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MIAMI UNIVERSITY the Graduate School Certificate for Approving The MIAMI UNIVERSITY The Graduate School Certificate for Approving the Dissertation We hereby approve the Dissertation of Stephen G. Holtkamp Candidate for the Degree: Doctor of Philosophy Michael R. Brudzinski Director Brian S. Currie Reader Elizabeth Widom Reader Jonathan Levy Reader Zhigang Peng External Representative Michael Pechan Graduate School Representative ABSTRACT NEW METHODS FOR DETECTING EARTHQUAKE SWARMS AND TRANSIENT MOTION TO CHARACTERIZE HOW FAULTS SLIP by Stephen G. Holtkamp The possibility for earthquakes to be triggered by or related to each other or an external “aseismic” factor impacts hazard assessment and mitigation. With this dissertation, we have worked towards improvement of observation and modeling for earthquake swarms, slow slip associated with episodic tremor and slip, and human induced seismicity. Each of these cases has the potential to influence when, where, and to what size an earthquake can grow. First, we produce geodetic inversions of slow slip events in Cascadia, and highlight two unique instances where slow slip and non-volcanic tremor are not spatially correlated. In Cascadia, the correlation is so strong that tremor has become an accepted proxy for slow slip, but we show that this is not always the case. We show that the depth of the tremor may resolve this discrepancy. Second, we conduct a search for earthquake swarms along major convergent margins and find 180 swarms occurring within the seismogenic megathrust. We find evidence that these swarms are driven by aseismic slip, and may be broadly anti-correlated with large, destructive megathrust events. Third, we investigate this apparent anti-correlation with large megathrust events in detail by examining all Mw>7.5 earthquakes and classify them based on their relationship to swarm-generating regions of the interface. We find that large earthquakes are five times more likely to terminate in swarm regions than they are to propagate through swarm regions, suggesting that swarm regions are delineating where megathrusts are segmented. Lastly, we develop a multiple station waveform cross-correlation technique to investigate local to regional seismic data which is able to detect earthquakes several orders of magnitude smaller than traditional techniques. We use this technique to create a ~20 fold increase in detected seismicity during the 2011 Youngstown, Ohio earthquake sequence, allowing us to go well beyond the standard “proximity test” and conclusively establish a causal relation between wastewater injection and earthquakes. In total, we expect this dissertation to improve our understanding of how these unique seismic sequences occur, what their underlying mechanism is, and how they may be related to the damaging earthquakes sought out by the hazard assessment community. NEW METHODS FOR DETECTING EARTHQUAKE SWARMS AND TRANSIENT MOTION TO CHARACTERIZE HOW FAULTS SLIP A Dissertation Submitted to the Faculty of Miami University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Geology and Environmental Earth Science by Stephen Gregg Holtkamp Miami University Oxford, Ohio 2013 Dissertation Director: Michael R. Brudzinski © Stephen Gregg Holtkamp 2013 Table of Contents Table of Contents .............................................................................................................................v List of Tables ................................................................................................................................ vii List of Figures .............................................................................................................................. viii INTRODUCTION..........................................................................................................................1 CHAPTER 1: Variable correlation between episodic tremor and slip along the Central Cascadia margin.............................................................................................................................3 Abstract ........................................................................................................................................3 1.1. Introduction ...........................................................................................................................3 1.2. Data and Methods ..................................................................................................................4 1.3.0 Results .................................................................................................................................4 1.3.1 Inter-ETS strain accumulation and slow slip strain release in northern Washington ......4 1.3.2 Slip gap during the May-June 2008 ETS event in Oregon and northern California .......5 1.4. Discussion .............................................................................................................................6 1.5. Conclusions ...........................................................................................................................6 CHAPTER 2: Earthquake swarms in circum-Pacific subduction zones ................................16 Abstract ......................................................................................................................................16 2.1 Introduction .........................................................................................................................16 2.2. Methods ..............................................................................................................................17 2.3. Characteristics of Earthquake Swarms ...............................................................................18 2.4. Discussion ..........................................................................................................................20 2.4.1. Magnitude-Duration Relations of Earthquake Swarms ...............................................21 2.4.2. Relationships Between Earthquake Swarms and the Megathrust Seismogenic Zone 22 2.5. Conclusions ........................................................................................................................23 2.6. Acknowledgements ............................................................................................................24 CHAPTER 3: Megathrust Earthquake Swarms Indicate Barriers to Large Earthquake Rupture ........................................................................................................................................53 Abstract ......................................................................................................................................53 3.1. Introduction ........................................................................................................................53 3.2. Comparison of Swarm Locations with Great Earthquake (M>8.5) Rupture Models ........55 iii 3.3. Comparison of Swarm Locations with all M>7.5 Cataloged Megathrust Events ..............56 3.4. Why do megathrust earthquakes preferentially terminate in swarm regions? ...................58 3.5. Discussion ..........................................................................................................................60 3.6. Conclusions ........................................................................................................................61 CHAPTER 4: Evidence for a causal relationship between wastewater injection and earthquakes in Youngstown, Ohio ............................................................................................84 Abstract ......................................................................................................................................84 4.1 Introduction .........................................................................................................................84 4.2 Methods ...............................................................................................................................85 4.3 Results .................................................................................................................................86 4.4 Discussion ...........................................................................................................................87 4.S1. History of the Northstar 1 Injection Well (API 34099231270000) ..................................88 4.S2. Characterization of the Youngstown Seismic Sequence ...................................................89 CONCLUSIONS ........................................................................................................................107 REFERENCES ...........................................................................................................................108 iv List of Tables 2.S1: Timing and selected properties of “megathrust” earthquake swarms ......................... 41-48 2.S2: Timing and selected properties of “volcanic” earthquake swarms ............................ 49-51 2.S3: Timing and selected properties of “other” earthquake swarms .......................................52 4.S1: Earthquake catalog for the Youngstown sequence ................................................ 101-106 v List of Figures 1.1: Our preferred Inverse model for inter-ETS plate coupling ..................................................8 1.2: Inversions of the May 2009 Washington ETS event ...........................................................9 1.3: Tests of our inversion of the May 2009 Washington
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