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Exploring Volcano-Tectonic Connections in Cascadia – Temporal Linkages Between Tephra Deposition and Megathrust Earthquakes

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Exploring Volcano-Tectonic Connections in Cascadia – Temporal Linkages Between Tephra Deposition and Megathrust Earthquakes AN ABSTRACT OF THE THESIS OF Joel C. Gutierrez for the degree of Master of Science in Geology presented on December 17, 2020 Title: Exploring Volcano-Tectonic Connections in Cascadia – Temporal Linkages between Tephra Deposition and Megathrust Earthquakes Abstract approved: _____________________________________________ Adam Kent Explosively erupting volcanoes and megathrust earthquakes (Mw 8+ magnitude) occur at subduction zones and adjacent volcanic arcs. Volcanic eruptions are observed occurring close in time to megathrust earthquakes in the historical record from at least the 18th century CE to present in locations globally, including Japan in 1707 CE (Chesley et al., 2012) and 2011 CE (JAXA Space Technology Directorate); Chile in 1960 CE (Lara et al., 2004) and 2010 CE (Swanson et al., 2016); Kamchatka in 1952 CE (Walter, 2007); Alaska in 1964 CE (Walter et al., 2009); Sumatra 2005 CE (Walter et al., 2009); and Indonesia 2018 CE (Kim Hjelmgaard, 2018). Additional timing linkages between megathrust earthquakes and volcanic eruptions are also identified in Kamchatka, Alaska, and Central America (Walter et al., 2009). Previous research has been conducted exploring possible triggering relationships in other subduction systems; however, the Cascadia Subduction Zone (CSZ) has yet to receive attention from researchers regarding CSZ and Cascadia Volcanic Arc (CVA) triggering potential. The CSZ poses a significant hazard to the North American Pacific Northwest. If synchronicity can be established between CSZ megathrust seismic earthquakes and CVA volcanism, further research is required to establish the physical mechanisms linking these phenomena. The first step in this process is to establish that such correlations exist, which is the central focus of the present work. Thus, refining scientific understanding of these dual geohazards provides improved geohazard assessments and better informs emergency planners. This analysis of the volcano-tectonic connections in Cascadia and temporal linkages tephra deposition and megathrust earthquakes includes the refinement of the Holocene paleoseismic and tephrochronology records. These records are found within both marine, and lacustrine sediment cores contain seismoturbidite sequences, and tephra deposits may provide detailed stratigraphic relationships and ages of seismic and volcanic events. The purpose of this research is to achieve a higher temporal resolution of regional CSZ megathrust earthquakes and eruptive histories of the CVA by correlating the 14C ages and stratigraphic occurrence of tephra and turbidite deposits between lake and marine sediment cores collected in the U.S. Pacific Northwest. Geophysical data collected from Lake Wapato and Rogue Apron sediment cores are stratigraphically correlated with previously established event bed data with sediment cores collected at inland Washington lakes and marine sediment cores collected along the CSZ margin. 14C age data collected within Lake Wapato provide stratigraphic control and correlates Lake Wapato and Rogue Apron records with established CSZ turbidite records. An analysis of the stratigraphic relationship between primary volcanic tephra beds and seismoturbidites in lake and marine cores in this study suggests that some CSZ and CVA event beds are observed in close stratigraphic proximity. Mazama tephra beds appear to occur immediately before the CSZ T14 event bed, observable in both lake and marine cores assessed in this study. Mount Saint Helens tephra bed Wn is observed in the Wapato core record and appears to occupy the CSZ T2 event bed's stratigraphic position. Additionally, the Mount Saint Helens tephra bed Yn is observed at the same depth as the CSZ T8 event bed in the Wapato core record. In the Bull Run Lake core record, the Mount Hood Timberline tephra bed is observed where the CSZ T5 event should be located. In assessing the extant CVA Holocene eruptive data compared against the CSZ Holocene turbidite record, numerous potential timing linkages are suggested. ©Copyright by Joel C. Gutierrez December 17, 2020 All Rights Reserved Exploring Volcano-Tectonic Connections in Cascadia – Temporal Linkages between Tephra Deposition and Megathrust Earthquakes by Joel C. Gutierrez A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented December 17, 2020 Commencement June 2021 Master of Science thesis of Joel C. Gutierrez presented on December 17, 2020 APPROVED: Major Professor, representing Geology Dean of the College of Earth, Ocean, and Atmospheric Sciences Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Joel C. Gutierrez, Author ACKNOWLEDGEMENTS I could not have completed this research and manuscript without the support of collaborators, peers, family, and friends. Thank you Bran Black, Ann Morey-Ross, and Chris Romsos for all technical instruction and moral support. Additional thanks to Maziet Chesby, Val Stanley, and Cara Fritz for assistance provided at the Oregon State University Marine & Geology Repository. I am also thankful for the efforts of my major advisor and graduate committee members Professors Adam Kent, Adam Schultz, Frank Tepley, James Liburdy, Chris Goldfinger and Dr. Randall Milstein as well as Graduate Director Robert Allan for facilitating the completion of this research and manuscript. Additional thanks to Chris Harpel at the USGS Cascade Volcano Observatory. Most importantly, thank you to my family, Irish Perry and Meredyth Gutierrez for their support and love throughout my studies, research, and writing. Additional thanks to Mark & Sue Perry, Lezly & Clayton Terao, Cecil, Kay, and Ginia Gutierrez. TABLE OF CONTENTS Page 1 Introduction...……………………………………………………………………… 1 2 Geologic Setting.…………………………………………………………………... 3 2.1 North American Pacific Northwest………………………………………. 3 2.2 Tectonic Setting: Cascadia Subduction Zone (CSZ)…………………….. 3 2.3 Volcanic Setting: Cascade Volcanic Arc (CVA)………………………... 6 3 Previous Work.…………………………………………………………………... 14 3.1 The offshore paleoseismic record…………………….………………… 14 3.2 Paleoseismic record in Cascade lakes …………………………….….… 16 3.3 Tephrochronology………………………………………………………. 17 3.4 Triggering Relations between Subduction Zones & Volcanic Arcs……. 18 4 Methods …………………………………………………………………………... 21 4.1 Magnetic Susceptibility and Gamma Density……………………………23 4.2 Computed Tomography (CT)……………………………………………23 4.3 Lithologic Description ………….……………………………………… 24 4.4 Particle Size Analysis ……………………………………………………24 4.5 X-ray Fluorescence (XRF) ………………………………………………25 4.6 Radiocarbon Dating …………….……………………………………… 25 4.7 OxCal Age Modelling ……………………...……………………………26 4.8 Tephrochronology ………………………...…………………………… 26 TABLE OF CONTENTS (Continued) Page 5 Results ……………………………………………..………………………………27 5.1 Lake Wapato Results ………………………………….………………...27 5.1.1 Wapato Lake Bathymetry……………………………………...28 5.1.2 Wapato Lake Sub-bottom Profiling……………………………29 5.2 Wapato Core Stratigraphy & Petrophysics …………………….………..32 5.2.1 Wapato CT & Magnetic Susceptibility................................…...37 5.2.2 Wapato Tephra & XRF ……………………………….…….... 39 5.2.3 Wapato Tephra Geochemical Biplots……………….………... 42 5.3 Wapato Core Samples & Descriptions ………………………...………..45 5.4 Wapato Lake OxCal Age Model………………………...………..……..46 5.5 Wapato Intra-lake Well-log Correlation………………………………... 49 5.6 Leland Lake Results ……………………………...……………..……… 52 5.6.1 Leland Age Model……………………………………………..56 5.7 Bull Run Lake Results………………………………………………...... 59 5.7.1 Bull Run Lake Tephra Results……………………..…………..59 5.8 Inter-lake Well-log Correlation ……………………………..……...…... 63 5.8.1 Wapato-Bull Run Inter-lake Correlations……….……….…….63 5.8.2 Wapato-Leland Inter-lake Correlations……….……….…...….67 5.9 Rogue Apron Tephra Results…………………………………….………69 5.9.1 Rogue Apron Tephra Geochemical Biplots……………………72 TABLE OF CONTENTS (Continued) Page 6 Discussion ………………………………………………………………………....73 6.1 Origin of Event beds…………..………………………………………... 74 6.1.1 Fire……………………………………………………………..75 6.1.2 Storms………………………………………………………….76 6.1.3 Crustal Earthquakes……………………………………………77 6.1.4 Slab Earthquakes…………………………………………….…77 6.1.5 Plate Boundary Earthquakes…………………………………...78 6.2 Wapato Lake & Cascadia Marine OxCal Age Model Comparison…..….79 6.3 Bull Run Discussion…………………………………...…………......… 83 6.3.1 Bull Run-Wapato Inter-lake Correlation………………………86 6.3.2 Bull Run OxCal Age Model………………………...…………87 6.4 Leland Lake Discussion……………………..……………………..….... 88 6.4.1 Leland OxCal Age Model……………………………………..88 6.5 Regional Well-log Correlations…….…………………………..........…..91 6.5.1 Inland Inter-lake Correlations…………………………...……..91 6.5.1.1 Wapato-Bull Run Correlation………………………..91 6.5.1.2 Wapato-Leland Correlation……………………...…..93 6.5.2 Offshore-Onshore Correlation………………………………....95 6.6 Rogue Apron Discussion…………………………………………..….....97 6.6.1 Rogue River Tephra Transportation…………………………..97 6.7 Tectono-Volcano Triggering in Cascadia ……………….…………......101 6.8 Evidence for Triggering Linkages in Cascadia ……….……………..... 119 TABLE OF CONTENTS (Continued) Page 7 Conclusion ……………………………………………………………………… 120 References Cited ………………..………………………………………………… 130 Appendices …………………………………………………………………………143 LIST OF FIGURES Figure Page 2.1. Map of the Cascadia Subduction Zone & Cascade Volcanic Arc ………….…...4 2.2. Cascadia Subduction Zone Profile Diagram ……...……………..……………....5 2.3. Select Pacific Northwest
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