CAREER: Does long-term topography preserve details of the seismic cycle? Seeing through, and exploiting, the diverse forcings influencing actively deforming landscapes.

The shape of topography in tectonically active regions reflects a balance between the uplift of rocks from tectonic forces and the removal of rock and sediment by erosive forces, the latter of which are mediated by the local details of the climate and the types of rocks exposed. If the climatic and rock type details are constrained, then aspects of topography, like the shape of rivers, can serve as proxies for details of the tectonic forces and reveal, for example, the location and relative activity of faults.

While providing critical insight into active tectonics, these approaches tend to idealize rock uplift along faults as a steady process. However, in reality rock uplift and the growth of topography usually occurs through more punctuated processes, specifically long periods of slow distributed deformation between earthquakes and then sudden and violent deformation during earthquakes, which combined over millennia, result in the integrated and idealized average rock uplift.

The extent to which details of this “seismic cycle” are preserved in topography is unclear, but unlocking potential records stored in topography would be transformative as it could provide insight into specifics critical for hazard assessments, like average time between earthquakes and the relative extents of earthquake ruptures, through relatively quick, easy, and cheap analyses from globally available topography data. This project explores the preservation potential of aspects of the seismic cycle through a two-pronged approach.

First, a large and comprehensive suite of simulations of landscapes developing through successive earthquake events and with varying climate and lithology details are being used to develop a set of fingerprints for relating landscape form to earthquake details. Secondly, these fingerprints are being applied to regions with independently established histories of fault and earthquake activity to vet and refine the results from the simulations.

The broad goal of this research is providing a critical set of tools for better understanding earthquake hazards, both domestically and abroad in regions that lack comprehensive seismic hazard assessments and improve the safety and security of populations living in regions of potential hazard. In addition to the research goals of this project, a set of unique educational tools to provide resources for understanding the ways in which topography more generally reflects the shaping tectonic and climatic forces is being developed.

The results of this effort include a LandscapeLibrary, a large set of landscape simulations developed under a wide array of controlled conditions, which will be made available to the public through an interactive web interface. Additionally, a series of educational exercises which use the LandscapeLibrary are being developed for a range of education levels from secondary to graduate level, providing a far-reaching educational resource that will contribute to development of the STEM workforce and promote general understanding of the critical context for the surface of the Earth.

Fundamental details of the tectonic history of actively deforming regions are encoded in their fluvial topography, but interpreting these histories requires full consideration of the array of forcing mechanisms contributing to their form. For example, significant prior work focused on the influence of spatially or temporally variable precipitation, variations in lithologic resistance to erosion, or autogenic processes within catchments, amongst others in complicating, the interpretation of tectonics from topography and the extent to which these additional forcings can be factored out and a meaningful tectonic signal can still be reliably extracted from fluvial topography.

The tectonic signals interpreted from this topography typically are first-order characteristics of fault systems, e.g., the location and relative activity of major structures, their subsurface geometries, or temporal changes in their average slip rates, but which largely treat the deformation on faults, and resulting patterns in rock uplift driving topographic development, simplistically as rigid block motion. However, fault motion typically occurs seismically and with significant spatial variability in surface deformation within a single seismic cycle, and indeed, likely between seismic cycles driven by interseismic creep on non-locked portions of fault and strain accumulation on locked portions of faults which is released coseismically.

The extent to which the seismic cycle influences the development of topography is fundamentally unknown, but a general assumption is that it can be safely ignored, and that topography reflects average slip rates and associated rates of rock uplift. However, some work has questioned this assumption, specifically whether a signal of incomplete recovery of interseismic strain by earthquakes may leave a signal in topography.

More broadly, it remains unclear whether topography can record any details of the seismic cycle, but it is hypothesized in this project that it may, specifically because of interactions between the seismic cycle and other forcing mechanisms, such as spatially and temporally variable precipitation. This project is testing this hypothesis with an integrated modeling study coupled with a large-scale topographic analysis effort.

Specifically, the project seeks to 1) use coupled surface processes and deformation models that simulate interseismic and coseismic deformation to identify topographic signatures of the seismic cycle and 2) assess whether these signals are recognizable in natural landscapes with independent constraint on at least parts of their seismic cycles. The project will provide crucial insight into the connections between the long-term topography developed in active deforming regions and short-term earthquake processes, which is a long-standing goal within both the tectonics and earth surface processes communities.

This project follows recent efforts that attempt to use the topographic characteristics of simulated landscapes to extract more quantitative information from topography directly, e.g., estimation of slip rate magnitudes, but promises to extend our view to details of the seismic cycle and fault behavior. These details of the seismic cycle are a fundamental input for seismic hazard analysis, which is of great societal relevance, but extracting this critical information is often challenging, laborious, and expensive.

As such, being able to assess even broad information about the seismic cycle of a fault system from something as ubiquitous and globally accessible as topography would be incredibly beneficial - and is a potential outcome from the proposed work. This effort will occur in tandem with the development of a large body of precomputed synthetic landscapes developed under diverse forcing conditions to build the LandscapeLibrary and an interface for easy access and visualization of this library.

This resource, and educational materials developed with it, are designed to help provide an easy visual representation of landscape evolution for a variety of classroom purposes. The LandscapeLibrary will provide an invaluable resource for other geoscientist educators around the world who wish to provide their students an intuitive view of the diverse forcing on landscape evolution. Finally, this project will support one PhD student and a postdoctoral researcher.

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.