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• 31. [Article] Appendix C—Deformation Models for UCERF3

  This document describes efforts to best characterize seismogenic deformation in and near California. The rate of hazardous earthquakes in California is expected to be proportional to deformation rates; ...

  Citation × Citation Citation Abstract Copy Title: Appendix C—Deformation Models for UCERF3 Author: Parsons, Tom, Johnson, Kaj M., Bird, Peter, Bormann, Jayne, Dawson, Timothy E., Field, Edward H., Hammond, William C., Herring, Thomas A., McCaffrey, Robert, Shen, Zheng-kang, Thatcher, Wayne R., Weldon, Ray J., II, Zeng, Yuehua Year: 2013 This document describes efforts to best characterize seismogenic deformation in and near California. The rate of hazardous earthquakes in California is expected to be proportional to deformation rates; in particular, the rates at which faults slip. Fault slip rates are determined from offsets of geologic and geomorphic features of measured age and by modeling geodetically determined surface displacement rates. Extensive use of geodesy in the form of Global Positioning System (GPS) observations is a new feature brought into the Working Group on California Earthquake Probabilities (WGCEP) forecasts for the Uniform California Earthquake Rupture Forecast, version 3 (UCERF3) model. Geodetic measurements are potentially more spatially comprehensive than geologic offset observations, which can be clustered. Applying either type of data is subject to considerable uncertainty. Geologic observations have dating and other measurement errors, and they often must be extrapolated long distances on fault sections. However, geodetic observations require a modeling step to translate them into estimates of fault slip rate, and they have poor resolution on closely spaced, locked faults. Details about fault slip rates from geologic offsets are presented in appendix B (this report). In this appendix we look at three deformation models that use geologic and geodetic constraints and compare/contrast them with the UCERF3 geological model and the UCERF2 deformation model. We present models, results, and evaluation for their use in the UCERF3 forecast. Title: Appendix C—Deformation Models for UCERF3 Author: Parsons, Tom, Johnson, Kaj M., Bird, Peter, Bormann, Jayne, Dawson, Timothy E., Field, Edward H., Hammond, William C., Herring, Thomas A., McCaffrey, Robert, Shen, Zheng-kang, Thatcher, Wayne R., Weldon, Ray J., II, Zeng, Yuehua Year: 2013 This document describes efforts to best characterize seismogenic deformation in and near California. The rate of hazardous earthquakes in California is expected to be proportional to deformation rates; in particular, the rates at which faults slip. Fault slip rates are determined from offsets of geologic and geomorphic features of measured age and by modeling geodetically determined surface displacement rates. Extensive use of geodesy in the form of Global Positioning System (GPS) observations is a new feature brought into the Working Group on California Earthquake Probabilities (WGCEP) forecasts for the Uniform California Earthquake Rupture Forecast, version 3 (UCERF3) model. Geodetic measurements are potentially more spatially comprehensive than geologic offset observations, which can be clustered. Applying either type of data is subject to considerable uncertainty. Geologic observations have dating and other measurement errors, and they often must be extrapolated long distances on fault sections. However, geodetic observations require a modeling step to translate them into estimates of fault slip rate, and they have poor resolution on closely spaced, locked faults. Details about fault slip rates from geologic offsets are presented in appendix B (this report). In this appendix we look at three deformation models that use geologic and geodetic constraints and compare/contrast them with the UCERF3 geological model and the UCERF2 deformation model. We present models, results, and evaluation for their use in the UCERF3 forecast. Close

• 32. [Article] Central Cascadia Subduction Zone Creep

  Central Cascadia between 43ºN and 46ºN has reduced interseismic uplift observed in geodetic data and coseismic subsidence seen in multiple thrust earthquakes, suggesting elevated persistent fault creep ...

  Citation × Citation Citation Abstract Copy Title: Central Cascadia Subduction Zone Creep Author: Schmalzle, Gina M., McCaffrey, Robert, Creager, Kenneth C. Year: 2014 Central Cascadia between 43ºN and 46ºN has reduced interseismic uplift observed in geodetic data and coseismic subsidence seen in multiple thrust earthquakes, suggesting elevated persistent fault creep in this section of the subduction zone. We estimate subduction thrust "decade-scale" locking and crustal block rotations from three-component continuous Global Positioning System (GPS) time series from 1997 to 2013, as well as 80 year tide gauge and leveling-derived uplift rates. Geodetic observations indicatecoastal central Oregon is rising at a slower rate than coastal Washington, southern Oregon and northern California. Modeled locking distributions suggest a wide locking transition zone that extends inland undercentral Oregon. Paleoseismic records of multiple great earthquakes along Cascadia indicate less subsidence in central Oregon. The Cascade thrust under central Oregon may be partially creeping for at least 6500 years(the length of the paleoseismic record) reducing interseismic uplift and resulting in reduced coseismic subsidence. Large accretions of Eocene age basalt (Siletzia terrane) between 43ºN and 46ºN may be less perme-able compared to surrounding terranes, potentially increasing pore fluid pressures along the fault interface resulting in a wide zone of persistent fault creep. In a separate inversion, three-component GPS time series from 1 July 2005 to 1 January 2011 are used to estimate upper plate deformation, locking between slow-slip events (SSEs), slip from 16 SSEs and an earthquake mechanism. Cumulative SSEs and tectonic tremor are weakest between 43ºN and 46ºN where partial fault creep is increased and Siletzia terrane is thick, suggesting that surrounding rock properties may influence the mode of slip. Title: Central Cascadia Subduction Zone Creep Author: Schmalzle, Gina M., McCaffrey, Robert, Creager, Kenneth C. Year: 2014 Central Cascadia between 43ºN and 46ºN has reduced interseismic uplift observed in geodetic data and coseismic subsidence seen in multiple thrust earthquakes, suggesting elevated persistent fault creep in this section of the subduction zone. We estimate subduction thrust "decade-scale" locking and crustal block rotations from three-component continuous Global Positioning System (GPS) time series from 1997 to 2013, as well as 80 year tide gauge and leveling-derived uplift rates. Geodetic observations indicatecoastal central Oregon is rising at a slower rate than coastal Washington, southern Oregon and northern California. Modeled locking distributions suggest a wide locking transition zone that extends inland undercentral Oregon. Paleoseismic records of multiple great earthquakes along Cascadia indicate less subsidence in central Oregon. The Cascade thrust under central Oregon may be partially creeping for at least 6500 years(the length of the paleoseismic record) reducing interseismic uplift and resulting in reduced coseismic subsidence. Large accretions of Eocene age basalt (Siletzia terrane) between 43ºN and 46ºN may be less perme-able compared to surrounding terranes, potentially increasing pore fluid pressures along the fault interface resulting in a wide zone of persistent fault creep. In a separate inversion, three-component GPS time series from 1 July 2005 to 1 January 2011 are used to estimate upper plate deformation, locking between slow-slip events (SSEs), slip from 16 SSEs and an earthquake mechanism. Cumulative SSEs and tectonic tremor are weakest between 43ºN and 46ºN where partial fault creep is increased and Siletzia terrane is thick, suggesting that surrounding rock properties may influence the mode of slip. Close

• 33. [Article] A Tale of Three Sisters: Reconstructing the Holocene glacial history and paleoclimate record at Three Sisters Volcanoes, Oregon, United States

  At least four glacial stands occurred since 6.5 ka B.P. based on moraines located on the eastern flanks of the Three Sisters Volcanoes and the northern flanks of Broken Top Mountain in the Central Oregon ...

  Citation × Citation Citation Abstract Copy Title: A Tale of Three Sisters: Reconstructing the Holocene glacial history and paleoclimate record at Three Sisters Volcanoes, Oregon, United States Author: Marcott, Shaun Andrew Year: 2005 At least four glacial stands occurred since 6.5 ka B.P. based on moraines located on the eastern flanks of the Three Sisters Volcanoes and the northern flanks of Broken Top Mountain in the Central Oregon Cascades. The youngest of these advances was the Little Ice Age (LIA) glaciation, which reached its maximum advance 150-200 yrs. B.P. and is defined by the large sharp crested and unvegetated moraines adjacent to the modern glaciers. In isolated locations less than 100 m downslope from these moraines, a second set of sparsely vegetated lateral moraines marks the Late-Neoglacial stand of the glaciers between 2.1 ± 0.4 and 7.7 ka B.P, A third set of Early-Neoglacial end moraines is 300-700 meters downslope of the modern glacier termini, and postdates 7.7 ka B.P. From SST temperature data (Barron et al., 2003) and a speleothem record (Vacco, 2003), we infer that this advance occurred between 4.5 and 6.5 ka B.P. Finally, the Fountonnor stand is marked by moraines 500-900 meters downslope of the modern glacier termini, and we infer these are latest Pleistocene or early Holocene. Modem equilibrium line altitudes (ELAs) at the Three Sisters and Broken Top are approximately 2500 - 2600 m. During the LIA, the ELAs were 40 - 180 m lower, requiring cooler mean summer temperatures by 0.7 - 1.0°C and winter snowfall to increase by 10 - 60 cm water equivalent. The average Early Neoglacial and Fountonnor ELAs were 130 - 300 m and 290 - 320 m lower than modem glaciers, respectively, requiring air temperatures to be 0.7 - 1.6°C and 1.5 - 1.7°C cooler during the summer and winter snowfall to be 40 - 100 cm water equivalent and 90 - 100 cm water equivalent greater. Title: A Tale of Three Sisters: Reconstructing the Holocene glacial history and paleoclimate record at Three Sisters Volcanoes, Oregon, United States Author: Marcott, Shaun Andrew Year: 2005 At least four glacial stands occurred since 6.5 ka B.P. based on moraines located on the eastern flanks of the Three Sisters Volcanoes and the northern flanks of Broken Top Mountain in the Central Oregon Cascades. The youngest of these advances was the Little Ice Age (LIA) glaciation, which reached its maximum advance 150-200 yrs. B.P. and is defined by the large sharp crested and unvegetated moraines adjacent to the modern glaciers. In isolated locations less than 100 m downslope from these moraines, a second set of sparsely vegetated lateral moraines marks the Late-Neoglacial stand of the glaciers between 2.1 ± 0.4 and 7.7 ka B.P, A third set of Early-Neoglacial end moraines is 300-700 meters downslope of the modern glacier termini, and postdates 7.7 ka B.P. From SST temperature data (Barron et al., 2003) and a speleothem record (Vacco, 2003), we infer that this advance occurred between 4.5 and 6.5 ka B.P. Finally, the Fountonnor stand is marked by moraines 500-900 meters downslope of the modern glacier termini, and we infer these are latest Pleistocene or early Holocene. Modem equilibrium line altitudes (ELAs) at the Three Sisters and Broken Top are approximately 2500 - 2600 m. During the LIA, the ELAs were 40 - 180 m lower, requiring cooler mean summer temperatures by 0.7 - 1.0°C and winter snowfall to increase by 10 - 60 cm water equivalent. The average Early Neoglacial and Fountonnor ELAs were 130 - 300 m and 290 - 320 m lower than modem glaciers, respectively, requiring air temperatures to be 0.7 - 1.6°C and 1.5 - 1.7°C cooler during the summer and winter snowfall to be 40 - 100 cm water equivalent and 90 - 100 cm water equivalent greater. Close

• 34. [Article] Relationships Among Physical Properties as Indicators of High Temperature Deformation or Post-Shock Thermal Annealing in Ordinary Chondrites

  Collisions and attendant shock compaction must have been important for the accretion and lithification of planetesimals, including the parent bodies of chondrites, but the conditions under which these ...

  Citation × Citation Citation Abstract Copy Title: Relationships Among Physical Properties as Indicators of High Temperature Deformation or Post-Shock Thermal Annealing in Ordinary Chondrites Author: Friedrich, John M., Ruzicka, Alex, Macke, Robert J., Thostenson, James O. Year: 2017 Collisions and attendant shock compaction must have been important for the accretion and lithification of planetesimals, including the parent bodies of chondrites, but the conditions under which these occurred are not well constrained. A simple model for the compaction of chondrites predicts that shock intensity as recorded by shock stage should be related to porosity and grain fabric. To test this model, we studied sixteen ordinary chondrites of different groups (H, L, LL) using X-ray computed microtomography (μCT) to measure porosity and metal fabric, ideal gas pycnometry and 3D laser scanning to determine porosity, and optical microscopy (OM) to determine shock stage. These included a subsample of six chondrites previously studied using transmission electron microscopy (TEM) to characterize microstructures in olivine. Combining with previous data, results support the simple model in general, but not for chondrites with low shock-porosity-foliation (low-SPF chondrites). These include Kernouvé (H6), Portales Valley (H6/7), Butsura (H6), Park (L6), GRO 85209 (L6), Estacado (H6), MIL 99301 (LL6), Spade (H6), and Queen's Mercy (H6), among others. The data for these meteorites are best explained by high ambient heat during or after shock. Low-SPF chondrites tend to have older 40Ar/39Ar ages (∼4435–4526 Ma) than other, non-low-SPF type 6 chondrites in this study. We conclude that the H, L, and LL asteroids all were shock-compacted at an early stage while warm, with collisions occurring during metamorphic heating of the parent bodies. Results ultimately bear on whether chondrite parent bodies have internal structures more akin to a metamorphosed onion shell or metamorphosed rubble pile, and on the nature of accretion and lithification processes for planetesimals. © 2017 Elsevier Ltd Title: Relationships Among Physical Properties as Indicators of High Temperature Deformation or Post-Shock Thermal Annealing in Ordinary Chondrites Author: Friedrich, John M., Ruzicka, Alex, Macke, Robert J., Thostenson, James O. Year: 2017 Collisions and attendant shock compaction must have been important for the accretion and lithification of planetesimals, including the parent bodies of chondrites, but the conditions under which these occurred are not well constrained. A simple model for the compaction of chondrites predicts that shock intensity as recorded by shock stage should be related to porosity and grain fabric. To test this model, we studied sixteen ordinary chondrites of different groups (H, L, LL) using X-ray computed microtomography (μCT) to measure porosity and metal fabric, ideal gas pycnometry and 3D laser scanning to determine porosity, and optical microscopy (OM) to determine shock stage. These included a subsample of six chondrites previously studied using transmission electron microscopy (TEM) to characterize microstructures in olivine. Combining with previous data, results support the simple model in general, but not for chondrites with low shock-porosity-foliation (low-SPF chondrites). These include Kernouvé (H6), Portales Valley (H6/7), Butsura (H6), Park (L6), GRO 85209 (L6), Estacado (H6), MIL 99301 (LL6), Spade (H6), and Queen's Mercy (H6), among others. The data for these meteorites are best explained by high ambient heat during or after shock. Low-SPF chondrites tend to have older 40Ar/39Ar ages (∼4435–4526 Ma) than other, non-low-SPF type 6 chondrites in this study. We conclude that the H, L, and LL asteroids all were shock-compacted at an early stage while warm, with collisions occurring during metamorphic heating of the parent bodies. Results ultimately bear on whether chondrite parent bodies have internal structures more akin to a metamorphosed onion shell or metamorphosed rubble pile, and on the nature of accretion and lithification processes for planetesimals. © 2017 Elsevier Ltd Close

• 35. [Article] Late Holocene Paleoseismicity along the Northern Oregon Coast

  Marsh paleoseismological studies were conducted in four bays (Necanicum, Nestucca, Siletz, and Yaquina) along the northern Oregon coast and compared with completed studies in two other bays (Netarts and ...

  Citation × Citation Citation Abstract Copy Title: Late Holocene Paleoseismicity along the Northern Oregon Coast Author: Darienzo, Mark Edward Year: 1991 Marsh paleoseismological studies were conducted in four bays (Necanicum, Nestucca, Siletz, and Yaquina) along the northern Oregon coast and compared with completed studies in two other bays (Netarts and Alsea). Coseismically buried peats were identified in all bays, based on 1) abrupt contacts, decreases in organic content, increases in sand content, increases in beach sand, and changes in diatom assemblages, all from the peat to the overlying sediments, 2) distinct sandy layers and key plant macrofossils, such as Triglochin, above the buried peat, and 3) widespread correlation of the buried peats within the bay. The stratigraphy and the ages and depths of the top six coseismically buried peats were compared between bays. The following similarities were noted: 1) All bays recorded five burial events in the top 2.6 meters within the last 2200 years. 2) Six burial events were recorded in six bays in the top 3.0 meters, except Alsea Bay (3.3 m), and all six events occurred within the last 2600 years except Yaquina (2780 years). 3) The depth to the top of each buried peat in the bays is consistent, falling within discrete ranges, except for the top two events at Yaquina. 4) Distinct sandy layers (tsunami-deposited) are present over the topmost buried peat in all bays except Yaquina and over the 4th in all bays except Yaquina and Nestucca. 5) Distinct tsunami-deposited sandy layers are absent over the third buried peat in Netarts, Nestucca, Siletz, Alsea, and possibly Yaquina, but present at Necanicum. The evidence strongly suggests synchroneity of coseismic events between the Necanicum River and Alsea Bay (a distance of 175 km), with the exception of the 2nd and 6th event. The 6th coseismic event would be synchronous between Alsea and Netarts, a distance of 105 km. The support for synchroneity of the 2nd event is weak. Synchroneity of coseismic burial events on the northern Oregon coast would argue for paleomagnitudes of at least 8.1 Mw, given a minimum rupture width of 50 km and a rupture length of 105 km. The paleomagnitudes were determined using the moment magnitude equation, Mw = 2/3 IOg10 Mo - 10.7 where Mo = shear modulus x rupture area x seismic slip. The seismic slip is estimated from a minimum recurrence interval of 300 years and a minimum convergence rate of 3.5 cm/yr.Marsh paleoseismological studies were conducted in four bays (Necanicum, Nestucca, Siletz, and Yaquina) along the northern Oregon coast and compared with completed studies in two other bays (Netarts and Alsea). Coseismically buried peats were identified in all bays, based on 1) abrupt contacts, decreases in organic content, increases in sand content, increases in beach sand, and changes in diatom assemblages, all from the peat to the overlying sediments, 2) distinct sandy layers and key plant macrofossils, such as Triglochin, above the buried peat, and 3) widespread correlation of the buried peats within the bay. The stratigraphy and the ages and depths of the top six coseismically buried peats were compared between bays. The following similarities were noted: 1) All bays recorded five burial events in the top 2.6 meters within the last 2200 years. 2) Six burial events were recorded in six bays in the top 3.0 meters, except Alsea Bay (3.3 m), and all six events occurred within the last 2600 years except Yaquina (2780 years). 3) The depth to the top of each buried peat in the bays is consistent, falling within discrete ranges, except for the top two events at Yaquina. 4) Distinct sandy layers (tsunami-deposited) are present over the topmost buried peat in all bays except Yaquina and over the 4th in all bays except Yaquina and Nestucca. 5) Distinct tsunami-deposited sandy layers are absent over the third buried peat in Netarts, Nestucca, Siletz, Alsea, and possibly Yaquina, but present at Necanicum. The evidence strongly suggests synchroneity of coseismic events between the Necanicum River and Alsea Bay (a distance of 175 km), with the exception of the 2nd and 6th event. The 6th coseismic event would be synchronous between Alsea and Netarts, a distance of 105 km. The support for synchroneity of the 2nd event is weak. Synchroneity of coseismic burial events on the northern Oregon coast would argue for paleomagnitudes of at least 8.1 Mw, given a minimum rupture width of 50 km and a rupture length of 105 km. The paleomagnitudes were determined using the moment magnitude equation, Mw = 2/3 IOg10 Mo - 10.7 where Mo = shear modulus x rupture area x seismic slip. The seismic slip is estimated from a minimum recurrence interval of 300 years and a minimum convergence rate of 3.5 cm/yr. Title: Late Holocene Paleoseismicity along the Northern Oregon Coast Author: Darienzo, Mark Edward Year: 1991 Marsh paleoseismological studies were conducted in four bays (Necanicum, Nestucca, Siletz, and Yaquina) along the northern Oregon coast and compared with completed studies in two other bays (Netarts and Alsea). Coseismically buried peats were identified in all bays, based on 1) abrupt contacts, decreases in organic content, increases in sand content, increases in beach sand, and changes in diatom assemblages, all from the peat to the overlying sediments, 2) distinct sandy layers and key plant macrofossils, such as Triglochin, above the buried peat, and 3) widespread correlation of the buried peats within the bay. The stratigraphy and the ages and depths of the top six coseismically buried peats were compared between bays. The following similarities were noted: 1) All bays recorded five burial events in the top 2.6 meters within the last 2200 years. 2) Six burial events were recorded in six bays in the top 3.0 meters, except Alsea Bay (3.3 m), and all six events occurred within the last 2600 years except Yaquina (2780 years). 3) The depth to the top of each buried peat in the bays is consistent, falling within discrete ranges, except for the top two events at Yaquina. 4) Distinct sandy layers (tsunami-deposited) are present over the topmost buried peat in all bays except Yaquina and over the 4th in all bays except Yaquina and Nestucca. 5) Distinct tsunami-deposited sandy layers are absent over the third buried peat in Netarts, Nestucca, Siletz, Alsea, and possibly Yaquina, but present at Necanicum. The evidence strongly suggests synchroneity of coseismic events between the Necanicum River and Alsea Bay (a distance of 175 km), with the exception of the 2nd and 6th event. The 6th coseismic event would be synchronous between Alsea and Netarts, a distance of 105 km. The support for synchroneity of the 2nd event is weak. Synchroneity of coseismic burial events on the northern Oregon coast would argue for paleomagnitudes of at least 8.1 Mw, given a minimum rupture width of 50 km and a rupture length of 105 km. The paleomagnitudes were determined using the moment magnitude equation, Mw = 2/3 IOg10 Mo - 10.7 where Mo = shear modulus x rupture area x seismic slip. The seismic slip is estimated from a minimum recurrence interval of 300 years and a minimum convergence rate of 3.5 cm/yr.Marsh paleoseismological studies were conducted in four bays (Necanicum, Nestucca, Siletz, and Yaquina) along the northern Oregon coast and compared with completed studies in two other bays (Netarts and Alsea). Coseismically buried peats were identified in all bays, based on 1) abrupt contacts, decreases in organic content, increases in sand content, increases in beach sand, and changes in diatom assemblages, all from the peat to the overlying sediments, 2) distinct sandy layers and key plant macrofossils, such as Triglochin, above the buried peat, and 3) widespread correlation of the buried peats within the bay. The stratigraphy and the ages and depths of the top six coseismically buried peats were compared between bays. The following similarities were noted: 1) All bays recorded five burial events in the top 2.6 meters within the last 2200 years. 2) Six burial events were recorded in six bays in the top 3.0 meters, except Alsea Bay (3.3 m), and all six events occurred within the last 2600 years except Yaquina (2780 years). 3) The depth to the top of each buried peat in the bays is consistent, falling within discrete ranges, except for the top two events at Yaquina. 4) Distinct sandy layers (tsunami-deposited) are present over the topmost buried peat in all bays except Yaquina and over the 4th in all bays except Yaquina and Nestucca. 5) Distinct tsunami-deposited sandy layers are absent over the third buried peat in Netarts, Nestucca, Siletz, Alsea, and possibly Yaquina, but present at Necanicum. The evidence strongly suggests synchroneity of coseismic events between the Necanicum River and Alsea Bay (a distance of 175 km), with the exception of the 2nd and 6th event. The 6th coseismic event would be synchronous between Alsea and Netarts, a distance of 105 km. The support for synchroneity of the 2nd event is weak. Synchroneity of coseismic burial events on the northern Oregon coast would argue for paleomagnitudes of at least 8.1 Mw, given a minimum rupture width of 50 km and a rupture length of 105 km. The paleomagnitudes were determined using the moment magnitude equation, Mw = 2/3 IOg10 Mo - 10.7 where Mo = shear modulus x rupture area x seismic slip. The seismic slip is estimated from a minimum recurrence interval of 300 years and a minimum convergence rate of 3.5 cm/yr. Close

• 36. [Article] Grounding Zone Processes: Ice Mechanics and Margin Lakes, Kamb Ice Stream and Whillans Ice Stream, West Antarctica

  The lateral "corners" where Kamb and Whillans Ice Streams (KIS and WIS) discharge into the Ross Ice Shelf share common geometries and ice mechanical settings. At both corners of the now-stagnant KIS outlet, ...

  Citation × Citation Citation Abstract Copy Title: Grounding Zone Processes: Ice Mechanics and Margin Lakes, Kamb Ice Stream and Whillans Ice Stream, West Antarctica Author: Fried, Mason Joseph Year: 2013 The lateral "corners" where Kamb and Whillans Ice Streams (KIS and WIS) discharge into the Ross Ice Shelf share common geometries and ice mechanical settings. At both corners of the now-stagnant KIS outlet, shear margins of apparently different ages confine regions with a relatively flat, smooth surface expression. These features are called the "Duckfoot" on the northern, right-lateral side and the "Goosefoot" on the other. It has been suggested, on evidence found in ice internal layers, that the flat ice terrains on KIS were afloat in the recent past, at a time when the ice stream grounding line was upstream of its present location. The overdeepening in the bed just upstream of the KIS grounding line supports this view of the past geometry. The right-lateral margin at the outlet of the currently active WIS, the location of Subglacial Lake Englehardt (SLE), appears to have many similarities with the right lateral margin of KIS, though with a less developed looking inboard margin. This paper presents a mechanical analysis using surface and bed topography and velocity datasets comparing the Duckfoot flat ice terrain with the terrain around Subglacial Lake Englehardt. At both locations mechanical thinning along shear margins and lows in the bed topography redirects basal water routing towards the features. Here, I consider the history of these features and their role in ice stream variability by comparison of the relict and modern features and via numerical modeling of ice shelf grounding and ungrounding in response to variations in ice flow. We propose two scenarios for the development of flat ice terrains/subglacial lakes at the outlets of ice streams. In the first, development of a lake in the hydraulic potential low along a shear margin forces a margin jump as shearing develops along the inboard shore of the margin lake. This thesis presents evidence for an inboard (relative to the main outboard shear margin) zone of shear along the inboard shoreline of SLE, suggesting that subglacial lakes along shear margins are capable of facilitating shear margin jumps. In the second, grounding line advance around a relative low in the bed, creating adjacent margins along the lakeshores, forms a remnant lake. Discerning which of these scenarios is appropriate at the KIS outlet has implications for understanding the history of the ice stream grounding line. An ice flow model is used to place these local conditions in a regional context by studying the effect of internal perturbations, such as ice rise stagnation or inward margin jumps, on grounding line position. Bathymetry is important in determining ice stream flow in the ways that might not be otherwise realized in 1-D flow model studies. In the numerical modeling experiments, grounding line advance across the KIS outlet is mediated by the overdeepening in the bed and proceeds not in the direction of ice flow but transverse to flow. This finding adds complexity to both a flowline view of grounding line migration and the theory that grounding lines are unstable in the presence of inward sloping bed topography. Title: Grounding Zone Processes: Ice Mechanics and Margin Lakes, Kamb Ice Stream and Whillans Ice Stream, West Antarctica Author: Fried, Mason Joseph Year: 2013 The lateral "corners" where Kamb and Whillans Ice Streams (KIS and WIS) discharge into the Ross Ice Shelf share common geometries and ice mechanical settings. At both corners of the now-stagnant KIS outlet, shear margins of apparently different ages confine regions with a relatively flat, smooth surface expression. These features are called the "Duckfoot" on the northern, right-lateral side and the "Goosefoot" on the other. It has been suggested, on evidence found in ice internal layers, that the flat ice terrains on KIS were afloat in the recent past, at a time when the ice stream grounding line was upstream of its present location. The overdeepening in the bed just upstream of the KIS grounding line supports this view of the past geometry. The right-lateral margin at the outlet of the currently active WIS, the location of Subglacial Lake Englehardt (SLE), appears to have many similarities with the right lateral margin of KIS, though with a less developed looking inboard margin. This paper presents a mechanical analysis using surface and bed topography and velocity datasets comparing the Duckfoot flat ice terrain with the terrain around Subglacial Lake Englehardt. At both locations mechanical thinning along shear margins and lows in the bed topography redirects basal water routing towards the features. Here, I consider the history of these features and their role in ice stream variability by comparison of the relict and modern features and via numerical modeling of ice shelf grounding and ungrounding in response to variations in ice flow. We propose two scenarios for the development of flat ice terrains/subglacial lakes at the outlets of ice streams. In the first, development of a lake in the hydraulic potential low along a shear margin forces a margin jump as shearing develops along the inboard shore of the margin lake. This thesis presents evidence for an inboard (relative to the main outboard shear margin) zone of shear along the inboard shoreline of SLE, suggesting that subglacial lakes along shear margins are capable of facilitating shear margin jumps. In the second, grounding line advance around a relative low in the bed, creating adjacent margins along the lakeshores, forms a remnant lake. Discerning which of these scenarios is appropriate at the KIS outlet has implications for understanding the history of the ice stream grounding line. An ice flow model is used to place these local conditions in a regional context by studying the effect of internal perturbations, such as ice rise stagnation or inward margin jumps, on grounding line position. Bathymetry is important in determining ice stream flow in the ways that might not be otherwise realized in 1-D flow model studies. In the numerical modeling experiments, grounding line advance across the KIS outlet is mediated by the overdeepening in the bed and proceeds not in the direction of ice flow but transverse to flow. This finding adds complexity to both a flowline view of grounding line migration and the theory that grounding lines are unstable in the presence of inward sloping bed topography. Close

• 37. [Article] Quaternary Chronology and Stratigraphy of Mickey Springs, Oregon

  Mickey Springs in the Alvord Desert, southeast Oregon, is analogous to other Basin and Range hydrothermal systems where the requisite conditions of heat source and permeable pathways are met through crustal ...

  Citation × Citation Citation Abstract Copy Title: Quaternary Chronology and Stratigraphy of Mickey Springs, Oregon Author: Mowbray, Leslie Allen Year: 2015 Mickey Springs in the Alvord Desert, southeast Oregon, is analogous to other Basin and Range hydrothermal systems where the requisite conditions of heat source and permeable pathways are met through crustal thinning due to normal faulting. This study examines the morphology and lifespan of near-surface spring features through use of ground penetrating radar, thermoluminescence (TL) dating, and elevation modeling. Duration of hydrothermal activity at Mickey Springs has not previously been determined, and age determinations of sinter at the site are conflicting. The reason for and timing of this change in silica saturation in the hydrothermal fluid has not been resolved. Three morphologies of silica sinter deposition have been identified at Mickey Springs. These are (1) well-sorted, fine-grained sandstone with ripple marks, cross beds and preserved root casts, to poorly-sorted conglomerate of primarily basalt clasts, both cemented by coeval silica deposition, (2) large depressions (12-32 m diameter) rimmed with sinter, characterized by fine silt and clay blanketing a sinter apron and infilling the central depression, and (3) quaquaversal sinter mounds identified by outcropping pool-edge sinter typically surrounding a shallow depression of loose sediment. Silica-cemented sandstone and conglomerate were the first features formed by coeval hydrothermal processes at the site, and were emplaced prior to 30 kya as suggested by structural and stratigraphic relationships. Structure between two interacting fault tips may have constrained the extent of silica cementation. By 30 kya, a left-stepping fault oriented roughly north/south further constrained the near-surface permeable zone. TL dates from sediment stratigraphically below and above sinter aprons around mounds and depressions (former spring vents) indicate sinter deposition between 30 and 20 kya. Location of these features was dictated by development of the left-stepping fault. As pluvial Lake Alvord filled at the end of the Pleistocene, lake sediment filled most vents, which were largely inactive, with fine-grained silt and clay. Today, hydrothermal activity persists in two modes: (1) The current high-temperature springs, steam vents and mudpots concentrated in a 50 x 50 m area south of the sinter mounds and depressions, and (2) scattered springs and steam vents that exploit previous permeable pathways that once provided the hydrothermal fluid which precipitated the sinter aprons. Currently there is no active silica sinter deposition at Mickey Springs. Structures and stratigraphic relationships identified through this study favor a transport-limited and structurally controlled model of fluid transport. Sinter deposition is determined to have occurred before the most recent highstand of pluvial Lake Alvord. A climate driven model, where groundwater recharge from pluvial Lake Alvord circulates to a deep heat source and enhances spring discharge, is not supported by these findings, as no evidence was found for sinter precipitation after the drying of the lake. Future studies of other hydrothermal systems in the Basin and Range may reveal that permeable pathways along local structures are the primary drivers in this region. Title: Quaternary Chronology and Stratigraphy of Mickey Springs, Oregon Author: Mowbray, Leslie Allen Year: 2015 Mickey Springs in the Alvord Desert, southeast Oregon, is analogous to other Basin and Range hydrothermal systems where the requisite conditions of heat source and permeable pathways are met through crustal thinning due to normal faulting. This study examines the morphology and lifespan of near-surface spring features through use of ground penetrating radar, thermoluminescence (TL) dating, and elevation modeling. Duration of hydrothermal activity at Mickey Springs has not previously been determined, and age determinations of sinter at the site are conflicting. The reason for and timing of this change in silica saturation in the hydrothermal fluid has not been resolved. Three morphologies of silica sinter deposition have been identified at Mickey Springs. These are (1) well-sorted, fine-grained sandstone with ripple marks, cross beds and preserved root casts, to poorly-sorted conglomerate of primarily basalt clasts, both cemented by coeval silica deposition, (2) large depressions (12-32 m diameter) rimmed with sinter, characterized by fine silt and clay blanketing a sinter apron and infilling the central depression, and (3) quaquaversal sinter mounds identified by outcropping pool-edge sinter typically surrounding a shallow depression of loose sediment. Silica-cemented sandstone and conglomerate were the first features formed by coeval hydrothermal processes at the site, and were emplaced prior to 30 kya as suggested by structural and stratigraphic relationships. Structure between two interacting fault tips may have constrained the extent of silica cementation. By 30 kya, a left-stepping fault oriented roughly north/south further constrained the near-surface permeable zone. TL dates from sediment stratigraphically below and above sinter aprons around mounds and depressions (former spring vents) indicate sinter deposition between 30 and 20 kya. Location of these features was dictated by development of the left-stepping fault. As pluvial Lake Alvord filled at the end of the Pleistocene, lake sediment filled most vents, which were largely inactive, with fine-grained silt and clay. Today, hydrothermal activity persists in two modes: (1) The current high-temperature springs, steam vents and mudpots concentrated in a 50 x 50 m area south of the sinter mounds and depressions, and (2) scattered springs and steam vents that exploit previous permeable pathways that once provided the hydrothermal fluid which precipitated the sinter aprons. Currently there is no active silica sinter deposition at Mickey Springs. Structures and stratigraphic relationships identified through this study favor a transport-limited and structurally controlled model of fluid transport. Sinter deposition is determined to have occurred before the most recent highstand of pluvial Lake Alvord. A climate driven model, where groundwater recharge from pluvial Lake Alvord circulates to a deep heat source and enhances spring discharge, is not supported by these findings, as no evidence was found for sinter precipitation after the drying of the lake. Future studies of other hydrothermal systems in the Basin and Range may reveal that permeable pathways along local structures are the primary drivers in this region. Close

• 38. [Article] The West Tidewater Earthflow, Northern Oregon Coast Range

  The West Tidewater earthflow, one of the largest in Oregon's history, occurred in December of 1994. The earthflow is located approximately 15 km north of Jewel, Oregon near the summit ofthe Northern Oregon ...

  Citation × Citation Citation Abstract Copy Title: The West Tidewater Earthflow, Northern Oregon Coast Range Author: Sanford, Barry A. Year: 2014 The West Tidewater earthflow, one of the largest in Oregon's history, occurred in December of 1994. The earthflow is located approximately 15 km north of Jewel, Oregon near the summit ofthe Northern Oregon Coast Range Mountains. The earthflow is 900 m long and 250 m wide, giving it a surface area of 9 ha, or 22 acres. Volume is 3.5 million m3. The earthflow occurred in low strength, well-bedded, tuffaceous, carbonaceous, micaceous, clay-rich mudstone, and very fine-grained, feldspathic, clay-rich siltstone of the lower Miocene age Northrup Creek Formation. The soil clay fractions contain up to 90% smectite with indications ofhalloysite. This earthflow is a reactivation ofa 650-year-old landslide (C-14 dating of uncovered buried trees). The failure mode is examined using a Janbu slope analysis and includes double wedge failure near the headscarp. High soil pore water pressure is one of the major causes of this slope failure. Rainfall levels for October, November, and December of 1994 were twice the previous five-year average. Present day groundwater level within the basin is less than one meter below ground surface. The earthflow is partially controlled by two faults of regional extent that dissect the basin near the headscarp in NW-SE and NE-SW directions. The Inceptisol soils in the basin remain moist below 20 cm year around. Soil in the basin may have been further weakened due to loss of root strength following timber harvest on the site in 1991. Soil liquid limits range from 42% to 95%, with PI values ranging from 2% to 77%. Soil clay content ranges between 18% and 30%. Direct shear tests on the mudstone and siltstone bedrock in both drained and undrained conditions produced internal friction angles of 14-18°, with cohesion values of 4 - 8 kPa. Back calculation of study area soil strength using the modified Bishop method results in a residual friction angle of 20.7°. The failure mode ofthe earthflow is from the headscarp downward and is modeled using Janbu methods. The study includes a detailed topographic map and a failure analysis of the earthflow basin. Title: The West Tidewater Earthflow, Northern Oregon Coast Range Author: Sanford, Barry A. Year: 2014 The West Tidewater earthflow, one of the largest in Oregon's history, occurred in December of 1994. The earthflow is located approximately 15 km north of Jewel, Oregon near the summit ofthe Northern Oregon Coast Range Mountains. The earthflow is 900 m long and 250 m wide, giving it a surface area of 9 ha, or 22 acres. Volume is 3.5 million m3. The earthflow occurred in low strength, well-bedded, tuffaceous, carbonaceous, micaceous, clay-rich mudstone, and very fine-grained, feldspathic, clay-rich siltstone of the lower Miocene age Northrup Creek Formation. The soil clay fractions contain up to 90% smectite with indications ofhalloysite. This earthflow is a reactivation ofa 650-year-old landslide (C-14 dating of uncovered buried trees). The failure mode is examined using a Janbu slope analysis and includes double wedge failure near the headscarp. High soil pore water pressure is one of the major causes of this slope failure. Rainfall levels for October, November, and December of 1994 were twice the previous five-year average. Present day groundwater level within the basin is less than one meter below ground surface. The earthflow is partially controlled by two faults of regional extent that dissect the basin near the headscarp in NW-SE and NE-SW directions. The Inceptisol soils in the basin remain moist below 20 cm year around. Soil in the basin may have been further weakened due to loss of root strength following timber harvest on the site in 1991. Soil liquid limits range from 42% to 95%, with PI values ranging from 2% to 77%. Soil clay content ranges between 18% and 30%. Direct shear tests on the mudstone and siltstone bedrock in both drained and undrained conditions produced internal friction angles of 14-18°, with cohesion values of 4 - 8 kPa. Back calculation of study area soil strength using the modified Bishop method results in a residual friction angle of 20.7°. The failure mode ofthe earthflow is from the headscarp downward and is modeled using Janbu methods. The study includes a detailed topographic map and a failure analysis of the earthflow basin. Close

• 39. [Article] Arsenic in the Soils of Northwest Oregon

  One hundred and eighty-six soil samples from Northwest Oregon were tested for arsenic content. The highest values measured were 13.9 ppm in the A horizon (site C4) and 20.4 ppm in the B horizon (Site P4). ...

  Citation × Citation Citation Abstract Copy Title: Arsenic in the Soils of Northwest Oregon Author: Ricker, Tracy Ryan Year: 2013 One hundred and eighty-six soil samples from Northwest Oregon were tested for arsenic content. The highest values measured were 13.9 ppm in the A horizon (site C4) and 20.4 ppm in the B horizon (Site P4). Arsenic was not detected in 28 A horizon samples and 23 B horizon samples. Data are grouped based on the age and rock type of underlying bedrock. Lithologic groups with six or more data points were compared statistically to ascertain if groups are distinct. Analysis of Variance (ANOVA) multiple comparison tests indicate that the arsenic content of the Marine Sediments and Sedimentary Rocks group samples is distinguishable from the Quaternary Basalts group in the A horizon and all other groups in the B horizon. Kruskal-Wallis multiple comparison tests indicate that the arsenic content of the Marine Sediments and Sedimentary Rocks group is distinguishable from the Quaternary Basalts, Quaternary/ Tertiary Sediments and Sedimentary Rocks and Volcanic Sediments groups in both the A and B soil horizons. The ANOVA and Kruskal-Wallis tests compared A and B horizon data by lithologic group. The ANOVA shows the Marine Sediments and Sedimentary Rocks group in the A horizon is distinct from the Quaternary Basalts in the A and B horizon. The Kruskal-Wallis test yielded the same result. Per the ANOVA, the Marine Sediments and Sedimentary Rocks in the B horizon are distinct from all other tested groups. The Kruskal-Wallis test shows the Marine Sediments and Sedimentary Rocks group in the B horizon as distinct from the Quaternary Basalts, Quaternary/ Tertiary Sediments, and Volcanic Sediments groups in the A and B horizon. A K-means cluster analysis was used to group all available data independent of underlying bedrock. Three, four, and five group analyses were conducted, and the results of these tests were compared to the data grouped by underlying rock type. No correlation between the groups resulting from the K-means cluster analysis and groups based on underlying lithology was found. This analysis supports the creation of a map distinguishing arsenic content in the soils above Marine Sediments and Sedimentary Rocks group units from arsenic content in all other tested lithologic groups. The mean and standard deviations of these groups (in ppm) are: A horizon: Marine Sediments (6.09 ±2.66); other groups (3.10 ±3.19); B horizon: Marine Sediments (10.26 ±4.65); other groups (3.13, ±2.52). This analysis indicates that geologic context must be taken into account when determining background levels of naturally occurring arsenic in soils. Title: Arsenic in the Soils of Northwest Oregon Author: Ricker, Tracy Ryan Year: 2013 One hundred and eighty-six soil samples from Northwest Oregon were tested for arsenic content. The highest values measured were 13.9 ppm in the A horizon (site C4) and 20.4 ppm in the B horizon (Site P4). Arsenic was not detected in 28 A horizon samples and 23 B horizon samples. Data are grouped based on the age and rock type of underlying bedrock. Lithologic groups with six or more data points were compared statistically to ascertain if groups are distinct. Analysis of Variance (ANOVA) multiple comparison tests indicate that the arsenic content of the Marine Sediments and Sedimentary Rocks group samples is distinguishable from the Quaternary Basalts group in the A horizon and all other groups in the B horizon. Kruskal-Wallis multiple comparison tests indicate that the arsenic content of the Marine Sediments and Sedimentary Rocks group is distinguishable from the Quaternary Basalts, Quaternary/ Tertiary Sediments and Sedimentary Rocks and Volcanic Sediments groups in both the A and B soil horizons. The ANOVA and Kruskal-Wallis tests compared A and B horizon data by lithologic group. The ANOVA shows the Marine Sediments and Sedimentary Rocks group in the A horizon is distinct from the Quaternary Basalts in the A and B horizon. The Kruskal-Wallis test yielded the same result. Per the ANOVA, the Marine Sediments and Sedimentary Rocks in the B horizon are distinct from all other tested groups. The Kruskal-Wallis test shows the Marine Sediments and Sedimentary Rocks group in the B horizon as distinct from the Quaternary Basalts, Quaternary/ Tertiary Sediments, and Volcanic Sediments groups in the A and B horizon. A K-means cluster analysis was used to group all available data independent of underlying bedrock. Three, four, and five group analyses were conducted, and the results of these tests were compared to the data grouped by underlying rock type. No correlation between the groups resulting from the K-means cluster analysis and groups based on underlying lithology was found. This analysis supports the creation of a map distinguishing arsenic content in the soils above Marine Sediments and Sedimentary Rocks group units from arsenic content in all other tested lithologic groups. The mean and standard deviations of these groups (in ppm) are: A horizon: Marine Sediments (6.09 ±2.66); other groups (3.10 ±3.19); B horizon: Marine Sediments (10.26 ±4.65); other groups (3.13, ±2.52). This analysis indicates that geologic context must be taken into account when determining background levels of naturally occurring arsenic in soils. Close

• 40. [Article] Coastal Eolian Sand-Ramp Development Related to Paleo-Sea-Level Changes during the Latest Pleistocene and Holocene (21–0 ka) in San Miguel Island, California, U.S.A.

  Coastal eolian sand ramps (5–130 m elevation) on the northern slope (windward) side of the small San Miguel Island (13 km in W-E length) range in age from late Pleistocene to modern time, though a major ...

  Citation × Citation Citation Abstract Copy Title: Coastal Eolian Sand-Ramp Development Related to Paleo-Sea-Level Changes during the Latest Pleistocene and Holocene (21–0 ka) in San Miguel Island, California, U.S.A. Author: Peterson, Curt D., Erlandson, Jon M., Stock, Errol, Hostetler, Steve W., Price, David M. Year: 2017 Coastal eolian sand ramps (5–130 m elevation) on the northern slope (windward) side of the small San Miguel Island (13 km in W-E length) range in age from late Pleistocene to modern time, though a major hiatus in sand-ramp growth occurred during the early Holocene marine transgression (16–9 ka). The Holocene sand ramps (1–5 m measured thicknesses) currently lack large dune forms, thereby representing deflated erosional remnants, locally covering thicker late Pleistocene sand-ramp deposits. The ramp sand was initially supplied from the adjacent island-shelf platform, extending about 20 km north of the present coastline. The sand-ramp deposits and interbedded loess soils were 14C dated using 112 samples from 32 archaeological sites and other geologic sections. Latest Pleistocene sand ramps (66–18 ka) were derived from across-shelf eolian sand transport during marine low stands. Shoreward wave transport supplied remobilized late Pleistocene sand from the inner shelf to Holocene beaches, where dominant NW winds supplied sand to the sand ramps. The onset dates of the sand-ramp deposition in San Miguel are 7.2 ± 1.5 ka (sample n = 14). The internal strata dates in the vertically accreting sand ramps are 3.4 ± 1.7 ka (n = 34). The sand ramps in San Miguel show wide-scale termination of sand supply in the latest Holocene time. The sand-ramp top dates or burial dates are 1.7 ± 0.9 ka (n = 28). The latest Holocene sand ramps are truncated along most of the island's northern coastline, indicating recent losses of nearshore sand reserves to onshore, alongshore, and, possibly, offshore sand sinks. The truncated sand ramps in San Miguel Island and in other sand-depleted marine coastlines provide warnings about future beach erosion and/or shoreline retreat from accelerated sea-level rise accompanying predicted global warming. Title: Coastal Eolian Sand-Ramp Development Related to Paleo-Sea-Level Changes during the Latest Pleistocene and Holocene (21–0 ka) in San Miguel Island, California, U.S.A. Author: Peterson, Curt D., Erlandson, Jon M., Stock, Errol, Hostetler, Steve W., Price, David M. Year: 2017 Coastal eolian sand ramps (5–130 m elevation) on the northern slope (windward) side of the small San Miguel Island (13 km in W-E length) range in age from late Pleistocene to modern time, though a major hiatus in sand-ramp growth occurred during the early Holocene marine transgression (16–9 ka). The Holocene sand ramps (1–5 m measured thicknesses) currently lack large dune forms, thereby representing deflated erosional remnants, locally covering thicker late Pleistocene sand-ramp deposits. The ramp sand was initially supplied from the adjacent island-shelf platform, extending about 20 km north of the present coastline. The sand-ramp deposits and interbedded loess soils were 14C dated using 112 samples from 32 archaeological sites and other geologic sections. Latest Pleistocene sand ramps (66–18 ka) were derived from across-shelf eolian sand transport during marine low stands. Shoreward wave transport supplied remobilized late Pleistocene sand from the inner shelf to Holocene beaches, where dominant NW winds supplied sand to the sand ramps. The onset dates of the sand-ramp deposition in San Miguel are 7.2 ± 1.5 ka (sample n = 14). The internal strata dates in the vertically accreting sand ramps are 3.4 ± 1.7 ka (n = 34). The sand ramps in San Miguel show wide-scale termination of sand supply in the latest Holocene time. The sand-ramp top dates or burial dates are 1.7 ± 0.9 ka (n = 28). The latest Holocene sand ramps are truncated along most of the island's northern coastline, indicating recent losses of nearshore sand reserves to onshore, alongshore, and, possibly, offshore sand sinks. The truncated sand ramps in San Miguel Island and in other sand-depleted marine coastlines provide warnings about future beach erosion and/or shoreline retreat from accelerated sea-level rise accompanying predicted global warming. Close