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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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Cretaceous extensional deformation of the Cuyamaca reservoir gneiss within the Scove Canyon segment of the Cuyamaca-Laguna Mountains shear zone (CLMSZ), Peninsular Ranges, California
Based on age and numerous geophysical, geochemical, and petrological discontinuities, the Peninsular Ranges batholith (PRb ), southern California, can be divided into western and eastern zones. Within the northern part of the PRb the eastern edge of the western zone contains the northwest-striking CLMSZ, which is characterized a by westward-verging eastward-dipping mylonitic to mylonitic gneissic fabric. Field and microscopic evidence, along with previously published data, suggests two periods of deformation. An early contractional deformation (Dl) occurred at -118 to -115 Ma, and was soon followed by extensional deformation (D2) producing the Scove Canyon segment (SCs) of the CLMSZ. The SCs of the CLMSZ can be traced to the southwest into the western edge of the Cuyamaca Reservoir gneiss (CRg). Along its northwestern edge the CRg occurs as segmented sheet-like bodies against the ~ 118 Ma Pine Valley granodiorite. Geochemical and petrographical data indicate the CRg to be a tonalite that probably formed within a volcanic arc setting where local contamination of mantle melts with sialic material may have occurred. The foliation (S2) produced by D2 becomes strongly developed toward the CRg's southwestern edge where it occurs in association with well developed S-C mylonite. S2 has an average attitude of N25W /59NE. Within the plane of S2 is a well developed stretching lineation (L2) trending 66/NSSE. Shear bands (C2) strike N19W /-80NE. Sigma-type porphroclasts with asymetric tails indicate an east-side­down sense of displacement. The S-C mylonites can be traced into the ~ 105 Ma Las Bancas tonalite, but do not cross cut the ~94 Ma La Posta pluton. These data imply that the S-C mylonite developed sometime between ~ 105 to ~ 94 Ma. Though the tectonic mechanism responsible for the extension in the SCs of the CLMSZ is not well understood, extension may best be explained by the gravitational­collapse model. In this model, east-dipping subduction produces copious amounts of magma which rose into the crust. Eventually the inflated crust became gravitationally unstable, and collapsed on itself. As material spread outward from the collapsing central portion extensional mylonite formed, thus reflecting the apparent subvertical orientation of the maximum principal stress direction., San Diego State University
Cross-bedding in the Torrey sandstone member of the eocene La Jolla formation of western San Diego County, California
The highly cross-bedded Torrey Sandstone, widely exposed between Delmar and Encinitas, is predominantly medium- to coarse-grained, well-sorted, and poorly consolidated. It is poorly fossiliferous and contains interbeds of shale and cobbles. Cross-bedded sedimentation unite range from less than one foot to greater than 15 feet in thickness. Both trough and tabular cross-bedding are common, but the tabular type is most prevalent. Dip directions of 202 cross-beds, at 130 outcrops indicate a predominant southeasterly paleo­current direction. Dip inclinations range from five to 38 degrees, with a mean dip of 19 degrees. Marine fossils, thin cross-bedded units similar to those found on modern beaches and off-shore bars, shale layers interbedded with the cross-beds, thin pebble and cobble layers, and massive sandstone suggest a shallow marine environment. However, the thick cross-bedded units which are unfossiliferous, and composed of well-sorted sandstone seem to indicate an aeolian origin. A multiple environment hypothesis seems to best explain the Torrey characteristics. The unit appears to represent a combination of a marine and subaerial environment, perhaps a spit or barrier beach topped by wind blown sand that separated the open coast from a lagoon or estuary., San Diego State University
Crustal thickness of the northern peninsular ranges, Southern California, from teleseismic reciever functions
Crustal thicknesses provide valuable constraints on models for the tectonic development of the North American continental margin. Previous gravity and seismic refraction surveys in the Peninsular Ranges Batholith (PRB) have yielded poorly constrained and conflicting crustal thickness estimates, ranging from 26 km to 43 km The teleseismic receiver function provides reliable estimates of crustal thickness through the identification of the P-to-S conversion (Ps) at the Moho. In a study by Ichinose et al., ( 11'16) observed Ps arrivals from receiver functions at the latitude of San Diego imply a relatively flat deep Moho (~40 km) under the western PRB, and a steeply shallowing of the Moho to the east (~40 km to ~25 km) under the eastern PRB. In this study, crustal thicknesses were estimated through analysis of teleseismic receiver functions at five stations in the northern PRB between the Elsinore Fault Zone and the eastern margin of the batholith. From observed Ps arrivals and tomographic velocity models, a northeastward thinning of the crust is inferred. The crustal thickness at the southwestern end of the 60-km profile was found to be ~37 km, thinning to ~28 km at the northeastern end. Unlike the Airy isostacy model, Moho topography does not mirror surface topography. Data from the receiver functions suggest a shallower Moho by ~9 km beneath the topographic high. This may be indicative of isostatic rebound of the crust due to footwall unloading during Miocene extension., San Diego State University
Cultural and linguistic influences on conceptions of rivers
This study investigates young adults' conceptions of rivers by using drawings and interviews as a measure of their understanding of scientific concepts. The goal of our exploratory pilot study was to discover if language or culture had any obvious direct influence on people's conceptions of rivers. We gathered six volunteers from distinct linguistic and cultural backgrounds to participate in this study. Three of our participants spoke only Spanish, two were bilingual and one only spoke English. The interviews were videotaped and transcribed for analysis, and for the Spanish speaking volunteers the transcribed interviews were translated. The drawings and interviews were analyzed and categorized into the five levels of understanding identified by Dove (1999) and for specific content and features. In the examination of the drawings and the interviews we realized that most of the drawings were incomplete based on their answers from their interviews and that the content of the rivers were mostly perceived in a rural setting. Once the participants' interviews were assigned an understanding level, we compared and contrast one participant to another to see if we could find any differences or similarities. According to our measurement of participants' levels of understanding, only two of our participants had the highest level of understanding and the rest of the participants fell under level 3. The two with the highest level of understanding were from two different cultural backgrounds and spoke different languages. The other four were either bilingual or spoke Spanish only. Our results show no clear correlation of either level of understanding or conceptions of river systems with language (or, by extension with culture) at least within this limited, exploratory subject pool. However, we did find an unexpected relationship between subjects' conceptions of rivers and whether or not they had lived in the Imperial Valley or Mexicali for the majority of their lives. Subjects who had recently relocated to this region or who had spent significant time outside of this region and who had had significant exposure to natural river systems had conceptions that were more scientifically accurate. Subjects whose experience was limited to the geographical area around El Centro and Mexicali consistently held conceptions of rivers which more closely resemble irrigation canals rather than natural rivers., San Diego State University
Data sheets for borax firebrake®ZB: a visual basic 6 sql program
Because of the varied background required for successful completion of an undergraduate degree at San Diego State University, graduating students sometimes end up working jobs that emphasize only one of their many skills. For example, for the flame­ retardant division of Borax it is often necessary to formulate and test data for the many industrial plastic products that contain a product called Firebrake® ZB. Each use of Firebrake® ZB requires knowledge of how much of the product to include, as well as test results which are important in determining the effectiveness of Firebrake® ZB. A salesperson working for Borax would need examples of how well Firebrake® ZB benefits a particular product as well as how much of it might be needed for a given project. Hence, it is important to have an easily manageable system for accessing such data. Before this project began information about the uses of Firebrake® ZB were held in an unorganized notebook containing nearly 200 pages. I therefore proposed to organize this information and to construct a program in Visual Basic 6.0 for easy and efficient access of the needed material. The first step in the development of the program was to organize data sheets of Firebrake® ZB into a database consisting of different characteristics tied to an identification number. These characteristics consisted of the types of plastics that are needed, whether the product contains halogens, and the identification number of a certain data sheet. The task of accessing the database, and searching specific criteria is achieved by a series of structured queries (SQL). An example of a SQL might be "SELECT [polymer] FROM [database}] WHERE [halogenated]= 'yes'". In the final VB 6 program this statement would access all the entries which had "yes" in the halogen field, and then would select only the information in the field labeled "polymer." Once the correct data sheet is found and selected by the user, the program opens the file corresponding to a field in the grid (in this case the identification number,) and displays it in a rich text box. Since each data sheet consists of one page, the user can view the entire data sheet on the screen. In order to manipulate the file, the computer takes the data stored in the text box, and either sends it to the printer, or allows the user to save it in a separate file. The resulting program will be delivered to Borax where it will be used by their sales teams., San Diego State University
Deformation of Marine Terraces on Santa Rosa Island and Implication for the activity of the Santa Rosa Island Fault
The uplift rate on Santa Rosa Island has been determined to range from 0.08-0.17 mm/yr based on field mapping and measurements of elevations of the first three emergent marine terraces on Santa Rosa Island, and the two uranium-thorium dates of solitary corals collected from the second emergent marine terrace near Johnsons Lee. The dates for the coral, Balanophyllia elegans, are 120±3 and 114±4 ka. Based on these dates, the second marine terrace is correlated to terraces formed during oxygen isotope substage Se. Relative to the second marine terrace, the first marine terrace would then probably correlate to the substage 5a high stand, and the third marine terrace would correspond to the stage 7. Using the uplift rate determined for the north coast of the island near Arlington and Tecolote canyons, a high (150-180 m) marine terrace is estimated to be about 0.9-1.1 Ma in age. Based on the 0.9-1.3 km deflection of canyon drainages that incise the high terrace, the approximate long-term slip rate of the Santa Rosa Island fault is 1 mm/yr. The relationship between the Santa Rosa Island fault, the Santa Cruz Island fault, and the Santa Monica fault suggest a minimum left-lateral rate of about 1 mm/yr for the Santa Monica fault near Los Angeles., San Diego State University
Depositional Structures at the Head of La Jolla Submarine Canyon, San Diego California
Bedforms and sediment studies were conducted using S.C.U.B.A., during Southern California's winter and summer seasons in the nearshore environment at La Jolla, California. The seasonal variations at the time of this study were limited in that, swells characteristic of the summer season were few if not absent. Observations yielded no significant changes in oscillation ripples from the start to the end of the study. The presence of troughs occurred in the latter half of the study. The deeper location of fresh ripple marks in the beginning of the study was evidence of the larger swells that had previously hit La Jolla Bay in January, 2000. The inactive zone, which roughly extends from about 40 feet of seawater (fsw), westward to deeper depths of the canyon, was characteristic throughout the summer season. Bedforms found at the head of La Jolla Canyon include symmetrical and asymmetrical oscillation ripples, troughs, sheet-flow structures and backwash ripple marks. The oscillation ripple wavelengths range from 6 to 20 cm with heights from 0.5 to 4 cm Oscillation ripple marks of these wavelengths are consistent with the sediment size as indicated by Inman (1957). Sediment analyses indicate that the shelf and nearshore environments consist of well-sorted, near symmetrical, fine sands. The beach foreshore contains well-sorted, positively skewed, fine sands. Extremes are present in both the troughs and crests of the ripple marks found at depths from 10 to 35 feet. Sediment analyses of the troughs found the worst sorting of all environments when shell fragments were included in the distribution parameters. When reanalyzed without the shell fragments, they generally contained the finest particles and were well-sorted. Ripple crests are well sorted and contain the coarsest particles. The best-sorted environments are the swash zone and beach face., San Diego State University
Determination of the orientation of the borehole seismic stations
Seismic instrumentation deployed in boreholes commonly has unknown horizontal orientation. This affects the interpretation of data since the registered amplitude of a seismic wave depends on the orientation of the sensor. I analyzed signals received at borehole seismometers located at Thornton Hospital, La Jolla, CA. Data from the 1999 Hector Mine earthquake are systematically rotated and compared with expected particle motion to determine the absolute orientation of the sensors. Testing of the method using data from surface instruments with known orientation indicates errors on the order of 5%. We then applied the method to data from sensors at depth to determine their orientations., San Diego State University
Determining confidence intervals for compositional data from point count analysis of thin sections and slabs: the student's t versus the bootstrap
The purpose of this study is to assess the efficiency of the bootstrap method versus conventional statistical methods for determining the confidence intervals for compositional data. Eight samples were taken from a large outcrop of the Oriflamme Canyon protomylonite within the Cuyamaca-Laguna Mountain shear zone. Each sample was made into a thin section. During point counting minerals that fell under the cross hair were assigned to quartz, feldspar, or biotite. Following study of thin sections, slabs of each sample were stained, and then scanned into a computer file using Adobe PhotoShop. A 0.25 cm by 0.25 cm grid was placed over the scanned images and points were again counted and assigned to quartz, feldspar, or biotite. Statistical data derived from point counting thin sections and stained rock slabs included the mean, standard deviation, standard error, t critical, and 95% confidence interval. The 95% confidence interval about the mean was estimated using the Student's t distribution and the bootstrap program Bootstraping Compositional Data (BOCD) written by Mr. Brett Heitman. Statistical data resulting from the two different methods for estimating the 95% confidence interval were reasonably close. For example, the Student's t distribution indicated that the 95% confidence band for the number of counts of quartz is ± 9 for data collected from thin sections, while the same statistic estimated from the bootstrap method is± 7. Similarly, the Student's t distribution gave± 6 while the bootstrap method yielded +4.5/-5 as estimates for the 95% confidence interval for the number of counts of quartz in stained slabs. Based on these data, and the commonly observed asymmetric form of frequency distributions derived from compositional data, the bootstrap method appears to provide a better estimate of the 95% confidence interval given its range preserving and nonparametric characteristics. It is therefore recommended that BOCD be considered when estimating the confidence intervals for compositional data., San Diego State University
Determining the effectiveness of small scale volcano hazard mapping and lahar education for rural villages in Central Java, Indonesia
The archipelago of Indonesia is located on the Sunda Arc where the Indo-Australian Plate is subducting to the north beneath the Eurasian Plate resulting in an active area of volcanism and seismicity. Mount Merapi on the island of Java in the central section of the Sunda Arc is considered one of the most dangerous volcanoes in the world due to 1) its proximity to a population center exceeding one million that includes the city of Yogyakarta, 2) its history of large destructive eruptions with an eruption frequency of 2 – 10 years, and 3) heavy monsoonal rainfall from November to March that mobilize large lahars. Volcanic hazard mitigation around Merapi is crucial and for this reason it is recognized as one of the 16 Decade Volcanoes identified by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) as a target for particular study. Using a community empowerment program at Gadjah Mada University in Yogyakarta as a vehicle for hazard mitigation, 3 weeks were spent in a field area near Bunder Village, on the southern flank of Merapi investigating prior hazard events and conducting interviews with local residents to determine the current state of hazard understanding by the villagers. Using historical records and imagery from previous work, a simple, localized hazard map was created for the area and presented to villagers. The map produced simplified more complex ideas as to create a more complete understanding for the residents. Information regarding the processes of lahar flows was presented to the residents as well. The impact on hazard mitigation by these efforts is difficult to determine initially but the true measure will come when Bunder Village faces the next disaster. The goal of this work was to take a first step in determining if this type of direct-intervention approach can be translated with similar efforts to benefit the hundreds of other villages living in the shadow of Mount Merapi., San Diego State University
Detrital thermochronology: Record of the local-to-extraregional provenance shift recorded by the northern Peninsular Ranges forearc
Previously measured detrital zircon U-Pb age distributions have revealed that Late Cretaceous to Eocene forearc strata in the Santa Ana Mountains region experienced a dramatic shift in sedimentary provenance from a 125-90 Ma northern Peninsular Ranges batholith (PRB) source region along the continental margin to a cratonal source area intruded by Late Cretaceous (85-75 Ma) plutons within the continental interior (western Sonora). To improve our understanding of the timing and magnitude of denudation prior to, and during this local to extraregional provenance shift, we have measured new detrital K-feldspar 40Ar/39Ar total fusion and zircon UPb age distributions from forearc sandstones. Our combined crystallization age and thermal history results confirm two pulses of rapid denudation of the PRB. These include a syn-batholith phase (Cenomanian) and a post-batholithic (Maastrichtian to Paleocene) phase attributed to shallow subduction. The new data require that significant (5-10 km) syn-batholithic erosional denudation of the northern PRB had already occurred by ca. 95 Ma and that post-emplacement denudation of the PRB accelerated again during the Maastrichtian with the eastern PRB providing the bulk of the detritus. Our new results demonstrate that deposition of the Paleocene Silverado Fm. occurred during a transitional period. Sand reaching the forearc during the Paleocene was derived from both the heavily denuded eastern PRB with additional input supplied either from Late Cretaceous plutons of northwestern Sonoran region and/or similar plutons emplaced in thrust sheets atop PRB basement within the Santa Rosa Mountains. In contrast, the Eocene Santiago Fm. was nearly entirely derived from extraregional sources that supplied abundant late Cretaceous (75-85 Ma) and Proterozoic (1.4 & 1.7 Ga) detritus with virtually no PRB-derived sediment detected., San Diego State University
Developing a scientific precedure for community-based landslide hazard mapping and introducing landslide education methods for rural communities in Central Java, Indonesia
Central Java, Indonesia is located north of the Sunda arc where the Australian Plate is subducting northward beneath the Eurasia Plate resulting in major volcanic and seismic activity that have built the island of Java as a record of long‐term island‐arc volcanism and sedimentation. Heavy rainfall mixed with steep topography, dense population, and highly erosive volcanic sediments all contribute to a high susceptibility to and danger from landslides. Under the sponsorship of a dedicated community empowerment program at the Universitas Gadjah Mada in Yogyakarta, two months were spent in field area near Plosorejo Village, Karanganyar, Kerjo, Central Java, Indonesia inventorying local landslides, producing a landslide susceptibility map, installing an early warning system, and enacting landslide awareness programs. The methods for gauging landslide susceptibility included making lithological observations, mapping evidence for recent and current land movements such as land cracking and visible loss of structural integrity in villager homes, and collaboration with local residents including the rescue and response teams familiar with the dangers of the region. The landslide inventory and susceptibility data were compiled into CorelDraw and Google Earth and disseminated into the community. The early warning system developed for the community was constructed to monitor land movement and slope inclination as well as to measure local rainfall in order to alert residents when calibrated thresholds and danger levels are exceeded. Work for this thesis also included developing low-cost methods for local residents to keep track of landslide hazards near their homes and report critical data to search and rescue teams. Overall, this study addressed the limited access to information on landslide processes in rural Indonesia and explored the use of educational programs to develop a culture of preparedness and encourage proactive preventative efforts with respect to landslide phenomena. By helping the rural people of Indonesia to recognize landslides and earth processes producing them, this effort should help save lives and reduce loss related to landslides in Java. It also serves as an example of using imagery, mapping, and expertise from the US to assist the people of Indonesia in better responding to the dangers of landslides in rural Indonesia., San Diego State University

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