Executive Summary: Fault Mechanics and Earthquakes

Although we have long understood that earthquakes occur along faults, our knowledge of the overall physical processes, in-situ mechanical, chemical and hydrological conditions, and temporal evolution of these processes before, during, and after an event remain poorly constrained. Furthermore, our understanding and ability to model such geologic systems and forecast their future evolution is hampered by the lack of observations of structures, conditions, and temporally evolving stresses, strains, temperatures, microseismicity, and fluid fluxes at seismogenic depths. This group seeks to better understand the physics of earthquakes and time evolution of the near fault volume in seismically active regions. As described below, a fundamental and comprehensive understanding of earthquakes and the seismogenic crust requires scientific drilling, sampling, downhole measurements, and long-term surface and borehole observations. The outcomes of described projects could: lead to improved constraints on factors controlling earthquake size, recurrence and stress interactions; provide key constraints on near-fault properties for complementary theory and modeling efforts; assist in mitigating anthropogenically induced seismicity related to energy exploration/development; play an important role in the green energy transition; and result in risk reduction in geologic carbon sequestration, enhanced geothermal systems, and saltwater disposal applications.

Scientific Question 1: What controls the initiation, propagation, and arrest of natural and induced fault slip?

●  How does the interplay between stress distribution, fluid conditions, fault material and geometry control slip behavior, timing, and potential earthquake size(s)? What is the role of aseismic fault slip in controlling earthquake nucleation and recurrence?

●  What triggers fault slip? How and under what conditions do subsurface fluid pressure or stress perturbations impact the resulting style and magnitude of slip? Can the resulting hazard, natural or induced, be simulated and forecast?

●  Do precursory geophysical signals occur prior to earthquake nucleation? Are those signals observable? How could they contribute to earthquake early warning?

Context: Seismic observations, laboratory studies of natural and simulated fault rocks and surfaces, and theoretical models hint at a complex interplay between fault geometry, fluids, friction, composition, and stress in controlling fault slip initiation, propagation, and arrest. Yet, we lack constraints on many of these properties, their interactions, and influence on earthquake occurrence at seismogenic depths. Further, precursory phenomena, specifically nucleation processes predicted by leading theories, have not been observed for natural earthquakes. Recent earthquakes like the 2011 Mw9.1 Tohoku, the 2014 Mw8.1 Iquique, and the 2024 Mw7.6 Noto earthquakes were preceded by slow slip and/or swarms of earthquakes. Nearfield observatories in areas of ongoing seismicity would allow subtle features associated with earthquake initiation, if present, to be observed and characterized. Further, installing instruments within a target fault zone via drilling, would allow for the direct test of current theories related to earthquake nucleation and rupture propagation. By understanding the controls on earthquake occurrence and whether precursory signals exist, we can provide more accurate estimates of hazard and potentially improve earthquake warnings for both natural and anthropogenic earthquakes.

Scientific Question 2: What are the in-situ conditions of the near-fault volume at seismogenic depths and how do they evolve through time?

●  What are the geometries, compositions, textures, petrophysical properties in the vicinity of faults and how do they evolve with time?

●  What are the fluid transport regimes, fluid pressures, fluid chemistries, and fluid-rock interactions in and near faults and how are they related to fault/earthquake behavior?

●  What temperatures are encountered near and within fault zones at seismogenic depths and what do they tell us about fluid flow, mineral stability, and static and dynamic fault strength?

●  How can improved understanding of tectonic and geochemical controls on the hydrogeology of active faults impact our ability to evaluate and utilize geothermal energy resources and better understand the formation of critical minerals?

Context: Fault zones are highly complicated structures composed of heterogeneous, chemically altered and broken materials that provide important heterogenous conduits for fluids. Further, the properties of the fault volume change throughout time. Characterizing faults and the surrounding volume at seismogenic depths is critical as these structures play an important role in a variety of societal issues. Slip along faults can lead to a host of geologic hazards, including large, damaging earthquakes. Additionally, fault zones provide both pathways and barriers to fluid migration in the crust that are key factors in controlling mineralization, temperature, and subsurface environments that promote microbiological communities. Most of our knowledge of these structures come from mapping and sampling of faults exposed at the surface. These studies have dramatically increased our knowledge of faults but may not reflect and preserve the conditions at depth, and often do not capture the change in properties over time. Quantifying a range of near-fault properties before, during, and after slip also supports theoretical and modeling efforts within the broader community. Scientific drilling combined with long-term downhole observations within and adjacent to fault zones is required to make progress in answering the questions above.

Characteristics of Potential Projects

●  Significant, recent, and/or ongoing perturbations to the geologic system resulting in detectable fault slip, i.e. a site with a high probability of a natural or induced earthquake over the project timescale.

●  A representative volume of rock that includes the fault must be well characterized and continuously monitored at depth.

●  Conditions (i.e. logistically accessible and clearly defined target) favorable for an in-situ experiment.

●  Potential opportunities for leveraging resources by studying faults associated with ongoing anthropogenic subsurface activities.

Context: Potential scientific drilling projects require several characteristics to ensure success. In order to make progress on the scientific questions above, any potential project would need to occur in an area that is already well-characterized and instrumented. Further, as the in-situ observation of fault slip is a goal of such projects, these projects could either be performed in an area with ongoing fault slip or entail a controlled, well-designed active earthquake experiment. Such target areas would ensure that perturbations would occur on typical project timescales. Finally, as mitigating (i.e. carbon sequestration and other deep geological repository applications) and enhancing (i.e. enhanced geothermal systems) subsurface fault slip is of critical societal importance, potential projects should seek participation and funding from multiple agencies and organizations, both national and international.

Necessary Resources

●  Guidance and assistance in securing funding from a range of government agencies and/or industry partners.

●  Continued support for site characterization and subsurface data collection.

●  PI access to project planning and management resources throughout the life of the project.

●  Core sample handling, processing, and storage with open and managed access for research

●  The resources and alacrity to support rapid response drilling projects.

●  Hardened downhole instrumentation to allow for long-term observation under elevated temperatures and pressures.

●  Utilization of improved deviated drilling technologies and crustal imaging techniques for study.

Context: The questions posed above require continuous observation of numerous controlling factors including strain and microseismicity, temperature, fluid fluxes and chemistries, rock physical properties and their anisotropy, and even microbiomes within the complex fault zone at seismogenic depths. These parameters need to be captured as the rock mass experiences significant perturbations and associated slip events or hydrologic transients. Thus, the scope of the drilling project and monitoring effort will be significant and ongoing, requiring funding and participation from multiple government and industry partners, resources committed to project planning and management, and site characterization studies. Projects would need to make a range of measurements of the near-fault region in 4D, requiring sampling and observing at dense locations along and across the fault. Technologies for drilling, completion and instrumentation of highly deviated boreholes have significantly advanced over the last decade, enabling vastly better access to the near-fault volume. The elevated depths and temperatures remain a challenge for long-term monitoring and will require hardened instrumentation. Fiber optic technologies for monitoring of absolute static and dynamic strains, pore pressures, permeability fields, seismic signals, and temperature will complement more traditional, higher fidelity point measurements.

Suggested Citation

Carpenter, B., Cochran, E., Eichhubl, P., Ellsworth, B., Guglielmi, Y., Hayman, N., Hickman, S., Kolawole, F., Petrie, E., Schmitt, D., Sone, H., Tobin, H., Zumberge, M., Zakharova, N., 2024. Fault Mechanics and Earthquakes Science Planning for Continental Drilling and Coring 2024. https://sites.google.com/umn.edu/csdscienceplanning/home/fault-mechanics-and-earthquakes-executive-summary

Fault Mechanics and Earthquakes Working Group

Brett Carpenter, University of Oklahoma

Elizabeth Cochran, United States Geological Survey

Peter Eichhubl, University of Texas

Bill Ellsworth, Stanford University

Yves Guglielmi, Lawrence Berkely National Lab

Nicholas Hayman, Oklahoma Geological Survey

Stephen Hickman United States Geological Survey

Folarin Kolawole, Lamont Doherty Earth Observatory Columbia University

Jeff McGuire, United States Geological Survey

Elizabeth Petrie, Western Washington University

Lara Rodriguez-Delgado, George Washington University

Demian Saffer, University of Texas Austin

Doug Schmitt, Purdue University

Martin Schoenball, National Cooperative for the Disposal of Radioactive Waste

Hiroki Sone, University of Wisconsin Madison

Harold Tobin, University of Washington

Robert Viesca, Tufts University

Mark Zumberge, Scripps Institute of Oceanography

Natalia Zakharova, Central Michigan University

Fault Mechanics and Earthquakes Community Editors

Rachel Abercrombie, Boston University

Kusumita Arora, CSIR-National Geophysical Research Institute

Ramon Arrowsmith, Arizona State University

Scott Ausbrooks, Arkansas Geological Survey

Andrew Barbour, United States Geological Survey

Pathikrit Bhattacharya, National Institute of Science Education and Research

Susan Bilek, New Mexico Institute of Mining and Technology

Michael Blanpied, United States Geological Survey

Emily Brodsky, University of California Santa Cruz

Megan Brown, Northern Illinois University

Marco Calo, National Autonomous University of Mexico

Frederic Cappa, Université Côte d'Azur

Jingyi Chen, University of Tulsa

Judith Chester, Texas A&M University

Cristiano Collettini, University of Rome

Michele Cooke, University of Massachusetts Amherst

Shanker Daya, Indian Institute of Technology Roorkee

Andrew Delorey, Los Alamos National Laboratory

Heather DeShon, Southern Methodist University

Scott DeWolf, Clemson University

John Doveton, Kansas Geological Survey

Eric Dunham, Stanford University

David Eaton, University of Calgary

Houda El Kerni, University of New Mexico

James Evans, Utah State University

Becky Flowers, University of Colorado Boulder

William Foxall, Lawrence Berkeley National Lab

James Gaherty, Lamont-Doherty Earth Observatory Columbia University

Dmitry Garagash, Dalhousie University

Peter Geiser, G-O Image

John Geissman, University of Texas Dallas

Leonid Germanovich, Clemson University

Charles Gilbert, University of Oklahoma

Sean Gulick, University of Texas Austin

Harsh Gupta CSIR-National Geophysical Research Institute

Todd Halihan, Oklahoma State University

Rebecca Harrington, BKV Corporation

Steve Holloway, University of Oklahoma

Ben Holtzman, Lamont-Doherty Earth Observatory Columbia University

Matt Ikari, Universität Bremen

Ahmed Ismail, Maxima Geophysics

Klaus Jacob, Lamont-Doherty Earth Observatory Columbia University

Priyank Jaiswal, Oklahoma State University

Randy Keller, University of Oklahoma

Won-Young Kim, Lamont-Doherty Earth Observatory Columbia University

Jamie Kirkpatrick, McGill University

Martha Kopper, Arkansas Geological Survey

Li-Wei Kuo, National Central University

Yajing Liu, McGill University

David Lockner, United States Geological Survey

Kuo-Fong Ma, National Central University

M. Beatrice Magnani, Southern Methodist University

Kurt Marfurt, University of Oklahoma

Chris Marone, Penn State University

Trenton McEnaney, Missouri University of Science & Technology

Art McGarr, United States Geological Survey

Greg McLaskey, Cornell University

Diane Moore, United States Geological Survey

James Mori, Kyoto University

Yusuke Mukuhira, Tohoku University

Larry Murdoch, Clemson University

Bhupati Neupane, Tribhuvan University

Kentaro Omura, National Research Institute for Earth Science and Disaster Resilience

Patricia Persaud, University of Arizona

Katrin Plenkers, Gesellschaft für Geophysik und Materialprüfung

Cecil Raleigh, University of Hawaii

Ze’ev Reches, University of Oklahoma

Christine Regalla, Northern Arizona University

Paul Richards, Lamont-Doherty Earth Observatory Columbia University

Alan Rooney, Yale University

Zach Rosson, GEOSITE

Christian Rowan, Columbia University

Shmuel Rubinstein, Hebrew University of Jerusalem

Seth Saltiel, Cornell University

Heather Savage, University of California Santa Cruz

Jean Schmittbuhl, University of Strasbourg

Chris Scholz, Columbia University

Marco Scuderi, Sapienza University

Bruce Shaw, Lamont-Doherty Earth Observatory Columbia University

Donna Shillington, Lamont-Doherty Earth Observatory Columbia University

Ramesh Singh, Chapman University

Rob Skarbek, Planetary Science Institute

Sean Solomon, Lamont-Doherty Earth Observatory Columbia University

Robert Stewart, University Houston

Ming Suriamin, University of Oklahoma

Takaaki Taira, University of California Berkeley

Christopher Thom, Rhenium Alloys

Terry Tullis, Brown University

Ben van der Pluijm, University of Michigan

Jake Walter, Oklahoma Geological Survey

Steven Wesnousky, University of Nevada Reno

Charles Wickstrom, Iron Hawk Energy

Chen Xiaowei, Texas A&M University

Yasuo Yabe, Tohoku University

Hongfeng Yang, Chinese University of Hong Kong

Zhuo Yang, Harvard University

Molly Yunker, Oklahoma Geological Survey

Tieyuan Zhu, Penn State University

Mark Zoback, Stanford University

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