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Bridget Scanlon, a hydrologist and senior research scientist at the University of Texas’ Bureau of Economic Geology, has been elected a member of the National Academy of Engineering (NAE), one of the highest professional honors accorded to engineers and scientists. “I’m extremely...

FEB
18

De Ford Lecture Series: Fiona Whitaker, University of Bristol (UK)
4:00 PM

De Ford Lecture Series: Fiona Whitaker, University of Bristol (UK)

  Start: February 18, 2016 at 4:00 pm     End: February 18, 2016 at 5:00 pm

FEB
19

UTIG Seminar Series: Demian Saffer, Penn State
10:30 AM

De Ford Lecture Series: Fiona Whitaker, University of Bristol (UK)

  Start: February 18, 2016 at 4:00 pm     End: February 18, 2016 at 5:00 pm

UTIG Seminar Series: Demian Saffer, Penn State

  Start: February 19, 2016 at 10:30 am     End: February 19, 2016 at 11:30 am
 Location:PRC, 10100 Burnet Road, Bldg 196, Rm 1.603, Austin, TX 78758
 Contact:Peter Flemings/Laura Wallace, pflemings@jsg.utexas.edu/lwallace@ig.utexas.edu, 512-475-8738/512-471
 URL:Event Link
"Phyllosilicates, Friction, and Fluids: The Role of Clays in Plate Boundary Fault Processes"

Abstract:

Clay minerals, and hydrous smectite family clays in particular, have been hypothesized to control both the low absolute shear strength and the nature of slip along plate boundary faults, including subduction megathrusts, low-angle normal faults, and continental transforms. In addition to their effects on frictional behavior, hydrous clays are the largest and shallowest source of bound water in systems undergoing prograde diagenesis and metamorphism. For example, the transformation from smectite to illite at temperatures of ~80-150 °C releases ~20 wt% H2O. As a result, the reaction has the potential to generate fluid overpressures through expulsion of bound water; to change the elastic, hydraulic, and frictional properties of the rock or sediment via mobilization of quartz and associated cementation or vein-filling; and to generate geochemical signatures that yield information about fluid flow pathways from source regions at depth to observation points at the surface. Here, I summarize a set of integrated laboratory, numerical modeling, and field studies that address these linked processes, focusing on examples from the Costa Rican and Nankai (SW Japan) subduction zones.

Laboratory shearing experiments on a suite of synthetic and natural fault gouges demonstrate that clay- and mudstones sampled from major fault zones, including the San Andreas Fault and the Costa Rican and Nankai subduction megathrusts, are frictionally weak, with friction coefficients in the range µ = ~0.08-0.35. These fault rocks exhibit rate-strengthening behavior, which should lead to only aseismic creep. However, they become increasingly rate-weakening (and therefore potentially able to host unstable slip) with increasing quartz abundance, raising the possibility that clay transformation, primarily through the by-product of silica mobilization, may play a role in controlling the upper aseismic-seismic transition and its spatial variability or “patchiness” at some subduction margins.

Numerical models describing the kinetics of clay dehydration and associated fluid expulsion show that at both the Costa Rican and Nankai margins, earthquakes nucleate only in areas down-dip of the reaction, after it has peaked and is near completion. This behavior is robust, and it parallels variations in thermal structure along the strike of the Costa Rican margin. Although the number of observations is limited, the correlation further supports the idea that the onset of unstable slip is linked to clay transformation, likely through the combination of changes in rock frictional properties and the dissipation of the bound water source that allows effective normal stress to increase. Interestingly, the rupture areas of large (M>6-7) events extend into the zone of dehydration, suggesting the possibility that nucleation may be restricted to depths where the clay reaction has progressed, but that slip may propagate up-dip into weak and potentially overpressured regions where the dehydration reaction is peaking. Finally, these models can also be used to predict the evolution of pore fluid composition within subducting and accreting sediments due to the release of bound (fresh) water and the desorption of fluid-mobile elements like B and Li. Comparison of simulated pore fluid compositions in these source regions with observations at seafloor seeps and in shallow drillholes provides evidence for long-distance (10’s of km) up-dip fluid migration along fault zones.

FEB
25

De Ford Lecture Series: G. Burch Fisher
4:00 PM

De Ford Lecture Series: Fiona Whitaker, University of Bristol (UK)

  Start: February 18, 2016 at 4:00 pm     End: February 18, 2016 at 5:00 pm

UTIG Seminar Series: Demian Saffer, Penn State

  Start: February 19, 2016 at 10:30 am     End: February 19, 2016 at 11:30 am
 Location:PRC, 10100 Burnet Road, Bldg 196, Rm 1.603, Austin, TX 78758
 Contact:Peter Flemings/Laura Wallace, pflemings@jsg.utexas.edu/lwallace@ig.utexas.edu, 512-475-8738/512-471
 URL:Event Link
"Phyllosilicates, Friction, and Fluids: The Role of Clays in Plate Boundary Fault Processes"

Abstract:

Clay minerals, and hydrous smectite family clays in particular, have been hypothesized to control both the low absolute shear strength and the nature of slip along plate boundary faults, including subduction megathrusts, low-angle normal faults, and continental transforms. In addition to their effects on frictional behavior, hydrous clays are the largest and shallowest source of bound water in systems undergoing prograde diagenesis and metamorphism. For example, the transformation from smectite to illite at temperatures of ~80-150 °C releases ~20 wt% H2O. As a result, the reaction has the potential to generate fluid overpressures through expulsion of bound water; to change the elastic, hydraulic, and frictional properties of the rock or sediment via mobilization of quartz and associated cementation or vein-filling; and to generate geochemical signatures that yield information about fluid flow pathways from source regions at depth to observation points at the surface. Here, I summarize a set of integrated laboratory, numerical modeling, and field studies that address these linked processes, focusing on examples from the Costa Rican and Nankai (SW Japan) subduction zones.

Laboratory shearing experiments on a suite of synthetic and natural fault gouges demonstrate that clay- and mudstones sampled from major fault zones, including the San Andreas Fault and the Costa Rican and Nankai subduction megathrusts, are frictionally weak, with friction coefficients in the range µ = ~0.08-0.35. These fault rocks exhibit rate-strengthening behavior, which should lead to only aseismic creep. However, they become increasingly rate-weakening (and therefore potentially able to host unstable slip) with increasing quartz abundance, raising the possibility that clay transformation, primarily through the by-product of silica mobilization, may play a role in controlling the upper aseismic-seismic transition and its spatial variability or “patchiness” at some subduction margins.

Numerical models describing the kinetics of clay dehydration and associated fluid expulsion show that at both the Costa Rican and Nankai margins, earthquakes nucleate only in areas down-dip of the reaction, after it has peaked and is near completion. This behavior is robust, and it parallels variations in thermal structure along the strike of the Costa Rican margin. Although the number of observations is limited, the correlation further supports the idea that the onset of unstable slip is linked to clay transformation, likely through the combination of changes in rock frictional properties and the dissipation of the bound water source that allows effective normal stress to increase. Interestingly, the rupture areas of large (M>6-7) events extend into the zone of dehydration, suggesting the possibility that nucleation may be restricted to depths where the clay reaction has progressed, but that slip may propagate up-dip into weak and potentially overpressured regions where the dehydration reaction is peaking. Finally, these models can also be used to predict the evolution of pore fluid composition within subducting and accreting sediments due to the release of bound (fresh) water and the desorption of fluid-mobile elements like B and Li. Comparison of simulated pore fluid compositions in these source regions with observations at seafloor seeps and in shallow drillholes provides evidence for long-distance (10’s of km) up-dip fluid migration along fault zones.

De Ford Lecture Series: G. Burch Fisher

  Start: February 25, 2016 at 4:00 pm     End: February 25, 2016 at 5:00 pm

FEB
26

UTIG Seminar Series: Diego Melgar, UC Berkeley
10:30 AM

De Ford Lecture Series: Fiona Whitaker, University of Bristol (UK)

  Start: February 18, 2016 at 4:00 pm     End: February 18, 2016 at 5:00 pm

UTIG Seminar Series: Demian Saffer, Penn State

  Start: February 19, 2016 at 10:30 am     End: February 19, 2016 at 11:30 am
 Location:PRC, 10100 Burnet Road, Bldg 196, Rm 1.603, Austin, TX 78758
 Contact:Peter Flemings/Laura Wallace, pflemings@jsg.utexas.edu/lwallace@ig.utexas.edu, 512-475-8738/512-471
 URL:Event Link
"Phyllosilicates, Friction, and Fluids: The Role of Clays in Plate Boundary Fault Processes"

Abstract:

Clay minerals, and hydrous smectite family clays in particular, have been hypothesized to control both the low absolute shear strength and the nature of slip along plate boundary faults, including subduction megathrusts, low-angle normal faults, and continental transforms. In addition to their effects on frictional behavior, hydrous clays are the largest and shallowest source of bound water in systems undergoing prograde diagenesis and metamorphism. For example, the transformation from smectite to illite at temperatures of ~80-150 °C releases ~20 wt% H2O. As a result, the reaction has the potential to generate fluid overpressures through expulsion of bound water; to change the elastic, hydraulic, and frictional properties of the rock or sediment via mobilization of quartz and associated cementation or vein-filling; and to generate geochemical signatures that yield information about fluid flow pathways from source regions at depth to observation points at the surface. Here, I summarize a set of integrated laboratory, numerical modeling, and field studies that address these linked processes, focusing on examples from the Costa Rican and Nankai (SW Japan) subduction zones.

Laboratory shearing experiments on a suite of synthetic and natural fault gouges demonstrate that clay- and mudstones sampled from major fault zones, including the San Andreas Fault and the Costa Rican and Nankai subduction megathrusts, are frictionally weak, with friction coefficients in the range µ = ~0.08-0.35. These fault rocks exhibit rate-strengthening behavior, which should lead to only aseismic creep. However, they become increasingly rate-weakening (and therefore potentially able to host unstable slip) with increasing quartz abundance, raising the possibility that clay transformation, primarily through the by-product of silica mobilization, may play a role in controlling the upper aseismic-seismic transition and its spatial variability or “patchiness” at some subduction margins.

Numerical models describing the kinetics of clay dehydration and associated fluid expulsion show that at both the Costa Rican and Nankai margins, earthquakes nucleate only in areas down-dip of the reaction, after it has peaked and is near completion. This behavior is robust, and it parallels variations in thermal structure along the strike of the Costa Rican margin. Although the number of observations is limited, the correlation further supports the idea that the onset of unstable slip is linked to clay transformation, likely through the combination of changes in rock frictional properties and the dissipation of the bound water source that allows effective normal stress to increase. Interestingly, the rupture areas of large (M>6-7) events extend into the zone of dehydration, suggesting the possibility that nucleation may be restricted to depths where the clay reaction has progressed, but that slip may propagate up-dip into weak and potentially overpressured regions where the dehydration reaction is peaking. Finally, these models can also be used to predict the evolution of pore fluid composition within subducting and accreting sediments due to the release of bound (fresh) water and the desorption of fluid-mobile elements like B and Li. Comparison of simulated pore fluid compositions in these source regions with observations at seafloor seeps and in shallow drillholes provides evidence for long-distance (10’s of km) up-dip fluid migration along fault zones.

De Ford Lecture Series: G. Burch Fisher

  Start: February 25, 2016 at 4:00 pm     End: February 25, 2016 at 5:00 pm

UTIG Seminar Series: Diego Melgar, UC Berkeley

  Start: February 26, 2016 at 10:30 am     End: February 26, 2016 at 11:30 am
 Location:PRC, 10100 Burnet Road, Bldg 196, Rm 1.603, Austin, TX 78758
 Contact:Adrian Arnulf, aarnulf@ig.utexas.edu, 512-471-0376
 URL:Event Link
"The 2015 Mw8.3 Illapel, Chile Earthquake: Along-dip Segmentation of Megathrust Properties and Lessons for Local Tsunami Warning"

Abstract:

The 2015 Mw8.3 Illapel, Chile earthquake is the latest megathrust event on the Chilean subduction zone. It generated strong ground motions and a large (up to 11m runup) tsunami which prompted the evacuation of more than 1 million people in the first hours following the event. Observations during recent earthquakes suggest that these phenomena can be associated with rupture on different parts of the megathrust. The deep portion generates strong shaking while slow, large slip on the shallow fault is responsible for the tsunami. It is unclear whether all megathrusts can have shallow slip during coseismic rupture and what physical properties regulate this. We resolve a kinematic slip model using regional geophysical observations and analyze it jointly with teleseismic back-projection. These observations show that the Illapel event ruptured both deep and shallow segments with substantial slip. We find that the shallow and deep portions of the megathrust are segmented and have fundamentally different behavior. We forward calculate local tsunami propagation from the resolved slip model and find good agreement with field measurements, independently validating the slip model.

Large earthquakes are of fundamentals scientific interest, they illuminate the properties of megathrusts. However, they also have substantial impacts on societies, and many of the tools used for studying them can be applied to hazards mitigation as well. I will discus the practical problem of local tsunami warning. With the example of the Illapel earthquake, as well as some other large events, I will discuss a flexible strategy for local tsunami warning that relies on regional geodetic and seismic stations. Rapid earthquake source information, provided by methodologies developed for earthquake early warning, can be used to generate timely estimates of maximum expected tsunami amplitude with enough accuracy for tsunami warning. This approach does not require deployment of new geodetic and seismic instrumentation in many subduction zones, and could be implemented rapidly by national monitoring and warning agencies.

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