Seismicity within Arizona During the Deployment of the EarthScope USArray Transportable Array

• Other Authors: Lockridge, Jeffrey (Author)
• Format: Dissertation
• Language: English
• Published: 2011
• Subjects: Geophysics; Geology; Arizona; Earthquakes; EarthScope; Seismicity; Seismology
• Online Access: http://hdl.handle.net/2286/R.I.9395

abstract: The goal of this study is to gain a better understanding of earthquake distribution and regional tectonic structure across Arizona. To achieve this objective, I utilized seismic data from EarthScope's USArray Transportable Array (TA), which was deployed in Arizona from April 2006 to March 2009. With station spacing of approximately 70 km and ~3 years of continuous three-component broadband seismic data, the TA provided an unprecedented opportunity to develop the first seismicity catalog for Arizona without spatial sampling bias. In this study I developed a new data analysis workflow to detect smaller scale seismicity across a regional study area, which serves as a template for future regional analyses of TA data and similar datasets. The final event catalog produced for this study increased the total number of earthquakes documented in Arizona by more than 50% compared to the historical catalog, despite being generated from less than three years of continuous waveform data. I combined this new TA catalog with existing earthquake catalogs to construct a comprehensive historical earthquake catalog for Arizona. These results enabled the identification of several previously unidentified areas of seismic activity within the state, as well as two regions characterized by seismicity in the deeper (>20 km) crust. The catalog also includes 16 event clusters, 10 of which exhibited clear temporal clustering and swarm-like behavior. These swarms were distributed throughout all three physiographic provinces, suggesting that earthquake swarms occur regardless of tectonic or physiographic setting. I also conducted a case study for an earthquake swarm in June of 2007 near Theodore Roosevelt Lake, approximately 80 miles northeast of Phoenix. Families of events showed very similar character, suggesting a nearly identical source location and focal mechanism. We obtained focal mechanisms for the largest of these events, and found that they are consistent with normal faulting, expected in this area of the Arizona Transition Zone. Further, I observed no notable correlation between reservoir water level and seismicity. The occurrence of multiple historical earthquakes in the areas surrounding the reservoir indicates that this swarm was likely the result of tectonic strain release, and not reservoir induced seismicity. === Dissertation/Thesis === Appendix A: Earthquakes recorded by EarthScope USArray === Appendix B: Total Arizona earthquake catalog === Appendix B: Earthquake catalog references === Appendix D: Mine Blast data === Appendix D: Potential mine blasts === Appendix D: Arizona blasting sites === Appendix E: Earthquake clusters === Appendix F: Antelope tutorial and parameter files === Appendix C: Stations used in this study === M.S. Geological Sciences 2011