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• 1. [Article] Stratigraphic correlation of seismoturbidites and the integration of sediment cores with 3.5 kHz chirp subbottom data in southern Cascadia

  In order to evaluate the shallow stratigraphy along the southern Cascadia abyssal margin and northern California abyssal plain, CHIRP subbottom profiles capable of imaging individual turbidite beds in ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphic correlation of seismoturbidites and the integration of sediment cores with 3.5 kHz chirp subbottom data in southern Cascadia Author: Black, Bran In order to evaluate the shallow stratigraphy along the southern Cascadia abyssal margin and northern California abyssal plain, CHIRP subbottom profiles capable of imaging individual turbidite beds in the upper tens of meters of the subsurface were collected. Reflectors imaged with the 3.5 kHz CHIRP subbottom data represent turbidite beds within the first 20-30 m of seafloor sediments that have sufficient impedance contrast and are separated by at least 20 cm vertically. Correlation of subbottom reflectors along both margins, constrained by core data at numerous sites along strike, revealed that many of these reflectors were contiguous over distances of hundreds of kilometers in southern Cascadia. The placement of subbottom reflectors coincided strongly with the configuration of many of the turbidite beds identified in nearby cores. A number of thin, low density beds evident in the cores are not imaged in the subbottom data in the northern part of the study area near Rogue Canyon, but become more robust southward where some are imaged as reflectors in the subbottom data. The independently derived core and subbottom based correlations of beds in southern Cascadia were found to be in fairly close agreement, and collectively support the continuity of beds over significant distances of up to 200 km along strike. Robustness of the beds between Trinidad and Rogue Canyons does not appear to be related to proximity to canyon mouths, suggesting that these beds and their transport are not exclusively related to canyon sources. The combined core and reflection data and the continuity of beds support a seismogenic source for Holocene beds correlated over long distances owing to the broad areal extent and lack of strong linkage to canyon systems. Data from paleoseismic studies worldwide were compiled in an effort to parameterize the likely triggering distances associated with turbidity currents initiated by earthquakes on the CSZ and NSAF. These ranges are estimated at 60-120 km for the CSZ and 40-75 km for the NSAF. A similar approach using MMI values associated with earthquakes linked to seismoturbidites yielded a threshold estimate for northern California of ~ MMI 5.5. A region from between Eel Canyon and Mendocino Channel in the north to the area north of Noyo Canyon in the south was identified as having a higher likelihood for recording at least a portion past seismicity from both the NSAF and CSZ in local sediments. The high frequency of turbidite beds in southernmost Cascadia could be the result of Cascadia and NSAF seismicity combined, though some input from hyperpycnal flows cannot be excluded. Further study of sediments in this zone may improve our understanding of potential stress triggering interactions between the CSZ and NSAF. Title: Stratigraphic correlation of seismoturbidites and the integration of sediment cores with 3.5 kHz chirp subbottom data in southern Cascadia Author: Black, Bran In order to evaluate the shallow stratigraphy along the southern Cascadia abyssal margin and northern California abyssal plain, CHIRP subbottom profiles capable of imaging individual turbidite beds in the upper tens of meters of the subsurface were collected. Reflectors imaged with the 3.5 kHz CHIRP subbottom data represent turbidite beds within the first 20-30 m of seafloor sediments that have sufficient impedance contrast and are separated by at least 20 cm vertically. Correlation of subbottom reflectors along both margins, constrained by core data at numerous sites along strike, revealed that many of these reflectors were contiguous over distances of hundreds of kilometers in southern Cascadia. The placement of subbottom reflectors coincided strongly with the configuration of many of the turbidite beds identified in nearby cores. A number of thin, low density beds evident in the cores are not imaged in the subbottom data in the northern part of the study area near Rogue Canyon, but become more robust southward where some are imaged as reflectors in the subbottom data. The independently derived core and subbottom based correlations of beds in southern Cascadia were found to be in fairly close agreement, and collectively support the continuity of beds over significant distances of up to 200 km along strike. Robustness of the beds between Trinidad and Rogue Canyons does not appear to be related to proximity to canyon mouths, suggesting that these beds and their transport are not exclusively related to canyon sources. The combined core and reflection data and the continuity of beds support a seismogenic source for Holocene beds correlated over long distances owing to the broad areal extent and lack of strong linkage to canyon systems. Data from paleoseismic studies worldwide were compiled in an effort to parameterize the likely triggering distances associated with turbidity currents initiated by earthquakes on the CSZ and NSAF. These ranges are estimated at 60-120 km for the CSZ and 40-75 km for the NSAF. A similar approach using MMI values associated with earthquakes linked to seismoturbidites yielded a threshold estimate for northern California of ~ MMI 5.5. A region from between Eel Canyon and Mendocino Channel in the north to the area north of Noyo Canyon in the south was identified as having a higher likelihood for recording at least a portion past seismicity from both the NSAF and CSZ in local sediments. The high frequency of turbidite beds in southernmost Cascadia could be the result of Cascadia and NSAF seismicity combined, though some input from hyperpycnal flows cannot be excluded. Further study of sediments in this zone may improve our understanding of potential stress triggering interactions between the CSZ and NSAF. Close

• 2. [Article] A 3-D Tomographic Model of the P-wave Velocity Structure of the Central Cascadia Forearc

  Signals from the R/V Langseth’s tuned airgun array were recorded on an array of 33 EarthScope FlexArray seismometers deployed in the Oregon Coast Range from 43.5° to 45°N as part of the 2012 Ridge2Trench ...

  Citation × Citation Citation Abstract Copy Title: A 3-D Tomographic Model of the P-wave Velocity Structure of the Central Cascadia Forearc Author: Kenyon, Christopher Bradford Signals from the R/V Langseth’s tuned airgun array were recorded on an array of 33 EarthScope FlexArray seismometers deployed in the Oregon Coast Range from 43.5° to 45°N as part of the 2012 Ridge2Trench experiment to image the structure of the Juan de Fuca plate. This segment of the Juan de Fuca/North America plate boundary slipped in 2 moderate low-angle thrust earthquakes in 2004, and continuing seismicity has clustered around these events since that time. Previously acquired bathymetric, potential field, and seismic data indicate the presence of subducted seamounts in this region and hinted at large velocity variations of the overlying forearc crust immediately above the plate boundary. Approximately 18000 airgun shots along 4 profiles on the continental shelf and upper slope and a profile oblique to the coast that extends across the margin to the trench provided sources for this study. Data quality is excellent, with strong Pg and PmP arrivals observed at most stations for most shots. We present velocity models that merge the new data with constraints from onshore/offshore data acquired in 1989 and 1996 to improve the resolution and extend the velocity model for this segment of the Cascadia subduction zone, which appears to be a segment boundary in the paleoseismic record and currently exhibits anomalous locking behavior as indicated by geodetic data. Our approach to modeling involved starting with a 1D P-wave velocity model and using an inversion process to modify the model to beetter fit the observed first arrival times of the airgun shots. In a subsequent step, we used a 2D starting model that incorporated constraints from prior 2D experiments that extended farther seaward and landward of the 3D study region. Finally, a smoothed version of the model obtained from the 2D inversion was used as a starting model to see if the final model could be further refined. Our final preferred model used a 2D starting model and moderate smoothing. The RMS misfit of predicted travel times is reduced from 0.48s for the initial 2D model to 0.040s for the final preferred 3D model. This model includes interesting velocity structure including possible subducted seamounts on the subducting Juan de Fuca plate and a mafic dike related to Cape Perpetua volcanics within the upper plate. These results contribute to the broader goal of understanding the relationship between plate boundary behavior and crustal structure. Title: A 3-D Tomographic Model of the P-wave Velocity Structure of the Central Cascadia Forearc Author: Kenyon, Christopher Bradford Signals from the R/V Langseth’s tuned airgun array were recorded on an array of 33 EarthScope FlexArray seismometers deployed in the Oregon Coast Range from 43.5° to 45°N as part of the 2012 Ridge2Trench experiment to image the structure of the Juan de Fuca plate. This segment of the Juan de Fuca/North America plate boundary slipped in 2 moderate low-angle thrust earthquakes in 2004, and continuing seismicity has clustered around these events since that time. Previously acquired bathymetric, potential field, and seismic data indicate the presence of subducted seamounts in this region and hinted at large velocity variations of the overlying forearc crust immediately above the plate boundary. Approximately 18000 airgun shots along 4 profiles on the continental shelf and upper slope and a profile oblique to the coast that extends across the margin to the trench provided sources for this study. Data quality is excellent, with strong Pg and PmP arrivals observed at most stations for most shots. We present velocity models that merge the new data with constraints from onshore/offshore data acquired in 1989 and 1996 to improve the resolution and extend the velocity model for this segment of the Cascadia subduction zone, which appears to be a segment boundary in the paleoseismic record and currently exhibits anomalous locking behavior as indicated by geodetic data. Our approach to modeling involved starting with a 1D P-wave velocity model and using an inversion process to modify the model to beetter fit the observed first arrival times of the airgun shots. In a subsequent step, we used a 2D starting model that incorporated constraints from prior 2D experiments that extended farther seaward and landward of the 3D study region. Finally, a smoothed version of the model obtained from the 2D inversion was used as a starting model to see if the final model could be further refined. Our final preferred model used a 2D starting model and moderate smoothing. The RMS misfit of predicted travel times is reduced from 0.48s for the initial 2D model to 0.040s for the final preferred 3D model. This model includes interesting velocity structure including possible subducted seamounts on the subducting Juan de Fuca plate and a mafic dike related to Cape Perpetua volcanics within the upper plate. These results contribute to the broader goal of understanding the relationship between plate boundary behavior and crustal structure. Close

• 3. [Article] A 2-D Magnetotelluric Investigation of the Cascadia Subduction Zone

  39 pages. A thesis presented to the Department of Physics and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2...

  Citation × Citation Citation Abstract Copy Title: A 2-D Magnetotelluric Investigation of the Cascadia Subduction Zone Author: Wogan, Nicholas Year: 2016 39 pages. A thesis presented to the Department of Physics and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2016. Title: A 2-D Magnetotelluric Investigation of the Cascadia Subduction Zone Author: Wogan, Nicholas Year: 2016 39 pages. A thesis presented to the Department of Physics and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2016. Close

• 4. [Article] A Magnetotelluric Investigation of the Cascadia Subduction Zone Plate Interface

  49 pages. A thesis presented to the Department of Physics and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2...

  Citation × Citation Citation Abstract Copy Title: A Magnetotelluric Investigation of the Cascadia Subduction Zone Plate Interface Author: Skidmore, Michael John-Barnett Year: 2017 49 pages. A thesis presented to the Department of Physics and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2017 Title: A Magnetotelluric Investigation of the Cascadia Subduction Zone Plate Interface Author: Skidmore, Michael John-Barnett Year: 2017 49 pages. A thesis presented to the Department of Physics and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2017 Close

• 5. [Article] Seismic Performance of Aging Prestressed Transmission Pole with Simulated Soil Foundation

  The Cascadia Subduction Zone has recently been identified as a source for an impending great earthquake. The potential of a large earthquake has created widespread interest into the resiliency of lifelines ...

  Citation × Citation Citation Abstract Copy Title: Seismic Performance of Aging Prestressed Transmission Pole with Simulated Soil Foundation Author: Argo, Maximo The Cascadia Subduction Zone has recently been identified as a source for an impending great earthquake. The potential of a large earthquake has created widespread interest into the resiliency of lifelines within the potentially affected areas. One critical lifeline is the electrical distribution and transmission systems which relies on legacy infrastructure components that were designed and constructed without regard to the seismic hazard. Of particular interest is the resiliency of prestressed concrete poles used for transmission towers within the region. Through material and structural testing of existing full scale specimens, moment capacities have been analyzed and compared to simulated earthquake moment demands. The structural testing allowed for an innovative solution to produce simulated site response through fabricating soil representative springs using steel plates. The soil simulated springs allowed for full scale testing with non-fixed base motions such as rotation and translation. After the conclusion of testing three different specimens, it was found that the poles remaining in the field are considerably vulnerable to site conditions but would structurally survive a subduction zone like earthquake. Title: Seismic Performance of Aging Prestressed Transmission Pole with Simulated Soil Foundation Author: Argo, Maximo The Cascadia Subduction Zone has recently been identified as a source for an impending great earthquake. The potential of a large earthquake has created widespread interest into the resiliency of lifelines within the potentially affected areas. One critical lifeline is the electrical distribution and transmission systems which relies on legacy infrastructure components that were designed and constructed without regard to the seismic hazard. Of particular interest is the resiliency of prestressed concrete poles used for transmission towers within the region. Through material and structural testing of existing full scale specimens, moment capacities have been analyzed and compared to simulated earthquake moment demands. The structural testing allowed for an innovative solution to produce simulated site response through fabricating soil representative springs using steel plates. The soil simulated springs allowed for full scale testing with non-fixed base motions such as rotation and translation. After the conclusion of testing three different specimens, it was found that the poles remaining in the field are considerably vulnerable to site conditions but would structurally survive a subduction zone like earthquake. Close

• 6. [Article] Debris Flow Network Morphology and a New Erosion Rate Proxy for Steepland Basins with Application to the Oregon Coast Range and Cascadia Subduction Zone

  Reaches dominated by debris flow scour and incision tend to greatly influence landscape form in steepland basins. Debris flow networks, despite their ubiquity, have not been exploited to develop erosion ...

  Citation × Citation Citation Abstract Copy Title: Debris Flow Network Morphology and a New Erosion Rate Proxy for Steepland Basins with Application to the Oregon Coast Range and Cascadia Subduction Zone Author: Penserini, Brian Year: 2015 Reaches dominated by debris flow scour and incision tend to greatly influence landscape form in steepland basins. Debris flow networks, despite their ubiquity, have not been exploited to develop erosion rate proxies. To bridge this gap, I applied a proposed empirical function that describes the variation of valley slope with drainage area in fluvial and debris flow reaches of steepland channel networks in the Oregon Coast Range. I calibrated a relationship between profile concavity and erosion rate to map spatial patterns of long-term uplift rates assuming steady state. I also estimated the magnitude and inland extent of coseismic subsidence in my study area. My estimates agree with field measurements in the same area along the Cascadia margin, indicating that debris flow valley profiles can be used to make interpretations from spatial patterns of rock uplift that may better constrain physical models of crustal deformation. This thesis includes unpublished co-authored material. Title: Debris Flow Network Morphology and a New Erosion Rate Proxy for Steepland Basins with Application to the Oregon Coast Range and Cascadia Subduction Zone Author: Penserini, Brian Year: 2015 Reaches dominated by debris flow scour and incision tend to greatly influence landscape form in steepland basins. Debris flow networks, despite their ubiquity, have not been exploited to develop erosion rate proxies. To bridge this gap, I applied a proposed empirical function that describes the variation of valley slope with drainage area in fluvial and debris flow reaches of steepland channel networks in the Oregon Coast Range. I calibrated a relationship between profile concavity and erosion rate to map spatial patterns of long-term uplift rates assuming steady state. I also estimated the magnitude and inland extent of coseismic subsidence in my study area. My estimates agree with field measurements in the same area along the Cascadia margin, indicating that debris flow valley profiles can be used to make interpretations from spatial patterns of rock uplift that may better constrain physical models of crustal deformation. This thesis includes unpublished co-authored material. Close

• 7. [Article] Automated detection and location of tectonic tremor along the entire Cascadia margin from 2005 to 2011

  This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/earth-and-planet...

  Citation × Citation Citation Abstract Copy Title: Automated detection and location of tectonic tremor along the entire Cascadia margin from 2005 to 2011 Author: Brudzinski, M. R., Allen, R. M., Boyarko, D. C., Porritt, R. W., Tréhu, A. M. This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/earth-and-planetary-science-letters/ Title: Automated detection and location of tectonic tremor along the entire Cascadia margin from 2005 to 2011 Author: Brudzinski, M. R., Allen, R. M., Boyarko, D. C., Porritt, R. W., Tréhu, A. M. This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/earth-and-planetary-science-letters/ Close

• 8. [Article] ETS in Tidal Records

  xiii, 75 p. : ill. (some col.)

  Citation × Citation Citation Abstract Copy Title: ETS in Tidal Records Author: Alba, Sequoia Kia Marie Year: 2012, 2011 xiii, 75 p. : ill. (some col.) Title: ETS in Tidal Records Author: Alba, Sequoia Kia Marie Year: 2012, 2011 xiii, 75 p. : ill. (some col.) Close

• 9. [Article] PattonJasonR2014_envelope.pdf

  Citation × Citation Citation Abstract Copy Title: PattonJasonR2014_envelope.pdf Author: Patton, Jason Robert Title: PattonJasonR2014_envelope.pdf Author: Patton, Jason Robert Close

• 10. [Article] A sedimentary and geophysical investigation offshore of Sumatra : subduction zone earthquakes, ground motions, and submarine landslides

  Subduction zone earthquake and tsunami hazards affect tens of millions worldwide and the recurrence of these disasters can be evaluated with paleoseismic techniques, because earthquake cycles (and their ...

  Citation × Citation Citation Abstract Copy Title: A sedimentary and geophysical investigation offshore of Sumatra : subduction zone earthquakes, ground motions, and submarine landslides Author: Patton, Jason Robert Subduction zone earthquake and tsunami hazards affect tens of millions worldwide and the recurrence of these disasters can be evaluated with paleoseismic techniques, because earthquake cycles (and their supercycles) typically span many millennia. In these three chapters, I discuss a suite of analyses I use to evaluate the sedimentary record of earthquakes as sampled in cores collected by the authors on the R/V Roger Revelle in 2007 offshore Sumatra, cruise RR0705, aka KNOX05RR. In the first chapter I discuss the mid- to late-Holocene recurrence of earthquakes in the region of the 2004 Sumatra-Andaman subduction zone earthquake. I estimate that the early Holocene to historic recurrence of turbidity current triggering earthquakes in the region of the 2004 Sumatra-Andaman subduction zone earthquake to be 260 ± 160 calendar years. I identify the uppermost turbidite in fifteen cores to have been deposited as a result of strong ground shaking from this 2004 earthquake. In the second chapter I compare and contrast the physiographic control of seismoturbidite deposition along the continental margins of the Sumatra-Andaman and Cascadia subduction zones. Cascadia’s margin is dominated by glacial cycle constructed pathways which promote turbidity current flows for large distances. Sumatra margin pathways do not inherit analogous sedimentary systems, so turbidity currents and their deposits are more localized. Finally, I discuss slope stability and earthquake ground motions along the continental margin offshore the coast of Sumatra. In this third chapter I relate the potential for slope instability with core stratigraphy in slope basin cores along the Sumatra-Andaman subduction zone, both for generic earthquakes and for the 2004 earthquake. Using 2-D profile factor of safety analyses, I estimate that slopes become unstable when a seismic load of <0.2 g is imparted. Using infinite slope factor of safety analyses, I conclude that turbidity currents are triggered by earthquakes of at least magnitude M = 7. For the 2004 Sumatra-Andaman subduction zone earthquake, I find that the shaking intensity from ground motion does not explain the thickness of turbidites, which must be explained by other factors like site effects, site geomorphology, or source proximity. Title: A sedimentary and geophysical investigation offshore of Sumatra : subduction zone earthquakes, ground motions, and submarine landslides Author: Patton, Jason Robert Subduction zone earthquake and tsunami hazards affect tens of millions worldwide and the recurrence of these disasters can be evaluated with paleoseismic techniques, because earthquake cycles (and their supercycles) typically span many millennia. In these three chapters, I discuss a suite of analyses I use to evaluate the sedimentary record of earthquakes as sampled in cores collected by the authors on the R/V Roger Revelle in 2007 offshore Sumatra, cruise RR0705, aka KNOX05RR. In the first chapter I discuss the mid- to late-Holocene recurrence of earthquakes in the region of the 2004 Sumatra-Andaman subduction zone earthquake. I estimate that the early Holocene to historic recurrence of turbidity current triggering earthquakes in the region of the 2004 Sumatra-Andaman subduction zone earthquake to be 260 ± 160 calendar years. I identify the uppermost turbidite in fifteen cores to have been deposited as a result of strong ground shaking from this 2004 earthquake. In the second chapter I compare and contrast the physiographic control of seismoturbidite deposition along the continental margins of the Sumatra-Andaman and Cascadia subduction zones. Cascadia’s margin is dominated by glacial cycle constructed pathways which promote turbidity current flows for large distances. Sumatra margin pathways do not inherit analogous sedimentary systems, so turbidity currents and their deposits are more localized. Finally, I discuss slope stability and earthquake ground motions along the continental margin offshore the coast of Sumatra. In this third chapter I relate the potential for slope instability with core stratigraphy in slope basin cores along the Sumatra-Andaman subduction zone, both for generic earthquakes and for the 2004 earthquake. Using 2-D profile factor of safety analyses, I estimate that slopes become unstable when a seismic load of <0.2 g is imparted. Using infinite slope factor of safety analyses, I conclude that turbidity currents are triggered by earthquakes of at least magnitude M = 7. For the 2004 Sumatra-Andaman subduction zone earthquake, I find that the shaking intensity from ground motion does not explain the thickness of turbidites, which must be explained by other factors like site effects, site geomorphology, or source proximity. Close