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• 1. [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

• 2. [Article] Fluid Boundaries: The Social Construction and Memory of Future Catastrophic Environmental Risk in a Community on the Oregon Coast

  The Oregon coast is facing the dual perils of climate change and the catastrophic Cascadia subduction zone earthquake and tsunami, yet many communities remain unprepared. Using qualitative interviews with ...

  Citation × Citation Citation Abstract Copy Title: Fluid Boundaries: The Social Construction and Memory of Future Catastrophic Environmental Risk in a Community on the Oregon Coast Author: Shtob, Daniel Year: 2016 The Oregon coast is facing the dual perils of climate change and the catastrophic Cascadia subduction zone earthquake and tsunami, yet many communities remain unprepared. Using qualitative interviews with residents of Coos Bay, Oregon, this study traces how communities facing these perils socially construct their visions of change by “remembering the future” and how this future memory influences unsettlement that, in turn, can trigger revision of strategies of action to deal with environmental risk. Participants understood these risks through three interrelated themes: analogy to familiar circumstances such as regular winter flooding, narratives of isolation and self-reliance based in collective history, and visions of symbolic preparedness. Each of these themes drew the conversation away from the material reality of environmental catastrophe, reducing relative unsettlement. Since the way that communities collectively understand environmental risk may influence preparatory action, these observations can help to explain the disjunction between knowledge of risks and response. Title: Fluid Boundaries: The Social Construction and Memory of Future Catastrophic Environmental Risk in a Community on the Oregon Coast Author: Shtob, Daniel Year: 2016 The Oregon coast is facing the dual perils of climate change and the catastrophic Cascadia subduction zone earthquake and tsunami, yet many communities remain unprepared. Using qualitative interviews with residents of Coos Bay, Oregon, this study traces how communities facing these perils socially construct their visions of change by “remembering the future” and how this future memory influences unsettlement that, in turn, can trigger revision of strategies of action to deal with environmental risk. Participants understood these risks through three interrelated themes: analogy to familiar circumstances such as regular winter flooding, narratives of isolation and self-reliance based in collective history, and visions of symbolic preparedness. Each of these themes drew the conversation away from the material reality of environmental catastrophe, reducing relative unsettlement. Since the way that communities collectively understand environmental risk may influence preparatory action, these observations can help to explain the disjunction between knowledge of risks and response. Close

• 3. [Article] Multi-hazard framework and analysis of soil-bridge systems : long duration earthquake and tsunami loading

  During the 2011 Great East Japan Earthquake and Tsunami, numerous bridge structures were damage or destroyed. The damage to bridge systems was caused by long duration strong ground shaking, tsunami inundation ...

  Citation × Citation Citation Abstract Copy Title: Multi-hazard framework and analysis of soil-bridge systems : long duration earthquake and tsunami loading Author: Carey, Trevor J. (Trevor James) During the 2011 Great East Japan Earthquake and Tsunami, numerous bridge structures were damage or destroyed. The damage to bridge systems was caused by long duration strong ground shaking, tsunami inundation forces, or both. Long duration strong ground shaking from subduction zone earthquakes and the multi-hazard scenario of combined earthquake and tsunami attack are particularly important in the Pacific Northwest (PNW) where the Cascadia Subduction Zone is located. The main objective of this thesis is to evaluate the safety and resilience of a typical PNW coastal bridge to solely long duration strong ground shaking and to the combined multi-hazard of a tsunami following an earthquake. Bridge system design and research has predominantly focused on short duration shallow crustal earthquakes, different from the long duration subduction zone earthquake expected in the PNW. Although the peak design demands (i.e., deck drift ratio) are typically the same for crustal and subduction zone motions, the duration and number of loading cycles is not. By not considering the effects of earthquake motion duration, the potential damage to a bridge system solely from a subduction zone earthquake motion may be under-predicted. To examine the effects of earthquake motion duration, a soil-bridge model was developed in the Open Systems for Earthquake Engineering Simulation (OpenSees) framework and the soil-bridge system response was evaluated for a suite of shallow crustal and subduction zone earthquake motions. The crustal and subduction zone motions were linearly scaled to pronounce ground motion duration and minimize amplitudinal differences. It was determined that earthquake intensity parameters that do not account for earthquake motion duration are poor predictors of potential damage to soil-bridge systems when subjected to subduction zone earthquake motions. The combined multi-hazard scenario of long duration strong ground shaking and tsunami attack extends two novel methods for determining hydrodynamic loading of the soil-bridge model. The Particle Finite Element Method (PFEM) was used to simulate impact of an idealized tsunami bore and the FEMA P-646 method was used to simulate quasi-steady state long duration tsunami loading. Originally designed for seismically induced lateral forces, the fluid-soil-bridge model was not able to resist tsunami lateral loading. Furthermore, the preceding earthquake motion had little effect on the fluid-soil-bridge models ability to resist hydrodynamic tsunami forces. Title: Multi-hazard framework and analysis of soil-bridge systems : long duration earthquake and tsunami loading Author: Carey, Trevor J. (Trevor James) During the 2011 Great East Japan Earthquake and Tsunami, numerous bridge structures were damage or destroyed. The damage to bridge systems was caused by long duration strong ground shaking, tsunami inundation forces, or both. Long duration strong ground shaking from subduction zone earthquakes and the multi-hazard scenario of combined earthquake and tsunami attack are particularly important in the Pacific Northwest (PNW) where the Cascadia Subduction Zone is located. The main objective of this thesis is to evaluate the safety and resilience of a typical PNW coastal bridge to solely long duration strong ground shaking and to the combined multi-hazard of a tsunami following an earthquake. Bridge system design and research has predominantly focused on short duration shallow crustal earthquakes, different from the long duration subduction zone earthquake expected in the PNW. Although the peak design demands (i.e., deck drift ratio) are typically the same for crustal and subduction zone motions, the duration and number of loading cycles is not. By not considering the effects of earthquake motion duration, the potential damage to a bridge system solely from a subduction zone earthquake motion may be under-predicted. To examine the effects of earthquake motion duration, a soil-bridge model was developed in the Open Systems for Earthquake Engineering Simulation (OpenSees) framework and the soil-bridge system response was evaluated for a suite of shallow crustal and subduction zone earthquake motions. The crustal and subduction zone motions were linearly scaled to pronounce ground motion duration and minimize amplitudinal differences. It was determined that earthquake intensity parameters that do not account for earthquake motion duration are poor predictors of potential damage to soil-bridge systems when subjected to subduction zone earthquake motions. The combined multi-hazard scenario of long duration strong ground shaking and tsunami attack extends two novel methods for determining hydrodynamic loading of the soil-bridge model. The Particle Finite Element Method (PFEM) was used to simulate impact of an idealized tsunami bore and the FEMA P-646 method was used to simulate quasi-steady state long duration tsunami loading. Originally designed for seismically induced lateral forces, the fluid-soil-bridge model was not able to resist tsunami lateral loading. Furthermore, the preceding earthquake motion had little effect on the fluid-soil-bridge models ability to resist hydrodynamic tsunami forces. Close

• 4. [Article] Earthquake Relocation in Three-Dimensional Velocity Models for Central Cascadia Continental Margin

  2017

  Citation × Citation Citation Abstract Copy Title: Earthquake Relocation in Three-Dimensional Velocity Models for Central Cascadia Continental Margin Author: Ghorbani, Paria 2017 Title: Earthquake Relocation in Three-Dimensional Velocity Models for Central Cascadia Continental Margin Author: Ghorbani, Paria 2017 Close

• 5. [Article] Earthquake Relocation in Three-Dimensional Velocity Models for Central Cascadia Continental Margin

  We used data from Cascadia Initiative and Blanco Transform Fault Zone array of ocean bottom seismometers and hydrophone to look at the seismicity and specially depth of the Central Cascadia Continental ...

  Citation × Citation Citation Abstract Copy Title: Earthquake Relocation in Three-Dimensional Velocity Models for Central Cascadia Continental Margin Author: Ghorbani, Paria We used data from Cascadia Initiative and Blanco Transform Fault Zone array of ocean bottom seismometers and hydrophone to look at the seismicity and specially depth of the Central Cascadia Continental Margin events. Events were detected and located automatically with Antelope software package (Boulder Real Time Technologies). We looked at the seismicity in a 1-degree square region (44N-45N and 124W-125W) of the Cascadia Subduction Zone from 2012 to 2013. There were about 40 events in our catalog which was more than any other land network catalogs as we expected. Automatic earthquake location procedure sometimes associated with respectively large residuals for sharp arrivals for stations in strongly heterogeneous structure that associated with continental margin and subduction zones. These large residuals force us to remove them from location procedure because they cannot be associated in a simple velocity model. For smaller events that even can remove the event from the catalog because of small number of sufficient arrival in close stations. We selected 7 larger events (with local magnitudes greater than 2) which were located by other networks before to preform accurate depth analysis. We used and 2.5D model based on the position along one of ORWELL Lines (Gerdom et al., 2000) that are closed to the area (44.75N). We located hypocenters in resulting 3D model in NonLinLoc (Lomax et al., 2000). We used a very fine grid spacing of 500 m, different distance weighting and phase inclusion/omission strategies to locating hypocenters in NonlinLoc. In order to reduce the azimuthal gap, we combined the OBS data with land station data. Our earthquake relocation results in overall shift of 7 km to the west in seismicity pattern. Based on depth results 1 out of 7 events occurred in overriding plate. 5 events seem be occurred on plate interface and one event depth is located in the base of oceanic crust. Plate inter face in our model is located in about 15 km depth. In order to get better understanding of seismicity and including more reliable S arrivals in our analysis we have to adjust Vp/Vs ratio on continental block of the model and relocate all events on continental margin with grid-search methods that contains S arrival picks as well. Title: Earthquake Relocation in Three-Dimensional Velocity Models for Central Cascadia Continental Margin Author: Ghorbani, Paria We used data from Cascadia Initiative and Blanco Transform Fault Zone array of ocean bottom seismometers and hydrophone to look at the seismicity and specially depth of the Central Cascadia Continental Margin events. Events were detected and located automatically with Antelope software package (Boulder Real Time Technologies). We looked at the seismicity in a 1-degree square region (44N-45N and 124W-125W) of the Cascadia Subduction Zone from 2012 to 2013. There were about 40 events in our catalog which was more than any other land network catalogs as we expected. Automatic earthquake location procedure sometimes associated with respectively large residuals for sharp arrivals for stations in strongly heterogeneous structure that associated with continental margin and subduction zones. These large residuals force us to remove them from location procedure because they cannot be associated in a simple velocity model. For smaller events that even can remove the event from the catalog because of small number of sufficient arrival in close stations. We selected 7 larger events (with local magnitudes greater than 2) which were located by other networks before to preform accurate depth analysis. We used and 2.5D model based on the position along one of ORWELL Lines (Gerdom et al., 2000) that are closed to the area (44.75N). We located hypocenters in resulting 3D model in NonLinLoc (Lomax et al., 2000). We used a very fine grid spacing of 500 m, different distance weighting and phase inclusion/omission strategies to locating hypocenters in NonlinLoc. In order to reduce the azimuthal gap, we combined the OBS data with land station data. Our earthquake relocation results in overall shift of 7 km to the west in seismicity pattern. Based on depth results 1 out of 7 events occurred in overriding plate. 5 events seem be occurred on plate interface and one event depth is located in the base of oceanic crust. Plate inter face in our model is located in about 15 km depth. In order to get better understanding of seismicity and including more reliable S arrivals in our analysis we have to adjust Vp/Vs ratio on continental block of the model and relocate all events on continental margin with grid-search methods that contains S arrival picks as well. Close

• 6. [Article] Kinematic Constraints on Tremor and Slow Slip in Cascadia and Implications for Fault Properties

  Subduction zone fault processes range from tsunami-generating megathrust events to aseismic creep along the deeper portions of the fault. Episodic tremor and slow slip (ETS) represents the transition between ...

  Citation × Citation Citation Abstract Copy Title: Kinematic Constraints on Tremor and Slow Slip in Cascadia and Implications for Fault Properties Author: Krogstad, Randy Year: 2016 Subduction zone fault processes range from tsunami-generating megathrust events to aseismic creep along the deeper portions of the fault. Episodic tremor and slow slip (ETS) represents the transition between these two regimes, where slip occurs at semi-regular recurrence intervals of months-to-years. These events are also accompanied by low frequency earthquakes, referred to as tremor. The study of ETS in Cascadia has been made possible by the enhancement of large-scale seismic and geodetic networks. In this dissertation, I use a range of geodetic and seismic observations at sub-daily to decadal time scales to investigate the kinematic behavior of individual ETS events, as well as the long-term behavior of the ETS zone and its relationship with the updip seismogenic zone. In Cascadia, current seismic hazard maps use the ETS zone as the downdip limit of rupture during future megathrust events. In Chapter II, I utilize uplift rates derived from 80 years of leveling measurements to explore the possibility that long-term strain accumulation exists near the ETS zone. The uplift rates are consistent with a region of 10-20% locking on the updip side of the ETS zone. The lack of associated topography indicates that the accumulated strain must be released during the megathrust cycle. The correlation of tremor and slip in Cascadia suggests there is an inherent relationship between the two. In Chapter III, I develop a method for using tremor as a proxy for slip to assess the spatial relationship of tremor and slip. I compare predictions of tremor-derived slip models to results from static inversions of GPS offsets by modeling slip based on the density of tremor. These comparisons suggest that the correlation of tremor and slip is variable along strike and along dip. In Chapter IV, I explore how borehole strainmeters can improve our resolution of slip on the plate interface. I incorporate strainmeters into joint, time-dependent kinematic inversions with GPS data. The temporal resolution of strainmeters provides improved constraints when deriving time-dependent slip estimates during slow slip events, allowing us to better image the kinematics of slow slip. This dissertation includes previously published and unpublished material. Title: Kinematic Constraints on Tremor and Slow Slip in Cascadia and Implications for Fault Properties Author: Krogstad, Randy Year: 2016 Subduction zone fault processes range from tsunami-generating megathrust events to aseismic creep along the deeper portions of the fault. Episodic tremor and slow slip (ETS) represents the transition between these two regimes, where slip occurs at semi-regular recurrence intervals of months-to-years. These events are also accompanied by low frequency earthquakes, referred to as tremor. The study of ETS in Cascadia has been made possible by the enhancement of large-scale seismic and geodetic networks. In this dissertation, I use a range of geodetic and seismic observations at sub-daily to decadal time scales to investigate the kinematic behavior of individual ETS events, as well as the long-term behavior of the ETS zone and its relationship with the updip seismogenic zone. In Cascadia, current seismic hazard maps use the ETS zone as the downdip limit of rupture during future megathrust events. In Chapter II, I utilize uplift rates derived from 80 years of leveling measurements to explore the possibility that long-term strain accumulation exists near the ETS zone. The uplift rates are consistent with a region of 10-20% locking on the updip side of the ETS zone. The lack of associated topography indicates that the accumulated strain must be released during the megathrust cycle. The correlation of tremor and slip in Cascadia suggests there is an inherent relationship between the two. In Chapter III, I develop a method for using tremor as a proxy for slip to assess the spatial relationship of tremor and slip. I compare predictions of tremor-derived slip models to results from static inversions of GPS offsets by modeling slip based on the density of tremor. These comparisons suggest that the correlation of tremor and slip is variable along strike and along dip. In Chapter IV, I explore how borehole strainmeters can improve our resolution of slip on the plate interface. I incorporate strainmeters into joint, time-dependent kinematic inversions with GPS data. The temporal resolution of strainmeters provides improved constraints when deriving time-dependent slip estimates during slow slip events, allowing us to better image the kinematics of slow slip. This dissertation includes previously published and unpublished material. Close

• 7. [Article] Local Seismicity Recorded by ChilePEPPER : Implications for Dynamic Accretionary Prism Response and Long-term Prism Evolution

  To investigate the dynamic response of the outer accretionary wedge updip from the patch of greatest slip during the Mw8.8 2010 Maule earthquake, 10 Ocean Bottom Seismometers (OBS) were deployed from May ...

  Citation × Citation Citation Abstract Copy Title: Local Seismicity Recorded by ChilePEPPER : Implications for Dynamic Accretionary Prism Response and Long-term Prism Evolution Author: de Moor, Alexander To investigate the dynamic response of the outer accretionary wedge updip from the patch of greatest slip during the Mw8.8 2010 Maule earthquake, 10 Ocean Bottom Seismometers (OBS) were deployed from May 2012 to March 2013 in a small array with an inter-instrument spacing of ~10 km. Nine instruments were recovered, with 4 recording data on 3 intermediate-band 3- component seismometers and a differential pressure gauge and 5 recording data from absolute pressure gauges. All instruments were also equipped with fluid flow meters to monitor the hydrologic response to fluid pressure changes within the wedge. Here we present hypocenters for 569 local events that have S-P times less than 17 seconds (i.e. within ~125 km of the array) using hand-picked arrival times and 1D velocity models derived from a 2D seismic refraction profile through the region (Moscoso et al 2011, EPSL). We analyze the distribution of seismicity in the context of published slip models, high resolution swath bathymetry, ChilePEPPER seismic reflection data, critical taper analysis done by Cubas et al 2013 (EPSL), and offshore gravity data. Based on a lack of seismicity in the outer wedge, steady state fluid flow rates at < 0.01cm/yr, and no indications of anomalous styles of rupture such as very low frequency earthquakes, we suggest that in the study region the outer wedge is in a stable state due to localized slip to the trench that transported this region of the forearc to the west during the 2010 earthquake. This local phenomenon is probably due to the velocity weakening properties of sediments within the subduction channel at high slip rates. Based on distinct changes in the morphology of the wedge as seen in the bathymetry data and critical taper, this may be a persistent feature of this section of the margin. Title: Local Seismicity Recorded by ChilePEPPER : Implications for Dynamic Accretionary Prism Response and Long-term Prism Evolution Author: de Moor, Alexander To investigate the dynamic response of the outer accretionary wedge updip from the patch of greatest slip during the Mw8.8 2010 Maule earthquake, 10 Ocean Bottom Seismometers (OBS) were deployed from May 2012 to March 2013 in a small array with an inter-instrument spacing of ~10 km. Nine instruments were recovered, with 4 recording data on 3 intermediate-band 3- component seismometers and a differential pressure gauge and 5 recording data from absolute pressure gauges. All instruments were also equipped with fluid flow meters to monitor the hydrologic response to fluid pressure changes within the wedge. Here we present hypocenters for 569 local events that have S-P times less than 17 seconds (i.e. within ~125 km of the array) using hand-picked arrival times and 1D velocity models derived from a 2D seismic refraction profile through the region (Moscoso et al 2011, EPSL). We analyze the distribution of seismicity in the context of published slip models, high resolution swath bathymetry, ChilePEPPER seismic reflection data, critical taper analysis done by Cubas et al 2013 (EPSL), and offshore gravity data. Based on a lack of seismicity in the outer wedge, steady state fluid flow rates at < 0.01cm/yr, and no indications of anomalous styles of rupture such as very low frequency earthquakes, we suggest that in the study region the outer wedge is in a stable state due to localized slip to the trench that transported this region of the forearc to the west during the 2010 earthquake. This local phenomenon is probably due to the velocity weakening properties of sediments within the subduction channel at high slip rates. Based on distinct changes in the morphology of the wedge as seen in the bathymetry data and critical taper, this may be a persistent feature of this section of the margin. Close