Date of Award
Doctor of Philosophy
Aaron A. Velasco
Chapter 1 results from a collaboration between researchers in Mexico and the United States, funded by the National Science Foundation; This collaboration led to deploying a temporary seismic network to study the Tehuantepec earthquake, aftershocks, and the vastly affected region of Juchitán de Zaragoza, Oaxaca. I explored the capabilities of 51 Magseis Fairfield Z-Land 5- Hz 3-component nodal seismometers that were deployed for three weeks to identify the site effects in order to understand the large discrepancy of damage in the region. I correlated the results with the local geology of JuchitÃ¡n and its surroundings.
Chapter 2 presents a study to understand the seismic vulnerability around the El Paso, Texas region. This project comes from the needs of the community and uses previous geophysical studies as a foundation. El Paso, Texas, is not ready for a seismic catastrophe because it is considered a low probability but high seismic impact region. I was in charge of a local seismic network to identify the vulnerabilities of the city. I requested permission to install and maintain seismic instruments in many different locations. The deployment was divided into three phases. The first phase consisted of deploying seven Broadbands in different houses within the city. The second phase of this experiment consisted of using specialized seismic equipment to measure seismic noise in situ for about 30 minutes per site to obtain resonance frequency and amplification. This second phase was conducted in more than forty churches, eight houses, forty parks, and all fire stations within the city. This experiment's third and final phase consisted of deploying stand-along seismometers (Magseis nodes, or simply called nodes) buried in shallow (~1 ft) holes for about three weeks of continuous recording at selected places of worship within the city. With this, I hope to understand the East Franklin Mountain Fault (EFMF) and study the potential shaking that a M7.0 earthquake could create.
Chapter 3: I explored the development of a data-driven framework to visualize the wavefield propagation around a strand of the San Andres Fault. This chapter aimed to gain information from the IRIS wavefield experiments. I used wave decomposition to extract the location of the fault by looking at the changes in seismic events as they propagate in the array. Specifically, I extracted the wavefield distortion before and after the fault and compared the actual data with different wavelets.
Chapter 4: In the final chapter, I focus on developing a methodology to extract geometrical information from geological targets migrating techniques from material sciences to seismology. I computed 6,000,000, 3-component synthetic seismograms in a controlled scenario simulating the seismic wave propagation of a Dirac delta function in a half-space of sandstone and granite. I perturbed the system by including cuboids of the most common petrophysical properties for ten different sizes. The perturbed wavefield was computed for 10,000 locations on top of the half-space. To simulate the wave propagation, I used SW4 software (developed in the Lawrence Livermore National Laboratory during The Serpentine). The goal is to provide a rapid tool to understand the geology under dense seismic arrays using a database of scattering profiles for well-known geometries. This approach is new to seismology and intended to help understand fluid migration for academia and industry.
Received from ProQuest
Solymar Ayala Cortez
Ayala Cortez, Solymar, "Case Studies Of Large-N Scattering And Site Response" (2022). Open Access Theses & Dissertations. 3648.
Available for download on Sunday, January 19, 2025