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Collection Description

The Department of Geological Sciences has a long-standing Senior Thesis research option for the B.S. Degree which involves a written thesis, and a public oral presentation done under the supervision of a faculty member. These independent research projects typically involve field work and laboratory analyses of samples, but can also include laboratory-based experimental projects, numerical modeling of geologic phenomena and literature reviews. Senior theses are kept in the permanent collection of the Malcolm A. Love Library on the SDSU campus.

Authors hold full copyright ownership of their original works. Please contact the repository manager at digital@sdsu.edu for any further questions.

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Comparative analysis of 2-D magnetotelluric modeling of a profile crossing the La Bajada fault, New Mexico
During the Summer of Applied Geophysical Experience (SAGE) in 2002 a magnetotelluric profile was set up on Cochiti Pueblo reservation land in the Santo Domingo Basin, which lies in the north-central portion of the Rio Grande Rift, New Mexico. The data were used to generate 2-D electrical resistivity models of the subsurface. The purpose of the modeling and analysis was to compare and further constrain the extent of the La Bajada Fault, an unnamed fault, a Tertiary monzonite intrusive (groundwater barrier), and groundwater salinity described by Quesada (2004). Regularized inverse modeling was accomplished using Winlink software, which is based on a nonlinear conjugate gradients algorithm (Rodi and Mackie, 2001). The modeling successfully imaged the unnamed fault, the La Bajada Fault, and possibly part of the monzonite intrusive. The models correlated well with a USGS reduced-to-pole magnetic map, gravity maps of the Cochiti Pueblo, and proprietary industry seismic reflection data. Modeling results from the 2002 MT data strongly correlated with modeling and analysis by Quesada (2004). In conclusion, the MT method provided valuable constraints on groundwater resources, groundwater quality, and geologic structure., San Diego State University
Comparative morphometrics of the diminutive Oligocene oreodont Sespia californica and the larger Sespia ultima from Southern California
The San Diego Natural History Museum has identified two species of oreodonts (Artiodactyla: Merycoidodontoidea) from the upper Oligocene (28-30 Ma) Otay Formation in San Diego County, California, the smaller Sespia californica and the larger Sespia ultima. The two species occur in separate localities, with no evidence of S. ultima found at sites where S. californica specimens were collected and vice versa. Morphometric data were gathered from the post-canine teeth in the upper and lower jaws of each species by measuring the length of post-canine tooth groups (i.e., m1-m3, P1-P4), as well as the width of the third molar in the upper jaw. Because there were many more specimens of S. californica available (N= 259) than S. ultima (N=10), the Kruskal-Wallis test was used, which is a non-parametric test for analyzing unequal populations. When compared by ranking, the morphometric data shows that the size difference observed between the two populations is significant and confirms that they are separate species. Comparing the data to previously published works, the sampled specimens fall within the expected size ranges of their respective species and confirms their identities as S. californica and S. ultima. Strong correlation between the P1-P4 and M1-M2 measurements has implications for the paleoecology of Sespia. Although size differences could also be explained by sexual dimorphism and/or ontogenetic variation, there is no morphologic evidence of these factors displayed in the post-canine teeth of either species., San Diego State University
Comparison of directivity effect on shallow and deep Sunda megathrust earthquakes
Megathrust earthquakes occur at subduction zones and contribute both the largest earthquakes and the most seismic energy release on Earth. The Sunda megathrust is an interplate thrust fault that represents the convergent plate boundary between the overriding Eurasian plate and the subducting Indo-Australian plate. Located on the southwestern side of Sumatra, Indonesia, the Sunda megathrust is curviplanar and defines the Sunda Trench. In the Sumatran segment, the dip of the fault plane increases gradually from about 5°-8° near the trench to about 50° below the coastline of Sumatra. The shallow megathrust earthquake that occurred on October 25, 2010 (MW 7.8) ruptured close to the trench with a dip angle of 8°. Having a shallow slip and being close to the surface at only 12 km in depth, this event excited strong surface waves and caused a very large and devastating tsunami. A second, much deeper, megathrust earthquake that occurred on September 30, 2009 (MW 7.6) ruptured closer to the coastline of Sumatra with a dip angle of 52°. This event occurred at a depth of 90 km in the heart of the subduction zone. This assessment compares the rupture directivity effect on wave propagation at various distances for both events, as well as makes a comparison of the amplitudes of their surface waves., San Diego State University
Complex blowout dune subsurface morphology using ground penetrating radar on Fraser Island, Australia
The Talitha Sand Blow was studied using ground penetrating radar to understand the shallow subsurface morphology of the blowout with an ultimate goal of understanding climate’s impact on blowout formation and evolution. The Talitha Sand Blow is located in southeastern Queensland, Australia on the east-facing coast of Fraser Island off the East. In March 2016 an interdisciplinary team used a MALA GeoSciences 160 MHz ground penetrating radar system to reveal the subsurface architecture to a depth of 25 m. A total of eight lines representing 600 m on survey lines were acquired. Lines were acquired parallel and perpendicular to blowout morphology with two additional lines obliquely crossing the main erosive area of the blowout. The subsurface architecture and spatial relationships were used to relate areas of erosion, deposition and bypassing to current surface morphology as well as understand how the blowout has evolved. Ultimately, the results from the survey will be used to establish present and palaeo wind directions, relate times of blowout activity to regional and global climate. The eastern coast of Fraser Island, and the sand rich coast of southeastern Queensland is lined with sand blowouts. Presently, the impact of these features on island stability and relationship to climate variations is poorly understood. This work serves to establish a stratigraphic framework for future work as well as understanding the defining characteristics of a coastal blowout in order for the team to recognize palaeo blowouts that have been buried during the >1,000,000-year evolutionary history of Fraser Island and the sand-rich coast of southeast Queensland., San Diego State University
Composition and deformation history of the Cantera Gneiss, Bahia de Los Angeles, Baja California
Prebatholithic rocks are exposed over a >200 km2 area in the Bahia de Los Angeles region at the southern end of the Peninsular Ranges batholith. Mapping at 1: 12,500 over a small portion of this area has documented four distinct map units, three metasedimentary and one granitic gneiss unit. All of the prebatholithic rocks in this area are steeply dipping and NW-striking. The granitic gneiss unit (here designated the Cantera Gneiss) is a mylonitic gneiss exposed over ~20 km2 that is characterized by a strong down-dip mineral stretching lineation defined by elongated quartz aggregrates and biotite concentrations. The Cantera Gneiss is relatively homogeneous internally and has the basic mineralogy of quartz, biotite, alkali feldspar, and plagioclase ± muscovite. The mineralogy, relative internal homogeneity and local preservation of relict igneous textures in thin section are all consistent with an igneous protolith for the gneiss. Stained slabs were prepared from six widely separated samples of the Cantera Gneiss to investigate modal mineralogy. The modes were determined from the stained slabs by digital image analysis of scanned slab images in Adobe Photoshop. Modes from 5 of the 6 samples cluster tightly in the monzogranite field in the standard QAP classification scheme of plutonic rocks. The sixth sample plots in the quartz monzonite field with slightly lower normative quartz and high alkali-feldspar relative to the other samples. The protolith of the Cantera Gneiss is inferred to have been a weakly peraluminous monzogranite based on the presence of muscovite in most of the samples. The gneiss and surrounding metasedimentary country rock was deformed by a NNE-SSW directed shortening produced the mylonitic fabrics in the gneiss. This compressional deformation may be related to a similar pattern of deformation recognized farther north in the Peninsular Ranges Batholith., San Diego State University
Conjugate fault systems in the San Felipe Hills: implications for the subsurface extension of the Clark fault
Conjugate faults are relatively common features that form in a wide variety of tectonic settings. When observed and well characterized they can be used to infer the principal stress directions during faulting. Such information can be useful in developing structural or tectonic models for a given area. Herein I describe and document a set of right and left-lateral strike-slip faults that occur within the San Felipe Hills, California. Both sets of fault systems involve the largely lacustrine sedimentary rocks of the Pliocene-Pleistocene(?) Borrego Formation. Within the field area right-lateral strike-slip faults strike N37W while left-lateral faults strike N37E. Both sets of faults offset hinge lines of major EW trending asymmetric folds, and have vertical dips. Right-lateral faults are more prevalent than are left-lateral faults. These relationships imply that the maximum principal stress direction is oriented NS while the minimum principal stress is oriented EW. The intermediate principal stress is vertical. The general directions of the principal stresses outlined above are consistent with movement on a NW striking wrench fault that may represent the subsurface extension of the Clark segment of the San Jacinto fault. This and other aspects of this work will be tested and assessed by two masters theses that are currently underway., San Diego State University
Construction of a torsion seismometer
An inexpensive. horizontal motion, torsion seismometer, of the Wood-Anderson type, was built and tested. It used photovoltaic cells to sense motion of the inertial mass, and electronic amplification in the recording system, rather than a strictly photo­graphic recording system. It was anticipated that this instrument and a duplicate of it would be able to give a two-axis record of sufficient linearity to allow determination of earthquake magnitude. How­ever, test results show that significant improve­ments in machining precision and in photovoltaic cell matching and linearity are necessary., San Diego State University
Contaminat flow delineation using a capture zone analysis
On February 29, 2000, detection of methyl tert-butyl ether (MTBE) at a concentration of 3.7 micrograms per liter (µg/L) was detected in the groundwater at production Well 118, operated by Rancho California Water District (RCWD). A data base search on Geotracker located several leaking underground storage tanks (LUST) within a 3000 ft radius of Well 118, and are suspected to be the main cause of the MTBE contamination found in the production well. Four capture zone models were generated using a geohydrology computer model WhAEM2000, based on a high and low hydraulic conductivity and flow rate range. The models were created on a base map to show the extent of each capture zone in relationship to the gas stations. Three leaking underground tanks are within the capture zone area, Former Delta Discount, Chevron, and 76 Station. Site characterizations indicated high concentrations of MTBE at the Former Delta Discount Gas and the 76 Station. Chevron had an unauthorized release in 1984 that contaminated the soil and groundwater. The contamination was cleaned up, and the monitoring wells have remained non-detect since then. Therefore, Chevron was eliminated from this investigation. From capture zone model 4, a contaminant front was delineated around the production well, which indicated it would take approximately thirteen years for the MTBE plume to travel from the 76 Station, and the Former Delta Discount using the parameters in that model., San Diego State University
Contamination of a gabbroic pluton by assimilation of metapelitic country rock, San Pedro, Baja California, Mexico
A previously unnamed andun studied gabbroic pluton was partially mapped and geochemically and petrographi­cally studied for evidence of contamination from the metapelitic component of the country rock. The sur­rounding moderately foliated granitic rocks are mainly adamellite and granodiorite. The metasedimentary rocks consist of gneisses and cordierite-sillimanite-mica schists which exist as steeply dipping screens subparallel to the regional foliation and as inclusions and screens in association with the margins of the gabbro. The gabbro is a layered, funnel-shaped amphibole gabbro with large hornblende oikocrysts and a coarse hornblendite cumulate grading upward into anorthositic gabbro. The gabbro is extensively cut by massive pegrnatite-aplite dike complexes. Field observations and petrographic examination indicate an increase in biotite, potassium-feldspar, tremolite and to a lesser extent quartz in the gabbro border facies adjacent to the metasedimentary rocks. Geochemical analysis of the gabbroic and metapelitic rocks showed general groupings correlatable to the gabbroic and metapelitic rocks with an intermediate group that correlates to the border facies in the gabbroic system and a group of metapelitic gneisses altered to gabbroic chemical composition. These data suggest that the gabbroic melt reacted with the pelitic metasedimentary units to produce a metasomatic exchange in MgO and CaO and to a lesser extent K2O and SiO2., San Diego State University
Correlation between operational parameters and seismicity rates at the Salton Sea Geothermal Field
The Salton Sea Geothermal Field is located on the southeast corner of the Salton Sea located in the Imperial Valley in southeastern California. Located within the geothermal field at approximately 33.2° N, 115.6° W is the Salton Sea geothermal plant. This geothermal plant is the study site for this research which attempts to identify a correlation between the plant operation parameters and seismicity originating at this site. Rising energy demands coupled with environmental awareness have led to an increased interest in natural and renewable resources. The geology of the southern California Imperial valley has created a viable geothermal resource that currently houses four operating geothermal power plants. The San Diego Gas and Electric Company (SDG&E) has stated its intent to use the Sunrise Powerlink as a conduit to carry renewable energy from the Imperial Valley. With a focus of wind, solar, and geothermal energy, the Sunrise Powerlink’s approval hinged on its ability to fulfill California’s regulation that 20% of the power supply must be generated from renewable resources (California ISO, 2006). This demand for renewable energy out of the Imperial Valley is certain to strain current production rates at the existing geothermal fields. Wastewater pumping accompanies geothermal energy production as an integral process. This process has been shown to induce seismicity in various studies (Majer et al., 2007; Nicol et al., 2011, National Research Council, 2012). For this reason, the effects of increased production need to be evaluated. While this study focuses on the Salton Sea Plant, the impact at all four existing geothermal plants, Brawley, Salton Sea, East Mesa, and Heber is of particularly interest because of their critical location. The location of these fields lies between the terminus of the San Andreas Fault to the north and the East Pacific Rise to the south. This area is a seismically sensitive location and therefore the effects of wastewater pumping are critical to understand., San Diego State University
Correlation of the Otay and Rosarito Beach formations
In 1973 Artim and Pinckney proposed two new formations in southwestern San Diego County in strata that was previously thought to be part of the Pliocene San Diego Formation. The upper unit which they named the Otay Formation was thought to be comparable to the Miocene Rosarito Beach Formation in northwestern Baja California, Mexico. In the area studied a positive correlation was made between the Otay Formation of San Diego County and the tuffa­ceous, fine-grained sandstones and siltstones of the Las Glorias and Los Buenos Members of the Rosarito Beach Formation. It is recommended that the Otay Formation be removed from the geologic literature in deference to the formation name, Rosarito Beach Formation, as established in 1970 by John Minch. The Rosarito Beach Formation thins northward from 76 (+) meters in the area mapped just east of Tijuana to zero meters just north of Sweetwater Valley in Southwestern San Diego County, where it pinches out. In the area mapped the hori­zontal strata of the Rosarito Beach Formation rests discon­formably upon the Sweetwater Formation., San Diego State University
Creep measurements and depth of slip along the superstition hills fault as observed by InSar
Data from 65 ERS-1 and ERS-2 interferograms (descending, track 356, frame 2943) covering the Western Salton Trough and spanning a time period from 1992 to 2000 are used to measure surface deformation along the Superstition Hills fault and Elmore Ranch fault. I model the near-fault (within 5 km) deformation along the Superstition Hills fault and Elmore Ranch fault using a 2D analytic model of a vertical strike-slip fault. All the observed signal is assumed to be due to shallow slip. Using data from 12 cross-sectional profiles of interferograms across the Superstition Hills fault, the average slip rate is 7. 7 ± 2.2 mm extending to a depth of 3 .1 ± 2.3 km. The lower bound of the shallow creep appears to increase to the northwest along the Superstition Hills fault from 0.6 km to 7 km., San Diego State University