Eric Kirby - US grants

Abstract
Intellectual Merit
One of the most striking aspects of the landscape east of the Tibetan Plateau, in China's Sichuan Province, is that tributaries of the Yangtze river are actively incising through Mesozoic bedrock of the Sichuan basin and the Eastern Sichuan Fold Belt (a Triassic-Jurassic fold belt related to the collision between the North and South China cratons). This incision is recorded by flights of strath (bedrock) terraces hundreds of meters above all of the major tributaries and the main stem of the Yangtze that extend nearly 500 km outboard of the plateau. Preliminary Chinese data suggest that all of these terrace sequences are Quaternary in age, implying relatively rapid, recent incision (hundreds of meters/m.y.). The question of what is driving this incision - whether it reflects a base-level change on the Yangtze or whether it is the result of active rock uplift beneath the fold belt and Sichuan basin - is essentially unknown. If regional terrace correlations are to be believed, the highest terraces in the landscape increase in elevation downstream, toward the fold belt. Clearly something interesting is going on - either the river has reversed course, the terrace profiles have been warped by regional deformation, or the terraces are miscorrelated. The PI proposes to examine the timing and rates of fluvial incision along the Yangtze River through the Three Gorges region in an effort to begin to test these hypotheses. The Three Gorges region (located in the fold belt, east of the Sichuan basin) represents the key locality for the following reasons:
o East of the Three Gorges, the Yangtze transitions to a depositional system on the coastal floodplain. Bedrock incision is confined to the reaches upstream of this point.
o The reach through the Gorges effectively sets the local base-level for the entire upstream basin.
o The Gorges region contains the highest flights of fluvial terraces, presumably reflecting the greatest rates of incision.
o The Three Gorges themselves are developed in limestone-cored anticlines. Numerous cave systems are developed adjacent to the river, affording the opportunity to trap fluvial sediment.
The PI proposes to establish a chronology of river incision by exploiting a technique for determining the age of fluvial sediment in caves adjacent to the river from the radioactive decay of cosmogenically produced isotopes (Granger et al., 1997).
Broader Impacts
This proposal will support a joint American - Chinese field expedition to the region, fostering intellectual exchange between the two groups. In particular, this research will expose Chinese colleagues to a new and developing technique for dating fluvial sediments in caves. In addition, the results of this work will be the first radiometrically-determined estimates of the timing and rates of development of the Three Gorges.

Despite recent advances in understanding of the mechanical and thermal response of
continental lithosphere to collisional orogenesis, important controversies remain. One of these centers on the role of large strike-slip faults during intracontinental deformation, and whether these structures 1) control the lateral 'escape' of quasi-rigid blocks in response to continental convergence (e.g., Tapponnier et al., 1982), or 2) reflect the passive localization of strain in a pervasively deforming and shearing crust (e.g., England and Molnar, 1990). The models make very different predictions regarding the variation of displacement along strike-slip faults, the relationship of fault displacement to deformation of the surrounding crustal blocks, and the nature of accommodation of slip at the terminations of the faults. In eastern Tibet, continuing debate over the nature of active deformation reflects, to a large degree, the limited number of rigorous geologic tests of these predictions.

The Kunlun fault is a first-order structural feature in the central and eastern Tibetan Plateau, where it presents a key opportunity to test among competing hypotheses for the role of strike-slip faults in the active deformation of eastern Tibet. Although Holocene slip rates appear to be uniform at ~11mm/yr along the central portion of the fault (Van der Woerd et al., 2000), several observations suggest that significant left-lateral shear along the eastern Kunlun fault does not reach the margin of the Tibetan Plateau: 1) the active trace of the fault on remote sensing (e.g., Tapponnier and Molnar, 1977) cannot be distinguished east of ~102 E; 2) field observations (Kirby) confirm that scarps associated with the Kunlun fault are not present east of this region; and 3) geodetic surveys indicate that, at present, little resolvable left-lateral shear passes through the eastern margin of the plateau (Chen et al., 2000). Determining what happens to left-lateral shear along the easternmost portion of the Kunlun fault is critical if we are to understand its kinematic and dynamic role in deformation of eastern Tibet and more generally the role of strike-slip faults during intracontinental deformation.

The PI's propose to test several hypotheses regarding the mechanisms of transfer and/or
accommodation of displacement at the apparent termination of an intracontinental strike-slip fault: ce Hypothesis 1: Displacement is transferred to kinematically linked, strike-slip faults that:
a. transmit displacement across and beyond the plateau margin, or
b. transmit displacement to shortening structures at the plateau margin.
ce Hypothesis 2: Displacement is absorbed by distributed shortening within the plateau resulting in crustal thickening.
ce Hypothesis 3: Displacement represents passive rotation of faults in response to a diffuse, clockwise regional shear.

Testing these hypotheses will focus on the following tasks:
ce Determining Late Pleistocene-Holocene slip rates along the easternmost segment of the Kunlun fault, with special attention to potential variations along strike.
ce Establishing the geometry, kinematics, and rates of displacement on candidate accommodation structures (both within the plateau and at its margin).
ce Assessing the magnitude and distribution of differential rock uplift and river incision in the Anyemaqen Shan (the prime candidate for shortening within the plateau)
This study promises to bring a detailed chronologic perspective to bear on the nature of
accommodation of strain at the terminations of large, intracontinental strike-slip faults. The PI's will document the presence or absence of displacement gradients present near the ends of such structures. The study will define the relationship of fault displacement to regional deformation patterns and will determine some of the mechanisms by which displacement is transferred to other structures. Finally, it will determine to what degree fault displacements are linked to deformation of the bounding blocks. The combined results will yield critical new insights into the problem of extrusion versus rotation during continental deformation.

Understanding the spatial and temporal distribution of surface deformation over various timescales can yield insight into lithospheric rheology, rupture behavior, and nature of slip transfer along fault networks. However, new insights provided by GPS bring new challenges: in particular, how does elastic strain accumulation measured over geodetic timescales (less than 10 yr) relate to geologic slip inferred over longer timescales (10,000 - 1,000,000 yr)? Over the past few years, much effort has been focused on an apparent discrepancy between geodetic rates of surface deformation and geologic rates of fault slip across the Eastern California Shear Zone. Recent hypotheses for this discrepancy center on temporal variations in the strain field which result from: 1) clustering of seismic strain release, 2) oscillatory strain release on conjugate fault systems, or 3) viscoelastic deformation following recent earthquakes. In order to fully understand the pace and tempo of variations in fault system behavior, however, a complete characterization of fault slip over geologic time is required.

This investigator team is collecting the basic geologic and geomorphic data necessary to critically assess rates of fault displacement across Owens Valley, California. In particular, the project is aimed at understanding the role played by diffuse arrays of small faults in accommodating strain across the region. The hypothesis that these fault networks may account for a significant component of geologic slip not considered by current interpretations of geodetic data is being tested by determining fault slip rates (exploiting geomorphic markers such as glacial moraines, river terraces and alluvial fans) on numerous fault arrays distributed throughout central and northern Owens Valley. Moreover, an alternative hypothesis holds that the discrepancy between geologic and geodetic data may reflect temporal variation in the rate of strain release. A refined understanding of the pace and tempo of distributed faulting across the region is being developed by exploiting sites with offset markers of varying age.

This project contributes towards larger goals articulated by the broader geologic/geophysical community by improving interpretations of geodetic data across the diffuse North American - Pacific plate boundary, and by developing new insight into the problem of temporal variations in fault slip.

0506622
Kirby

The goal of this project is to study the possible feedback between topography, deformation, atmospheric circulation and climate in the NE portion of the Tibetan plateau. The proposal seeks to understand the timing and spatial pattern of plateau uplift and from this, infer the mechanism of uplift (density foundering and/or channel flow) and determine what effect, if any, the uplift had on climate change at local, regional and global scales. To do this, the PIs will employ a variety of methods and personnel:

Molnar: project coordinator, analysis of GPS, gravity and seismic data, modeling of deformation and atmospheric interactions;
Burbank: magnetostratigraphy, sed. structures, U-Pb dating of zircons, structures and balanced cross sections ;
Clark: structures and balanced cross sections, U-Th/He dating, analysis of gravity and seismic refraction data ;
Garzione: U-Pb detrital zircons, oxygen and carbon isotopes of basin sediments, structures and balanced cross sections;
Kirby: structures and balanced cross sections, subset of U-Th/He dating;
Farley: U-Th/He dating;
Roe: atmospheric modeling (utilizing oxygen data);
Chinese collaborators: magnetostratigraphy, apatite fission track, provision of GPS and seismic data.

0607534
Kirby

This project is a follow up to a series of previous CD funded Rocky Mountain focused projects building on the discovery of a low velocity anomaly in the mantle beneath central Colorado. The proposed project involves a wide variety of techniques assembled to address the cause of the so called "Aspen anomaly", its history, and its effect on crustal evolution. The PIs are interested in the connection between changes in the mantle causing modification of surface topography. They have observed that the Aspen anomaly is located beneath the highest portion of the Rocky Mountains. They equate low mantle seismic velocities with low mantle densities to cause uplift. They will investigate whether the very large velocity variations in the mantle beneath this area are: a) in the lithosphere or asthenosphere, b) reflect Proterozoic lithospheric sutures reactivated by Cenozoic tectonism, c) are caused by a plume, and d) are caused by the presence of melt. These are all important and relevant questions for Continental Dynamics.

Specifically, the PIs will use:
- passive seismology to better define the anomaly using tomography, receiver functions, surface waves, and anisotrophy;
- geological studies (magmatic history, low temperature thermochronology, tectonic geomorphology) to identify Cenozoic tectonic and magmatic history to define long term and current history;
- geodynamical models of topography uplift and mantle processes to study their connection.

The interaction of intersecting fault systems can be complex and can lead to complicated deformation and overprinting on structures at all scales. An area of particular interest in this regard is in eastern California where the Eastern California shear zone (ECSZ) and the Garlock fault intersect. The ECSZ is a 100 km wide belt of north-northwest trending strike-slip faults of similar type and orientation as the San Andreas fault; the Garlock fault a roughly east trending strike-slip fault of opposite sense of motion. The Garlock is through going whereas faults of the ECSZ seem to end as they approach the Garlock. Although the Garlock appears to be the more continuous structure, GPS and satellite information seem to show that deformation related to the ECSZ passes continuously across it. The project is investigating how these two systems interact at mesoscopic and macroscopic scales. In particular, mapping in the field of faults and folds related to both structural systems is aimed at assessing whether faults of the ECSZ do indeed end (and if so how) before reaching the Garlock. Mapping is also showing if the Garlock is as continuous as previously thought. Samples are also being collected to determine the ages of various offset landforms and surface features. This provides the rate at which each fault is moving. This information complements the mapping showing how the faults end in that the loss of motion can be correlated with the rates of motion. In some locations, Ground Penetrating Radar is used to image how faults are oriented in the subsurface. This information is also critical to assess the rates of motion. By the collection of all these different types of information, the project is attempting to understand in detail the interaction of the ECSZ and Garlock and thus determine how the crust of the earth deforms in areas of complicated faulting. This is critical to understanding the overall deformation of the crust in the western part of North America.

Subduction zones play an important role in the long-term mass balance of earth?s crustal materials - they can serve as either sites of continental margin growth (accretionary margins) or continental margin denudation (erosional margins). This study will quantify shortening rates, erosion rates, and surface uplift rates in the forearc of a classical erosive convergent margin in northeastern Japan. The mass balance across the forearc will be assessed and patterns of permanent strain accumulation will be compared with elastic strain inferred from seismic and geodetic data. Erosive margins often exhibit systematically opposed behavior in the inner and outer portions of the forearc, with 1) an outer forearc that is mostly submarine, showing evidence for extension, and having an extensive slope apron that records subsidence of the margin; and 2) an inner forearc with coastal mountains, uplift, and rocks that show evidence for shortening and permanent strain. The relative ubiquity of this couplet along erosive margins worldwide suggests a potential genetic relationship. This project is testing the hypothesis that outer forearc subsidence due to basal erosion, or underthrusting, is matched by inner forearc uplift driven by underplating, or overthrusting. If this hypothesis is correct, global long-term estimates of continental denudation that are based on outer forearc subsidence grossly overestimate the amount of continental margin material subducted. The research team will employ a multi-disciplinary approach that includes structural mapping and fault-related fold analysis, tephrachronology, low-temperature thermochronometry (including apatite fission track analysis and (U-Th)/He dating), analysis of marine terraces, and geodynamic (thermal and deformational) modeling.

It has become increasingly apparent over the last two decades that many, if not the majority, of the earth?s subduction zones experience basal erosion, whereby the outer forearc is removed through upward migration of the plate boundary into the existing margin wedge. What is not known is how long are basal erosion rates sustained and where does eroded material go? This study addresses these problems by examining the inner forearc of an active system. Inner forearc uplift was first noted by Charles Darwin during the Beagle expedition of 1846 when he observed sea shells atop marine terraces located a kilometer above sea level and argued for regional uplift of the western coast of South America. Modern surveys of offshore bathymetry show that the local regions of uplift described by Darwin lie inboard of areas with pronounced outer forearc erosion. Inner forearc uplift may balance forearc subsidence due to basal erosion.

0841901
Kirby

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

This grant supports acquisition of ground penetrating radar (GPR) equipment, a real-time kinematic GPS system, 3-D visualization software and field hardened notebook computers. The equipment will support research and research training in the Department of Geosciences at Penn State University that will benefit from the capability of GPR to image the near subsurface. Specific equipment to be purchased includes a GPR system with multiple borehole antennas (at frequencies of 50, 100 and 200 MHz) to support stratigraphic, tectonic and hydrologic studies and a high frequency pulsed GPR system to be deployed for imaging the thickness, internal structure and basal contacts of glaciers. The equipment will support a range of PI and student research including studies of the dynamics of rivers of ice draining the West Antarctic Ice Sheet, studies of the movement of solutes through ground water systems, morphodynamic investigations of meandering and braided river systems, studies of pedogenesis and hill slope processes, and paleoseismological investigations of buried faults near active plate margins. In particular, research use of the GPR systems for study of the response of polar continental ice sheets to climate change is of profound and timely societal interest. GPR, in conjunction with seismic reflection techniques, offers the means to image glacial structure at high resolution to hundreds of meters and to probe the structure and nature of underlying deposits that serve to lubricate or slow glacial advance toward the sea. Students trained in GPR operation, data analysis and interpretation are well poised to gain employment in a host of civil engineering and environmental consulting fields that increasingly rely on GPR as a tool for near subsurface imaging.

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

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

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

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

Direct measurements of the deformational properties of actively deforming lithosphere remain elusive and lead to fundamental gaps in the understanding of how the evolution of rheology controls the evolution of orogenic systems. Despite abundant geophysical and geological data for the Indo-Asian collisional orogen, the mobility of the lower crust beneath central Tibet, its physical state, and the role that localized channel flow has played in the evolution of the Plateau and the Himalaya remain first-order questions. This project focuses on characterizing the deformational response of Tibetan lithosphere to time-varying surface loads to place quantitative constraints on the rheology of the crust. The project utilizes flights of relict shorelines around several large lakes within the internally-drained interior of the Tibetan Plateau. These shorelines indicate former positions of more extensive lake levels, and the withdrawal of the lakes in response to climatically-driven hydrologic changes represents a load removed from the lithosphere. Because the shorelines represent a paleo-horizontal datum, deflection of these markers during flexural isostatic rebound can place constraints on the elastic strength of the lithosphere and the viscosity of the underlying substrate. The study will couple detailed field observations and geochronology with rigorous deformational modeling (elastic flexure and 3-D visco-elastic deformation) to link the history of lake unloading to physical properties of the lower crust and mantle. In doing so, two fundamental questions about the Tibet-Himalayan orogen will be addressed: (1) Is Tibetan crust capable of lateral flow on geologic timescales, and (2) Do the rheologic properties of Tibetan lithosphere vary among the individual terranes comprising the plateau? The answers to these questions extend far beyond the specifics of the Tibet-Himalayan orogen and will provide additional constraints on the conditions that favor or impede lower-crustal flow during orogenesis in both active and ancient mountain belts.

Deformation within the deep crust is a fundamental process that links the driving forces for plate tectonics - flow in the earth's mantle - to slip on tectonic faults in the upper, brittle crust. Because direct measurements of the physical properties of the deep crust are technically infeasible, the behavior of the deep crust during mountain building is hotly debated. In particular, whether the deep crust is capable of widespread, lateral flow has implications for both strain accumulation on plate boundary fault systems - transient deformation along the Cascadia margin in the Western US is thought to be related to deformation in the deep crust - as well as the rates and patterns of development of high topography in Asia. The latter problem is one of great interest in that high topography of the Tibetan Plateau fundamentally influences atmospheric circulation. Understanding the processes and rates by which this high topography developed will enable more rigorous tests of the possibility that growth of the Tibetan Plateau played a central role in climate change over geologic timescales. This study will yield new insight into the nature of deformation within the deep crust beneath Tibet, information that is sorely lacking in today?s models of mountain building. In doing so, the project will also provide new constraints on climatically-driven changes in lake levels, information that is central to a more comprehensive understanding of the water budget in this resource-limited part of the world. Finally, the results will guide a more general understanding of how flow in the deep crust influences the overall deformation of the earth?s surface, including the potential for earthquake-generating slip on tectonic faults.

As was clearly demonstrated in the 2011 Mw 9.0 Tohoku (Japan) earthquake and tsunami, earthquakes that occur along subduction zone plate boundaries can be both among the largest and most devastating natural events on Earth. One key to anticipating what regions of subduction zones are most vulnerable to these mega-thrust events is to estimate the magnitude and location of un-released plate motion that accumulates prior to a major earthquake. Current subduction zone models assume a relatively simple link between observed deformation on the upper plate above the subduction interface and this slip deficit on the plate interface; however it is becoming clear that the actual distribution of co-seismic slip on the plate interface and the resulting upper plate response is substantially more complex. In order to map the accumulation of unreleased seismic moment, it is necessary to better understand how to map the observations of pre-, co- and post-earthquake deformation (made on land away from the plate interface) to the actual processes of slip accumulation and release on the plate boundary fault itself. This project will utilize a very rich data set of observed crustal deformation (GPS, geologic mapping, seismicity), observed on time scales ranging from geologic (millions of years) to earthquake cycle (hundreds-to-thousands of years) to earthquake rupture (minutes-to-seconds) in the vicinity of the Tohoku event. By combining geologic time-scale and seismic cycle time-scale observations conceptual models of subduction zone strain evolution can be improved. With a better understanding of how the upper plate in a subduction zone acts as a deformational filter, using observations of upper plate deformation the research team will be able to develop substantially improved estimates of plate boundary slip deficits, post-seismic loading of active structures on the upper plate (which may becomes seismically activated in response the main earthquake), and a better sense of seismic potential of subduction boundaries.

This project is an attempt to bridge a substantial gap in current subduction science - the gap between tectonic observations on geologic time-scales and current geophysical/geodetic observations of deformation through the earthquake cycle. Outcomes from this research will move subduction science toward better informed estimates of earthquake potential, maximum magnitudes that could be expected, and improved estimates of locations of maximum energy (moment) release during major earthquakes - all key components in reducing human vulnerability to major subduction zone earthquake hazards.

An Accomplishment-Based Request for Renewal of the Susquehanna - Shale Hills Critical Zone Observatory (SSHO)

With funding from the NSF Critical Zone Observatory (CZO) program, CZO workers led by PI Susan Brantley and coInvestigator Chris Duffy (Pennsylvania State University) will focus on cross-disciplinary synthesis, data sharing, and outreach at the Susquehanna Shale Hills CZO. Established originally in the 1970s as a site to study water flow in forested catchments, the 8-hectare Shale Hills watershed was expanded in 2007 as a CZO to understand broader questions targeting the interplay of water, energy, atmospheric gases, biota, soils, and the land surface. In addition to the small Shale Hills catchment, the CZO includes a suite of satellite sites that overly the same bedrock type (shale) but which are situated in different climate regimes. One additional satellite site is located on organic-rich Marcellus shale. These satellites allow researchers to understand how climate and organic content control water flow and soil formation while working with minority-and undergrad-serving institutions. CZO researchers are investigating i) new methodologies to model the age and chemistry of water as it moves from the atmosphere to groundwater; ii) new techniques to synthesize measurements of soil moisture for incorporation into land-atmosphere models; iii) observations that constrain water, energy, and solute fluxes related to trees; iv) models that quantify how soil grows on shale; v) new uses of isotopes to measure soil formation; and vi) observations concerning how variables describing characteristics at depth such as the fracture distribution in bedrock combine with features at Earth's surface such as the sunniness of hillslopes to control the evolution of soils and hillslopes over time. Datasets of isotopes, chemistry, soil moisture, CO2 and energy flux, LiDAR, sapflux, and other observables collected at high spatial and temporal resolution are published online. Outreach activities include community education about natural gas development on shale and K-12 educational opportunities.

The surface geology of the eastern United States is extraordinary in its complexity. This complexity reflects a wide range of tectonic processes that have operated in the region over the past billion years, including episodes of subduction and rifting associated with two complete cycles of supercontinent assembly and breakup. A record of these processes is preserved in the geological units and topography we see at the surface today. It is unknown, however, how the crust and mantle lithosphere have responded to these tectonic forces over time, and whether and how the geological units preserved at the surface relate to deeper structures. The persistence of Appalachian topography through time remains a major outstanding problem in the study of landscape evolution. There is an ongoing interplay among erosion, topography, rock type, and mantle flow at depth that controls the structures we see at the surface today. However, understanding the complex role played by each of these factors requires better constraints on the history of topographic change and its relationship to the deep structure and dynamics of the mantle. Our project, known as the Mid-Atlantic Geophysical Integrative Collaboration (MAGIC), aims to address these fundamental questions about the geophysical evolution of the eastern United States by studying surface processes, crustal and lithospheric structure, and deep mantle flow across Virginia, West Virginia, and Ohio.

MAGIC involves a collaborative effort among seismologists, geodynamicists, and geomorphologists. We are undertaking a two-year deployment of 28 broadband seismometers in a dense linear transect from the Atlantic coast to the continental interior. In combination with EarthScope USArray Transportable Array (TA) stations our experiment geometry will provide an opportunity to image isotropic and anisotropic crust and mantle structure from the coast to the continental interior in unprecedented detail, using techniques such as shear wave splitting, receiver function analysis, and tomographic inversions. The dense linear array allows us to target small-scale crustal and lithospheric variations for imaging. Our geodynamical modeling effort focuses on quantitatively testing several different hypotheses for the pattern of mantle flow by using 3-D, time-dependent, numerical models to make testable predictions about mantle anisotropy and surface topographic change, which will be tested against results from the seismology and geomorphology components of the project. The geomorphology component of the project uses quantitative stream profile data and cosmogenic isotopes to understand the history of erosion rates and topographic change throughout the Appalachian region. Insights into uplift history and the approach to equilibrium among lithology, topography, and erosion (and their spatial variation) will be compared to inferences on the mantle flow field and deep crustal and lithospheric structure gained from the geodynamics and seismology components of the project. Insight from all three efforts will be combined to obtain a vertically integrated picture of tectonic processes from the surface through the crust and mantle lithosphere to the asthenosphere and deeper mantle. The education and outreach component of this project focuses on the involvement of undergraduates in scientific research, opportunities for graduate students to mentor and advise undergraduate students, and forging ties with colleges and universities (including many primarily undergraduate institutions) in our study region that are not currently involved with the EarthScope initiative.

The recognition that climatically modulated erosion acts to govern the development of active mountain ranges is arguably one of the most transformative conceptual shifts in the geosciences subsequent to the plate tectonic revolution. Topography in tectonically active regions results from an interplay among climatic, tectonic, and surface processes. The building of mountains increases topographic slopes, which directly influences the rate and efficiency of erosional processes. Rising landmasses can also influence climate by altering patterns of airflow and heating, influencing the magnitude and pattern of precipitation. Feedbacks between the redistribution of mass by climate-driven erosion can influence the state of stress, thermal structure, and subsequent deformation patterns within mountain belts, the very mechanisms that drive the growth of topography. The strength of these various interactions and coupling, however, is still contested. Furthermore, these processes have strong impacts on the well being of humans living in mountainous terrains. This project supports a U.S.-Taiwan workshop that would assess the current state of research and identify future interdisciplinary research directions. A key objective of the workshop is to increase partnerships between the U.S. and Taiwan through the development of collaborative research projects that benefit from research expertise in both countries, thereby strengthening research activities within each country while advancing understanding of the complex linkages among mountain building, climate, and surface processes. The participation of students and early-career scientists in the workshop will ensure the development of long-term collaborations that are mutually beneficial both from the perspective of the development of the scientific workforce and the exchange of scientific ideas.

This project supports the participation of U.S. based scientists in a U.S. Taiwan workshop, which will be held at Oregon State University in 2017. The overarching purpose of this workshop is to promote interdisciplinary research on the linkages and feedbacks among mountain building, climate, and surface processes. The active Coast and Cascade Ranges, which will be explored during pre- and post-meeting field trips, will provide the backdrop for the workshop. Specifically, the workshop goals are four-fold: (1) evaluate the current state of understanding in how feedbacks among climate, mountain building, and landscape evolution govern the trajectory of orogenic systems; (2) identify and refine research goals that capitalize on transdisciplinary approaches that will lead to the next set of advances in our understanding of coupled solid and fluid earth systems; (3) strengthen emerging collaborations between U.S. and Taiwan scientists and to foster the development of specific research strategies to address research goals; and (4) broaden the scope of research goals to include systems beyond the Taiwan orogeny and to increase participation from a broader swath of U.S. researchers. The workshop is organized around two key themes:

This project is supported by the Tectonics Program and the Geomorphology and Land Use Dynamics (both in the Earth Sciences Division, Geosciences Directorate) and NSF's Office of International Science and Engineering.

Topography influences stress in the Earth’s crust and the pattern of deformation that arises during mountain building. Because the material properties of rocks near the surface of the Earth depend on their burial and exhumation history, in collisional mountain belts feedbacks may exist between the burial history of rocks in the subsurface, their strength at the surface, and topography. However, few field data exist to evaluate the strength of such feedbacks between surface and deep-Earth processes. This project will address this knowledge gap by quantifying the tectonic origin and geomorphic implications of variations in rock material properties across the Taiwan Central Range. In addition, this project will facilitate international collaboration between US and Taiwanese scientists through paired field expeditions and a student exchange program, leveraging new and existing research collaborations.<br/><br/>To explore relationships among burial and exhumation history, rock strength, and topography, this project will collect and integrate a paired dataset of structural and geomorphic observations. Existing and new measurements of erosion rates and thermal and deformation history will constrain patterns in burial and exhumation. Field surveys of river corridors assisted by small unmanned aerial vehicles will facilitate characterization of how rock properties influence river incision and hillslope-channel coupling at high resolution (centimeter-scale) and large spatial extent (kilometer-scale). Repeat surveys will enable high-resolution analysis of river response to individual storms. Data from this project will serve as a baseline for quantifying landscape response to future extreme events and help to address hazards associated with landslides, floods, and sedimentation.<br/><br/>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 are the sites of the Earth's largest and most damaging earthquakes. Between earthquakes, the Earth's crust accumulates strain, which is observed in gradual movement of GPS markers affixed to the ground (geodetic observations). In addition, the Earth's crust deforms over longer timescales of millions of years, such as the uplift of mountain ranges. The relationship between geodetic observations and long-term deformation is not well understood, especially with respect to earthquake hazards in subduction zones. This problem is particularly challenging at the southern end of the Cascadia Subduction zone, offshore of northern California and southern Oregon, where the Earth's crust is influenced both by subduction and by tectonic plate motion transferred from the San Andreas fault system to the south. However, the geologic characteristics of southern Cascadia make this region well-suited for understanding and isolating the processes that could drive upper crustal deformation and earthquakes. These characteristics include a combination of high topography, high uplift rates, and high erosion rates; rocks and deposits suitable for dating; and three potential, and testable, processes that could generate crustal deformation and subduction zone earthquakes. The goal of this research is to better understand how subduction zones work and to anticipate the size and timing of future earthquakes. In addition to the research objectives, this project includes partnering with faculty at Hoopa Valley Elementary School to develop geoscience field and laboratory exercises for sixth grade students. Hoopa Elementary is located in the heart of the region of scientific focus and serves primarily American Indian students. Hoopa Elementary School teachers will join the research team for summer field work. The project's university faculty and students will join the teachers in developing hands-on activities and field trips that will enable sixth grade students to practice each step of scientific research using real data - the results from this research. The research project would also advance other desired societal outcomes such as full participation of women and underrepresented minorities in STEM and development of a diverse, globally competitive STEM workforce through graduate and undergraduate student training and support of an early career researcher.<br/><br/>The southern end of the Cascadia plate boundary in North America is marked by transition from Cascadia lithospheric subduction to San Andreas transform faulting. This complex region of deformation, the Mendocino Triple Junction, is migratory in space and time. Localized rock uplift and erosion rates, terrace formation, and river channel morphology have responded to northward movement of the Mendocino Triple Junction and possibly the Blanco Fracture Zone, which is a physiographic boundary between the Juan de Fuca plate and its Gorda segment. Limited understanding of the long-term deformation in the upper-plate of the Cascadia forearc and its tectonic drivers make it difficult to isolate the earthquake-cycle signal within observed patterns of present-day deformation. In particular, overprinting from different geologic signals - migratory differences in the character of the subducting plate and the propagating wave of crustal thickening associated with the Mendocino Triple Junction - requires an evaluation of deformation and topographic change across a range of timescales. This project is an integrated study of the Late Cenozoic uplift, exhumation and erosion of Southern Cascadia. By using multiple geochronologic proxies that are sensitive to different rates and timings of processes (i.e., AHe thermochronology [rock exhumation >1Ma], cosmogenic radionuclide burial dating on buried surfaces that are presently uplifted [uplift rate constrained from ~0-5Ma], and cosmogenic radionuclide-derived basin averaged erosion rates [averaged over last ~100ka]), it will be possible to develop a record of exhumation and erosion through time and detect spatial variations in the southern forearc. The preservation of relict landscape remnants will be exploited to reconstruct long-wavelength deformation/uplift patterns and to quantify relief production in the Late Cenozoic. Finally, geodynamic models will be used to explore the mechanisms driving permanent upper plate deformation, and address how tectonic deformation of southern Cascadia may impact the signal recorded in observed geodetic data. This research will aid estimation of earthquake hazards at subduction zones by isolating and identifying the contribution of (recoverable) earthquake cycle deformation and of tectonically-driven, geologic time scale deformation at a site well suited to record ongoing tectonic deformation and associated strain.<br/><br/>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.