic core complexes.
3. Compare our seismic parameters with laboratory measurements of rock properties from crustal and mantle xenoliths from nearby localities (an independent study by Mihai Ducea at the University of Arizona).
4. Develop sufficient preliminary data to make a compelling case for “AzSCOPE”, a EarthScope/USArray Flexible Array experiment that we hope to propose when Bigfoot begins stomping across Arizona.

The primary role for the intern will be to help us service the stations during the summer, help with data processing and archiving, and initiate an independent research project with the new data.

The Swiss Digital Seismic Network (SDS-Net) has recently been upgraded to a 29-station high-quality broadband seismic network (STS-2) with a station density of 40-50 km, comparable only to networks in Japan and California and, when installed, the temporary US-array deployments. To increase SDS-Net aperture for our research purposes, we will install an additional 10-15 temporary broadband stations in the vicinity of Switzerland during 2003.
With this dense broadband seismic network, we can perform detailed 3-D studies of the wave propagation and the crust and upper mantle structure beneath the tectonically complex western-central Alpine region. Small plate fragments, sandwiched between the converging African and Eurasian plates, currently form the plate boundary in the Alpine region. The goal of the investigations is to significantly improve our understanding of the geodynamics of collisional zones. Initial projects include receiver-function analysis to determine crust-mantle stratification, regional surface wave propagation for 3-D structural analysis, and shear-wave splitting measurements to characterize crust-mantle anisotropy.

The seismic hazard in Las Vegas, NV has been underestimated until recently. It has been estimated that Las Vegas could experience a M6.5 to 7 earthquake. Very little is known about the basin geometry in Las Vegas other than there appears to amplification in varying areas of the basin. We are going to collect controlled-source seismic refraction data to constrain the velocity information within the basin as well as define the geometry of the basin including the basin/bedrock contact. This information will then be integrated with existing data to produce a 3-D community model to analyze the site response of the basin. Acquiring these data will provide answers to key questions such as: (1). Why is there such as variability in amplification across the basin; and (2). define any new structures such as sub-basins within the valley. This summer we will need to compile the existing seismic reflection and refraction data in the valley, which will be used to create a starting model in which the new refraction data will be integrated.

The proposed study will compare lower crustal seismic structure to previously imaged mantle structure. The results of the imaging will be used to constrain models of the magma plumbing system.The three-dimensional nature of the lowermost crust beneath ridges is still poorly known. There is presently little known about how magma is supplied to the crust and few observations that constrain the models that have been proposed. Seismic techniques are capable of imaging a ridge's magmatic system, since seismic waves are sensitive to high temperatures and the presence of melt. The results of the proposed study should provide new insight into a number of problems including the variability in magma supply along the ridge and the importance of along-axis magma transport at deep versus shallow levels.

The role and probable activities of the student intern.
2. Analyze data to identify seismic arrivals. The first step in the data analysis will be the construction of record sections for each station. Next, lower crustal and wide-angle reflection data will be picked and assigned uncertainties. The student will be instructed in these methods and will gain a knowledge of basic seismic data analysis. The data will be plotted and analyzed for trends related to crustal thickness variations and mantle anisotropy.
1. Forward and inverse model the travel time data. The student will be instructed on the use of tomographic imaging code, which will be used to obtain the three-dimensional images. Although tomographic imaging is not a simple task and can be time intensive, I believe that preliminary images can be obtained within the time frame of the summer internship.

The Jemez Volcanic Field in north central New Mexico has been erupting intermittently since 16
Ma. A magma chamber collapse following a cataclysmic eruption at 1.2 Ma created a 20 km caldera. The Valles Caldera is one of the type localities for massive silicic caldera-forming eruptions. Several lines of evidence suggest that magma is currently accumulating beneath the Jemez Volcanic Field. Between 1993 and 1995, a PASSCAL-supported seismic field campaign was carried out with the goal of imaging the deep structure of the caldera, the underlying crust and a possible magma body. The project included both a passive and active source seismic array. Analysis of the passive recordings, now complete, revealed several reflective features in the crust, interpreted as sills, and a region of seismic velocities decreased by up to 25%, which was interpreted as a magma body with at least 10% partial melt. A much denser array of short period PASSCAL instruments was used to record explosive and Vibroseis sources. This data offers a higher resolution glimpse of the shallow features of the system. No analysis of this data for volcanic structure has been published and funding for the project no longer exists. The original PIs at Los Alamos National Lab have recently given us the prepared data and have offered to work with us to develop the analysis. The geophysics group at NMSU has a long-established history working with LANL. In light of the results from the passive seismic experiment, a new look at the dense-array active source recordings is clearly warranted. The proposed project will examine first and secondary arrivals from this data to obtain an improved image of the interior volcanic structure, with an emphasis on the proposed magma body and the lid which separates it from the overlying crust.
This project is ideal for an undergraduate internship for three reasons:
1. Preliminary processing and data preparation has already been completed.
2. The 2D nature of the data (three linear arrays) allows it to be modeled quickly within the time frame of a summer internship.
3. The raytracing techniques used to model this data are conceptually straight-forward and provide an excellent introduction to seismology.

The project is within the Western Earthquake Hazards Team of the US Geological Survey in Menlo Park, California. We conduct high-resolution seismic reflection and refraction surveys related to earthquake hazards, water resources, and environmental contamination remediation. Typically, these studies involve components of all three studies. In April and May of 2003, we plan to use IRIS-PASSCAL instruments to conduct a seismic investigation across the eastern Santa Clara Valley (Silicon Valley- San Jose) and the San Bernardino Valley (east of Los Angeles). In addition, if Earthscope funds are approved by Congress, we expect to acquire seismic data across the SAFOD drill site and San Andreas fault near Parkfield, California. During the summer months, we may also acquire smaller surveys across the San Andreas and related faults. In addition to data acquisition, we will spend at least half of our time working with data in the lab and writing papers on the results of our studies.

The IRIS/PASSCAL Insturment Center maintains a large national pool of portable seismographs, broadband sensors, portable telemetered networks, and high resolutions cable reflections systems. Working with PASSCAL staff, interns will learn about repair and maintenance of seismographic equipment, assist in the deployments around the US and overseas, and participate in the processing of the data under the direction of the Instrument Center Director and Staff. A focused researcdh and testing project related to next generation instrumentation and US Array will also be undertaken.

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