SCEC5 Bridge Period (2022-2023)

The Southern California Earthquake Center (SCEC) was founded as a Science & Technology Center on February 1, 1991, with joint funding by the National Science Foundation (NSF) and the U. S. Geological Survey (USGS). Since 2002, SCEC has been sustained as a stand-alone center under cooperative agreements with both agencies in three consecutive, five-year phases (SCEC2–SCEC4). The Center was extended for another 5-year period, effective 1 February 2017 to 31 January 2022 (USGS SCEC5) and 1 May 2017 to 30 April 2022 (NSF SCEC5). NSF has extended SCEC5 for a 6th year and the USGS has invited a separate bridge proposal to span the anticipated 2 year time period for the start of a potential new earthquake center. We refer to this time as “The Bridge Period.”

The SCEC5 strategic framework (see full SCEC5 proposal) has updated priorities that build on established strengths of the SCEC collaboration in coordinating fundamental PI-driven research and integrating the results into state-of-the-art community models, software and other products. This includes updated research topics that advance the understanding of earthquake processes. Given the limited time and resources available during the bridge period, these steps will be limited, judicious. As during SCEC5, the science plan is cast in terms of five basic questions of earthquake science that form the basis of the SCEC research program: (1) How are faults loaded on different temporal and spatial scales? (2) What is the role of off-fault inelastic deformation on strain accumulation, dynamic rupture, and radiated seismic energy? (3) How do the evolving structure, composition and physical properties of fault zones and surrounding rock affect shear resistance to seismic and aseismic slip? (4) How do strong ground motions depend on the complexities and nonlinearities of dynamic earthquake systems? (5) In what ways can system-specific studies enhance the general understanding of earthquake predictability?

1. How are faults loaded across temporal and spatial scales?

1a. Refine the geologic slip rates on faults in Southern California, including offshore faults, and optimally combine the geologic data with geodetic measurements to constrain fault-based deformation models, accounting for observational and modeling uncertainties.

1b. Determine the spatial scales at which tectonic block models (compared to continuum models) provide descriptions of fault-system deformation that are useful for earthquake forecasting.

1c. Develop an integrated quasi-static modeling framework incorporating information in the community models, and apply it to estimate the stress field and its uncertainties, to be updated periodically.

1d. Quantify stress heterogeneity on faults at different spatial scales, correlate the stress concentrations with asperities and geometric complexities, and model their influence on rupture initiation, propagation, and arrest.

1e. Quantify stress heterogeneity on faults at different spatial scales, with various techniques including ML analyses of fault maps and topographic and imagery data, and model their influence on rupture initiation, propagation, and arrest.

2. What is the role of off-fault inelastic deformation on strain accumulation, dynamic rupture, and radiated seismic energy?

2a. Determine how off fault deformation contributes to geodetic estimates of strain accumulation and what fraction of seismic-moment accumulation is relaxed by aseismic processes.

2b. Explore machine learning (ML) and other approaches to represent the effects of nonlinearity that would allow the continued use of linear wave propagation as an effective approximation.

2c Constrain the properties of rock damage in fault-zones and in the subsurface, as well as the factors, such as initial properties, loading conditions and pore fluid pressure, that are likely to influence it.

2d. Understand how inelastic strain and changes of elastic moduli within and around faults influences rupture propagation, seismic radiation, and scaling of earthquake source parameters.

2e Describe how fault geometry and rock damage interact to determine the probability of rupture propagation through structural complexities, and determine how model-based hypotheses about these interactions can be tested by the observations of accumulated slip,paleoseismic chronologies, and other near-fault observations.

3. How do the evolving structure, composition and physical properties of fault zones and surrounding rock affect shear resistance to seismic and aseismic slip?

3a. Assess the roles of transient volumetric changes before, during and after ruptures by: analyzing near-fault seismic and geodetic data, conducting geological studies of signatures of tensile failures (e.g., pulverization), performing related laboratory experiments, and through numerical modeling.

3b. Constrain the geometry of active faults across the full range of seismogenic depths, including structures that link and transfer deformation between faults.

3c. Assess how shear resistance and dilatational effects depend on the maturity of the fault system, and how these and different products of energy dissipation on and off-faults are expressed geologically.

3d. Determine how damage zones, crack healing and cementation, fault zone mineralogy, and off-fault damage govern the degree of strain localization, the state and stability of slip (e.g., creeping vs. locked, seismic vs aseismic), interseismic strength recovery, and rupture propagation.

3e Constrain the extent of permanent, off-fault deformation, and its contribution to geologic and geodetic fault slip-rate estimates.

3f. Study the mechanical and chemical effects of fluid flows, both natural and anthropogenic, on faulting and earthquake occurrence, and how they vary throughout the earthquake cycle.

3g. Assess the importance of the mechanical properties of the near-surface in reconciling geodetic and seismological estimates of fault slip at depth with fault offset at the surface.

4. How do strong ground motions depend on the complexities and nonlinearities of dynamic earthquake systems?

4a. Determine the relative roles of fault geometry, heterogeneous frictional resistance, crustal material heterogeneities, intrinsic attenuation, shallow crust nonlinearities and ground surface topography in controlling and bounding ground motions.

4b. Develop multi-scale velocity models, with high-resolution information around faults and near the surface embedded in the regional models, and validate the merged multi-scale models.

4c. Perform elastic ground-motion simulations for anticipated large events suitable for probabilistic seismic hazard and risk analysis, using the multi-scale velocity models up to frequencies justified by the small-scale information included in the models.

4d. Develop ML techniques to modify linear ground-motion simulations to fit observed ground motion generated by moderate and large earthquakes at various sites.

4e. Communicate the impact of physics-based seismic hazard analysis to earthquake engineers, emergency responders, and the general public.

5. In what ways can system-specific studies enhance the general understanding of earthquake predictability?

5a. Develop earthquake simulators that encode the current understanding of earthquake physics including off-fault yielding and predictability.

5b. Place useful geologic bounds on the character and frequency of multi-segment and multi-fault ruptures of extreme magnitude.

5c. Assess the limitations of long-term earthquake rupture forecasts by combining patterns of earthquake occurrence and strain accumulation with neotectonic and paleoseismic observations of the last millennium.

5d. Test the hypothesis that “seismic supercycles, seen in earthquake simulators actually exist in nature and explore the implications for earthquake predictability.

5e. Exploit anthropogenic (induced) seismicity as experiments in earthquake predictability.

SCEC5 (2017-2021)

The SCEC5 Science Plan was developed by the non-USGS members of the SCEC Planning Committee and Board of Directors with extensive input from issue-oriented “tiger teams” and the community at large. The strategic framework for the SCEC5 Science Plan is cast in the form of five basic questions of earthquake science: (1) How are faults loaded on different temporal and spatial scales? (2) What is the role of off-fault inelastic deformation on strain accumulation, dynamic rupture, and radiated seismic energy? (3) How do the evolving structure, composition and physical properties of fault zones and surrounding rock affect shear resistance to seismic and aseismic slip? (4) How do strong ground motions depend on the complexities and nonlinearities of dynamic earthquake systems? (5) In what ways can system-specific studies enhance the general understanding of earthquake predictability? These questions cover the key issues driving earthquake research in California, and they provide a basis for gauging the intellectual merit of proposed SCEC5 research activities (see full SCEC5 proposal).

1. How are faults loaded across temporal and spatial scales?

1b. Determine the spatial scales at which tectonic block models (compared to continuum models) provide descriptions of fault-system deformation that are useful for earthquake forecasting.

1c. Constrain how absolute stress and stressing rate vary laterally and with depth on faults, quantifying model sensitivity, e.g. to rheology, with inverse approaches.

1e. Evaluate how the stress transfer among fault segments depends on time, at which levels it can be approximated by quasi-static and dynamic elastic mechanisms, and to what degree inelastic processes contribute to stress evolution.

2. What is the role of off-fault inelastic deformation on strain accumulation, dynamic rupture, and radiated seismic energy?

2a. Determining how much off fault plasticity contributes to geodetic estimates of strain accumulation and what fraction of seismic-moment accumulation is relaxed by aseismic processes.

2b. Explore approaches to represent the effects of non-linearity that would allow the continued use of linear wave propagation as an effective approximation.

2c Constrain the form of fault-zone and distributed non-linearity, as well as the factors, such as cohesion and pore fluid pressure, that are likely to influence it.

2d. Understand how inelastic strain associated with fault roughness and discontinuities influences rupture propagation, seismic radiation, and scaling of earthquake source parameters.

2e Describe how fault complexity and inelastic deformation interact to determine the probability of rupture propagation through structural complexities, and determine how model-based hypotheses about these interactions can be tested by the observations of accumulated slip and paleoseismic chronologies.

3. How do the evolving structure, composition and physical properties of fault zones and surrounding rock affect shear resistance to seismic and aseismic slip?

3a. Refine the geometry of active faults across the full range of seismogenic depths, including structures that link and transfer deformation between faults.

3b. Constrain the active geometry and rheology of the ductile roots of fault zones.

3c. Assess how shear resistance and energy dissipation depend on the maturity of the fault system, and how these are expressed geologically.

3d. Determine how damage zones, crack healing and cementation, fault zone mineralogy, and off-fault plasticity govern strain localization, the stability of slip (creeping vs. locked), interseismic strength recovery, and rupture propagation.

3e Constrain the extent of permanent, off-fault deformation, and its contribution to geologic and geodetic fault slip-rate estimates.

3f. Study the mechanical and chemical effects of fluid flows, both natural and anthropogenic, on faulting and earthquake occurrence, and how they vary throughout the earthquake cycle.

3g. Assess the importance of the mechanical properties of the near-surface in the commensurability of geodetic and seismological images of fault slip at depth with fault offset expressed at the surface.

4. How do strong ground motions depend on the complexities and nonlinearities of dynamic earthquake systems?

4a. Determine the relative roles of fault geometry, heterogeneous frictional resistance, crustal material heterogeneities, intrinsic attenuation, near-surface nonlinearities and ground surface topography in controlling ground motions.

4b. Construct methods for validating ground-motion predictions that account for the paucity of recordings in the near-field, where the motions are strong and inelastic effects may be large.

4c. Develop ground-motion simulations for anticipated large events that are suitable for probabilistic seismic hazard and risk analysis.

4d. Communicate improvements in physics-based seismic hazard analysis to the earthquake engineers, emergency responders, and general public.

5. In what ways can system-specific studies enhance the general understanding of earthquake predictability?

5a. Develop earthquake simulators that encode the current understanding of earthquake predictability.

5b. Place useful geologic bounds on the character and frequency of multi-segment and multi-fault ruptures of extreme magnitude.

5d. Test the hypothesis that “seismic supercycles’’ seen in earthquake simulators actually exist in nature and explore the implications for earthquake predictability.

5e. Exploit anthropogenic (induced) seismicity as experiments in earthquake predictability.

SCEC4 (2012-2016)

Six fundamental problems constitute the basic-research focus of SCEC4. They are listed in the preamble and expanded in detail below. They are interrelated and require an interdisciplinary, multi-institutional approach. Interdisciplinary research initiatives focus on special fault study areas, the development of a community geodetic model for Southern California, and a community stress model. The latter is a new platform where the various constraints on earthquake-producing stresses can begin to be integrated. In addition, improvements are to be made to SCEC’s unified structural representation and its statewide extensions.

1. Stress transfer from plate motion to crustal faults: long-term fault slip rates

1a. Mapping and studying faults in Southern California to determine slip rates for faults at multiple time scales and characterize fault zone properties for which brittle/ductile transitions have been exposed by detachment faulting or erosion.

1b. Focused laboratory, numerical, and geophysical studies of the character of the lower crust, its rheology, stress state, and expression in surface deformation. We will use surface-wave dispersion to improve depth resolution relative to teleseismic studies.

1c. Regional searches for seismic tremor at depth in Southern California to observe if (some) deformation occurs by slip on discrete structures at depth.

1d. Development of a Community Geodetic Model (CGM) for California, in collaboration with the UNAVCO community, to constrain long-term deformation and fault-slip models.

1e. Combined modeling/inversion studies to interpret GPS and InSAR geodetic results on postseismic transient deformation without traditional simplifying assumptions.

2. Stress-mediated fault interactions and earthquake clustering: evaluation of mechanisms

2a. Improvement of earthquake catalogs, including non-point-source source descriptions, over a range of scales. Traditional aftershock catalogs can be improved through better detection of early aftershocks. Long-term (2000-yr) earthquake chronologies, including slip-per-event data, for the San Andreas Fault system and other major faults are necessary to constrain long-term recurrence behavior.

2b. Improved descriptions of triggered earthquakes. While temporal earthquake clustering behavior (Omori’s Law) is well known, the spatial and coupled temporal-spatial behavior of triggered earthquakes, potentially key diagnostics, are not well constrained.

2c. Lowered thresholds for detecting aseismic and infraseismic transients, and improved methods for separating triggering by aseismic transients from triggering by other earthquakes.

2d. Development of a Community Stress Model (CSM) for Southern California, based on merging information from borehole measurements, focal mechanisms, paleo-slip indicators, observations of damage, topographic loading, geodynamic and earthquake-cycle modeling, and induced seismicity. Use of seismicity to constrain CSM and investigate how stress may control earthquake clustering and triggering. Collaboration with other organizations in fault-drilling projects for in situ hypothesis testing of stress levels.

2e. Development of physics-based earthquake-cycle simulators that can unify short-term clustering statistics with long-term renewal statistics, including the quasi-static simulators that incorporate laboratory- based nucleation models.

2f. Development of a better understanding of induced seismicity, specifically induced by geothermal power production in the Salton Sea area, which warrant study as potential hazards.

3. Evolution of fault resistance during seismic slip: scale-appropriate laws for rupture modeling

3a. Analysis of laboratory experiments on fault materials under appropriate confining stresses, temperatures, and fluid contents/pressures through targeted experiments in collaboration with rock mechanics laboratories.

3b. Observations of geological, geochemical, paleo-temperature, microstructural, and hydrological indicators of specific resistance mechanisms that can be measured in the field. In particular, evidence of thermal decomposition in exhumed fault zones. Collaboration with other organizations involved in fault-drilling projects to measure observables for constraining coseismic resistance mechanisms, such as the temperature on faults before and after earthquakes.

3c. Formulation of theoretical and numerical models of specific fault resistance mechanisms for seismic radiation and rupture propagation, including interaction with fault roughness and damage-zone properties.

3d. Development of parameterized fault rheologies suitable for coarse-grained numerical modeling of rupture dynamics and for simulations of earthquake cycles on interacting fault systems. (Currently, the constitutive laws for co-seismic slip are often represented as complex coupled systems of partial differential equations, contain slip scales of the order of microns to millimeters, and hence allow detailed simulations of only small fault stretches.)

3e. Construction of computational simulations of dynamic earthquake ruptures to help constrain stress levels along major faults, to help explain the heat-flow paradox, and to help us understand extreme slip localization, the dynamics of self-healing ruptures, and the potential for repeated slip on faults during earthquakes.

3f. Development of computational earthquake-cycle simulators that can incorporate realistic models of fault-resistance evolution during earthquake cycles and the wave-propagation that occurs during seismic events.

4. Structure and evolution of fault zones and systems: relation to earthquake physics

4a. Detailed geologic, seismic, geodetic, and hydrologic investigations of fault complexities at Special Fault Study Areas and other important regions.

4b. Investigations of along-strike variations in fault roughness and complexity (including slip rate and geometry) as well as the degree of localization and damage perpendicular to the fault.

4c. Improvements to the CFM using better mapping, including LiDAR, and precise earthquake relocations. We will also extend the CFM to include spatial uncertainties and stochastic descriptions of fault heterogeneity.

4d. Use of special fault study areas to model stress heterogeneities both deterministically and stochastically. We will integrate the results of these special studies into the CSM.

4e. Use of earthquake and earthquake-cycle simulators and other modeling tools, together with the CFM and CSM, to quantify how large-scale fault system complexities govern the probabilities of large earthquakes and rupture sequences.

5. Causes and effects of transient deformations: slow slip events and tectonic tremor

5a. Improvement of detection and mapping of the distribution of tremor across southern California by applying better instrumentation and signal-processing techniques to data collected in the special study areas, such as those outlined in the proposal.

5b. Application of geodetic detectors to the search for aseismic transients across southern California. We will use the CGM as the time-dependent geodetic reference frame for detecting geodetic anomalies.

5c. Collaboration with rock mechanics laboratories on laboratory experiments to understand the mechanisms of slow slip and tremor.

5d. Development of physics-based models of slow slip and tectonic tremor. We will constrain these models using features of tremor occurrence and its relationship to seismicity, geodetic deformation, and tectonic environment, as well as laboratory data.

5e. Use of physics-based models to understand how slow slip events and tremor activity affect earthquake probabilities in Southern California.

6. Seismic wave generation and scattering: prediction of strong ground motions

6a. Development of a statewide anelastic Community Velocity Model (CVM) that can be iteratively refined through 3D waveform tomography. Integration of new data (especially the Salton Sea Imaging Project) into the existing CVMs with validation of improvements in the CVMs. We will extend current methods of full-3D tomography to include ambient-noise data and to estimate seismic attenuation, and we will develop methods for estimating and representing CVM uncertainties.

6b. Modeling of earthquake ruptures that includes realistic dynamic weakening mechanisms, off-fault non-elastic deformation, and is constrained by source inversions. The priority is to produce physically consistent rupture models for broadband ground motion simulations of hazard-scale ruptures, such as ruptures envisioned in UCERF3. An important issue is how to treat multiscale processes; for example, might off-fault plasticity regularize the Lorentzian scale collapse associated with strong dynamic weakening? If not, how might adaptive meshing strategies be most effectively used to make full-physics simulations feasible?

6c. Development of stochastic representations of small-scale velocity and attenuation structure in the CVM for use in modeling high-frequency (> 1 Hz) ground motions. We will test the stochastic models with seismic and borehole logging data and evaluate their transportability to regions of comparable geology.

6d. Measurement of earthquakes with unprecedented station density using emerging sensor technologies (e.g., MEMS). The SCEC Portable Broadband Instrument Center will work with IRIS to make large portable arrays available for aftershock and flexible array studies.

6e. Collaboration with the engineering community in validation of ground motion simulations. We will establish confidence in the simulation-based predictions by continuing to work with engineers in validating the simulations against empirical attenuation models and exploring coherency and other standard engineering measures of ground motion properties.

SCEC3 (2007-2011)

The research objectives outlined below are priorities for SCEC3. They carry the expectation of substantial and measurable success during the coming year. In this context, success includes progress in building or maintaining a sustained effort to reach a long-term goal. How proposed projects address these priorities will be a major consideration in proposal evaluation, and they will set the programmatic milestones for the Center’s internal assessments. In addition to the priorities outlined below, the Center will also entertain innovative and/or "risky" ideas that may lead to new insights or major advancements in earthquake physics and/or seismic hazard analysis.

There are four major research areas with the headings A, B, C and D with subheadings given by numbers. The front page of the proposal should specifically identify subheadings that will be addressed by the proposed research.

A. Develop an extended earthquake rupture forecast to drive physics-based SHA

A1. Define slip rates and earthquake history of southern San Andreas Fault system for the last 2000 years

A2. Investigate implications of geodetic/geologic rate discrepancies

A3. Develop a system-level deformation and stress-evolution model

A4. Statistical analysis and mapping of seismicity and source parameters with an emphasis on their relation to known faults

A5. Develop a geodetic network processing system that will detect anomalous strain transients

A6. Test scientific prediction hypotheses against reference models to understand the physical basis of earthquake predictability

A7. Determine the origin, evolution and implications of on- and off-fault damage

A8. Test hypotheses for dynamic fault weakening

A9. Assess predictability of rupture extent and direction on major faults

A10. Develop statistical descriptions of heterogeneities (e.g., in stress, strain, geometry and material properties), and understand their origin and implications for seismic hazard by observing and modeling single earthquake ruptures and multiple earthquake cycles.

A11. Constrain absolute stress and understand the nature of interaction between the faulted upper crust, the ductile crust and mantle, and how geologic history helps to resolve the current physical properties of the system.

B. Predict broadband ground motions for a comprehensive set of large scenario earthquakes

B1. Develop kinematic and dynamic rupture representations consistent with seismic, geodetic, and geologic observations.

B2. Investigate bounds on the upper limit of ground motion.

B3. Develop high-frequency simulation methods and investigate the upper frequency limit of deterministic ground-motion predictions

B4. Validate ground-motion simulations and verify simulation methodologies.

B5. Improve our understanding of site effects and develop methodologies to include these effects in broadband ground-motion simulations.

B6. Collaborate with earthquake engineers to develop rupture-to-rafters simulation capability for physics-based risk analysis.

C. Improve and develop community products (data or descriptions) that can be used in system-level models for the forecasting of seismic hazard. Proposals for such activities should show how they would significantly contribute to one or more of the numbered goals in A or B

D. Prepare post-earthquake response strategies. Some of the most important earthquake data are gathered during and immediately after a major earthquake. Exposures of fault rupture are erased quickly by human activity, aftershocks decay rapidly within days and weeks, and post-seismic slip decays exponentially. SCEC solicits proposals to improve coordination and rapid data processing that will allow for rapid determination of source parameters, maps, and other characteristics of the source and ground motion patterns, to develop plans for use of simulations in post-earthquake response for evaluation of short-term earthquake behavior and seismic hazards, and to improve the SCEC post-earthquake response plan.

SCEC5 Bridge Period (2022-2023)

SCEC5 (2017-2021)

SCEC4 (2012-2016)

SCEC3 (2007-2011)

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