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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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Sediment transport and deposition of marine sands through the Silver Strand littoral cell
Seasonal storms and sea-level rise cause erosion of the present shoreline and effect Southern California’s coastal infrastructure. Local and regional projects replenish several beaches along the San Diego coast from Oceanside to Imperial Beach, with the most recent regional replenishment in 2012. The importance of understanding sediment transport and deposition along the San Diego continental margin is key not only to plan for future beach replenishments but also to understand the sediment source and how sediment characteristics change along their transport pathway, which is important for contaminant transport studies. In order to assess changes to sediment along the transport path from river mouth, through longshore beach transport, and then transport into the offshore, samples were collected from three different locations within the Silver Strand littoral cell: 1) The beach adjacent to the Tijuana River mouth, 2) Coronado Beach to the north, and 3) ~3.6 km offshore from the Silver Strand. A Laser Diffraction Particle Size Analyzer (LS 13 320) was used for grain size analysis of sediment from each location, to further understand the longshore and offshore transport. The Tijuana River mouth includes coarse to very coarse, sub-angular sands and Coronado beach is made up of fine to medium sub-rounded sand. As we go further offshore, a sediment core captured the upper 65 cm of sediment below the seafloor, which are made up of silty and very fine sands that don’t vary much with depth. The Silver Strand littoral cell has a northward transport path, and extends from Ensenada, Mexico to Coronado Island. From Coronado Island, the current changes to flow westward, away from the beach into deeper water. The primary source of sediment for the littoral cell is from the Tijuana River. From our results, the sediment deposited in the littoral cell becomes finer and better sorted moving away from the Tijuana River mouth. The two beach samples have very few fine grained sediments compared to the offshore sample, which is likely due to the higher energy on beaches compared to the offshore environment., San Diego State University
Sediment transport in the Santa Margarita River
Most studies of sediment budgets along coastlines divide the coast into "littoral cells". The Oceanside Littoral Cell, which begins at Dana Point and extends south to the heads of Scripps Submarine Canyon derives most of it's sediment from the rivers within the system such as the Santa Margarita River which is the subject of this report. To determine the amount of sediment the Santa Margarita River deposits during Spring of a given year I took water samples at high and low tide, before and after a rainfall and recorded the river flow velocity. By using a millipore filter system I found that there was more beach sediment in the water at all times except after a 0.03 inch rainfall. The increased amount of water flowing out to sea contained more silt sized or river derived sediment than beach sand which indicates active depo­sition. The river flow velocities did not fluctuate much between high and low tide although at very high tides there was no flow out of the river mouth. The Santa Margarita River is therefore a major sediment cource for the Oceanside Littoral Cell but only after significant rain fall. The contribution of sand to the beaches has become more significant as new dams have intercepted the flow of sediment from other rivers in the Oceanside Littoral Cell., San Diego State University
Sedimentation rates at Buena Vista Lagoon, San Diego, CA, as determined by 210pb dating techniques
Buena Vista Lagoon is a closed lagoon situated in northern San Diego county. The lagoon is transversed by Interstate 5, railroad tracks and Route 101 and is bordered by Route 78 on the north. The lagoon is in a state reserve and therefore is considered to be relatively undisturbed. This study was part of acollaboration with Jeannie Chick to obtain sedimentation rates and a records of metal contamination through analysis of sediments from the lagoon. Three continuous core samples were taken from Buena Vista Lagoon in the fall of 1993. The first sample (core 1) was collected in an enclosed (salt pond) section on the north side of the lagoon. The second and third cores were taken from the approximate center of the eastern section of the lagoon bounded by Interstate 5 and Route 101. Only the first and third cores were analyzed for sedimentation rates. The sedimentation rates for cores 1 and 3 were determined by the use of 210Pb geochronology. 210Pb has a half-life of 22.3 years. By plotting the 210pb activity an a function of depth in the core, and using the half-life of the isotope, the sedimentation rate for the lower portion of core one was calculated to be 2.6 cm./yr. whereas the average sedimentation rate for core three was determined to be 3.2 cm./ yr. A total age in years of core 1 and specific year dates for different depths could not be calculated for the core because of a radical drop in 210pb activity in the top 10 cm. of the core. This anomaly (reverse slope of radioactive decay with depth) is most easily explained by the isolation of the small salt pond from the rest of the lagoon by cattail growth, thus changing the influx of 210:fb from the constant value assumed for all calculations. The 60 cm. length of core 3 was calculated to contain a record of the last 19 years (from 1993 to 1975) .. The 210pb plot versus depth for both cores exhibited considerable scatter. The major causes of the scatter are thought to be: (l)The varying and pulsating seasonal deposition of the sediment from winter rains combined with the fact that each sample depth' analyzed was less than one year, (2)the sporadic introduction of sea water into the lagoon, and (3)the small total volume of the lagoon. Using the high sedimentation rate calculated from core 3 the area of the lagoon bounded by Interstate 5 and Route 101 is projected to completely silt up in the next 30-40 years., San Diego State University
Sedimentology of the ancient North Yuba River, Sierra County, California
Since 1849 the Goodyears Bar Mining District has produced well over 150,000 ounces of gold. Sources of gold in this area include late Jurassic lode gold deposits, Tertiary river deposits, Quaternary and Holocene gravel deposits and modern river placer deposits. Initial mapping of the ancient North Yuba River was performed with the intention of locating a buried section of the paleochannel known as the Golden Slide Mine ore body. Using paleocurrent indicators such as clast imbrication and epsilon cross stratification, bench placers of the ancient river have been mapped, including the section of buried ore reserves. The 4 kilometer section of the river under investigation lies between the Goodyears Creek Fault and the Melones Fault within the Feather River Peridotite Belt. Paleocurrent indicators from the auriferous gravel of the ancient North Yuba, classified as a sandy pebble gravel, trend towards the southwest. Additionally, previous research on the paleoplacers of the Tertiary Yuba river show a southeasterly paleocurrent direction near this location., San Diego State University
Seismic data visualization with ArcView
ArcView, produced by ESRI (Environmental Systems Research Institute), is an easy-to­use GIS (Geographic Information System) package for map display and database management. ArcView allows the user to link and query database tables and to quickly display the results. This can be extremely helpful to seismologists with large and often cumbersome datasets. In this study, Arcview's seismic data manipulation and mapping abilities are investigated. Eight months of data (January - October 1998) from the Anza Seismic Network is used as a test set. This data is available through the Geological Sciences Department at San Diego State University as well as UCSD, SCEC (Southern California Earthquake Center), Stephan Birch Aquarium at the Scripps Institute of Oceanography, or the IRIS DMC. Data arrives in textfiles formatted according to the CSS 3.0 Database Schema. UNIX scripts are used to convert these tables into a form readable by ArcView. Different forms of information about single events and detections are stored in separate tables within the CSS 3 .0 Database Schema. Arcview can link these tables together through common field names. This allows the user to create and customize multiple displays of information on sets of seismic events. Each generated map (or "display") has a uniquely associated attribute file from which the user can query information and display the results on the same map view. This GIS-approach may facilitate and/or initiate new alternatives for seismic data visualization., San Diego State University
Sidescan sonar investigation of the Sacramento-San Joaquin Delta
The Sacramento-San Joaquin Delta is a crucial element of California’s water conveyance system that is at major risk of saltwater inundation due to sea level rise and seismic activity. Currently the Midland fault, the Thorton Arch source zone, and the Montezuma Hills source zone all pose a threat to the local infrastructure, which includes the extensive system of levees that currently protect the surrounding ecosystem. Little is known about these blind faults due to the lack of surveys done in the area. In order to assess the risk produced by these faults more needs to be understood about their location and seismic history. Sidescan sonar data collected within the delta displays topographical differences, as well as anomalous morphological features along the seabed that are potential expressions of the faults that extend through the delta. These features are most often observed near small localized faults that do not have any deep expression and are unlikely to generate earthquakes. Seafloor expression is also observed at the Kirby Hills Fault, which is located in the very western extent of the delta and has ruptured during the Quaternary. This work is helping to improve the accuracy of fault locations throughout the delta allowing for a better understanding of the risk they pose to the region in the event of a future rupture., San Diego State University
Simple Shear 98 an intuitive graphical approach for understanding simple strain transformations
Simple Shear 98 is a computer program with graphical user interface that was developed to aid beginning geologists in understanding the mechanics of simple shear. It was created using Visual Basic 5, an object oriented intermediate-level programming language, and will run on any PC using Windows 95 or NT 4. The program displays data to the user through two windows, one a strain grid and the other a table of coordinates. The user picks one of several objects to strain from a drop down menu, and is allowed to input shear strain values. Following each increment of strain instigated by the user the program calculates and displays elongation, stretch, quadratic elongation, and angular shear strain values. Finally, progressive simple shear can be visualized through a movie function. The following six key concepts can be illustrated through the use of Simple Shear 98: (1) Individual material particles are translated linearly in planes parallel to the direction of shear. (2) Line segments rotate about the intermediate principal strain direction in a clockwise sense for dextral shear and in a counterclockwise sense for sinistral shear. (3) Lines that lie in the NE and SW quadrants undergo elongation, whereas lines that lie in the NW and SE quadrants undergo shortening during dextral sense progressive simple shear. During sinistral simple shear these conditions are reversed. (4) Angles between adjacent line segments undergoing shortening become larger while angles between adjacent line segments undergoing extension become smaller. (5) Lines rotate toward the direction of shear but never reach it. (6) Under the right geometrical conditions, simple shear can produce very unusual results such as the nearly complete unfolding of a fold., San Diego State University
Simulation of shear wave splitting in a 3D transversely isotropic medium
Anisotropy in crustal seismic wave propagation is a well-documented phenomenon. There are several proposed causes; the cause at any specific site must be determined by local geology. The presence of anisotropy can be identified by shear-wave splitting, when shear-wave arrival times are slightly offset due to different travel speeds. When simulating anisotropy, a common simplification is that of transverse isotropy (TI). By simulating anisotropy in a general case, new insights may be gained. The goal of this research was to model seismic anisotropy using TI and observer shear-wave splitting. A finite element scheme was used to implement the TI model. Anisotropy was introduced in the vertical direction in the form of a slowed shear-wave velocity. The seismic source was a Gaussian pulse. By visualizing discrete timesteps during the simulated propagation, a non-uniform wave front was detected. This deformed wave front was most prominent in the z-velocities. Comparison to isotropic wave fronts illustrate the differences. Another method of visualization is the seismogram. A synthetic seismogram on the surface of the model clearly showed the difference in shear-wave speeds. Rotating the seismogram in the radial, SV and SH coordinates showed similar results. Observational data from a seismogram in southern California shows a real case of shear-wave splitting. The results indicate that the model worked as planned. Shear-wave splitting was observed by two methods of visualization. Though the model is basic, it can be expanded in complexity and scale to bring its realism and relevance to a higher level., San Diego State University
Slug test study of the hydraulic characteristics of vertically contiguous intervals in the S.D.S.U. aquifer National City, California
The purpose of this thesis was to determine the hydraulic conductivity of discrete five foot intervals in the aquifer located at the Bonita, S.D.S.U well field. Slug tests were used to test vertically contiguous five foot intervals of a monitoring well using a system of straddle packers. Two cycles of coarsening downward sediment were revealed by the slug test. A chief goal of this thesis was to compare the slug test straddle packer method to electrical conductivity data and the relatively labor intensive tracer test method., San Diego State University
Solute transport model of a shallow groundwater aquifer
San Diego State University
Stratigraphic signatures of lake-level changes at Swallow Lagoon, North Stradbroke Island, Australia
Lakes have a great capacity to hold records of climate archived in various sedimentary proxies. Coring is the primary method used to access the sedimentary archive layers to assess paleoclimates. These methods rely on proxies related to microfossils, macrofossils, isotopic composition and sedimentary changes that relate to specific environmental conditions. The use of proxies is constrained by preservation potential and ability of proxies to record environmental changes of interest. However, the recorded changes rarely reflect lake levels. Imaging the architecture of lake fill sediments provides a direct measurement of lake levels through the lifespan of the basin. In small, shallow lakes, ground penetrating radar (GPR) has been utilized to assess sediment thickness and paleoshorelines related former lake surfaces. While GPR alone cannot answer the questions related to changes in paleoclimate, adding stratigraphic context to core locations and direct observation of lake levels can be a crucial component of understanding., San Diego State University
Stratigraphy of a marine conglomerate and other observations from the south west corner of Isla Tiburon
A geologic study was made of an area on the southwest corner of Isla Tiburon, located in the northern half of the Gulf of California. The emphasis of this report is placed on the description and interpretation of a 988 meter thick section of fossiliferous marine conglomerate (Fig. 4). Other geologic, as well as archaeologic, obser­vations were made and are discussed in this report. The area studied is divided into two distinct physio­graphic provinces, one of older and one of younger vol­canic terrane, which are separated by a major fault. Out­crops of a marine conglomerate are found in the younger volcanic rocks. The conglomerate has been divided into three members, an upper fossiliferous member (mcg-1), a middle nonfossiliferous member (mcg-2), and a lower foss­iliferous member (mcg-3). Foraminifera collected from member mcg-1, of the conglomerate, indicate deposition took place during Neogene time; possibly upper Miocene. The conglomerate was deposited in the marine tropical waters of a shallow, nearshore trough, located near the mouth of a fluvial system which supplied the sediment to form the conglomerate. Subsidence of the trough approx­imately equaled the rate of sedimentation. Genesis of the trough was probably the result of the dilation that took place during the formation of the proto Gulf of California. This type of rift produced trough (or basin) is analogous to the rift valleys of Africa or the Triassic basins of the east coast of North America which formed durinf the rifting of Laurasia. Isla Tiburon is also of archaeological interest. Abundant shell mounds, pottery fragments, and stone tools, left by the past inhabitants of the island, are found un­disturbed along the coast. These artifacts show the inhabitants (The Seri Indians) were of a Stone Age culture; although they did have the technology to produce fired clay pottery., San Diego State University

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