DYNAMICALLY TRIGGERED EARTHQUAKES AND TREMOR: A STUDY OF WESTERN NORTH AMERICA USING TWO RECENT LARGE MAGNITUDE EVENTS A Thesis Presented to the Faculty of California State Polytechnic University, Pomona In Partial Fulfillment Of the Requirements for the Degree Master of Science In Geological Sciences By Rachel L. Hatch 2015 SIGNATURE PAGE THESIS: DYNAMICALLY TRIGGERED EARTHQUAKES AND TREMOR: A STUDY OF WESTERN NORTH AMERICA USING TWO RECENT LARGE MAGNITUDE EVENTS AUTHOR: Rachel L. Hatch DATE SUBMITTED: Summer 2015 Geological Sciences Department Dr. Jascha Polet _________________________________________ Thesis Committee Chair Geological Sciences Dr. Nick Van Buer _________________________________________ Geological Sciences Ernest Roumelis _________________________________________ Geological Sciences Dr. Stephen Osborn _________________________________________ Geological Sciences ii ACKNOWLEDGEMENTS I’d like to thank first, my family for their love and support throughout all of my schooling and especially this last year. I’d also like to thank my fellow students at Cal Poly Pomona for always being so helpful and assisting me in staying motivated; especially Terry and Stephen for all of our great science talks, Julie for helping me with edits, Melissa for assisting me with GIS, and Kennis for keeping me going when we were in the grad lab together. I’d especially like to thank my fantastic professors at Cal Poly Pomona for showing me the world of Geophysics, Seismology, and Geology. Most of all, a big thanks to my advisor for holding me to the highest standards and continuing to push me to be better. In addition, I’d like to thank Chad Trabant and Gillian Sharer of IRIS for helping determine the cause of the instrumental noise, along with the professors at the IRIS short course who contributed to the discussion. Lastly, a thank you to the networks from which I acquired data: 7D - Cascadia Initiative Community Experiment-OBS component at University of Oregon; AZ - Anza Regional Network; BC - Red Sismica del Noroeste (Mexico); BK - Berkeley Digital Seismograph Network; CC - Cascade Chain Volcano Monitoring; CI - Caltech Regional Seismic Network; EN - CalEnergy Sub Network; GS - US Geological Survey Networks; IE - Idaho National Engineering Laboratory; IU - Global Seismograph Network; LB - Leo Brady Network; MB - Montana Regional Seismic Network; NC - USGS Northern California Regional Network; NN - W. Great Basin/E. Sierra Nv (UNR); NP - US National Strong Motion Network; NV - Neptune Canada; PB - Plate Boundary Observatory Borehole Seismic Network; PO - Portable Observatories for Lithospheric Analysis (Geologic Survey of Canada); PG - PG&E Central Coast Seismic iii Network; SN - Southern Great Basin Network; TA - USArray Transportable Array (IRIS); UO - University of Oregon Regional Network; UU - University of Utah Regional Network; UW - Pacific Northwest Regional Seismic Network; WR - California Division of Water Seismic Network; WY - Yellowstone Wyoming Seismic Network; XN - Central Oregon Locked Zone Array; YK - North Bay Seismic Experiment (USGS); YN - San Jacinto Fault Zone (UC San Diego); YU - Delta Levy Northern California (USGS) iv ABSTRACT We present the results of the analysis of waveform data from nearly 1400 stations throughout Western North America to identify triggering from the magnitude 7.2 El Mayor-Cucapah 2010 earthquake and the magnitude 6.8 Northern California 2014 earthquake, just North of the Mendocino Triple Junction. Triggered earthquakes and tremor were detected through visual inspection of the seismograms after applying a high- pass filter to remove the significantly higher amplitude, long period, ground motions from the main shock wave train. The results of our analysis indicate that both main shocks triggered earthquakes and tremor, up to distances of 1300 km. The El Mayor earthquake triggered earthquakes or tremor at or near 117 stations, while the Northern California event produced triggering at or near 47 stations. A comparison of results for stations within and outside of geothermal and volcanic areas shows that triggering inside these areas occurred as frequently as outside, for both main shocks. Triggered earthquakes occurred more often than triggered tremor within these regions, whereas the opposite is the case outside of the geothermal areas. Triggering was found in different types of tectonic regions: the San Andreas Fault Zone, the San Jacinto Fault Zone, the Salton Sea Geothermal Field, Yellowstone, the Geysers, offshore Northwestern North America, Southern Utah, North of Lake Tahoe, and the Cascade Range. Based on our analysis and previous studies in these areas, our results suggest multiple mechanisms of dynamic triggering may be at work. v TABLE OF CONTENTS Signature Page .............................................................................................................. ii Acknowledgements ....................................................................................................... iii Abstract ......................................................................................................................... v List of Tables ................................................................................................................ viii List of Figures ............................................................................................................... ix Chapter 1: Introduction and Background ...................................................................... 1 Earthquake Triggering: The Landers Sequence ................................................ 1 Seismic Wave Basics ........................................................................................ 3 Static Stress and Dynamic Stress ...................................................................... 4 Triggered Earthquakes and Triggered Tremor ................................................. 5 Possible Triggering Mechanisms ...................................................................... 6 Motivation ........................................................................................................ 10 Previous Studies on Triggering ........................................................................ 11 Specifics of Our Study ..................................................................................... 14 2010 El Mayor Cucapah, Baja California, Earthquake ........................ 16 2014 Mendocino, Offshore Northern California Earthquake .............. 19 Chapter 2: Methods ...................................................................................................... 21 Chapter 3: Results and Discussion ............................................................................... 41 Correlation Between Triggering and Geothermal Areas ................................. 49 Specific Regions of Interest ............................................................................. 52 San Andreas Fault ................................................................................ 52 vi San Jacinto Fault Zone ......................................................................... 55 Salton Sea Geothermal Field ............................................................... 59 The Geysers ........................................................................................ 62 Yellowstone ......................................................................................... 66 Offshore Washington and Oregon Coast ............................................. 69 Cascade Range ..................................................................................... 73 Southern Utah ...................................................................................... 74 North of Lake Tahoe ............................................................................ 74 Triggered Tremor ............................................................................................. 75 Triggered Earthquakes ..................................................................................... 76 Mechanisms ..................................................................................................... 77 Future Work ..................................................................................................... 80 Chapter 4: Conclusions ................................................................................................. 82 References ..................................................................................................................... 84 Appendix A: Alternate Methodologies ......................................................................... 95 Appendix B: Surface Wave Induced Instrumental Clipping ........................................ 97 Appendix C: S-P Time Measurements for EMC and NCE ..........................................100 Supplementary CD: Digital Files of Figures 21, 22, 23, 24, 25 and Table S1 ............. CD vii LIST OF TABLES Table 1 EMC: Categories ......................................................................................... 41 Table 2 NCE: Categories ......................................................................................... 43 Table 3 For EMC, a Comparison with Stations Inside Geothermal and Volcanic Areas Versus Stations Outside These Areas .............................................. 50 Table 4 For NCE, a Comparison with Stations Inside Geothermal and Volcanic Areas Versus Stations Outside These Areas ............................................... 51 Table