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• 1. [Article] Heat flow along the NanTroSEIZE transect: Results from IODP Expeditions 315 and 316 offshore the Kii Peninsula, Japan

  [1] We report detailed thermal measurements undertaken during Integrated Ocean Drilling Program (IODP) Expeditions 315 and 316 along the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) transect offshore ...

  Citation × Citation Citation Abstract Copy Title: Heat flow along the NanTroSEIZE transect: Results from IODP Expeditions 315 and 316 offshore the Kii Peninsula, Japan Author: Schmidt‐Schierhorn, Friederike, Spinelli, Glenn, Harris, Robert N. [1] We report detailed thermal measurements undertaken during Integrated Ocean Drilling Program (IODP) Expeditions 315 and 316 along the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) transect offshore the Kii Peninsula, Japan. Geothermal objectives included determining thermophysical rock properties of the cored material and characterizing the background thermal regime along this transect. New thermal conductivity measurements made with a divided bar are reported and supplement shipboard full‐ and half‐space thermal conductivity measurements for a total of 938 thermal conductivity measurements. Thermal conductivity varies between about 1.0 W m⁻¹ K⁻¹ near the seafloor to 1.6 W m⁻¹ K⁻¹ at a depth of 1 km. Thermal conductivity generally increases with depth and correlates with variations in porosity and lithology. Thermal gradients along the transect are characterized by 48 sediment temperature measurements from 6 sites. Thermal corrections for the effects of bathymetric relief and sedimentation improve the confidence with which the heat flow values can be interpreted. Heat flow generally decreases with landward distance from the deformation front and varies from 70 mW m⁻² just landward of the deformation front to 54 mW m⁻² at sites characterizing the outer fore‐arc high and to 57 mW m⁻² at the Kumano Basin Site. IODP heat flow measurements are significantly lower than nearby seafloor heat flow measurements. This difference is most likely due to variations in bottom water temperature that have a large effect on values of seafloor heat flow. Thus the heat flow of the Nankai accretionary prism is lower than previously thought. We present thermal models of subduction along this transect and explore the impact of the initial geotherm. Conductive plate cooling based on the age of subducting seafloor (20 Myr) under predicts the observed heat flow. We find a good fit to the data using a geotherm appropriate for 10 Myr seafloor. The extra heat is interpreted in terms of back‐arc thermal environments. Title: Heat flow along the NanTroSEIZE transect: Results from IODP Expeditions 315 and 316 offshore the Kii Peninsula, Japan Author: Schmidt‐Schierhorn, Friederike, Spinelli, Glenn, Harris, Robert N. [1] We report detailed thermal measurements undertaken during Integrated Ocean Drilling Program (IODP) Expeditions 315 and 316 along the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) transect offshore the Kii Peninsula, Japan. Geothermal objectives included determining thermophysical rock properties of the cored material and characterizing the background thermal regime along this transect. New thermal conductivity measurements made with a divided bar are reported and supplement shipboard full‐ and half‐space thermal conductivity measurements for a total of 938 thermal conductivity measurements. Thermal conductivity varies between about 1.0 W m⁻¹ K⁻¹ near the seafloor to 1.6 W m⁻¹ K⁻¹ at a depth of 1 km. Thermal conductivity generally increases with depth and correlates with variations in porosity and lithology. Thermal gradients along the transect are characterized by 48 sediment temperature measurements from 6 sites. Thermal corrections for the effects of bathymetric relief and sedimentation improve the confidence with which the heat flow values can be interpreted. Heat flow generally decreases with landward distance from the deformation front and varies from 70 mW m⁻² just landward of the deformation front to 54 mW m⁻² at sites characterizing the outer fore‐arc high and to 57 mW m⁻² at the Kumano Basin Site. IODP heat flow measurements are significantly lower than nearby seafloor heat flow measurements. This difference is most likely due to variations in bottom water temperature that have a large effect on values of seafloor heat flow. Thus the heat flow of the Nankai accretionary prism is lower than previously thought. We present thermal models of subduction along this transect and explore the impact of the initial geotherm. Conductive plate cooling based on the age of subducting seafloor (20 Myr) under predicts the observed heat flow. We find a good fit to the data using a geotherm appropriate for 10 Myr seafloor. The extra heat is interpreted in terms of back‐arc thermal environments. Close

• 2. [Article] Climate change on the Colorado Plateau of eastern Utah inferred from borehole temperatures

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Climate change on the Colorado Plateau of eastern Utah inferred from borehole temperatures Author: Chapman, David S., Harris, Robert N. copyrighted by American Geophysical Union Title: Climate change on the Colorado Plateau of eastern Utah inferred from borehole temperatures Author: Chapman, David S., Harris, Robert N. copyrighted by American Geophysical Union Close

• 3. [Article] Repeat temperature measurements in borehole GC-1, northwestern Utah: towards isolating a climate-change signal borehole temperature profiles

  Copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Repeat temperature measurements in borehole GC-1, northwestern Utah: towards isolating a climate-change signal borehole temperature profiles Author: Chapman, David S., Harris, Robert N. Copyrighted by American Geophysical Union Title: Repeat temperature measurements in borehole GC-1, northwestern Utah: towards isolating a climate-change signal borehole temperature profiles Author: Chapman, David S., Harris, Robert N. Copyrighted by American Geophysical Union Close

• 4. [Article] Snow and the ground temperature record of climate change

  Copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Snow and the ground temperature record of climate change Author: Bartlett, Marshall G., Chapman, David S., Harris, Robert N. Copyrighted by American Geophysical Union Title: Snow and the ground temperature record of climate change Author: Bartlett, Marshall G., Chapman, David S., Harris, Robert N. Copyrighted by American Geophysical Union Close

• 5. [Article] Variations in air and ground temperature and the POM-SAT model: Results from the Northern Hemisphere

  The POM-SAT model for comparing air and ground temperatures is based on the supposition that surface air temperature (SAT) records provide a good prediction of thermal transients in the shallow subsurface ...

  Citation × Citation Citation Abstract Copy Title: Variations in air and ground temperature and the POM-SAT model: Results from the Northern Hemisphere Author: Harris, Robert N. The POM-SAT model for comparing air and ground temperatures is based on the supposition that surface air temperature (SAT) records provide a good prediction of thermal transients in the shallow subsurface of the Earth. This model consists of two components, the forcing function and an initial condition, termed the pre-observational mean (POM). I explore the sensitivity of this model as a function of forcing periods at time scales appropriate for climate reconstructions. Synthetic models are designed to replicate comparisons between borehole temperatures contained in the global database of temperature profiles for climate reconstructions and gridded SAT data. I find that the root mean square (RMS) misfit between forcing functions and transient temperature profiles in the subsurface are sensitive to periods longer than about 50 years, are a maximum when the period and the 150-year time series are equal and then decreases for longer periods. The magnitude of the POM is a robust parameter for periods equal to or shorter than the length of this time series. At longer periods there is a tradeoff between the amplitude of the forcing function and the POM. These tests provide guidelines for assessing comparisons between air and ground temperatures at periods appropriate for climate reconstructions. The sensitivity of comparisons between the average Northern Hemisphere gridded SAT record and subsurface temperature-depth profile as a function of forcing period is assessed. This analysis indicates that the Northern Hemisphere extratropical average SAT and reduced temperature-depth profile are in good agreement. By adding modest heat to the subsurface at intermediate periods some improvement in misfit can be made, but this extra heat has negligible influence on the POM. The joint analysis of borehole temperatures and SAT records indicate warming of about 1.1°C over the last 500 years, consistent with previous studies. Title: Variations in air and ground temperature and the POM-SAT model: Results from the Northern Hemisphere Author: Harris, Robert N. The POM-SAT model for comparing air and ground temperatures is based on the supposition that surface air temperature (SAT) records provide a good prediction of thermal transients in the shallow subsurface of the Earth. This model consists of two components, the forcing function and an initial condition, termed the pre-observational mean (POM). I explore the sensitivity of this model as a function of forcing periods at time scales appropriate for climate reconstructions. Synthetic models are designed to replicate comparisons between borehole temperatures contained in the global database of temperature profiles for climate reconstructions and gridded SAT data. I find that the root mean square (RMS) misfit between forcing functions and transient temperature profiles in the subsurface are sensitive to periods longer than about 50 years, are a maximum when the period and the 150-year time series are equal and then decreases for longer periods. The magnitude of the POM is a robust parameter for periods equal to or shorter than the length of this time series. At longer periods there is a tradeoff between the amplitude of the forcing function and the POM. These tests provide guidelines for assessing comparisons between air and ground temperatures at periods appropriate for climate reconstructions. The sensitivity of comparisons between the average Northern Hemisphere gridded SAT record and subsurface temperature-depth profile as a function of forcing period is assessed. This analysis indicates that the Northern Hemisphere extratropical average SAT and reduced temperature-depth profile are in good agreement. By adding modest heat to the subsurface at intermediate periods some improvement in misfit can be made, but this extra heat has negligible influence on the POM. The joint analysis of borehole temperatures and SAT records indicate warming of about 1.1°C over the last 500 years, consistent with previous studies. Close

• 6. [Article] Climate change on the Colorado Plateau of eastern Utah inferred from borehole temperatures

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Climate change on the Colorado Plateau of eastern Utah inferred from borehole temperatures Author: Chapman, David S., Harris, Robert N. Copyrighted by American Geophysical Union. Title: Climate change on the Colorado Plateau of eastern Utah inferred from borehole temperatures Author: Chapman, David S., Harris, Robert N. Copyrighted by American Geophysical Union. Close

• 7. [Article] Geothermics and climate change : 2. joint analysis of borehole temperature and meteorological data

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Geothermics and climate change : 2. joint analysis of borehole temperature and meteorological data Author: Chapman, David S., Harris, Robert N. copyrighted by American Geophysical Union Title: Geothermics and climate change : 2. joint analysis of borehole temperature and meteorological data Author: Chapman, David S., Harris, Robert N. copyrighted by American Geophysical Union Close

• 8. [Article] Reply to comment by T.J. Osborn and K.R. Briffa on "Mid-latitude (30°-60°N) climatic warming inferred by combining borehole temperatures with surface air temperatures"

  Citation × Citation Citation Abstract Copy Title: Reply to comment by T.J. Osborn and K.R. Briffa on "Mid-latitude (30°-60°N) climatic warming inferred by combining borehole temperatures with surface air temperatures" Author: Chapman, David S., Harris, Robert N. Title: Reply to comment by T.J. Osborn and K.R. Briffa on "Mid-latitude (30°-60°N) climatic warming inferred by combining borehole temperatures with surface air temperatures" Author: Chapman, David S., Harris, Robert N. Close

• 9. [Article] Does hydrologic circulation mask frictional heat on faults after large earthquakes?

  Knowledge of frictional resistance along faults is important for understanding the mechanics of earthquakes and faulting. The clearest in situ measure of fault friction potentially comes from temperature ...

  Citation × Citation Citation Abstract Copy Title: Does hydrologic circulation mask frictional heat on faults after large earthquakes? Author: Brodsky, Emily E., Saffer, Demian M., Fulton, Patrick M., Harris, Robert N. Knowledge of frictional resistance along faults is important for understanding the mechanics of earthquakes and faulting. The clearest in situ measure of fault friction potentially comes from temperature measurements in boreholes crossing fault zones within a few years of rupture. However, large temperature signals from frictional heating on faults have not been observed. Unambiguously interpreting the coseismic frictional resistance from small thermal perturbations observed in borehole temperature profiles requires assessing the impact of other potentially confounding thermal processes. We address several issues associated with quantifying the temperature signal of frictional heating including transient fluid flow associated with the earthquake, thermal disturbance caused by borehole drilling, and heterogeneous thermal physical rock properties. Transient fluid flow is investigated using a two‐dimensional coupled fluid flow and heat transport model to evaluate the temperature field following an earthquake. Simulations for a range of realistic permeability, frictional heating, and pore pressure scenarios show that high permeabilities (>10−14 m2) are necessary for significant advection within the several years after an earthquake and suggest that transient fluid flow is unlikely to mask frictional heat anomalies. We illustrate how disturbances from circulating fluids during drilling diffuse quickly leaving a robust signature of frictional heating. Finally, we discuss the utility of repeated borehole temperature profiles for discriminating between different interpretations of thermal perturbations. Our results suggest that temperature anomalies from even low friction should be detectable at depths >1 km 1 to 2 years after a large earthquake and that interpretations of low friction from existing data are likely robust. Title: Does hydrologic circulation mask frictional heat on faults after large earthquakes? Author: Brodsky, Emily E., Saffer, Demian M., Fulton, Patrick M., Harris, Robert N. Knowledge of frictional resistance along faults is important for understanding the mechanics of earthquakes and faulting. The clearest in situ measure of fault friction potentially comes from temperature measurements in boreholes crossing fault zones within a few years of rupture. However, large temperature signals from frictional heating on faults have not been observed. Unambiguously interpreting the coseismic frictional resistance from small thermal perturbations observed in borehole temperature profiles requires assessing the impact of other potentially confounding thermal processes. We address several issues associated with quantifying the temperature signal of frictional heating including transient fluid flow associated with the earthquake, thermal disturbance caused by borehole drilling, and heterogeneous thermal physical rock properties. Transient fluid flow is investigated using a two‐dimensional coupled fluid flow and heat transport model to evaluate the temperature field following an earthquake. Simulations for a range of realistic permeability, frictional heating, and pore pressure scenarios show that high permeabilities (>10−14 m2) are necessary for significant advection within the several years after an earthquake and suggest that transient fluid flow is unlikely to mask frictional heat anomalies. We illustrate how disturbances from circulating fluids during drilling diffuse quickly leaving a robust signature of frictional heating. Finally, we discuss the utility of repeated borehole temperature profiles for discriminating between different interpretations of thermal perturbations. Our results suggest that temperature anomalies from even low friction should be detectable at depths >1 km 1 to 2 years after a large earthquake and that interpretations of low friction from existing data are likely robust. Close

• 10. [Article] Thermal regime of the Costa Rican convergent margin: 2. Thermal models of the shallow Middle America subduction zone offshore Costa Rica

  At the Costa Rica margin along the Middle America Trench along‐strike variations in heat flow are well mapped. These variations can be understood in terms of either ventilated fluid flow, where exposed ...

  Citation × Citation Citation Abstract Copy Title: Thermal regime of the Costa Rican convergent margin: 2. Thermal models of the shallow Middle America subduction zone offshore Costa Rica Author: Ranero, César R., Spinelli, Glenn, Harris, Robert N. At the Costa Rica margin along the Middle America Trench along‐strike variations in heat flow are well mapped. These variations can be understood in terms of either ventilated fluid flow, where exposed basement allows fluids to freely advect heat between the crustal aquifer and ocean, or insulated fluid flow where continuous sediment cover restricts heat advection to within the crustal aquifer. We model fluid flow within the subducting aquifer using Nusselt number approximations coupled with finite element models of subduction and explore its effect on temperatures along the subduction thrust. The sensitivity of these models to the initial thermal state of the plate and styles of fluid flow, either ventilated or insulated, is explored. Heat flow measurements on cool crust accreted at the East Pacific Rise are consistent with ventilated hydrothermal cooling that continues with subduction. These models yield much cooler temperatures than predicted from simulations initialized with conductive predictions and without hydrothermal circulation. Heat flow transects on warm crust accreted at the Cocos‐Nazca spreading center are consistent with models of insulated hydrothermal circulation that advects heat updip within the subducting crustal aquifer. Near the trench these models are warmer than conductive predictions and cooler than conductive predictions downdip of the trench. Comparisons between microseismicity and modeled isotherms suggest that the updip limit of microseismicity occurs at temperatures warmer than 100°C and that the downdip extent of microseismicity is bounded by the intersection of the subduction thrust with the base of the overriding crust. Title: Thermal regime of the Costa Rican convergent margin: 2. Thermal models of the shallow Middle America subduction zone offshore Costa Rica Author: Ranero, César R., Spinelli, Glenn, Harris, Robert N. At the Costa Rica margin along the Middle America Trench along‐strike variations in heat flow are well mapped. These variations can be understood in terms of either ventilated fluid flow, where exposed basement allows fluids to freely advect heat between the crustal aquifer and ocean, or insulated fluid flow where continuous sediment cover restricts heat advection to within the crustal aquifer. We model fluid flow within the subducting aquifer using Nusselt number approximations coupled with finite element models of subduction and explore its effect on temperatures along the subduction thrust. The sensitivity of these models to the initial thermal state of the plate and styles of fluid flow, either ventilated or insulated, is explored. Heat flow measurements on cool crust accreted at the East Pacific Rise are consistent with ventilated hydrothermal cooling that continues with subduction. These models yield much cooler temperatures than predicted from simulations initialized with conductive predictions and without hydrothermal circulation. Heat flow transects on warm crust accreted at the Cocos‐Nazca spreading center are consistent with models of insulated hydrothermal circulation that advects heat updip within the subducting crustal aquifer. Near the trench these models are warmer than conductive predictions and cooler than conductive predictions downdip of the trench. Comparisons between microseismicity and modeled isotherms suggest that the updip limit of microseismicity occurs at temperatures warmer than 100°C and that the downdip extent of microseismicity is bounded by the intersection of the subduction thrust with the base of the overriding crust. Close