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 region of , 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 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. In addition, no evidence for a fault could be found on the seismic refraction images, and so there was nothing from this data to support the presence of a fault.

Tail Mute of the Seismic Reflection of the Espanola Basin in the Caja del Rio area Susan Konkol Abstract: The Espanola basin is part of the southern Rio Grande rift. Seismic analysis was performed in this basin for the purpose of discovering faults and identifying the stratigraphic formations. 862 geophones were planted 20 m apart in a NNW direction. There were 80 channels on one line and 120 channels on the second line. A vibroseis truck was used to produce P-waves in the subsurface. The frequency of the vibration was 8-80 hertz. Seven spreads were recorded. Seismic data was downloaded to the computer program. All files were checked for corruption and poor data files were eliminated. The data were preprocessed using a Ban Pass filter which arranged the data that were retained. Deconvolution was not useful and therefore was not applied to suppress noise of the same frequency as the reflection signals. Common Midpoint shot gathers were produced with the shots to receiver equaling an 80 fold. Editing was performed using a muting application. Muting was applied to eliminate the airwave and the noise in the deeper part of the subsurface. Tail muting was chosen to edit the data. The medium wide tail mute was chosen as the best mute editing. Constant Velocity Stacking (CVS) was applied. Various velocities were tested. The best fit velocity to the data was chosen. Velocities to specific layers were applied. The CVS was the chosen method. The reflection group analyzed the velocity of the data. The Ancha Basalt, the , and the Espinaso Formation were located using the velocities. There may be a fault at 2600 m. The depth to the basin is approximately 3 km.

Regional Gravity Profile and Basement Architecture of the Espanola Basin Encompassing the Cerros Del Rio Volcanic Field, New Mexico Austin McGlannan Abstract: An understanding of the structural signature of the Espanola Basin in relation to the tectonic evolution of the Rio Grande Rift is vital to interpreting further geological and geophysical studies. Creating a two-dimensional forward gravity model will provide information regarding the architecture of the basin, delineate faults and basement features. Several geologic constraints were accounted for providing a foundation to construct a gravity model for interpretation of geologic structure and lateral changes in densities. Faults were located along the profile correlating with steep rises in the complete bouguer anomaly. The presence of a horst block within the region is noted as a basement high trending west along the profile, a feature of interest.

STRATIGRAPHY OF THE CAJA DEL RIO SAGE AMT LINE Benjamin Murphy Abstract: Analysis of data from eight audio magnetotelluric stations reveals two volcanic flows that are interbedded with Ancha Formation sediment and that overlie sediment beneath the electromagnetic study area in the Summer of Applied Geophysical Experience 2012 field area. The upper flow is inferred to extend beyond the eastern end of the electromagnetic methods area and therefore does not follow the bounds for the Cerros del Rio Volcanic Field as recently redefined in work by the USGS. Further research will be necessary both to resolve the lateral extent of volcanic flows in this area and to examine subsurface resistivity anomalies.

CMP Stacking of Seismic Reflection Data Collected in the Cerros Del Rio, NM, and an Interpretation of Geologic Structure Johnathon Osmond Abstract: The interpretation of the geologic structure and tectonic evolution within the Rio Grande Rift in the southwestern United States has been problematic to researchers for many years. Traditional geological studies have provided important information about the stratigraphy and petrology of outcropping features but the structural complexity of the rift makes subsurface analysis quite difficult. Application of geophysical techniques in the Santa Fe area has shed some light on subsurface features throughout the Rio Grande Rift and has helped define the geology to a certain degree. Seismic reflection data collected by the Summer of Applied Geophysical Experience (SAGE) group in the summer of 2012 was undertaken to provide a better understanding of the subsurface structure and lithology of Cerros Del Rio volcanic field west of Santa Fe. After processing, the resulting common midpoint (CMP) stacked seismic profile may help support current interpretations of the subsurface geology of the Cerros Del Rio. It is hoped that this data can be used to address not only geological problems in the area, but also allow for better analysis of the geothermal systems around Santa Fe.

Transient Electromagnetic Investigation of the Cajadel Rio Plateau John H. Smith Abstract: Transient electromagnetic (TEM) soundings were collected along the Caja del Rio plateau, coincident with magnetotelluric (MT) soundings. The TEM data had low signal-to-noise ratios, determined to be not useful for constraining static shift in MT apparent resistivity curves. ElectroMagnetic Model Analysis was used to investigate the effect of the Caja del Rio’s geology on the various TEM instruments used. The analysis found that a shallow, highly resistive layer of volcanics in the region resulted in insufficient quality late-time data to provide static shift corrections.

Preprocessing of Audio Magnetotellurics: Coherency Jerlyn Swiatlowski Abstract: The SAGE 2012 program was focused in the Caja del Rio Region just to the right of Santa Fe, New Mexico. The main goal of this year was to try and see if we could find the edge of the volcanic rocks or at least to where it starts to thin out. This is what the audio magnetotellurics (AMT) method was trying to find in the shallow surface of the earth (approximately 500 m below). After taking data in the field, one of the preprocessing methods done before any of the actual processing of the data is to look at the coherency of the data we have. Coherency looks at how clean the data signal is. There is a dimensionless scale from 1 to 0 stating whether the signal is coherent (a value of around 1) or whether the signal is poor with a lot of incoherent noise (a value less that 1). The way to look at the coherency is through a program called Imagem where it compares the orthogonal magnetic and electric fields against one another. The three different coherencies that was looked at, were 0.9, 0.7 and 0.5. At first 0.7 was thought to be the best to use but after preprocessing the data, found that some 0.5 coherencies were better than the 0.7 coherencies and this was used instead. After the preprocessing was done, the results of processing the data in 1D and 2D inversions we found that it looks like there is a thinning of the volcanic rocks to the East, it then goes away and reappears later on towards the East. This is also confirmed with results from the transient electromagnetics (TEM) as well.

Algorithmic Techniques for Proper Inversion Convergence of Transient Electromagnetic Data from Disparate Receivers Using Common Transmitter Christopher W. Volk Abstract: Transient Electromagnetic (TEM) data was collected along a five-kilometer transect in order to better image the margins of the Tertiary-age basaltic flows of the Caja del Rio region west of Santa Fe, New Mexico. Investigation of said images provided insight into whether the region is suitable for potential geothermal development. In total, eleven locations were monitored employing both a single-receiver and a dual-receiver method. For the latter, two receivers of different moments were used in conjunction with a single transmitter. Upon processing, discrepancies were encountered and difficulties arose in the modeled response of various inversion attempts, and no real-earth model would fit the data. The unique system response of the different receivers was the basis of the lack of coherency in the inversions and resulted in being the nature of the problem. This paper addresses processing difficulties that arose and the algorithm employed to later more correctly invert the data. The parameters of the following inversion would then be used along the entire transect to construct a data model (interpretive) from the same, two-receiver set up.

Seismic Refraction at San Marcos Pueblo Rosalynn Wang Abstract: Seismic refraction data are recorded and processed to investigate non-invasively the archeological site of San Marcos Pueblo during The Summer of Applied Geophysical Exploration (SAGE) program. Two lines 19 and 20 were placed at the site, 114 meters and 96 meters in length respectively. 30 Hz geophones were inserted into the ground at every 0.5 meter interval and a shot point was placed and recorded at every 6 meter interval. The seismic data recorded in the seismometer was then analyzed with GEOMOD, a Matlab program. The resulting traveltime curves are interpreted as thickness correlating to different velocities at each layer and its depth. The geology of these layers is also determined by the velocity of the layer. The velocity can be compared to velocity ranges of different materials to verify the material of that layer. The velocities correspond to underlying layers of the San Marcos Pueblo area of soil, terraces, the Ancha formation, and the . Velocity anomalies present in the traveltime curves are possible areas of interest for archeological research in the future.

Application of Velocity Analysis to Seismic Reflection Data from the Caja del Rio, New Mexico Results of Applying Normal Moveout (NMO) Correction Anne Wasik Abstract: Analysis of reflection data across 6km of Forest Road 24 reveals several subsurface layers beneath the Summer of Applied Geophysical Experience 2012 seismic line. This analysis is based on the velocity analysis method, normal moveout, used to process the data. Seismic Processing Workshop software was used to apply pre-processing, velocity correction, and then constant velocity stacks were used to gather the shots and expose the reflectors. Constant velocity stacks produce the most prominent reflectors, which are seen dipping to the north, the first starting at 1200 milliseconds two-way time and the second at 1600 milliseconds.

A Sensitivity Analysis on 1D AMT Models of the Cerro Los Rios Volcanic Field Mark Welch Abstract: In order to understand and quantify the accuracy of inherently non-unique inverse models of AMT data, a sensitivity analysis was performed on the SAGE 2012 AMT data. The sensitivity analysis was performed by independently varying the parameters of resistivity and depth in one dimensional three layer AMT models. The parameters were increased and decreased by a fixed range of multipliers from “good fitting” base models for two of eight SAGE 2012 AMT sites. The thickness and resistivity of a conductor and resistor were then varied simultaneously. Through this analysis, bounds of relative accuracy for one dimensional AMT models were quantified. Furthermore, the sensitivity analysis of SAGE AMT data was found to be in support of two basic tenets of magnetotellurics: a resistor at depth is manifested by its thickness and a conductor by its conductance. From this project, much insight was gained into the confidence of the accuracy of AMT inverse models.