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

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  • 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.
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  • Gutierrez, Joel C., 2020. Exploring Volcano-Tectonic Connections in Cascadia – Temporal Linkages between Tephra Deposition and Megathrust Earthquakes. Oregon State University, Master of Science in Geology Thesis.
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