Abstracts of REU Student Reports (SAGE 2012): Evaluating Galvanic Distortion: A Comparison of Phase Tensors and Polar Diagrams Diana Brown Abstract: Galvanic distortions result from conductivity gradients. This is a fundamental concept in magnetotellurics (MT). However, distortions from shallow, small-scale heterogeneities can lead to statically shifted data. MT sites taken from a geophysical study of the Caja del Rio region of New Mexico, were analyzed for the presence of galvanic distortion. Utilizing phase tensors and polar diagrams, a comparative study was completed. Comparing the dimensionality represented by polar diagrams to that of phase tensors provides a qualitative indicator of distortion. Sites with opposing dimensionalities were those with statically shifted data. Conversely, sites with diagrams in agreement were distortion free. 1D inversion models were run from both pre and post static shift corrected sounding curves. This direct comparison of inversions illustrates how distortions can be manifested in a geologic model. Seismic Reflection: Velocity Analysis using Constant Velocity Stacks Emily Butler Abstract: The Caja del Rio area is characterized with volcanics near the surface. The goal of the seismic reflection line is to be able to determine the depth and thickness of the volcanics as well as any other significant formations. Specifically, applying an appropriate velocity analysis is key in determining the correct reflectors and reflector depth. The goal of velocity analysis using constant velocity stacks is to flatten out as many reflectors as possible by applying the correct velocity function in order to produce a stack that can be interpreted. Velocity analysis using constant velocity stacking involves developing many stacks, all with different constant velocities and determining where each reflector flattens out and at which velocity. Then, a velocity function is developed from the determinations and applied to the stack through a normal moveout correction. The stack is then compared with other velocity methods to determine which stack is better for interpretation. In the end, the constant velocity stack method was picked to be better for interpretation. The depth and thickness of the basalt layer is difficult to determine from the seismic line due to the lack of energy reflecting off of it. This could be because the layer is relatively thin and the nature is volcanic. On the other hand, the Madera Limestone Formation has clear reflectors at around a depth of 1200 meters – 1400 meters and is dipping to the north. This is consistent with previous seismic line interpretations in the area. Overall, the seismic line is unclear and should be pre-processed and processed more to improve the reflectors to lead to better interpretations. Potential refinements for velocity models at San Marcos Sam Friedman Abstract: SAGE (Summer of Applied Geophysical Experience) has been investigating the geophysical properties of San Marcos Pueblo since 2008. Data collected using seismic refraction have assisted in modeling the underlying stratigraphy of the Pueblo, most importantly in modeling the aquifer unit for the Pueblo: the Ancha Formation. Data collected by SAGE 2012 indicate that the current models do not accurately represent the boundaries of the Ancha Formation. In addition, the modeled velocities of the river terrace unit along Lines 19 and 20 are inconsistent with the velocity modeled for the unit along Line 18 Analysis of the Ground Magnetic Data at the Caja del Rio Area Madison Gallegos Abstract: The ground magnetic data along two local profiles located in the Caja del Rio area were analyzed. The ground magnetic data along the SAGE 2012 seismic line suggest a possible rise in basement eastward along the profile, of which is supported by the seismic data. The ground magnetic data along the SAGE 2012 AMT line shows a volcanic flow extending past the most eastern point of the AMT line. This suggests volcanic flows being present past the end of a Cerros del Rio Volcanic Field boundary that was recently defined by the USGS. Mapping the Edge of the Cerros Del Rio Volcanic Field Using the Transient Electromagnetic Method Meredith Goebel Abstract: As part of the Summer of Applied Geophysics (SAGE) 2012 survey, the transient electromagnetic method (TEM) was applied at 10 stations along the edge of the Cerros Del Rio volcanic field in the southwestern Espanola basin in northern New Mexico. The line spanned 5 km roughly east west, and measurements were able to reach depths of investigation as deep as 395 m. The data was processed using programs SiTEM and Semdi through which both 20 layer and 5 layer models were created to represent the subsurface. The models indicate the resistive volcanic are thickest in the west and thin out towards the east. They also show upper and lower resistive units in the West separated by a thin conductor. Possible explanations for the observed structure include multiple volcanic flows, fault control, and the presence of water. 2D Inversion Study of the Caja Del Rio Basement Depth and Geothermal Potential Using Magnetotelluric Data Derek S. Goff Abstract: The Caja del Rio, located in the Española Basin in the northern portion of the Rio Grande rift, holds potential to be used as a geothermal resource.By determining the depth to basement from the magnetotelluric data of SAGE 2012 and 2011, we hope to give a clearer picture on the feasibility of developing this resource. To determine basement depth, I created multiple2D inversions, utilizing the actual sounding data. One set of inversions was created using a static shift based upon the surrounding geology, while the other set utilized the raw data. The results of the inversions showed two different depths to basement, and with the shifted data not being justified by actual data, this study determined a basement depth of three kilometers to be more likely. With such a shallow basement, the probability of a usable geothermal resource being present increases. Using Seismic Refraction to Model the Subsurface of the Caja Del Rio near Santa Fe, New Mexico Scott Greenhalgh Abstract: The Caja Del Rio lies just to the north-west of Santa Fe, New Mexico. Geophysical research has been performed yearly by the Summer of Applied Geophysical Experience (SAGE) research group for the past 30 years. Thirty years of work has resulted in quality data of the Rio Grande Rift in various sites surrounding Santa Fe. This years’ research was conducted over the volcanic fields of the Caja Del Rio (figure 1). Volcanics, such as basalts, can have serious impact on the quality of data collected from geophysical techniques. These basalts scatter and attenuate seismic signals quite rapidly and make it difficult for seismic energy to reach great depths without coming back as complete noise. The purpose of this study is to image below the volcanic rocks from which we can create a model of the subsurface. Also, using ray trace theory, visualize how seismic rays travel through the earth as a function of depth. A Gravity Profile Across the Rio Grande Rift, Northern New Mexico Christopher Harper Abstract: The target of this study is the Los Alamos graben in the Espanola basin of the Rio Grande rift. A gravity profile across the Rio Grande rift is created using data collected during the past thirty years of SAGE. A brief geologic setting is given and methods of data acquisition are detailed. A MATLAB script is used to create a forward density contrast model along the profile using the collected gravity data. Two previously unmapped faults are identified, including the east bounding fault of the Los Alamos graben. Seismic Reflection and Velocity Analysis Using the Normal Moveout Correction Ashley Hutton Abstract: The Caja del Rio plateau in Santa Fe County, New Mexico, east of the Valles Caldera, is suspected to be a geothermal source. The 2012 Summer of Applied Geophysics (SAGE) program conducted a seismic survey across an approximately 6.5 km transect situated southeast to northwest using a Vibroseis truck. The surface geology consists of volcanic rock interbedded with loose sediment, which produced poor quality data. The data underwent simplified processing, including editing, geometry application, common midpoint sorting, muting, velocity analysis and stacking. Deconvolution and time variant filtering were not employed because those processing methods did not improve the data. The normal moveout (NMO) velocity analysis is one of the most important processing techniques. NMO is an effect due to increasing offsets between source and receiver. The NMO correction involves correcting the hyperbolic reflections by applying velocities that stretch the waveform to a zero-offset travel time. This stretching was corrected for using a stretch mute of 50%. Once the correct velocities were recorded for different positions and two-way travel times, a velocity scattergram was composed and contoured so that the stacking velocities could be applied across all the CMP gathers. This is essential for the final stack. The NMO stack contains some unappealing artifacts from refractions, so a different stack using constant velocity stack velocity analysis was used. It is believed that the Precambrian basement and the Madera formation as well as a prominent strike-slip fault have been imaged. Seismic Refraction at Cajadel Rio Utilizing the Slope Intercept Method Colleen Klockow Abstract: In July of 2012, a group of students and professors (SAGE) set out to map an area near the Caja del Rio landfill. The group was seeking to find confirmation of faults listed previously in the literature using a 6 km long seismic survey, which in turn could potentially give a 1.2 km deep survey using seismic refraction. In this instance, due to time constraints on data processing, and the presence of volcanic rock, specifically basalt, that number was dramatically decreased to roughly 200 m, and only 3 layers of sediment could be determined instead of the 4 that had been hoped for.