Search

Search Results

• 1. [Article] Melting in the Mantle Wedge: Quantifying the Effects of Crustal Morphology and Viscous Decoupling on Melt Production with Application to the Cascadia Subduction Zone

  Arc magmatism is sustained by the complex interactions between the subducting slab, the overriding plate, and the mantle wedge. Partial melting of mantle peridotite is achieved by fluid-induced flux melting ...

  Citation × Citation Citation Abstract Copy Title: Melting in the Mantle Wedge: Quantifying the Effects of Crustal Morphology and Viscous Decoupling on Melt Production with Application to the Cascadia Subduction Zone Author: Yang, Jiaming Year: 2017 Arc magmatism is sustained by the complex interactions between the subducting slab, the overriding plate, and the mantle wedge. Partial melting of mantle peridotite is achieved by fluid-induced flux melting and decompression melting due to upward flow. The distribution of melting is sensitive to temperature, the pattern of flow, and the pressure in the mantle wedge. The arc front is the surface manifestation of partial melting in the mantle wedge and is characterized by a narrow chain of active volcanoes that migrate in time. The conventional interpretation is that changes in slab dip angle lead to changes in the arc front position relative to the trench. We explore an alternative hypothesis: evolution of the overlying plate, specifically thickening of the arc root, causes arc front migration. We investigate the effects of varying crustal morphology and viscous decoupling of the shallow slab-mantle interface on melt production using 2D numerical models involving a stationary overriding plate, a subducting plate with prescribed motion, and a dynamic mantle wedge. Melt production is quantified using a hydrous melting parameterization. We conclude: 1) Localized lithospheric thickening shifts the locus of melt production trenchward while thinning shifts melting landward. 2) Inclined LAB topography modulates the asthenospheric flow field, producing a narrow, well-defined arc front. 3) Thickening of the overriding plate exerts increased torque on the slab, favoring shallowing of the dip angle. 4) Viscous decoupling produces a cold, stagnant forearc mantle but promotes arc front melting due to reduction in the radius of corner flow, leading to higher temperatures at the coupling/decoupling transition. Title: Melting in the Mantle Wedge: Quantifying the Effects of Crustal Morphology and Viscous Decoupling on Melt Production with Application to the Cascadia Subduction Zone Author: Yang, Jiaming Year: 2017 Arc magmatism is sustained by the complex interactions between the subducting slab, the overriding plate, and the mantle wedge. Partial melting of mantle peridotite is achieved by fluid-induced flux melting and decompression melting due to upward flow. The distribution of melting is sensitive to temperature, the pattern of flow, and the pressure in the mantle wedge. The arc front is the surface manifestation of partial melting in the mantle wedge and is characterized by a narrow chain of active volcanoes that migrate in time. The conventional interpretation is that changes in slab dip angle lead to changes in the arc front position relative to the trench. We explore an alternative hypothesis: evolution of the overlying plate, specifically thickening of the arc root, causes arc front migration. We investigate the effects of varying crustal morphology and viscous decoupling of the shallow slab-mantle interface on melt production using 2D numerical models involving a stationary overriding plate, a subducting plate with prescribed motion, and a dynamic mantle wedge. Melt production is quantified using a hydrous melting parameterization. We conclude: 1) Localized lithospheric thickening shifts the locus of melt production trenchward while thinning shifts melting landward. 2) Inclined LAB topography modulates the asthenospheric flow field, producing a narrow, well-defined arc front. 3) Thickening of the overriding plate exerts increased torque on the slab, favoring shallowing of the dip angle. 4) Viscous decoupling produces a cold, stagnant forearc mantle but promotes arc front melting due to reduction in the radius of corner flow, leading to higher temperatures at the coupling/decoupling transition. Close

• 2. [Article] Links from Mantle to Microbe at the Lau Integrated Study Site: Insights from a Back-Arc Spreading Center

  The Lau Integrated Study Site (ISS) has provided unique opportunities for study of ridge processes because of its back-arc setting in the southwestern Pacific. Its location allows study of a biogeographical ...

  Citation × Citation Citation Abstract Copy Title: Links from Mantle to Microbe at the Lau Integrated Study Site: Insights from a Back-Arc Spreading Center Author: Tivey, Margaret K., Becker, Erin, Beinart, Roxanne, Fisher, Charles R., Girguis, Peter, Langmuir, Charles H., Michael, Peter J., Reysenbach, Anna-Louise Year: 2012 The Lau Integrated Study Site (ISS) has provided unique opportunities for study of ridge processes because of its back-arc setting in the southwestern Pacific. Its location allows study of a biogeographical province distinct from those of eastern Pacific and mid-Atlantic ridges, and crustal compositions along the ridge lie outside the range of mid-ocean ridge crustal compositions. The Lau ISS is located above a subduction zone, at an oblique angle. The underlying mantle receives water and other elements derived from the downgoing lithospheric slab, with an increase in slab influence from north to south. Water lowers the mantle melting temperature and leads to greater melt production where the water flux is greater, and to distinctive regional-scale gradients along the ridge. There are deeper faulted axial valleys with basaltic volcanism in the north and inflated axial highs with andesites in the south. Differences in igneous rock composition and release of magmatic volatiles affect compositions of vent fluids and deposits. Differences in vent fluid compositions and small-scale diffuse-flow regimes correlate with regional-scale patterns in microbial and megafaunal distributions. The interdisciplinary research effort at the Lau ISS has successfully identified linkages between subsurface processes and deep-sea biological communities, from mantle to microbe to megafauna. Title: Links from Mantle to Microbe at the Lau Integrated Study Site: Insights from a Back-Arc Spreading Center Author: Tivey, Margaret K., Becker, Erin, Beinart, Roxanne, Fisher, Charles R., Girguis, Peter, Langmuir, Charles H., Michael, Peter J., Reysenbach, Anna-Louise Year: 2012 The Lau Integrated Study Site (ISS) has provided unique opportunities for study of ridge processes because of its back-arc setting in the southwestern Pacific. Its location allows study of a biogeographical province distinct from those of eastern Pacific and mid-Atlantic ridges, and crustal compositions along the ridge lie outside the range of mid-ocean ridge crustal compositions. The Lau ISS is located above a subduction zone, at an oblique angle. The underlying mantle receives water and other elements derived from the downgoing lithospheric slab, with an increase in slab influence from north to south. Water lowers the mantle melting temperature and leads to greater melt production where the water flux is greater, and to distinctive regional-scale gradients along the ridge. There are deeper faulted axial valleys with basaltic volcanism in the north and inflated axial highs with andesites in the south. Differences in igneous rock composition and release of magmatic volatiles affect compositions of vent fluids and deposits. Differences in vent fluid compositions and small-scale diffuse-flow regimes correlate with regional-scale patterns in microbial and megafaunal distributions. The interdisciplinary research effort at the Lau ISS has successfully identified linkages between subsurface processes and deep-sea biological communities, from mantle to microbe to megafauna. Close

• 3. [Article] Seismic Hazard Assessment of Oregon Highway Truck Routes

  This research project developed a seismic risk assessment model along the major truck routes in Oregon. The study had adopted federally developed software tools called Risk for Earthquake Damage to Roadway ...

  Citation × Citation Citation Abstract Copy Title: Seismic Hazard Assessment of Oregon Highway Truck Routes Author: Dusicka, Peter, Mehary, Selamawit Tesfayesus Year: 2012 This research project developed a seismic risk assessment model along the major truck routes in Oregon. The study had adopted federally developed software tools called Risk for Earthquake Damage to Roadway Systems (REDARS2) and HAZUS-MH. The model was the first time REDARS2 has been adopted and used in research outside of the original development team, presenting a number of unique challenges. The development of the model was a complex, intensive process that required a significant research effort, manipulation and adjustment of data. Furthermore, limitations of the software tools themselves had been identified that prevented the inclusion of important aspects such as liquefaction induced damage and refinement of the transportation network. The main objective of this research were to refine the data from a first generation of the model to more realistically represent the bridge inventory, to address the seismicity of the Pacific Northwest, conduct sensitivity analyses of soil data on the analyses results and develop a seismic network model of Oregon bridges for purposes of assessing the seismic vulnerability of roadway segments. The first generation model relied on default settings within the program to determine the economic loss due to repair and replacement of damaged bridges. The assumptions used in the analyses have been reviewed and Oregon specific data was incorporated for the model. The largest earthquake now considered to be at a highest level of probability in the Pacific Northwest is a subduction zone earthquake. The major shortcoming of REDARS2 is its inability to incorporate the subduction zone attenuation relationship into the analysis. To incorporate that capability into the model, shakemaps were developed by USGS for Cascadia subduction zone scenario events and incorporated as the demand on the refined model. Analyses of the transportation network incorporating bridge routes and post processing of the data with input from Oregon DOT bridge engineers resulted in recommendations toward bridge route priority strategies. The majority of the bridges that indicated the possibility of damage were types associated with multi-column bents, simply-supported concrete superstructures and simply-supported steel superstructures. Of the major highway routes that were considered, I-405, section of I-5 (from Multnomah to Clackamas Counties), I-84, I-205 and US-101 were the top five on the preliminary priority for seismic retrofit. These routes need to be analyzed more and advanced cost-benefit investigations should be done before retrofit decisions are made. Title: Seismic Hazard Assessment of Oregon Highway Truck Routes Author: Dusicka, Peter, Mehary, Selamawit Tesfayesus Year: 2012 This research project developed a seismic risk assessment model along the major truck routes in Oregon. The study had adopted federally developed software tools called Risk for Earthquake Damage to Roadway Systems (REDARS2) and HAZUS-MH. The model was the first time REDARS2 has been adopted and used in research outside of the original development team, presenting a number of unique challenges. The development of the model was a complex, intensive process that required a significant research effort, manipulation and adjustment of data. Furthermore, limitations of the software tools themselves had been identified that prevented the inclusion of important aspects such as liquefaction induced damage and refinement of the transportation network. The main objective of this research were to refine the data from a first generation of the model to more realistically represent the bridge inventory, to address the seismicity of the Pacific Northwest, conduct sensitivity analyses of soil data on the analyses results and develop a seismic network model of Oregon bridges for purposes of assessing the seismic vulnerability of roadway segments. The first generation model relied on default settings within the program to determine the economic loss due to repair and replacement of damaged bridges. The assumptions used in the analyses have been reviewed and Oregon specific data was incorporated for the model. The largest earthquake now considered to be at a highest level of probability in the Pacific Northwest is a subduction zone earthquake. The major shortcoming of REDARS2 is its inability to incorporate the subduction zone attenuation relationship into the analysis. To incorporate that capability into the model, shakemaps were developed by USGS for Cascadia subduction zone scenario events and incorporated as the demand on the refined model. Analyses of the transportation network incorporating bridge routes and post processing of the data with input from Oregon DOT bridge engineers resulted in recommendations toward bridge route priority strategies. The majority of the bridges that indicated the possibility of damage were types associated with multi-column bents, simply-supported concrete superstructures and simply-supported steel superstructures. Of the major highway routes that were considered, I-405, section of I-5 (from Multnomah to Clackamas Counties), I-84, I-205 and US-101 were the top five on the preliminary priority for seismic retrofit. These routes need to be analyzed more and advanced cost-benefit investigations should be done before retrofit decisions are made. Close

• 4. [Article] Reducing Seismic Risk to Highway Mobility: Assessment and Design Examples for Pile Foundations Affected by Lateral Spreading

  Damage in pile supported structures due to liquefaction and liquefaction induced deformation were reported in past earthquakes around the world (e.g., Ansal et al. 1999; Seed et al. 1990; EERI 2010, EERI ...

  Citation × Citation Citation Abstract Copy Title: Reducing Seismic Risk to Highway Mobility: Assessment and Design Examples for Pile Foundations Affected by Lateral Spreading Author: Ashford, Scott A., Scott, Michael H., Rayamajhi, Deepak Year: 2013 Damage in pile supported structures due to liquefaction and liquefaction induced deformation were reported in past earthquakes around the world (e.g., Ansal et al. 1999; Seed et al. 1990; EERI 2010, EERI 2011; GEER 2010a, GEER 2010b, GEER 2011). For example, a reconnaissance report from a recent subduction zone event, the 2010 Chile earthquake (Mw=8.8), showed the pervasive nature of liquefaction and liquefaction-induced lateral spreading damage to bridge foundations (GEER 2010a, Yen et al. 2011). In terms of seismic hazard, the Pacific Northwest shares similar conditions from a Cascadia Subduction Zone (CSZ) earthquake source with the expected earthquake magnitude of 9.0 (Mw) and return period of 300 years (Atwater et al. 1995, Atwater and Hemphill-Halley 1997). The risk and damage from a CSZ earthquake event is widely recognized by the Oregon Department of Transportation (ODOT) as presented in a report by ODOT (2009). A large number of bridges were found to be vulnerable to a CSZ event, and repair and replacement costs of Oregon bridges have been estimated at more than 1 billion USD (ODOT 2009). Moreover, thousands of bridges require some kind of modification and/or seismic retrofitting to the foundation in order to improve seismic performance under liquefaction induced lateral spreading. To evaluate the seismic performance of bridge foundations and liquefaction mitigation alternatives, ODOT/OTREC funded collaborative research between Oregon State University (OSU), University of California at Davis (UCD), University of California at San Diego (UCSD), Hayward Baker Inc., and Pacific Earthquake Engineering Research Center (PEER). The main objectives of the research were to develop design charts for different liquefaction mitigation alternatives and to develop methodologies for assessing the performance of bridge pile foundations in laterally spreading ground. The cooperative research focuses on two aspects of liquefaction and liquefaction induced lateral spreading: (1) ground improvement methods, particularly using stone columns and deep soil mixing (DSM) grids, and (2) assess the seismic performance of bridge foundations (e.g., drilled shaft, pile groups) and seismic retrofitting alternatives for the bridge foundation. Stone columns for liquefaction mitigation and pile groups foundation assessment were investigated by the OSU team, while DSM and large diameter piles/shafts alternatives were investigated by the UCD team. Research teams used OpenSees (http://opensees.berkeley.edu/), an open source computational platform for three dimensional (3D) finite element (FE) modeling and analysis. OpenSeesPL, a graphical user interface developed by the UCSD team, was used to investigate liquefaction mitigation alternatives (i.e., stone columns and DSM grids) and the performance of pile foundations in liquefaction induced laterally spreading ground. Title: Reducing Seismic Risk to Highway Mobility: Assessment and Design Examples for Pile Foundations Affected by Lateral Spreading Author: Ashford, Scott A., Scott, Michael H., Rayamajhi, Deepak Year: 2013 Damage in pile supported structures due to liquefaction and liquefaction induced deformation were reported in past earthquakes around the world (e.g., Ansal et al. 1999; Seed et al. 1990; EERI 2010, EERI 2011; GEER 2010a, GEER 2010b, GEER 2011). For example, a reconnaissance report from a recent subduction zone event, the 2010 Chile earthquake (Mw=8.8), showed the pervasive nature of liquefaction and liquefaction-induced lateral spreading damage to bridge foundations (GEER 2010a, Yen et al. 2011). In terms of seismic hazard, the Pacific Northwest shares similar conditions from a Cascadia Subduction Zone (CSZ) earthquake source with the expected earthquake magnitude of 9.0 (Mw) and return period of 300 years (Atwater et al. 1995, Atwater and Hemphill-Halley 1997). The risk and damage from a CSZ earthquake event is widely recognized by the Oregon Department of Transportation (ODOT) as presented in a report by ODOT (2009). A large number of bridges were found to be vulnerable to a CSZ event, and repair and replacement costs of Oregon bridges have been estimated at more than 1 billion USD (ODOT 2009). Moreover, thousands of bridges require some kind of modification and/or seismic retrofitting to the foundation in order to improve seismic performance under liquefaction induced lateral spreading. To evaluate the seismic performance of bridge foundations and liquefaction mitigation alternatives, ODOT/OTREC funded collaborative research between Oregon State University (OSU), University of California at Davis (UCD), University of California at San Diego (UCSD), Hayward Baker Inc., and Pacific Earthquake Engineering Research Center (PEER). The main objectives of the research were to develop design charts for different liquefaction mitigation alternatives and to develop methodologies for assessing the performance of bridge pile foundations in laterally spreading ground. The cooperative research focuses on two aspects of liquefaction and liquefaction induced lateral spreading: (1) ground improvement methods, particularly using stone columns and deep soil mixing (DSM) grids, and (2) assess the seismic performance of bridge foundations (e.g., drilled shaft, pile groups) and seismic retrofitting alternatives for the bridge foundation. Stone columns for liquefaction mitigation and pile groups foundation assessment were investigated by the OSU team, while DSM and large diameter piles/shafts alternatives were investigated by the UCD team. Research teams used OpenSees (http://opensees.berkeley.edu/), an open source computational platform for three dimensional (3D) finite element (FE) modeling and analysis. OpenSeesPL, a graphical user interface developed by the UCSD team, was used to investigate liquefaction mitigation alternatives (i.e., stone columns and DSM grids) and the performance of pile foundations in liquefaction induced laterally spreading ground. Close

• 5. [Article] Seismic Retrofit Benefit Considering Statewide Transportation Assessment

  The purpose of this study was to identify and demonstrate a methodology to prioritize bridges for retrofit in the State of Oregon. Given the limited resources available, retrofitting all vulnerable bridges ...

  Citation × Citation Citation Abstract Copy Title: Seismic Retrofit Benefit Considering Statewide Transportation Assessment Author: Mehary, Selamawit Tesfayesus, Dusicka, Peter Year: 2015 The purpose of this study was to identify and demonstrate a methodology to prioritize bridges for retrofit in the State of Oregon. Given the limited resources available, retrofitting all vulnerable bridges in the foreseeable future would not be practical. Instead, a retrofit strategy needs to be developed to prioritize the inventory and enumerate the retrofit cost. In this study, a prioritization methodology used a holistic assessment of overall roadway system to consider highway route segments, rather than individual bridges. The overall assessment was based on a cost-benefit analysis including retrofit cost, expected economic loss (with or without retrofit) and social loss caused by system wide travel time delays. A review of 2010 ODOT bridge inventory suggested that a continuous concrete girder bridge (CCGS) with three spans could be utilized to represent a sizeable portion of vulnerable inventory for Oregon highways bridges. After reviewing several potential retrofit measures, carbon fiber composite material was selected for retrofit of vulnerable columns representing those built from the 1950s to mid-1970s. Four full-scale typical square columns were tested to failure. The results showed that despite the intentionally selected square geometry of the reinforced concrete columns, the CFRP composite material showed to be an effective retrofit measure and could be deployed for to address this deficiency. The software package REDARS2 was used for seismic risk analysis (SRA) of the highway network in this study. This platform was adopted to simulate the impact of scenario earthquakes in an effort to assess the expected benefit considering direct bridge costs as well as social costs from traffic induced delays resulting from seismic retrofitting of a particular bridge type. The assessment considered three scenario Cascadia Subsection Zone earthquakes of magnitudes 9.0, 8.5 North, and, 8.5 South. The study area included all highway routes west of the I-5 corridor, highway routes in the Portland area, the entire length of US-101 and extending partially east on I-84 Columbia River Highway. Due to the considerations of a single bridge type and other limitations identified in the seismic analysis software (REDARS2), the retrofit assessment outcomes should be regarded as a first order estimate. Title: Seismic Retrofit Benefit Considering Statewide Transportation Assessment Author: Mehary, Selamawit Tesfayesus, Dusicka, Peter Year: 2015 The purpose of this study was to identify and demonstrate a methodology to prioritize bridges for retrofit in the State of Oregon. Given the limited resources available, retrofitting all vulnerable bridges in the foreseeable future would not be practical. Instead, a retrofit strategy needs to be developed to prioritize the inventory and enumerate the retrofit cost. In this study, a prioritization methodology used a holistic assessment of overall roadway system to consider highway route segments, rather than individual bridges. The overall assessment was based on a cost-benefit analysis including retrofit cost, expected economic loss (with or without retrofit) and social loss caused by system wide travel time delays. A review of 2010 ODOT bridge inventory suggested that a continuous concrete girder bridge (CCGS) with three spans could be utilized to represent a sizeable portion of vulnerable inventory for Oregon highways bridges. After reviewing several potential retrofit measures, carbon fiber composite material was selected for retrofit of vulnerable columns representing those built from the 1950s to mid-1970s. Four full-scale typical square columns were tested to failure. The results showed that despite the intentionally selected square geometry of the reinforced concrete columns, the CFRP composite material showed to be an effective retrofit measure and could be deployed for to address this deficiency. The software package REDARS2 was used for seismic risk analysis (SRA) of the highway network in this study. This platform was adopted to simulate the impact of scenario earthquakes in an effort to assess the expected benefit considering direct bridge costs as well as social costs from traffic induced delays resulting from seismic retrofitting of a particular bridge type. The assessment considered three scenario Cascadia Subsection Zone earthquakes of magnitudes 9.0, 8.5 North, and, 8.5 South. The study area included all highway routes west of the I-5 corridor, highway routes in the Portland area, the entire length of US-101 and extending partially east on I-84 Columbia River Highway. Due to the considerations of a single bridge type and other limitations identified in the seismic analysis software (REDARS2), the retrofit assessment outcomes should be regarded as a first order estimate. Close

• 6. [Article] Research Project Work Plan for Impact of Cascadia Subduction Zone Earthquake on the Seismic Evaluation Criteria of Bridges

  The goal of this project is to provide ODOT with the best rational estimate of ground acceleration values for designing new and retrofitting existing bridges. The objectives are to: evaluate the hazard ...

  Citation × Citation Citation Abstract Copy Title: Research Project Work Plan for Impact of Cascadia Subduction Zone Earthquake on the Seismic Evaluation Criteria of Bridges Author: Dusicka, Peter Year: 2013 The goal of this project is to provide ODOT with the best rational estimate of ground acceleration values for designing new and retrofitting existing bridges. The objectives are to: evaluate the hazard by contrasting the acceleration values from individual CSZ events to PSHA values provide experimental evidence of damage difference under longer duration shaking expected from CSZ event Title: Research Project Work Plan for Impact of Cascadia Subduction Zone Earthquake on the Seismic Evaluation Criteria of Bridges Author: Dusicka, Peter Year: 2013 The goal of this project is to provide ODOT with the best rational estimate of ground acceleration values for designing new and retrofitting existing bridges. The objectives are to: evaluate the hazard by contrasting the acceleration values from individual CSZ events to PSHA values provide experimental evidence of damage difference under longer duration shaking expected from CSZ event Close

• 7. [Article] Mapped Overland Distance of Paleotsunami High-Velocity Inundation n Back-Barrier Wetlands of the Central Cascadia Margin, U.S.A

  Investigations of back-barrier, open-coastal plain settings have been used to establish minimum inundation distances of prehistoric tsunamis produced by great subduction zone earthquakes in the central ...

  Citation × Citation Citation Abstract Copy Title: Mapped Overland Distance of Paleotsunami High-Velocity Inundation n Back-Barrier Wetlands of the Central Cascadia Margin, U.S.A Author: Schlichting, Robert B., Peterson, Curt D. Year: 2006 Investigations of back-barrier, open-coastal plain settings have been used to establish minimum inundation distances of prehistoric tsunamis produced by great subduction zone earthquakes in the central Cascadia margin. Distinctive sand sheets were characterized at four localities within the central Cascadia margin, a shoreline distance of about 250 km. The sand sheets vary in thickness from 0.2 to 25 cm. They thin in the landward direction and consist of well-sorted beach sand that fines upsection. Many of the sand sheets include capping layers of organic-rich detritus, as well as assimilated mud rip-up clasts and soil litter. Marine diatoms and bromine (i.e., marine tracers) were used to confirm marine surge origins for the anomalous sand sheets. Radiocarbon dating of the sand sheets demonstrates correspondence with reported great Cascadia earthquake events at 0.3, ~1.1, ~1.3, ~1.7, and ~2.5 Ka. One sand sheet mapped at all four localities is dated at 600-950 calibrated radiocarbon years before present. This interpreted paleotsunami event does not correspond to a central Cascadia rupture, so it is tentatively assigned to a far-field source. Minimum overland inundation distances of the near field (Cascadia tsunami) at the four study localities range from 0.3 to 1.3 km, with a mean inundation for all sand sheets of 0.5 km. Title: Mapped Overland Distance of Paleotsunami High-Velocity Inundation n Back-Barrier Wetlands of the Central Cascadia Margin, U.S.A Author: Schlichting, Robert B., Peterson, Curt D. Year: 2006 Investigations of back-barrier, open-coastal plain settings have been used to establish minimum inundation distances of prehistoric tsunamis produced by great subduction zone earthquakes in the central Cascadia margin. Distinctive sand sheets were characterized at four localities within the central Cascadia margin, a shoreline distance of about 250 km. The sand sheets vary in thickness from 0.2 to 25 cm. They thin in the landward direction and consist of well-sorted beach sand that fines upsection. Many of the sand sheets include capping layers of organic-rich detritus, as well as assimilated mud rip-up clasts and soil litter. Marine diatoms and bromine (i.e., marine tracers) were used to confirm marine surge origins for the anomalous sand sheets. Radiocarbon dating of the sand sheets demonstrates correspondence with reported great Cascadia earthquake events at 0.3, ~1.1, ~1.3, ~1.7, and ~2.5 Ka. One sand sheet mapped at all four localities is dated at 600-950 calibrated radiocarbon years before present. This interpreted paleotsunami event does not correspond to a central Cascadia rupture, so it is tentatively assigned to a far-field source. Minimum overland inundation distances of the near field (Cascadia tsunami) at the four study localities range from 0.3 to 1.3 km, with a mean inundation for all sand sheets of 0.5 km. Close

• 8. [Article] Late Holocene Tsunami Deposits at Salt Creek, Washington, USA

  We interpret two thin sand layers in the estuarine marsh at Salt Creek, on the southern shore of the Strait of Juan de Fuca, as the products of tsunamis propagated by earthquakes at the Cascadia subduction ...

  Citation × Citation Citation Abstract Copy Title: Late Holocene Tsunami Deposits at Salt Creek, Washington, USA Author: Hutchinson, Ian, Peterson, Curt D., Sterling, Sarah L. Year: 2013 We interpret two thin sand layers in the estuarine marsh at Salt Creek, on the southern shore of the Strait of Juan de Fuca, as the products of tsunamis propagated by earthquakes at the Cascadia subduction zone. The sand layers extend for about 60 m along the left bank of the creek about 800 m from the mouth, and can be traced to the base of a nearby upland area. One layer is exposed in the creek bank about 400 m further upstream, but they are only patchily distributed in the rest of the central area of the marsh. Both layers contain brackish-marine epipsammic diatoms. The lower sand layer marks a sharp contact between intertidal peaty mud and overlying mud, perhaps reflecting modest coseismic subsidence in association with tsunami deposition, but little or no change in the bracketing sediment occurs in association with the upper sand layer. The ages of the sand layers are not closely constrained, but were most likely deposited by tsunamis generated by great earthquakes at the Cascadia subduction zone about 1650 and 1300 years ago. The Cascadia great earthquake of AD1700 may have induced slight subsidence in the marsh, but no tsunami deposit was detected at the inferred contact. The absence of deposits from the marsh immediately inland of the 4 m-high barrier beach indicates that the largest tsunamis in the late Holocene at this site have not overtopped the barrier, which suggests that these tsunamis were likely only 2-3 m high. Title: Late Holocene Tsunami Deposits at Salt Creek, Washington, USA Author: Hutchinson, Ian, Peterson, Curt D., Sterling, Sarah L. Year: 2013 We interpret two thin sand layers in the estuarine marsh at Salt Creek, on the southern shore of the Strait of Juan de Fuca, as the products of tsunamis propagated by earthquakes at the Cascadia subduction zone. The sand layers extend for about 60 m along the left bank of the creek about 800 m from the mouth, and can be traced to the base of a nearby upland area. One layer is exposed in the creek bank about 400 m further upstream, but they are only patchily distributed in the rest of the central area of the marsh. Both layers contain brackish-marine epipsammic diatoms. The lower sand layer marks a sharp contact between intertidal peaty mud and overlying mud, perhaps reflecting modest coseismic subsidence in association with tsunami deposition, but little or no change in the bracketing sediment occurs in association with the upper sand layer. The ages of the sand layers are not closely constrained, but were most likely deposited by tsunamis generated by great earthquakes at the Cascadia subduction zone about 1650 and 1300 years ago. The Cascadia great earthquake of AD1700 may have induced slight subsidence in the marsh, but no tsunami deposit was detected at the inferred contact. The absence of deposits from the marsh immediately inland of the 4 m-high barrier beach indicates that the largest tsunamis in the late Holocene at this site have not overtopped the barrier, which suggests that these tsunamis were likely only 2-3 m high. Close

• 9. [Article] Probabilistic Tsunami Hazard Assessment at Seaside, Oregon, for Near- and Far-Field Seismic Sources

  The first probabilistic tsunami flooding maps have been developed. The methodology, called probabilistic tsunami hazard assessment (PTHA), integrates tsunami inundation modeling with methods of probabilistic ...

  Citation × Citation Citation Abstract Copy Title: Probabilistic Tsunami Hazard Assessment at Seaside, Oregon, for Near- and Far-Field Seismic Sources Author: González, Frank, Geist, Eric L., Jaffe, Bruce, Kânoğlu, Utku, Mofjeld, Harold O., Synolakis, Costas, Titov, Vasily V., Arcas, Diego Rodriguez, Bellomo, Douglas, Carlton, David, Horning, Thomas, Johnson, Jeff, Newman, Jean, Parsons, Thomas, Peters, Robert, Peterson, Curt D., Priest, George, Venturato, Angie, Weber, Joseph, Wong, Florence L., Yalçıner, Ahmet Year: 2009 The first probabilistic tsunami flooding maps have been developed. The methodology, called probabilistic tsunami hazard assessment (PTHA), integrates tsunami inundation modeling with methods of probabilistic seismic hazard assessment (PSHA). Application of the methodology to Seaside, Oregon, has yielded estimates of the spatial distribution of 100- and 500-year maximum tsunami amplitudes, i.e., amplitudes with 1% and 0.2% annual probability of exceedance. The 100-year tsunami is generated most frequently by far-field sources in the Alaska-Aleutian Subduction Zone and is characterized by maximum amplitudes that do not exceed 4 m, with an inland extent of less than 500 m. In contrast, the 500-year tsunami is dominated by local sources in the Cascadia Subduction Zone and is characterized by maximum amplitudes in excess of 10 m and an inland extent of more than 1 km. The primary sources of uncertainty in these results include those associated with interevent time estimates, modeling of background sea level, and accounting for temporal changes in bathymetry and topography. Nonetheless, PTHA represents an important contribution to tsunami hazard assessment techniques; viewed in the broader context of risk analysis, PTHA provides a method for quantifying estimates of the likelihood and severity of the tsunami hazard, which can then be combined with vulnerability and exposure to yield estimates of tsunami risk. Title: Probabilistic Tsunami Hazard Assessment at Seaside, Oregon, for Near- and Far-Field Seismic Sources Author: González, Frank, Geist, Eric L., Jaffe, Bruce, Kânoğlu, Utku, Mofjeld, Harold O., Synolakis, Costas, Titov, Vasily V., Arcas, Diego Rodriguez, Bellomo, Douglas, Carlton, David, Horning, Thomas, Johnson, Jeff, Newman, Jean, Parsons, Thomas, Peters, Robert, Peterson, Curt D., Priest, George, Venturato, Angie, Weber, Joseph, Wong, Florence L., Yalçıner, Ahmet Year: 2009 The first probabilistic tsunami flooding maps have been developed. The methodology, called probabilistic tsunami hazard assessment (PTHA), integrates tsunami inundation modeling with methods of probabilistic seismic hazard assessment (PSHA). Application of the methodology to Seaside, Oregon, has yielded estimates of the spatial distribution of 100- and 500-year maximum tsunami amplitudes, i.e., amplitudes with 1% and 0.2% annual probability of exceedance. The 100-year tsunami is generated most frequently by far-field sources in the Alaska-Aleutian Subduction Zone and is characterized by maximum amplitudes that do not exceed 4 m, with an inland extent of less than 500 m. In contrast, the 500-year tsunami is dominated by local sources in the Cascadia Subduction Zone and is characterized by maximum amplitudes in excess of 10 m and an inland extent of more than 1 km. The primary sources of uncertainty in these results include those associated with interevent time estimates, modeling of background sea level, and accounting for temporal changes in bathymetry and topography. Nonetheless, PTHA represents an important contribution to tsunami hazard assessment techniques; viewed in the broader context of risk analysis, PTHA provides a method for quantifying estimates of the likelihood and severity of the tsunami hazard, which can then be combined with vulnerability and exposure to yield estimates of tsunami risk. Close

• 10. [Article] Bridge Seismic Retrofit Measures Considering Subduction Zone Earthquakes

  Over the years, earthquakes have exposed the vulnerability of reinforced concrete structures under seismic loads. The recent occurrence of highly devastating earthquakes near instrumented regions, e.g. ...

  Citation × Citation Citation Abstract Copy Title: Bridge Seismic Retrofit Measures Considering Subduction Zone Earthquakes Author: Dusicka, Peter, Bazaez, Ramiro, Knoles, Sarah Year: 2015 Over the years, earthquakes have exposed the vulnerability of reinforced concrete structures under seismic loads. The recent occurrence of highly devastating earthquakes near instrumented regions, e.g. 2010 Maule, Chile and 2011 Tohoku, Japan, has demonstrated the catastrophic impact of such natural force upon reinforced concrete structures. Research was conducted to investigate the effect of subduction zone earthquakes on structural damage. The study suggests that large magnitude ground motions of long duration have the potential of significantly increasing the number of inelastic excursions and consequently incur more extensive structural damage as compared to ground motions with similar elastic spectral demands but of shorter duration. This increase in demand plays a crucial role in the Pacific Northwest where a mega subduction zone earthquake is impending. Typical reinforced concrete bridge bents constructed in the 1950 to mid-1970 in the State of Oregon were designed and built with minimum seismic considerations. This resulted in inadequate detailing within plastic hinge zones, leaving numerous RC bents highly susceptible to damage following an earthquake. In this study, the cyclic performance of an as-built RC square column and a reinforced concrete bridge bent retrofitted using buckling restrained braces (BRBs) was experimentally evaluated using quasi-static cyclic loading protocols aiming to reflect subduction zone earthquake demands up to displacement ductility. The buckling restrained braces were designed as replaceable elements in order to take the earthquake-induced energy and dissipate it through nonlinear hysteretic behavior. Two BRB designs were considered in the study in an effort to assess the influence of BRB stiffness on the overall structural performance. The results of these large-scale experiments successfully demonstrated the effectiveness of utilizing buckling restrained braces for achieving high displacement ductility of the retrofitted structure, while also controlling the damage of the existing vulnerable reinforced concrete bent up to the design performance levels. The potential of improving the overall seismic behavior and the design performance levels with BRBs offers structural design professionals a viable method for performance driven retrofit of reinforced concrete bents. Title: Bridge Seismic Retrofit Measures Considering Subduction Zone Earthquakes Author: Dusicka, Peter, Bazaez, Ramiro, Knoles, Sarah Year: 2015 Over the years, earthquakes have exposed the vulnerability of reinforced concrete structures under seismic loads. The recent occurrence of highly devastating earthquakes near instrumented regions, e.g. 2010 Maule, Chile and 2011 Tohoku, Japan, has demonstrated the catastrophic impact of such natural force upon reinforced concrete structures. Research was conducted to investigate the effect of subduction zone earthquakes on structural damage. The study suggests that large magnitude ground motions of long duration have the potential of significantly increasing the number of inelastic excursions and consequently incur more extensive structural damage as compared to ground motions with similar elastic spectral demands but of shorter duration. This increase in demand plays a crucial role in the Pacific Northwest where a mega subduction zone earthquake is impending. Typical reinforced concrete bridge bents constructed in the 1950 to mid-1970 in the State of Oregon were designed and built with minimum seismic considerations. This resulted in inadequate detailing within plastic hinge zones, leaving numerous RC bents highly susceptible to damage following an earthquake. In this study, the cyclic performance of an as-built RC square column and a reinforced concrete bridge bent retrofitted using buckling restrained braces (BRBs) was experimentally evaluated using quasi-static cyclic loading protocols aiming to reflect subduction zone earthquake demands up to displacement ductility. The buckling restrained braces were designed as replaceable elements in order to take the earthquake-induced energy and dissipate it through nonlinear hysteretic behavior. Two BRB designs were considered in the study in an effort to assess the influence of BRB stiffness on the overall structural performance. The results of these large-scale experiments successfully demonstrated the effectiveness of utilizing buckling restrained braces for achieving high displacement ductility of the retrofitted structure, while also controlling the damage of the existing vulnerable reinforced concrete bent up to the design performance levels. The potential of improving the overall seismic behavior and the design performance levels with BRBs offers structural design professionals a viable method for performance driven retrofit of reinforced concrete bents. Close