Chris Marone - US grants

This award will provide one-half the funding needed to build a biaxial testing apparatus to be installed and operated in the rock mechanics laboratory of the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology. MIT is committed to providing the remaining funds required for the project. The materials testing system will be used by the staff of the rock mechanics group at MIT as an integral part of their research on rock friction and its role in faulting of the Earth' crust and the generation of earthquakes.

This award provides one-half the funding necessary for the acquisition of a triaxial testing device to be installed and operated in the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology. MIT is committed to providing the remaining funds needed. Understanding the physical properties of fluid-saturated rocks at high pressures and temperatures (such as acoustic wave velocity, permeability to fluids, electrical resistivity, and mechanical strength) will be made possible with the new generation testing device.

9316082 Marone The PI will perform experiments to determine the critical slip distance, which plays a key role in determining the rupture nucleation dimension, the magnitude of the precursive moment release, and the maximum seismic ground acceleration. He will measure this parameter for a wider range of materials, normal stresses, and slip rates than previous studies, will investigate in detail the frictional behavior and constitutive parameters for shear within fractally-rough surfaces, and will systematically model the data collected. In this way, he will develop an understanding of the underlying mechanics and physical processes, and investigate how these mechanics and processes relate to those operative in natural fault zones. ****

9805327
Marone

During an earthquake, fault surfaces slip at speeds of several cm/s to several m/s. The frictional properties at these slip rates play an important role in determining key aspects of seismic rupture, including earthquake stress drop, heat production, and the mode of dynamic rupture expansion. However, little is known about friction at dynamic slip velocities. The limited available data have been collected under a narrow range of conditions and significant discrepancies exist between these data and the friction database at lower velocities appropriate to earthquake nucleation. This proposal is to conduct laboratory experiments spanning slip speeds from mm/s to m/s. An important goal will be to quantitatively connect friction observations over the entire velocity range and to study the problem of scaling laboratory friction data to seismogenic faults. Bare rock surfaces and granular fault gouge will be studied under a range of normal stresses and surface conditions, and friction data will be analyzed in terms of existing friction theory. A major goal of the experimental program will be to identify the micromechanical causes of velocity-dependent friction and friction evolution (state) effects.

The PI proposes to develop a structural model of the subduction thrust from the seaward edge of the subduction zone through the seismogenic zone with the geological conditions at the Nankai Subduction Zone as a constraint. The objective is to understand the progressive fabric development across the aseismic to seismic transition, to provide information that will help interpret geophysical images and guide experimental lab studies and assist in the interpreting of the drill hole data through the seismogenic zone. The PI will use ODP holes at the frontal part of the Nankai subduction zone and uplifted equivalent complexes on land.

MARONE
EAR-0001127

During an earthquake, fault surfaces slip at speeds of several cm/s to several m/s. The frictional properties at these slip rates play an important role in determining key aspects of seismic rupture, including earthquake stress drop, heat production, and the mode of dynamic rupture expansion. However, little is known about friction at dynamic slip velocities. The limited available data have been collected under a narrow range of conditions and significant discrepancies exist between these data and the friction database at lower velocities appropriate to earthquake nucleation. This proposal is to conduct laboratory experiments spanning slip speeds from m/s to micron/s. An important goal will be to quantitatively connect friction observations over the entire velocity range and to study the problem of scaling laboratory friction data to seismogenic faults. Bare rock surfaces and granular fault gouge will be studied under a range of normal stresses and surface conditions, and friction data will be analyzed in terms of existing friction theory. A major goal of the experimental program will be to identify the micromechanical causes of velocity-dependent friction and friction evolution (state) effects.

Collaborative Research: Mechanics of Earthquake Fault Zones:
Particle Dynamics Simulations and Laboratory Experiments
PROJECT ABSTRACT

Laboratory studies have contributed significantly to our understanding of earthquake nucleation, dynamic rupture, and shear deformation, however, results of these experiments are often difficult to scale up to natural fault systems. Particle-based numerical models, which have successfully reproduced a wide-range of observed laboratory and natural phenomena, can help. This collaborative research project is designed to (a) improve and refine existing particle-based numerical techniques to better replicate laboratory experimental results, in particular, first and second order variations in frictional strength and sliding stability, and (2) bridge the gap between these improved models and natural faults, allowing investigation of the structural evolution of complex tectonic faults
This research involves parallel laboratory and numerical experiments, conducted under a wide range of identical initial and boundary conditions. The experimental and numerical results are being compared, guiding updates of the numerical interparticle contact laws to better reproduce realistic physico-chemical surface interactions. The primary focus is on accurately constraining the base ("Byerlee's Law") coefficient of sliding friction in the two sets of experiments, as well as its variation with shear, dilation, and compaction. Focus will also include the 2nd-order variations in friction with contact time and slip velocity, i.e., rate- and state-dependent friction. The numerical models further help to isolate the deformation mechanisms acting within the fault zones under different boundary conditions, including shear localization, grain-boundary sliding, particle rolling, translation, and fracture. Results of the proposed work will have significant impact on understanding fault mechanics and earthquake physics including fault interaction, earthquake triggering, and seismic hazard assessment.

0345813
Marone

Support from this grant will facilitate construction of a custom-design biaxial deformation apparatus that will allow for fundamental studies of the behavior of earth materials at upper- to mid-crustal temperatures, pressures, and pore fluid conditions when subjected to fault zone stresses. Pressure vessels, a load frame, and hydrothermal control systems will be built in-house at Penn State using existing machine shop and electronics equipment and expertise. The system will be assembled by a dedicated technician within a two-year time period under the supervision of PI Chris Marone. Study of the properties of earth materials under realistic earthquake hypocentral conditions will greatly improve our understanding of earthquake fault rupture initiation processes. Relevant experimental data is sparse and successful development of this apparatus will add new empirical data to the field of rock mechanics. Experimental data that will be obtained with this device is highly complementary to planned in situ observation of the mechanical and physical environment experienced by San Andreas fault zone materials (i.e., the SAFOD drilling project).
***

.Elsworth
0510182
Intellectual Merit: The competition between agents that either destroy or generate porosity controls the evolution of the transport properties of fractured rocks. Changes in permeability resulting from chemo-mechanical effects have been shown to occur under modest stresses 2 MPa) and temperatures (T80C, with H2O as the permeant), to be rapid (c. days), of significant magnitude (permeability reductions of 10-2), and moreover, to surprisingly result in permeability reduction even when dissolution net removes mineral mass.
Despite these observations, a consistent view of the processes and indexing parameters that control the switching between porosity generation and destruction in fractures is still sought. Important controls on rates of precipitation and dissolution are exerted by local shear and normal stresses, the chemical potential field, and the evolving topology of the fracture. In turn, these effects mediate the evolution of the transport (permeability) and mechanical properties (stiffness and shear strength) of fractures in rock. This study will clarify how these transformations progress with paths of deviatoric stress, temperature, fluid flux, and chemical potential, and for different fluid saturations.

These effects will be examined via flow-through tests on fractures continuously sheared within a double direct shear loading apparatus to return continuous measurements of evolving permeabilities, stiffnesses, and shear strengths. Tests will be conducted under controlled temperatures (20-300C), flow rates (0-2 cc/min), ambient stresses (0-50 MPa), and under controlled displacement rates (10-106 nm/s) slow enough to approach rates of mineral redistribution within the fracture. Recorded histories of flow impedance, mineral mass efflux, and normal displacement rate, will provide three independent measurements of evolving fracture aperture or porosity, in vivo. These observations, anchored with pre- and post-test fracture surface profilometry ~O(5 m), will provide uniquely constrained micro-mechanical data to support the development of process-based models. Particulate mechanics models will be developed to represent the essential features of two rough surfaces in contact, and to accommodate the birth and destruction of asperities bridging fractures via mechanical and chemical processes. These models will necessarily incorporate the serial processes of stress-mediated dissolution, diffusive transport, and free-face dissolution and precipitation, which together define the evolution of the mechanical and transport characteristics of the fracture. Transport modeling will be via linked Eulerian-Lagrangian methods that accommodate advection dominated flows, that interface with the evolving topology of the particulate mechanics model, and both constrain experimental observations and enable upscaling of the observations to field scale. Results will define critical processes and constrain the magnitudes of strain rates and fluid and mass fluxes where the generation of porosity out-competes its destruction, for a broad range of ambient stresses, temperatures, and paths of chemical potential.

Broader Impacts: In addition to the broad impacts these transport processes have in the safe entombment of radioactive wastes, the recovery of hydrocarbons, geothermal fluids, and potable water, and in the understanding of fluid cycling within the crust, a number of broader impacts are apparent. These include the cross-disciplinary exchange between the engineering and geophysics communities, the broad training of undergraduate and graduate students, and timely presentation and publication of results in the engineering and scientific literature.

0538195
Marone
This award supports a project to conduct laboratory experiments and numerical modeling to determine the constitutive properties of subglacial till under dynamic stressing and to test the hypothesis that granular properties of till are sufficient, when coupled elastically to a large ice stream, to reproduce the field observations of triggered slip and subglacial seismicity. Testing will be carried out in a servo-controlled biaxial shear device under controlled temperature and stress conditions, which will allow both sliding and microstructural processes to be studied in detail. The main focus of the work will be on laboratory measurements. In addition, we will construct continuum models to evaluate whether our results can predict complex ice sheet motions and observed characteristics of subglacial seismicity. In terms of broader impacts, the proposed work will encourage interactions between the rock-mechanics and glaciology communities and will bring together members of different scientific backgrounds and vocabularies, but similar problems and data. The project will train undergraduate and graduate students at Penn State University and the scientists involved plan to give presentations to grade school classes, scout groups, and at community open houses. Results will be presented at professional meetings and will be published in a timely manner. The work will result in a better understanding of glacial motion and the physics of earthquake slip, which is essential for understanding ice sheet dynamics and earthquake hazard.

0545702
Marone

The principal goal of the SAFOD borehole, and one of the main motivations for the NSF EarthScope initiative, is to gather critical data needed to understand fault mechanics and earthquakes. Through sampling, down-hole measurements, and long-term monitoring, the SAFOD experiment will provide data to test key hypotheses regarding long-term fault strength, earthquake nucleation, and fault slip behavior. However, the borehole itself will penetrate only a small part of the crustal volume surrounding the San Andreas Fault zone, and will sample only a subset of lithologies present in the subsurface. Although SAFOD will provide observations of the shallow seismogenic zone of a major plate bounding fault in unprecedented detail, additional characterization of rock physical properties for the 3-D volume containing SAFOD and the San Andreas Fault are critical for addressing several of the most important outstanding questions in fault mechanics and earthquake physics. These include: 1) What causes spatial variability in fault slip behavior and seismicity? 2) Are elevated fluid pressures within the SAFOD 3-D volume plausible? 3) How are geophysical observations such as low velocity or resistivity linked to in situ conditions of stress and fluid pressure? 4) What do thermal data in the shallow subsurface tell us about the fault energy budget?
We are conducting a comprehensive study of the processes and properties that affect mechanical behavior and transport properties of fault zones. The research involves laboratory measurements of SAFOD core and outcrop samples. These measurements are designed to characterize the deformation processes and physical properties of rocks from the 3-D SAFOD volume. This work complements ongoing work on SAFOD samples. The data we collect will inform regional geologic, hydrologic, and thermal models.
Our research is designed to address the following key objectives:
- Determine the frictional strength and constitutive properties for SAFOD core material and host rock adjacent to the San Andreas Fault.
- Test the hypothesis that the upper stability transition from aseismic to seismic faulting is associated with a change in mineralogy of fault gouge and/or host rock.
- Develop experimental constraints necessary to test 1) the hypothesis that the San Andreas Fault is weak in an absolute and relative sense, and 2) models of long-term pore pressure generation and dynamic fault weakening.
- Provide constraints on processes relevant to the energy budget of faulting: including frictional heat generation, advective heat transport, and thermal refraction.
- Investigate the relationship between frictional strength (including healing and steady-state velocity dependence), seismic wave speed, and permeability.
- Investigate the stress and pore pressure dependence of P and S wave speeds and their anisotropies in fault zone and wall rock, to evaluate and improve seismic-attribute proxies for pore pressure, effective stress, frictional strength, fluid content, and other properties inferred from borehole log and surface seismic data.
This research will provide an understanding of processes that govern the strength and stability of major faults. In addition, we will measure those properties of fault rock that determine remotely sensed geophysical signatures, which is important for better assessment of earthquake hazard and for linking observations of fault behaviors with fundamental physical processes.

Intellectual Merit: This research investigates the cause of the world's largest earthquakes, which occur along subduction plate boundaries. These "megathrust" earthquakes rupture sections of the plate boundary, but we still do not understand how the limits of these rupture patches are determined. Goals of the work are to identify reasons why some sections of subduction plate boundaries fail catastrophically in large earthquakes whereas other sections fail by aseismic creep. Identifying these processes is essential to understanding the seismic cycle and predicting the behavior of subduction zones on time scales relevant to tsunami generation and seismic hazard. The research tests two hypotheses for the up dip limit of the seismogenic zone using a complementary set of laboratory-based approaches that focus on (1) frictional properties, including the effect of lithification and consolidation state, clay mineralogy, effective stress, and drainage conditions on frictional constitutive properties; and (2) fluid transport properties between lithification and consolidation state, composition, permeability, and rheology. Samples from ocean drilling cores, exhumed faults, and synthetic fault gouge will be analyzed in carefully controlled laboratory experiments on natural and synthetic samples over P-T, fluid, mineralogical, cementation, and compaction conditions that span the stability transition. Experiments include friction measurements, consolidation tests, measurement of elastic properties and permeability to constrain elastic stiffness, and measurements of effective stress. Biaxial and frictional shear experiments will be carried out as will uniaxial deformation and flow through tests.

Broader Impacts: This research has the potential for significant societal impact from an improved understanding of fault mechanics and earthquake physics including tsunami generation and seismic hazard assessment. The effort also complements the NSF IODP and MARGINS programs. The project will train two graduate students and four undergraduate students with the students also getting opportunities to present the results of their research at professional meetings.

Collaborative Research: Laboratory Study of the Mechanics and Physical Properties of the active San Andreas Fault zone from Phase III SAFOD cores

Demian Saffer & Chris Marone, The Pennsylvania State University
Harold Tobin, The University of Wisconsin-Madison

One of the primary goals of EarthScope, and the SAFOD experiment in particular, is to improve our understanding of faulting and earthquakes. Through sampling, down-hole measurements, and long-term monitoring, the SAFOD experiment will provide data to test hypotheses regarding long-term fault strength, earthquake nucleation and recurrence, and the role of fluids in faulting. Laboratory investigations of the frictional, elastic, and fluid transport properties of fault and wall rocks are a key part of achieving these goals. This collaborative project focuses on laboratory measurements of frictional, permeability, and elastic properties for both the active San Andreas Fault (SAF) zone sampled during SAFOD Phase 3 drilling, and for outcrop samples of lithologies that represent the host rock for the cored SAF material. The PI's are applying their experimental results to understand processes governing (1) the strength, sliding stability, and healing of major faults, (2) the hydraulic behavior of faults - both locally as related to long-term and dynamic weakening mechanisms and regionally as elements within crustal scale fluid flow systems, and (3) the rock properties and in situ conditions that cause signatures observed remotely by geophysical surveys. The friction and permeability measurements are being carried out in the Penn State rock and sediment mechanics laboratory, under a range of stress conditions in both a uniaxial loading system and a true triaxial system. The friction experiments include measurements of shear strength and rate-and state parameters relevant to sliding stability, on both powdered gouge and intact "wafers" of material. Permeability measurements are being conducted using flow-through and transient techniques under a range of uniaxial strain and triaxial stress boundary conditions. The elastic property component of the study includes ultrasonic wave velocity and attenuation measurements on intact mini-cores conducted in a pressure vessel at the University of Wisconsin-Madison, and measurements on shearing layers as part of friction experiments at Penn State. Ultimately, this ongoing research will provide experimental constraints on rock properties for the San Andreas Fault system that relate to its mechanical strength, sliding stability, potential role as a barrier to regional fluid flow, and the interpretation of in situ conditions from geophysical data.

This is a proposal to complete a coordinated series of laboratory analyses of the properties and composition of sediments recovered from the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) drilling by the Integrated Ocean Drilling Program. The proposed work will generate laboratory data needed to test the core hypotheses of NanTroSEIZE, particularly as they relate to fault strength, pore pressure, and fault sliding stability. The work will produce comprehensive datasets describing mechanical and transport properties, lab-based constraints on in situ pore pressure and permeability within a fault system that generates great earthquakes and tsunamis, and integration of datasets to better understand how fluids, grain fabric, and mineral composition combine to modulate fault behavior.

Broader Impacts
The results will be broadly applicable to understanding fault strength, slip behavior, and pore pressure generation in seismogenic fault zones of all types. Societal relevance of NanTroSEIZE work is very strong. The project will support seven graduate students, several of whom were selected to sail during Stage 1 as shipboard scientists. It will also support several undergrads as lab assistants and for senior theses. Lab work will provide valuable data for the rest of the NanTroSEIZE research community, build a scientific foundation for planning forthcoming riser drilling, and generate considerable interest within the global fault-zone-drilling community. Outreach programs through IODP, CDEX, and JOI E&O structure.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

This project will investigate slip on tectonic faults and important processes that occur during earthquakes. We will focus on the frictional strength of faults and the role of underground fluids in modifying fault strength. Damaging earthquakes occur on major tectonic faults in a sequence that is often separated by 50 to 100 years or more. One important question for seismic hazard analysis is that of how fault strength is regained between earthquakes ?so called fault healing. This project will investigate fault healing via a combination of detailed laboratory experiments coupled with computational modeling and microscope-based studies of the fault zone textures. Faults in Earth's crust undergo a range of slip behaviors including earthquakes and non-damaging 'creep' events in which slip occurs without releasing damaging seismic waves. One of the goals of this project is to determine the microscopic and larger-scale factors that cause each type of slip behavior. This information will help us build more realistic models for seismic hazard around the country. Results of the project are expected to have significant impact on understanding faults and earthquakes including triggering of seismic and aseismic fault slip, fault interaction, and seismic hazard assessment.

Fault healing plays a central role in earthquake rupture processes at time scales ranging from tectonic to elastodynamic. Frictional healing (as evidenced by increasing static friction during quasi-stationary contact) is considered the most likely mechanism of interseismic and dynamic fault strengthening, and there is good agreement between laboratory-based friction laws and field observations of fault healing in some cases. However, laboratory data are limited in quantity and scope. Existing lab data do not provide a consistent explanation of fault healing as observed via repeating earthquakes, which indicate both increases and decreases in seismic moment as a function of time between successive events. Moreover, the physical processes of fault healing and, more generally, the micro-mechanisms of frictional rate/state effects are poorly understood.
This project will support a multidisciplinary investigation of fault healing. The work includes two general tasks. 1) Laboratory study of frictional healing and fault zone transport properties for a range of conditions (shearing rate, gouge material, normal stress, fluid properties, temperature). Experiments will be conducted under true-triaxial stress conditions using the double-direct shear configuration with controlled pore fluid pressure and flow through. We will measure healing via frictional strength, elastic properties of the fault zone, and hydraulic transmissivity during shear. Detailed microstructural studies of the deformed samples will be used to identify processes responsible for healing. 2) Coupled numerical, laboratory, and microstructural studies aimed at identifying the physico-chemical processes that determine fault healing, creep consolidation, and time-dependent fault weakening. Preliminary data are available in each area of proposed study

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Understanding the factors controlling the stress state and nature of slip on major tectonic faults is a fundamental problem in earthquake physics and fault mechanics. In particular, many major fault zones, including the San Andreas Fault, several well-studied subduction zone plate boundaries, and low angle normal faults appear to slip under anomalously low shear stresses (i.e., they are mechanically weak). Recent studies also provide conflicting views about the potential for seismic slip on modern low angle normal faults, which is of importance for earthquake hazard assessment. Much recent and ongoing work has focused on identifying the mechanisms causing fault weakness through sampling and instrumentation of active fault zones by drilling. Another approach is to study well-exposed exhumed faults that formed earlier in Earth's history, and which serve as analogs for active faults. This project focuses on low angle normal faults that formed in response to the regional crustal extension during the Miocene epoch (24 to 6 million years ago) in the area that is now the Mojave Desert of California and Arizona. These low angle normal faults dip shallowly, have accommodated tens of kilometers of slip, and appear to have slipped while severely misoriented, with the (vertical) maximum principal stress nearly perpendicular to the fault surface. Subsequent erosion has exhumed the fault zones from depths of 2-10 km, and has provided access to excellent exposures. This research project will characterize the frictional properties and stability of gouge and fault rock from these exhumed faults using a pressure vessel in the rock mechanics laboratory at Pennsylvania State University, in order to address two outstanding questions about low angle normal faults that bear on the underlying causes of fault weakness in general: (1) What is the absolute strength of natural fault gouge from low angle normal faults, and is the presence of weak clay minerals sufficient to explain their apparent mechanical weakness?; and (2) Are the frictional properties of the fault rock consistent with the possibility of earthquake nucleation on these structures? A particular feature of this work is the ability to test samples of intact fault gouge, which preserve their distinctive fabric and are likely to play a key role in governing their frictional behavior.

Earthquakes pose a major hazard to populated regions in much of the United States and globally. Both the overall mechanical strength and the nature of slip (whether it occurs via creep or by episodic failure in earthquakes) on major tectonic faults depend, to a large extent, on the physical properties of rock and gouge within these fault zones. Many major fault zones at plate tectonic boundaries appear to slip under anomalously low stresses, implying that they are mechanically weak. Low angle normal faults are one class of faults that exhibit this apparent mechanical weakness, and which are common throughout the southwestern United States. The potential for earthquakes on these faults is also a subject of significant debate, owing mainly to overall low slip rates and potentially long recurrence times that make hazard difficult to assess. This study will investigate the factors that control the strength and slip behavior of low angle normal faults through field mapping, sampling, and detailed laboratory study of fault material. The project will provide new insight into the mechanics of these structures, and will shed light on the mechanical behavior and stability of mechanically weak faults in general.

This project will develop a preliminary design and work-breakdown-structure for a large-scale subsurface experimental facility to investigate coupled thermal-hydrological-mechanical-chemical-biological processes in fractured rock at depth. The experiment will be part of the proposed Deep Underground Science and Engineering Laboratory (DUSEL) in the Homestake Mine, South Dakota. Many natural and engineered earth systems involve coupling of multiple processes in rocks that vary across a wide range of scales. The most pervasive process in the Earth?s crust that gives rise to strongly coupled phenomena is the flow of fluids (water, CO2, hydrocarbons, magmas) through fractured heated rock under stress. Understanding changes in the reactivity, deformability, life-supporting and transport properties of rocks that fluids infiltrate is important in a broad range of geological engineering and geological science endeavors. Despite this fundamental importance, the interactions remain poorly understood.

The project will: (1) Determine properties of Homestake rocks: geological, geochemical, mechanical, thermal, isotopic, and reactivity. (2) Upscale these data to elucidate transport mechanisms (conductive versus convective), natural reaction rates in fractures, and microbial community evolution. (3) Evaluate monitoring strategies, in-situ probes and sampling methods, and necessary measurements. (4) Select a candidate site for the evaluating coupled processes. (5) Develop a work-breakdown-structure. (6) Develop a coupled numerical model to evaluate potential effects on the rock mass and optimal heater configuration, power, and monitoring borehole orientations.

The models and insight from these experiments will have broad applicability to engineered systems, e.g., enhanced geothermal systems, CO2 sequestration and subsurface contaminant transport. Educational outreach will involve facility tours and a traveling benchscale ?mock-up? demonstration experiment.

We are working to understand the physical properties of large-scale tectonic faults in Earth's crust, with particular focus on the San Andreas Fault in California. As part of the San Andreas Fault Observatory at Depth (SAFOD) drilling recently penetrated the fault at a depth of ~ 2.5 km. We are studying core recovered during this drilling (SAFOD phase III) along with synthetic fault gouge, samples collected at the surface in the vicinity of the SAFOD borehole, and cuttings from drilling in and around the fault. Only a small amount of core was recovered from the active strand of the fault; therefore, we are using the other materials to expand our data set and investigate physical processes within the fault. Our work is focused on: 1) detailed measurements of frictional properties and permeability of the samples, 2) development of process-based models for controls on fault strength and stability, 3) development of innovative methods to study the role of fault zone fabric on frictional stability and physical properties, and 4) integration of laboratory results with models for fluid flow and heat transport, which will allow critically evaluation of hypotheses for apparent fault weakness. Outstanding questions that we are addressing include: 1) What causes spatial variability in fault slip behavior and seismicity? 2) Are elevated fluid pressures within the SAFOD 3-D volume plausible? 3) How are geophysical observations such as low velocity or resistivity linked to in situ conditions of stress and fluid pressure? 4) Does the fault zone act as a barrier for regional and local fluid flow? 4) Does significant fault healing occur in materials comprising the active SAF, and if so, what is the acoustic (seismic) signature, if any? 5) How are fault zone frictional, elastic, and transport properties linked with those of the surrounding protolith (in other words, how does protolith composition influence fault zone properties)?

Our work complements studies by other groups working on SAFOD samples as well as a substantial body of work at Penn State focused on other fault zone drilling projects, such as NanTroSEIZE. Results of the proposed experiments will have societal impact through improved understanding of fault mechanics and earthquake physics, applied to the best-studied and best-instrumented plate boundary fault on Earth.

This project will investigate fluid flow within rock masses in the shallow regions of Earth's crust, from the surface to ~10 km. Our work will focus on how dynamic stresses, for example caused by seismic waves, change flow properties of Earth's crust. Previous work shows that fluid permeability can change dramatically when rocks are shaken during earthquakes. The effects of strong shaking can be estimated, but the effects of weak shaking, for example due to a distant earthquake, are less well understood. We will perform laboratory experiments to investigate the processes and mechanisms that cause transient and permanent permeability changes due to dynamic stressing. The lab work will be coupled with theory and numerical methods to develop conceptual and quantitative models for permeability changes.

Elastic waves produced during earthquakes can trigger a range of phenomena including seismicity, volcanic eruptions, and geyser activity. Dynamic stressing via the passage of seismic waves (or from other sources of transient loads) can also increase spring discharge, fluid flow in streams, and oil production, in some cases tripling the effective permeability of the natural system. These observations have been attributed to shaking-induced changes in permeability of shallow aquifers. However, the underlying mechanisms and the affect of dynamic stresses on poromechanical properties of rocks are poorly understood. Here we propose to investigate permeability enhancement by dynamic stressing using a multidisciplinary approach. Our preliminary work shows clear evidence of permeability enhancement in fractured rock subject to fluid pressure oscillations. The proposed work will expand the laboratory data while developing the theory and focusing on the underlying mechanisms. We will use knowledge of the processes and mechanisms operative in the laboratory to address the problem of upscaling our results to field conditions. We propose a series of experiments and models informed by observations of natural systems to (1) establish clear relationships between the controlling variables and the resulting changes in permeability, (2) analyze the physics of the enhancement and identify the underlying processes and (3) build appropriate numerical models of the results that can be applied at the laboratory and field scales. Results of the proposed experiments are expected to have significant impact on understanding fluid flow in the Earth's crust and seismic hazard. Understanding the physical basis for transient changes in permeability will lead to improved engineering approaches for oil reservoir and hydrological use.

Abstract

Funds are provided for a post-doctoral study of deformation and slip behaviors in subduction systems by an experimental approach combined with seismic data and microstructure observations. The PIs will conduct friction experiments on smectite and illite at elevated temperature and measure the acoustic wave velocities on sediment core samples at different stress states. Results of the friction experiments will be used to further test the hypothesis of smectite-illite transition for updip limits of seismicity. The measurements of acoustic wave velocities at different stress states will allow the PIs to estimate the in-situ stress states and pore pressure in subduction systems by incorporating with seismic data. Samples and data from the IODP NanTroSEIZE transect area will be used to investigate the in situ stress and pore pressure conditions.

Broader Impacts
The award will support a young female researcher as a MARGINS/GeoPRISMS postdoctoral fellow. The proposed research aims to understand the evolution of slip behavior at the upper limit of the seismogenic zone and the deformation mechanisms in subduction zone fault systems and accretionary prisms. The focal points of the proposed study are also aligned with key questions of the Subduction Cycles and Deformation initiative within the new GeoPRISMS program. Understanding the mechanics and in situ conditions of faulting deformation at subduction plate boundaries has both scientific and social significance in terms of earthquake prediction and disaster prevention.

Scientists have long known that most large, destructive earthquakes are caused by the slow buildup of stress on fault zones at the boundaries between tectonic plates. Friction between the two sides of the fault holds it together and prevents slip while stress accumulates until the point of failure, precipitating the earthquake itself. However, the nature of how and why that failure occurs and grows into a large earthquake remains poorly understood. It is thought to be governed in large part by the materials that make up the fault zone ? the rock that is fractured and broken down by past earthquakes and the water that fills pore spaces in that rock, as well as the tectonic stresses at the depth of earthquakes.

To further our understanding of how faults work, an international team of scientists is conducting a 3-stage project to drill into New Zealand?s Alpine Fault, a major fault zone similar to the San Andreas of California, with a history of magnitude 7-8 earthquakes, and future potential for more. Drilling into the Alpine Fault will provide fresh samples from the fault zone unaltered by the negative effects of earth-surface weathering and erosion. The first stage, already drilled to 150 meters depth, obtained core samples across the fault zone and made measurements of the rock properties made by instruments placed down the holes. In the next stage, one or more holes will be drilled to more than 1500 meters depth, and is intended to sample across the fault at earthquake depths. As part of that effort, the University of Wisconsin-Madison and Penn State University partnership will measure a range of properties of these samples, including their strength (friction-based resistance to slip and the capacity to store up strain without breaking), permeability to pore water movement, and the speeds with which they transmit two types of seismic waves (a widely used way to measure rock properties remotely) under realistic conditions.

Furthermore, instruments lowered down the drill holes will be used to measure similar and additional properties at a broader scale. Using the results of sample and the drillhole data, the investigators will evaluate competing hypotheses for the strength of fault zones and the conditions therein, helping discover what happens inside faults between earthquakes, and how they may change leading up to future seismic activity. They will also evaluate the nature of groundwater flow (or lack thereof) in and around the fault zone at depth, important for understanding the pressure and temperature conditions during fault activity. This research, when combined with the complementary work by New Zealand-based collaborators and others, will yield a new understanding of how fault zones work and why earthquakes happen in the ways that they do. It will likely also yield new clues to understanding the future earthquake hazard on the Alpine Fault in particular and on major faults in general.

This workshop is to bring together the Rock Mechanics and COMPRESS Mineral Physics communities to gather requirements for the NSF-funded EarthCube initiative whose goal is to design and implement a new data and knowledge management system for the geosciences. The workshop will assemble a group of about 70 experts in rock deformation and high-pressure mineral physics to discuss their cyberinfrastructure needs in terms of data, modeling, and visualization. Goals will be to surface cyberinfrastructure needs that are presently holding these communities back and to enable their ability to address fault-slip behaviors, brittle-ductile transitions in lithologic materials, scientific drilling, deformation processes in subduction zones, and the physical, chemical, and electronic properties of geologic materials in the deep Earth. The two and a half day workshop will be held in Alexandria, Virginia in early November of 2013. A catalyzing issue of the workshop concerns the nature and reporting of experimental and observational data. Addressing these cyberinfrastructure needs represents a fundamental challenge to digital representation/integration and allowance of broad public access to data from this field that can be aided by involvement with EarthCube. This project is important for both the scientific and cyberinfrastructure development of the geosciences. Future progress of the geosciences will be based on the integration of rich and diverse datasets. This workshop will identify the needs of one of the most important and societally relevant groups in Earth Science. There will be a vast array of intellectually challenging tasks in describing and integrating data across a spectrum of scales as well as granularity that will be addressed at the workshop. Broader impacts of the work include provisions for improving public access to data from these fields, especially for those interested in studying earthquakes or assessing and manageing their impacts. it also builds infrastructure for science in terms of helping create more effective and interoperable data and modeling frameworks. The workshop will also emphasize the inclusion of early career researchers, thus ensuring the needs are met of the next generation of rock deformation professionals.

Subduction zone earthquakes where 'runaway slip' allows faulting to rupture from depth all the way up to the seafloor can cause enormous tsunamis that devastate coastal population centers. Not all subduction zone earthquakes develop runaway slip- details of a particular fault's frictional behavior dictate what happens. This study will conduct laboratory experiments to determine how different types of fault rock respond to applied forces. Results could improve understanding of whether some subduction zones are more, or less, likely to generate megathrust earthquakes.

Current understanding of the mechanical response to shear stress of fault rock is limited by the lack of measurements on relevant natural samples at in-situ conditions. Laboratory shear measurements will document friction at in-situ pressures and temperatures using natural fault zone material. A transition in clay structure is thought to play an important role, along with mineral fabric and pore fluid pressure. A series of experiments on both crushed samples and intact wafers will be conducted. Start and end microstuctural and geochemical analyses will quantify the shearing impacts. Interpretation will focus on the nucleation phase of megathrust earthquakes. A female postdoctoral scientist will lead the study and the results will contribute to advancing knowledge within the GeoPRISMS program initiative 'Subduction Cycling and Deformation'.

Earthquakes represent a sudden release of elastic energy that is stored in the rocks adjacent to tectonic faults, driving catastrophic failure. In normal (fast) earthquakes the rupture zone expands at a few kilometers per second, and fault slip rates reach 1 to 10 meters per second. However, tectonic faults also fail in slow earthquakes with rupture durations of months or more and fault slip speeds of a of small fraction of an inch per second or less. Recent work shows that tectonic faults fail in spectrum of slip modes that includes slow earthquakes, normal (fast) earthquake, and many other forms of slip. These slow modes of slip can transfer stress to the fast earthquake zone and potentially trigger damaging, normal earthquakes. However, we know very little about the mechanics of slow earthquakes. This research effort will address questions such as: what determines the rupture speed of slow earthquakes? A central element of this work is carefully conducted laboratory studies of repetitive, slow stick-slip events with continuous measurement of acoustic emission, elastic wave speed and amplitude, and fault zone friction behavior. Hypotheses to be tested include: 1) does slow slip failure represents prematurely arrested normal (fast) slip for a range of materials and 2) can the same fault zone can host slow and fast slip behaviors.

Slow earthquakes are one form of transient fault slip that may load seismogenic portions of fault zones and abet damaging earthquakes. The origin of slow earthquakes and related forms of transient fault slip is poorly understood. The project will take a systematic approach to investigate: 1) the underlying processes of slow slip, with focus on the frictional mechanisms and continuum coupling that may explain the spectrum of fault slip behaviors in nature, 2) microstructural studies of the laboratory samples to assess how shear localization and strain distribution compare between normal (fast) and slow stick-slip, and 3) acoustic measurement of fault zone elastic properties, with particular focus on precursors to failure. The proposed study will extend the analogy between frictional stick-slip and normal (fast) earthquakes to include slow slip events. The results will provide insight on the mechanics of slow earthquakes and other forms of quasi-dynamic fault slip. All data and results obtained will be published in peer-reviewed journals and made available via public websites.

In the earthquake-cycle, tectonic faults slowly accumulate stress, due to plate tectonic motion of Earth?s surface, and then fail catastrophically in earthquakes. One of the keys to simulating the earthquake cycle are friction laws that can be applied to both the fast, dynamic motion of earthquakes, as fault rocks rub and slide past one another in frictional contact, and the slow processes of stress accumulation between earthquakes that can take hundreds of years. In this collaborative work between Princeton and Penn State Universities, unusually well-controlled measurements of frictional sliding will be conducted while collecting simultaneous ultrasonic data on the sliding interfaces and sheared layers of fault gouge. The proposed work has important societal implications for seismic hazard assessment, earthquake forecasting, and an improved, fundamental understanding of earthquake nucleation.

Rate-and-state friction laws represent the current state-of-the-art in the laboratory and for numerical simulations of earthquake physics, including nucleation, dynamic rupture and the complete seismic cycle. However, our understanding of friction memory effects and slip velocity dependence remains primarily empirical, which limits our ability to apply laboratory measurements to earthquake faults and/or to address the problems associated with predicting the behavior of tectonic faults from laboratory measurements. To address these shortcomings, recent advances in ultrasonic monitoring of sliding rock surfaces and sheared granular fault gouge will provide fundamental insights into the physics and micro-mechanical origins of frictional behavior of tectonic faults.

When viewed at the micro-scale, rocks reveal structures that help to interpret the processes and forces responsible for their formation. These microstructures help to explain phenomena that occur at the scale of mountains and tectonic plates. Interpretation of microstructures formed in nature during deformation is aided by comparison with those formed during experiments, under known conditions of pressure, temperature, stress, strain and strain rate, and experimental rock deformation benefits from the ground truth offered through comparison with rocks deformed in nature. However, the ability to search for relevant naturally or experimentally deformed microstructures is hindered by the lack of any database that contains these data. The researchers collaborating on this project will develop a single digital data system for rock microstructures to facilitate the critical interaction between and among the communities that study naturally and experimentally deformed rocks. To aid in the comparison of microstructures formed in nature and experiment, we will link to commonly used analytical tools and develop a pilot project for automatic comparison of microstructures using machine learning.

Rock microstructures relate processes at the microscopic scale to phenomena at the outcrop, orogen, and plate scales and reveal the relationships among stress, strain, and strain rate. Quantitative rheological information is obtained through linked studies of naturally formed microstructures with those created during rock deformation experiments under known conditions. The project will develop a single digital data system for both naturally and experimentally deformed rock microstructure data to facilitate comparison of microstructures from different environments. A linked data system will facilitate interaction between practitioners of experimental deformation, those studying natural deformation and the cyberscience community. The data system will leverage the StraboSpot data system currently under development in Structural Geology and Tectonics. To develop this system requires: 1) Modification of the StraboSpot data system to accept microstructural data from both naturally and experimentally deformed rocks; and 2) Linking the microstructural data to its geologic context ? either in nature, or its experimental data/parameters. The researchers will engage the rock deformation community with the goal of establishing data standards and protocols for data collection, and integrate our work with ongoing efforts to establish protocols and techniques for automated metadata collection and digital data storage. To analyze the microstructures studied and/or generated by these communities, we will ensure StraboSpot data output is compatible with commonly used microstructural tools. They will develop a pilot project for comparing and analyzing microstructures from different environments using machine-learning.