Thorsten W. Becker, Ph.D. - US grants

This project will evaluate the robustness, resolution, and required
complexity of global seismologic and geodynamic models of upper
mantle azimuthal anisotropy in order to improve our understanding of
mantle dynamics. Recent years have seen a refinement of
seismological models of anisotropy, presumably indicative of shearing
in mantle flow. Particularly surface wave inversions have been linked
to models of mantle circulation with some success. Such findings make
it appear feasible to test hypotheses for regional tectonic models
using sophisticated synthetic data sets in the near future. However,
while several questions about the implications of anisotropy remain
unanswered, it is also true that comprehensive and quantitative
models with thorough estimates of uncertainties are still lacking.
This project addresses some of the relevant issues of seismological
analysis and improved geodynamic models, such as: How stable are
azimuthal anisotropy patterns with respect to data selection and
inversion methods? How well constrained is anisotropy under
continents and oceanic regions? What are the characteristic to
convection models, from Newtonian to power-law rheology, from
laterally constant to varying viscosity, and from finite strain to
texture modeling. A range of resolution and synthetic model tests
will be performed to evaluate the robustness of the seismological
models. Such a combined seismologic and geodynamic research program
will lead to new insights into upper mantle structure, anisotropy
formation, and mantle convection. The aim is to formalize our
understanding of lithospheric and upper mantle deformation based on
mantle flow, in order to develop models with specific regional
predictions that are useful for the design of field campaigns and
geologic hypothesis testing.

Using upper mantle circulation models to evaluate the role of the asthenosphere:tectosphere contrast and subduction dynamics for global plate tectonics

Research focuses on global, numerical convection models with realistic plate boundaries, rheological and thermo-chemical contrasts, and improved constraints from seismology. The force partitioning in the mantle affects intraplate and plate boundary seismo-tectonics, and studying the mantle system by mechanical modeling holds the key to understanding plate motions and geologically recorded tectonic events. Efforts are divided into two research projects which are interrelated and have strong educational components. Project one uses circulation computations for an inversion of seismology data to evaluate the range of viscosity variations that are required by observables and laboratory results on the creep behavior of rocks (viscous tomography). Project two incorporates faulted margins into a global model (slabs, keels, and plates). Slabs drive and control the speed of the plates, and a more realistic inclusion of plate boundaries into global models is needed. It is evaluated to what degree slabs and trench motions vs. the tectosphere: asthenosphere contrast control global dynamics such as geopotential fields and seismic coupling. The unifying theme of research and educational efforts is the use of global flow models and structure derived from seismology and mineral physics. The goal is to arrive at a new kind of mantle circulation model that elucidates the roles of the asthenosphere in shaping plate tectonics and organizing deep Earth structure. The educational efforts in this project focus on course material for a new numerical methods class and two solid earth software modules for exploring mantle flow and tomography, both openly developed and freely shared. The goal is to allow learning through experimentation with modified research tools. Those tools are customizable so that they are useful for both general undergrad and graduate classes. Efforts strengthen the quantitative skills of students needed to tackle interconnected problems; useful for grad students to solve outstanding questions in mantle dynamics, and for non-specialists who need to make informed choices during planetary environmental challenges. Work contributes to a more transparent representation of disciplinary research results where traditional means of scientific communication are becoming unduly limiting. By providing both fundamental training in quantitative analysis and examples for novel seismological and geodynamical model sharing, the robustness of extra-disciplinary constraints are easier to evaluate. This is crucial if we are to accelerate progress on complex problems in plate tectonics and earth science in general.

The Alboran Sea was created in the wake of the young subduction zones that swept across the Western Mediterranean in the Neogene during the convergence of Africa and Europe. The Gibraltar Arc and Alboran Sea are the westernmost part of the system and one of the most confusing. The mixture of westward rollback, extension, strike-slip, volcanism, uplift and subsidence has defied attempts to compose a consistent scenario that explains all of the obervations. Partly as a result of inadequate data, there are many models that have been proposed involving subduction, slab breakoff, delamination and drips. There is credible evidence that the lithospheric mantle of the overriding plate of a west-facing subduction zone has been thinned by both back-arc stretching and some type of convective removal (e.g. drips, delamination, etc.). The process of convective thinning is poorly understood but is believed to be important in driving uplift and subsidence of the Earth?s surface, influencing rates of deformation in active orogens, and contributing to recycling of continental materials back into the mantle.

This award provides for a multidisciplinary, international investigation of the Alboran Sea, Gibraltar arc, Atlas Mountains and surrounding areas in the western Mediterranean using passive and active seismology, magnetotellurics, geochemistry, petrology/structural geology, and geodynamic modeling. The overall goal of the project is to study the processes responsible for convective thinning in the Gibraltar-Alboran Sea region. The project, known as PICASSO, has now been funded in Spain and Ireland as a colloaborative EU-US program, with proposals from a number of other EU nations submitted or in process. The project was selected as the pilot experiment for TopoEurope, an EarthScope-like initiative recently approved by the European Science Foundation. A large part of the field deployments will be done by European scientists, including a 3D EarthScope-type rolling array (IberArray), with additional targeted field experiments by US investigators. The IberArray is already underway with ~60 stations deployed in the PICASSO field area.

This project studies the causes and consequences of mantle flow beneath the western United States (U.S.). Several, interacting spatio-temporal scales of geologic activity need to be considered: (1) circulation related to North America plate motion, (2) sinking of old Farallon plate in the lower mantle beneath the eastern U.S., (3) sinking of younger, more recently subducted plate in the upper mantle beneath the western U.S., and (4) small-scale convective dripping of the lithosphere. Related deep structure has recently been mapped to unprecedented detail thanks to EarthScope; the consequences of the resulting mantle flow are geologically important for the forces applied to the lithosphere, and for melting anomalies caused by mantle ascent and decompression. Induced flow is also important because it results in observable predictions that can be used as a constraint for physics-based models, such as seismic anisotropy, and the uplift and deformation of the continental crust.

The project analysis method involves mapping seismic images of the mantle into density structure that can then be used to drive computer models of mantle flow. Global seismic images and flow modeling are used to account for the large-scale processes, and high-resolution seismic images and regional flow modeling is used beneath the western U.S. EarthScope GPS data provide a highly resolved crustal strain-rate field and EarthScope teleseismic data provide detailed seismic images used to infer density, temperature, and anisotropy structure. Those parameters that affect resolvable constraints are explored in a search for the models that best account for the observations, leading to an improved understanding of issues such as the strength and mechanical behavior of plates.

Of particular interest are: (1) the magnitude of coupling between the large-scale flow patterns and the North American plate (with special emphasis on the effects of a cratonic root that penetrates deeply into the asthenosphere); (2), the importance of the sinking young slab beneath western U.S. on Yellowstone plume ascent and regional-scale flow that may be concentrated beneath the active northern Basin and Range province; (3), the lithospheric drips that are imaged adjacent to many of the young western U.S. uplifts and volcanic fields, and, (4), the general role such processes may play for the long-term tectonic and thermal evolution of the Earth.

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

The goal of the proposed work is to understand the dynamics of the Earth?s interior and the long-term evolution of our planet. The motion of tectonic plates and the attendant earthquakes are surface expressions of a large-scale flow in the interior, which is driven by a combination of thermal and compositional buoyancy as the planet cools. Most of the geological processes we observe at the surface are related in one way or another to this large-scale flow. However, our understanding of the flow from a dynamical perspective is far from complete. What is the origin of the buoyancy that drives the flow? How does this flow interact with tectonic plates at the surface? How and why does the flow reorganize and cause (relatively) abruptly changes in plate motions. We propose to address these questions developing a new theoretical model for the large-scale flow and by introducing several new observations to test and refine the model.

We propose several important advances over previous studies. First, we plan to develop a more complete treatment of subduction zones in global models of flow. The dynamics of subduction is described by a new viscous sheet model that explicitly includes the effects of plate bending as well as the tensile stresses inside the plate due to the weight of the cold and dense subducted plate. Observations of deep earthquakes in subducted plates provide valuable information about the stress state inside the plates. We plan to make use of this information for the first time in global flow models. Second, we propose to develop a self-consistent description of lateral variations in viscosity. Thermal buoyancy is expected to cause large variations in viscosity due to the strong temperature dependence of important transport properties (like viscosity). We propose to use this self-consistent model to predict flow when the buoyancy forces are inferred from tomographic models of seismic heterogeneity. The conversion from seismic anomaly to density anomaly is a controversial issue, particularly in the lower part of the mantle. The relative importance of thermal and composition buoyancy is not well known. We plan to use a recently detected free oscillation of the Earth to constrain the gravity field in the interior. Different conversions from seismic anomaly to density anomaly have different consequences for the global gravity field, which can be tested using gravity measurements at the surface and our new constraint on the gravity field in the interior. We hope to gain a better understanding of the buoyancy forces that drive the flow and provide new insights into the role of plates in organizing the flow. The proposed work supports two young female investigators (Dr. Kayla Lewis and Ms. Melanie Gerault) and fosters a new collaboration between USC and UC Berkeley. The proposed work will also use, adapt and improve an existing computer code in the CIG repository (an NSF-funded initiative). We intend to contribute the new code back to CIG when the project is completed.

This project focuses on slab mass transport into the lower mantle. It will, 1), expand the range of constraints on the degree of slab stagnation, e.g. by detailed analysis of transition zone thickness as well as hypothesis-driven reinversion of seismological data; 2), construct, by means of further software development, regional dynamic models and simplified global parameterizations for stagnation systematics in a thermo-chemical, multi-phase transition mantle system; and, 3), benchmark these computational convection models for vertical and horizontal transport. A graduate student from an under-represented group will be trained in interdisciplinary research. All project software will be developed openly and shared freely online. The tomographic inversion and modeling tools will be implemented into the Solid Earth Teaching and Research Environment software framework, allowing data-driven hypothesis testing for entirely different geodynamic questions and facilitating the training of Earth science students in interdisciplinary research.

Better estimates of the slab flux, over time and with error bars, will help to constrain geochemical mixing and thermal Earth evolution models. The study will contribute to the use of slabs for absolute plate-tectonic reference frames, and slab dynamics has other, broad implications such as on net rotations of the lithosphere with respect to the lower mantle, interactions with the super-continental cycle, and sealevel variations.

The March 11, 2011, Tohoku-Oki earthquake at magnitude 9 was the largest event in Japan's 1400+ years of recorded history. The impact of the earthquake and resulting tsunami on the people of Japan was severe, from the approximately 20,000 fatalities and unaccounted persons to the estimated ¥10 trillion (US$ 120 billion) of economic loss. The Tohoku-Oki rupture was located north of Tokyo, leading to a strong societal interest within Japan as to what is in store for their capital city. Specifically, whether the Tohoku-Oki earthquake may have accelerated the next significant earthquake to more directly impact the Tokyo metropolitan region. Recent Japan government studies estimate that a shallow megathrust earthquake similar to the 1923 M7.9 "Great Kanto" earthquake would result in ~11,000 fatalities and up to US$ 3 trillion in economic damage. Concern for a worsening of seismic hazards in Tokyo region is warranted based on recent advances in earthquake science that indicate (a) that an earthquake that relieves stress in one area will build up stress in adjacent areas, and (b) while stress changes occur rapidly during the earthquake, postseismic processes will lead to the redistribution of crustal stresses for years to many decades after a large earthquake. Understanding the ongoing time-evolution of stress buildup in the Tokyo region adjacent to the 2011 Tohoku-Oki rupture, and its influence on active faults in that region is the primary objective of this NSF-supported project. This project is a collaboration with Japanese scientists who seek improved estimates of seismic hazards in the Tokyo region both currently and for decades to come. This project will provide research training to U.S. students, as well as international research experience, and also seeks to help our Japanese colleagues improve their ability to conduct this type of seismic hazard research.
This project seeks to understand the evolution of crustal stresses and associated seismic hazards in the Tokyo region in the years and decades to following the Tohoku-Oki earthquake. Stress changes will occur due to two primary postseismic processes, afterslip and viscoelastic relaxation. The former is associated with aseismic slip along the North America/Pacific plate interface within and below the region of coseismic slip, while the latter involves the relaxation of hot weak mantle beneath the converging plates. Both processes will cause a time-dependent transfer of stress to the seismogenic upper crust. It is our goal to understand this process of stress transfer and how it works to load active faults in the Tokyo region. This will be achieved by developing an observationally constrained finite element model that can accurately calculate stress changes due to afterslip and viscoelastic relaxation. Observational constraints will primarily consider seismological data that describes the tectonic geometry and elastic structure of the region, and geodetic constraints that will enable a determination of the rheology (viscous strength) of the region. Most importantly, the model should enable us to separate out the relative contributions of afterslip and viscous relaxation to postseismic geodetic data, which is not only required for an accurate calculation of stress changes, but will provide invaluable insights as to the nature of these two processes that will benefit our general understanding of subduction zone tectonics. It is the unprecedented postseismic GPS coverage within Japan that will enable these insights to be achieved.

Eastern Indonesia is one of the least well-understood geological domains of our planet, and yet the region provides a truly remarkable natural experiment for unraveling some of the major puzzles of plate tectonics. The recent collision of the Australian continent with the active volcanic arc in the Banda region effectively captures the initiation of continental mountain building and the cessation of island arc volcanism, offering a rare glimpse into a set of processes that have shaped Earth's evolution over geologic time. Since oceanic subduction and subsequent continental collision have occurred in different stages along the Banda arc, we plan to use the region to study and assess the spatio-temporal evolution of this transition. This work will help fill fundamental gaps in general understanding of collisional tectonics and formulate answers to outstanding questions about the interrelationships between the history of convergence and the present-day crustal, lithospheric and mantle structure, and the way this relates to topography. This study of the Banda arc holds promise for clarifying the relationships between surface uplift, crustal deformation and recycling, lithospheric structure, subduction, and mantle convection.

We have assembled an international multidisciplinary research team to constrain a sophisticated dynamical model of regional collision and subduction using passive seismology, topographic analysis, targeted geochronology, and a collaboratively led geodetic campaign. The research group includes scientists from Indonesia, Australia, Germany, the Netherlands, Portugal, and the U.S., and an important outcome will be to strengthen and catalyze future scientific collaboration between these countries. The award is co-funded by the NSF Geophysics and Tectonics Programs, and the Office of International Science and Engineering (OISE). All results, data, and newly developed methods will be shared freely online, benefiting future similar imaging or tectonic modeling efforts.

Atmospheric CO2 rise is one of the most pressing societal and scientific issues, but future projections of
system behavior often rely heavily on models rather than data. Earth underwent a very relevant analog
experiment 200 million years ago, and this project seeks to learn and abstract from that experiment. The
CO2 release associated with the Triassic-Jurassic (T-J) boundary is estimated to have risen at a rate
comparable to the present-day (as a result of the Central Atlantic Magmatic Province volcanism, CAMP),
and tellingly, it was associated with a mass extinction. Notably, representatives of the fauna that inhabits
today's seas, the so-called modern fauna were preferentially negatively affected by the T-J event versus other mass extinctions, making the T-J perhaps the most relevant mass extinction with respect to the present-day impact of high CO2 levels on the biosystem.

The T-J event is arguably the least studied of the mass extinctions that frame the Mesozoic, and it
represents an underutilized opportunity to investigate a geologically rapid injection of CO2 into the Earth
system. The results of this CO2 pulse are quantifiable, and will serve to establish new models of system
response to punctuated perturbations. The PIs believe that using novel geochemical tracers for
weathering and redox, coupled with biofacies analysis, will result in a paradigm shift in our knowledge of
such an event. The proxies will inform a novel model that links a solid Earth model, carbon cycle model,
and ecological model. This project will help to elucidate the details of the most significant mass extinction
to affect the modern fauna. Moreover, the new models developed for the T-J event will have relevance for
other mass extinctions, including the ongoing Anthropocene event.

Non-technical Description

Numerous geological features and phenomena observed on the surface of the Earth -- such as giant mountain belts, deep ocean basins, earthquakes, and volcanoes -- are the results of dynamic processes operating in the Earth's crust, mantle, and core. Therefore, an improved understanding of these processes are essential for the understanding of the origin and development of the Earth and for mitigation of natural hazards. At the present time, however, only the shallowest part of the Earth can be observed directly using cores from drill holes; consequently, an array of computing-intensive geophysical techniques are applied to image the active planet. Those techniques are similar to those used in the hospital to image the human body.

Technical Description

Shear-wave splitting is a fundamental geophysical observation that uniquely indicates the presence of azimuthal anisotropy along the ray path. Such anisotropy is the result of dynamic processes in the Earth's asthenosphere and lithosphere. However, dynamic interpretation of shear-wave splitting requires homogeneous, high quality measurements, and quantitative forward models. This project will measure shear-wave splitting parameters at all of the USArray Transportable Array and other broadband seismic stations in the eastern U.S. and update measurements throughout the North American plate. The data product includes ~10,000 shear-wave splitting measurements that we are merging with ~16,000 measurements that we produced for the western and central U.S. with NSF prior funding via EarthScope. We are utilizing a set of procedures for reliably measuring and ranking the splitting parameters for producing a uniform database, quantifying shear-wave splitting complexity and likely depth of anisotropy along the way. To complement this reference shear-wave splitting database, we are computing a large number of geodynamic forward models of synthetic shear-wave splitting and anisotropic structure for surface wave studies by computing fabrics from mantle flow and simplified tectonic models. This way, we can test which hypotheses for the origin of anisotropy can be reliably discerned, which tectonic scenarios best reflect observations, and how to guide regional refinement of our understanding of continental and upper mantle structure and dynamics. Using this joint approach, we are addressing a number of significant questions regarding the origin of seismic anisotropy, including lithospheric inheritance and recent asthenospheric flow, and the nature of mantle convection underneath the North American plate. In addition, all our measurements, as well as synthetic waveforms, are being openly shared so as to allow others to refine their resulting reference models; this ensures our data product will have a significant impact on a broad range of Earth science questions.

The discovery of feedbacks between geomorphic and tectonic processes has revolutionized the understanding of the mechanics of mountain building and of the interactions between landscapes and climate. While the basics are established, the details of coupling remain debated. Separating the effects of climate and erosion from the effect of tectonics in the geological record remains a challenge. One approach to study these interactions are computer models that couple surface and tectonic processes in order to quantify the effects of a wide range of geologic and geomorphic parameters. This allows testing hypotheses derived from field observations and to develop new surface process-tectonics hypotheses. This project supports a workshop that gathers leading U.S. and international geoscientists who use and develop long-term tectonic and landscape evolution models to discuss numerical techniques that have the potential of revolutionizing the understanding of the interactions between surface processes and tectonics, as well as solve some of the most difficult technical challenges for developing models that require coupling over highly disparate spatial and temporal scales. The workshop advances desired societal outcomes by participation of women and underrepresented minorities and development of a diverse, globally competitive STEM workforce through engagement of early career scientists, post-doctoral scholars, and students in the workshop.

This project supports the participation of U.S. and international scientists in a workshop, which will be held in 2018 at the University of Texas at Austin. The first goal of the workshop is to work to develop the next generation of coupled surface processes and long-term tectonic models to explore key questions linking tectonics, climate, and landscape evolution. This will require defining the numerical techniques used by the two communities and identifying the challenges in coupling across different temporal and spatial scales. The second goal is to strengthen the U.S. long-term tectonics modeling community and build new links/collaborations between the long-term tectonics community at NSF-supported Computational Infrastructure for Geodynamics and the surface processes community at NSF-supported Community Surface Dynamics Modeling System. Bringing together the two communities will do more than just facilitate code development; each community can help the other with the science by bringing new perspective to existing questions and ideas. The workshop participants will discuss specific, immediate questions for surface process and lithospheric deformation codes, including: (1) the role of topography and topographic stresses; (2) physically based erosion laws rather than diffusion based; (3) Inclusion of the seismic cycle in tectonic models; (4) inclusion of the seismic cycle in landscape evolution models; (5) the importance of 3D heterogeneity in material properties in both geodynamic and geomorphologic modelling; and (6) incorporation of atmosphere as a third component to models.

Earth's tectonic plates get recycled back into the mantle at subduction zones. The largest earthquakes happen there, and these megathrust environments also generate a range of other geohazards including tsunamis and volcanoes, making their study of great societal relevance. Recently, seismological and geodetic measurements have revealed a range of phenomena associated with megathrust behavior that are not captured by a simple, stick-slip earthquake cycle model of slow loading and catastrophic rupture. These newly discovered phenomena include transient, creeping events of fault slip on decadal scales which may indicate preparatory behavior of the fault system, perhaps systematically linked to the main seismic event. Mechanical models have not quite kept up with these new discoveries and our understanding of the physical processes behind these phenomena is incomplete. A new, integrative framework is therefore needed to understand the physical mechanisms and fault constitutive laws behind complex deformation and seismicity patterns. This project seeks to develop such a mechanical model, initially for the data rich Japan setting, in order to understand regional megathrust dynamics and fault interaction patterns, as well as improve seismic hazard estimates. Later, such a mechanical model may potentially be deployed at other subduction zones such as Cascadia and assist in interpreting existing and planned monitoring data streams for earthquake forecasting and early warning.

To capture the spatial and temporal scales involved in this complex problem, three sub-projects are to be pursued in collaboration between researchers at University of Texas Austin (UTIG), Purdue University, and the University of Tokyo: 1) The development of sets of multi earthquake-cycle scenarios based on numerical models of visco-elastic, inter-, pre-, co- and post-seismic fault loading in Japan. 2) The development of global mantle flow and regional, time-evolving mantle convection models to understand long-term, subduction induced forcing of plate boundaries and backarcs in the region. 3) The development of cross-timescale, visco-elasto-plastic models in 3-D, incorporating rate and state friction as well as other fault constitutive laws in a dynamically consistent, thermo-mechanical convection framework. This will enable, for example, studying the role of pre-seismic, slow slip phenomena for fault zone evolution, eventually in the presence of fluid flow. All project parts will be integrated, and results from different approaches cross-checked. Moreover, all sub-projects are complementary and will guide the establishment of the general subduction zone model that is needed to understand earthquake cycle observations and seismicity in Japan and elsewhere.

Subduction zones are fundamental expressions of the evolution of our planet. Subduction zones also host cascading natural hazards, from volcanoes, to earthquakes, to landslides and tsunamis, often in regions with high population density. Any dynamic understanding of our planet therefore has to include a comprehensive theoretical framework for subduction zone dynamics, and such a framework should have utility for monitoring and for physics-based forecasting to meet our fundamental responsibility to society. Several recent community efforts have focused on subduction zone science, including volcanic and megathrust processes within that geologic setting. This Research Coordination Network (RCN) will provide a mechanism for collaboration and interaction of scientists to organize modeling efforts to understand subduction zones. In particular, this RCN will serve to identify knowledge gaps and serve to evaluate the tools and strategies needed by the scientific community to leverage the rich data sets from international subduction zone observatories and tp create a new generation of multiphysics and multiscale models. This RCN will strengthen international collaboration, including researchers from Chile, Costa Rica, Germany, Greece, Indonesia, Italy, Japan, Mexico, Switzerland, and the United Kingdom. The RCN will contribute to the training of a diverse workforce, and outreach efforts will publicize the relevance of subduction zone science to the larger public. The RCN will engage a diverse community of researchers, including early career researchers and those from under-represented groups.

This is a Research Coordination Network focuses on a modeling collaboratory for subduction zone science and explores developing physical models for short- to long-term deformation associated with megathrust and arc volcano systems. Physical understanding of earthquake cycles and volcanoes within a plate boundary remains incomplete, even though numerical models have seen tremendous improvements. This implies that more observations,laboratory data and better understanding of the underlying physical processes need to be integrated in better ways to explore interactions between different parts of the subduction system that affect the temporal evolution of tectonics and hazards. The scientific community is poised to unify existing data collection efforts, design new observational and infrastructural initiatives, and harness diverse international efforts with new integrative approaches. This RCN has several goals: 1) helping to identify knowledge gaps; 2) developing multiscale, multiphysics modeling frameworks; 3)providing a pathway for integrative model development and validation; and, 4) providing tools for transforming geological, rock mechanics, geophysical and geodetic data into formats that can be effectively assimilated into models and used for model validation. This effort would facilitate the development and enhancement of models, ranging from conceptual to numerical simulators, aimed at subduction zone megathrust cycles and associated tectonic processes including magma transport and volcanic eruptions. The work will progress through a series of workshops and community interactions to ensure a broad representation of the researchers and scientific fields involved in subduction science.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

At continental transform faults such as the San Andreas, one tectonic plate slides horizontally relative to its neighbor. Because such faults lie on land and often in populated areas, the resulting earthquakes dramatically impact local populations. It remains debated how plates deform beneath the shallow (~10 km), top layer where earthquakes are generated. At larger depths, underlying rocks transition from brittle to ductile deformation. But whether the shear zone underneath the fault remains narrow for tens of km, or whether deformation widens right away is not clear. These different scenarios affect how faults are loaded, and have significant implications for seismic hazard assessment. Here, the team uses existing seismic records to investigate six major continental transform faults. Deformed rocks often exhibit crystal preferred orientations, fabrics, that can be detected with seismic waves. This is because rock fabrics affect the wave velocity which then depends on the propagation direction. By analyzing the anisotropy of seismic waves passing underneath the fault zones, the researchers probe the geometry and extent of rocks deformation. They also use geodynamic modeling constrained by geological observations; for given fault geometries and deformation properties, they predict seismic anisotropy features underneath the faults. By comparing observations and predictions, the team unravels the deformation behavior of continental transform faults. The project fosters an international collaboration with Australia and Switzerland. It provides support and training to a female graduate student, and outreach toward undergraduates and K12 students - notably from group underrepresented in Sciences - and the public.

The team uses data from existing deployments crossing six continental transform faults (San Andreas, North Anatolian, Denali, New Zealand Alpine, Altyn Tagh/Kunlun, and Dead Sea). It conducts full-waveform 2-D and 3-D modeling of teleseismic shear wave splitting, as well as anisotropic receiver function analysis. The goal is to image the shear zone and broader deformation field surrounding each transform fault. The selected faults represent transforms of different ages and maturity. Existing splitting observations show systematic contrasts between faults. Combining high-resolution shear zone imaging and geodynamic modeling, the researchers investigate the degree of strain localization in the lithosphere and the shear zone geometry. They also study the possible roles of mechanical anisotropy and inherited fabrics. This project is a critical step toward establishing a model for continental lithospheric transforms and better assessing the corresponding earthquake hazards.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

The RAPID project responds to the July Ridgecrest earthquakes in Southern California and develops and tests a tool to monitor stress in the Earth and how it changes after large earthquakes. The project takes GPS and satellite radar data and in near real time computes how the Earth's crust and upper mantle are deforming from the mainshocks and aftershock sequences. This project supports two graduate students to work on developing these new tools and testing them in the immediate aftermath of an earthquake. This project could lead to a future real-time aftershock forecasting method.

The first major earthquake in southern California in the last 20 years provides an opportunity to test a postseismic stress evolution monitoring system that would operate in near-real time. Coulomb stress changes from the mainshock of an earthquake are routinely computed to examine the potential for triggering earthquakes on nearby faults. It is known that aftershocks within about one fault-length of the rupture can largely be attributed to coseismic stress changes, but at larger distances, stress changes due to deeper postseismic deformation process such as mantle flow are larger than the coseismic stress change. The Ridgecrest earthquake triggered aftershocks greater than 100 km from the mainshock that are not consistent with Coulomb stress changes from the mainshock.The near real time technique developed through this research has potential to be implemented in future real-time aftershock forecasting. An advantage of this approach is that much of the heavy computation required to compute postseismic deformation is pre-computed and stored. The postseismic deformation calculations are relatively inexpensive and suites of models can be easily computed near real time. The Ridgecrest earthquake sequence provides the first opportunity with modern geodetic data to test a stress evolution monitoring system.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

This project will expand our understanding of how a specific tectonic setting, flat slab subduction, affects the continents on which we live. Flat slab subduction occurs when an oceanic plate that normally descends into the Earth`s mantle at a constant angle of dip changes its geometry and instead sinks only to ~50 miles depth and then travels horizontally for hundreds of miles beneath the continent before returning to the deep Earth`s interior. An episode of flat slab subduction beneath the western United States is believed to be responsible not only for the formation of the Rocky Mountains and the extensive ore deposits of the Colorado Mineral Belt, but also for wide spread explosive volcanism that erupted ~500,000 km3 of silicic magma across the western United States between 36 and 18 million years ago (Mt. St. Helens erupted ~1 km3 for comparison). This volcanism is believed to be due to the effects of the removal of the flat slab and the resumption of a normal subduction geometry, but it has been difficult to study because of the amount of time that has passed since this occurred in the western United States, and because of uncertainty about the geometry of the flat slab that existed before that. In Colombia, there is a unique setting where a once extensive flat slab has split into two parts, one of which remains flat, and one that has comparatively recently foundered and returned to a normal subduction geometry. While this flat slab is much smaller than the one that affected the western United States, the researchers will study the processes responsible for the mountain building, ore deposits, and volcanic hazards in Colombia to gain a better understanding about how continents evolve over time and how these types of volcanic events are related to this specific tectonic environment. This project includes an embedded teacher training initiative led by the Carnegie Academy for Science Education (CASE) which will involve six teachers, two from each PI city (DC, Austin, and Phoenix). Teachers will participate in training, fieldwork, and all-hands meetings throughout the project, and will develop bilingual lesson plans that can be shared through STEM teacher networks. PIs will work closely with the teachers and with CASE in the development of these lesson plans, and will visit teacher classrooms to interact directly with students and to provide feedback. In addition, this project brings together a diverse team that includes two female PIs, and four international collaborators.

This research seeks to take advantage of Colombia`s unique tectonic setting to evaluate the effects of flat slab subduction and subsequent foundering on the geochemical, structural, and dynamic evolution of continental lithosphere. Flat slab subduction has been identified along most ocean-continent convergent margins, and has been invoked to explain major tectonic events including the Laramide Orogeny, the evolution of the Altiplano Plateau, and intraplate deformation and volcanism in China. The northern Andes of Colombia provide an ideal location to assess flat slab effects as the retroarc region in central Colombia directly juxtaposes a modern flat slab with a segment that re-steepened over ~4 Ma. The investigators will compare and contrast flat slab and normal subduction, allowing for both across-strike and along-strike comparison of the records of magmatism, crustal structure, lithospheric metasomatism, basin subsidence, and orogenic uplift. To accomplish these objectives, the research team will include multiple disciplines like geochronology, geochemistry, seismology, basin analysis, structure, tectonics, thermochronology, and geodynamics. Project PIs and collaborators will 1) seismically image both the flat and normally dipping slab regions, and the transition between the two, to obtain evidence of the developing and persistent effects of flat slab subduction on the overriding lithosphere; 2) study the magmatic and geochemical effects of flat subduction on the overriding lithosphere through time by analyzing the resulting igneous products, both above the flat slab and along the region of flat slab foundering; 3) investigate the spatial and temporal patterns of subsidence and uplift associated with flat slabs and their foundering through sedimentary and thermochronologic analyses of the Magdalena and Llanos basins and flanking Central and Eastern Cordilleras in both settings, and 4) integrate these constraints into geodynamic models that will improve our understanding of the conditions and parameters that control the dynamics of flat slabs and subduction in general.

This award is cofunded by the Prediction of and Resilience against Extreme Events (PREEVENTS) program.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Subduction zones, where tectonic plates are recycled back into the mantle as in the Cascadia margin of the Pacific Northwest of the United States, host the largest earthquakes and give rise to significant hazard through ground shaking, landslides, and tsunami. This project seeks to better utilize existing geophysical and geological observations from important “natural laboratories” (Cascadia, Japan and New Zealand) by merging them more fully into new, comparative computer models of system behavior. Developing new modeling software and integrating constraints is expected to lead to new insights into the physics of subduction zone earthquakes, what observations imply for future earthquakes, and, importantly, which observations are needed to improve our understanding of subduction zone hazards and how to reduce uncertainties about system behavior. The project will involve international collaborations, leverage past investments, and will contribute to defining future, optimal observational strategies. An interdisciplinary workforce of students and post-docs will be trained through research and educational efforts, and all project software, tutorials and “cookbooks” for subduction earthquake modeling will be shared with the community, contributing to advancing computational geoscience approaches in general. A program for precollege, undergrad, and early grad students will be developed to emphasize computational geoscience as an avenue to enhance diversity in the geosciences.

This collaborative effort seeks to integrate seismological, geodetic, experimental, and geological constraints for the Japan, New Zealand and Japan natural subduction zone laboratories into numerical models to advance our understanding of megathrust earthquakes. Forward models and a new numerical modeling framework for data assimilation will be deployed to get closer to versatile tools for data-driven, physics-based hazard assessment. The focus is on the evolution of fault stress and strength over a range of spatio-temporal scales, quantifying uncertainties and sensitivity to parameters. This will allow formulating best strategies for inferring relevant parameters from data in the presence of ambiguous physics, including optimal observational design within the ongoing SZ4D community effort. All code will be made publicly available along with cookbooks and tutorials, and a networked effort will establish new, quantitative links and leverage individual efforts greatly. FRES funding will support a growing community of solid Earth geodynamicists who want to deploy their models in a hazard and monitoring context. A focus will be on training and sharing material for interdisciplinary computational geoscience efforts, from undergraduate to post-doc and practitioner level. Project participants will develop sustainable pathways for participation and work to enhance representation and inclusion in the geosciences by providing new pathways of entry based on modeling and remote sensing to complement field-based approaches.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.