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Summary report of the 2022 GeoPRISMS Synthesis Workshop: Structure and Deformation at Plate Boundaries held at University of Hawaiʻi at Mānoa from March 16 - 18, 2022., NSF OCE: 2025668

This contribution is provided to complement the manuscript submitted to Geophysical Journal International by these authors. The paper is entitled Instantaneous 3D tomography-based convection beneath the Rungwe Volcanic Province, East Africa: implications for melt generation. Here we provide our instantaneous 3D tomography-based convection (TBC) model that incorporates melt generation beneath the Rungwe Volcanic Province (RVP), the southernmost volcanic center in the Western Branch of the East African Rift. The 3D TBC was simulated using the open source code ASPECT version 2.2.0. The aim of this work is to test the hypothesis that the interaction of a thermally heterogeneous asthenosphere (plume material) with the base of the lithosphere enables localization of deep melt sources beneath the Western Branch where there are sharp variations in lithospheric thickness. To test our hypothesis, we investigate sublithospheric mantle flow beneath the Rungwe Volcanic Province (RVP), which is the southernmost volcanic center in the Western Branch. We use seismically constrained lithospheric thickness and sublithospheric mantle structure to develop an instantaneous 3D thermomechanical model of tomography-based convection (TBC) with melt generation beneath the RVP using ASPECT. Shear wave velocity anomalies suggest excess temperatures reach ~250 K beneath the RVP. We use the excess temperatures to constrain parameters for melt generation beneath the RVP and find that melt generation occurs at a maximum depth of ~140 km. The TBC models reveal mantle flow patterns not evident in lithospheric modulated convection (LMC) that do not incorporate upper mantle constraints. The LMC model indicates lateral mantle flow at the base of the lithosphere over a longer interval than the TBC model, which suggests that mantle traction from LMC might be overestimated. The TBC model provides higher melt fractions with a slightly displaced melting region when compared to LMC models. Our results suggest that upwellings from a thermally heterogeneous asthenosphere distribute and localize deep melt sources beneath the Western Branch in locations where there are sharp variations in lithospheric thickness. Our TBC models demonstrate the need to incorporate upper mantle constraints in mantle convection models and have global implications in that small-scale convection models without upper mantle constraints should be interpreted with caution. The models provided are contained in the following directories : 1. TBC_1473K_0.15factor 2. TBC_1473K_0.20factor 3. TBC_1473K_0.25factor 4. TBC_1483K_0.20factor 5. TBC_1473K_0.20factor_zero_compressibility 6. TBC_litho100km_1473K_0.20factor 7. LMC_compressible_1723K 8. LMC_compressible_1733K 9. LMC_compressible_1743K The directories in (1), (2) and (3) are models of TBC with excess sublithospheric mantle temperature derived from shear wave velocity perturbations (Emry et al., 2019) and whose background temperatures are constrained with mantle potential temperatures, Tp = 1473K and velocity-density conversion factors, 0.15, 0.20 and 0.25 respectively. The directory in (3) corresponds to TBC models for Tp = 1487 K and velocity-density conversion factor of 0.20. The directory in (5) is for TBC models without compressibility in the density equation of state with Tp =1473 K and conversion factor 0.20. The directory in (6) is model of TBC with a uniform 100 km thick lithosphere with Tp = 1473K and conversion factor = 0.20. The directories in ( (7), (8) and (9) correspond to models without seismic constraints of excess sublithospheric mantle temperature. Thus are models of lithospheric modulated convection (LMC) in which the sublithospheric mantle temperatures are constrained with Tp = 1723K, 1733K and 1743 K respectively. Each of the above models (directories) include a log.txt file that contains information of the maximum melt fraction and the corresponding model time, which permit use to test the different Tp values and conversion factors in melt generation. And also to test the relative role of lithospheric thickness variations versus sublithospheric heterogeneities in upper mantle flow and melt generation beneath the RVP. The above models also include files that allow for visualization in 3D using the software VISIT or PARAVIEW. Visualization parameters include: temperature field, viscosity, density, pressure, compositional fields, mesh, and velocities. We also provide corresponding csv files of above models. Each of these csv files contain 16 columns with the following names: "velocity:0","velocity:1","velocity:2","p","T","crust","mantle_lithosphere","porosity","peridotite","density","viscosity","melt_fraction","nonadiabatic_temperature","Points:0","Points:1","Points:2". These csv files can be used to extract information from the models and plot in another software such as Generic Mapping Tools (GMT).

This contribution is provided to complement the manuscript submitted to the Journal of Geophysical Research - Solid Earth by these authors. The paper is entitled "A Geodynamic Investigation of Plume-Lithosphere Interactions Beneath the East African Rift". Here we provide our 3D thermo-mechanical models of plume-lithosphere interactions of the East African Rift (EAR). The 3D thermo-mechanical models were simulated using the open source code ASPECT version 2.2.0. The aim of this work is to test the hypothesis the observed anomalous rift-parallel surface deformation (GNSS/GPS data) and seismic anisotropy (SKS splitting measurements) are driven and induced by northward mantle associated with the African Superplume. To test our hypothesis, we use extended the experiment by Rajaonarison et al. (2021) in which the surface deformation was driven only by lithospheric buoyancy forces (from variations of Gravitational Potential Energy (GPE), by incorporating multiple plume or superplume beneath the EAR. We tested a combined tectonic driving forces: lithospheric buoyancy forces with multiple plumes model and lithospheric buoyancy forces with superplume model. We found that mantle tractions arising from interactions of northward mantle flow from the African Superplume drive northward rift-parallel deformation in the EAR and such single plume is also the source mechanism of the onset first-order rift parallel seismic anisotropy. The models provided are contained in the following directories : 1. EAR_GPE_and_Multiple_Plumes 2. EAR_GPE_and_Superplumes Directory (1) is a model in which the forces acting on the lithosphere are the combination of 1) lithospheric buoyancy forces (or GPE arising from surface topography ETOPO1and crustal density variations CRUST1.0) and 2) mantle tractions from multiple plume mantle flow incorporated using shear wave velocity perturbations (Emry et al., 2019). Directory (2) is a model in which the forces acting on the lithosphere are the combination of 1) lithospheric buoyancy forces and 2) mantle tractions from mantle flow from the African Superplume. The African Superplume is simulated by applying a northward mantle-wind 2 cm/yr northward boundary conditions below 200 km depth. Each of the above models (directories) include a original.prm file which can be to re-run the model the the open source code ASPECT (version Rajaonarison, Stamps, and Naliboff, et al., 2020; https://zenodo.org/record/4005094#.Y_1EDC9Q2qA) to reproduce the model results. The above models also include files that allow for visualization in 3D using the software VISIT or PARAVIEW. Visualization parameters include: temperature field, viscosity, density, pressure, compositional fields, mesh, and velocities. We also provide the csv files of derived quantities for our model results to reproduce figures from our paper: a. EAR_GPE_and_Multiple_Plumes_Rigid_Block_Surface_Velocities.csv (Format: b. EAR_GPE_and_Superplume_Rigid_Block_Surface_Velocities.csv c. EAR_GPE_and_Multple_Plumes_Rift_Surface_Velocities.csv d. EAR_GPE_and_Superplume_Rift_Surface_Velocities.csv Files (a) and (b) contain surface velocities (depth=0) form rigid blocks extracted from model in directory (1) and (2), respectively. Files (c) and (d) contain surface velocities form the rifts (deforming zones) extracted from model in directory (1) and (2), respectively. We also provide csv files containing calculated seismic anisotropy or TI-axis (or Transverse Isotropy-axis). Calculations where made using the open source code DRex. The files are described as follow: e. EAR_Multiple_Plumes_TI.csv f. EAR_Superplume_TI.csv File (e) and (f) contain synthetic anisotropy or TI calculated using mantle flow from the multiple plumes model and superplume model in Directory (1) and (2), respectively. We also provide csv files containing GNSS/GPS data and seismic anisotropy used for comparisons in our paper: g. EAR_GNSS_GPS_velocities_Stamps_etal_2021.csv h. EAR_Observed_SKS.csv File (g) contain GNSS/GPS data from Stamps et al., 2021 which we use for comparisons with modeling results. File (h) contain SKS splitting measurements in the EAR (We refer the use to our paper for references). For each csv file above, the file format is shown in the header.

This is a poster submitted to the 2021 EarthCube Annual Meeting about the NSF EarthCube BALTO project.

Driven by data-rich use cases that span geodesy, geodynamics, seismology, and ecohydrology, the BALTO project enables brokered access to diverse geoscience data, including data that have been collected/organized by individual scientists in novel or unusual forms, also known as “long-tail” datasets. In BALTO, “brokering” means Web services that match diverse data-usage needs with heterogeneous types of source-data. This matching addresses form and semantics, which includes protocols, data structures, encodings, units of measure, variable names, and sampling meshes. The BALTO broker employs an extensible hub-and-spoke architecture: its hub will combine well-established, open-source, data-as-service software (from OPeNDAP) with the Geoscience Standard Names (GSN) to establish canonical representations for brokered datasets; each spoke—called an accessor—comprises (source-specific) data-access software along with metadata mappings that yield GSN-compliant variable names.

The NSF funded EarthCube initiative began in 2011 with the vision to transform geoscience research by developing cyberinfrastructure to improve access, sharing, visualization, and analysis of all forms of geosciences data and related resources. As a community-governed effort, EarthCube's overarching scientific goal is to enable geoscientists to tackle the challenges of understanding and predicting complex and evolving solid Earth, hydrosphere, atmosphere, and space environment systems. In order to assist in the planning, the EarthCube Science Committee has developed a selection of resources for the NSF-GEO domain data workshops. The resources are intended: 1) to share some lessons learned from prior EarthCube NSF-sponsored domain workshops so that new ground can be covered, and 2) to offer both technology and community resources in data management for the Geosciences.

GEM Technical Report 2015-03, Regional Projects, In this report we describe the Sub-Saharan Africa Geodetic Strain Rate Model 1.0, which is a contribution to the Global Earthquake Model Foundation (GEM) Strain Rate Project. The objective of this work is to improve the latest GEM geodetic strain rate model with an updated strain rate field of sub-Saharan Africa. Sub-Saharan Africa encompasses the East African Rift System (EARS), the active divergent plate boundary between the Nubian and Somalian plates, which accommodates strain along the boundaries of at least 3 microplates. The current version of the GEM geodetic strain rate model is constrained by published geodetic data along the EARS and includes microplates between the Nubian and Somalian plates. In this work we developed an improved strain rate field for sub-Saharan Africa that incorporates 1) an expanded geodetic velocity field within the Nubia-Somalia plate system and along the EARS 2) redefined regions of deforming zones guided by seismicity distribution, and 3) updated constraints on block rotations from the recent publication of Saria et al. (2014). The Sub-Saharan Africa Geodetic Strain Rate Model 1.0 spans longitudes 22 to 55.5 and latitudes -52 to 20 with 0.5° (longitude) by 0.4° (latitude) spacing, which includes part or all of the following plates and/or sub-plates: Somalia, Nubia, Rovuma, Lwandle, Victoria, Antarctica, and Arabia. For these plates/sub-plates we assign rigid block rotations as boundary constraints on the strain rate calculation that is determined using the Haines and Holt method of fitting splines to geodetic data for an interpolated velocity gradient tensor field. We derive strain rates, velocities, and vorticity rates from the velocity gradient tensor field. Following the work of Kreemer et al. 2014 for the GEM geodetic strain rate field we also provide estimates of model uncertainties, velocities, vorticity, and strain rates in a Nubia-fixed reference frame relative to the lower mantle for a 0.1° x 0.1° mesh.

The surface expression of upper crustal deformation varies widely based on geologic settings. Normal faults within an intra-arc basin, strike-slip faulting within a wide shear zone, and creeping fault behavior all manifest differently and require a variety of techniques for analysis. In this dissertation I studied three different actively deforming regions across a variety of geologic settings. First, I explored the drivers of extension within the La Pine graben in the Oregon Cascades. I mapped >20 new Quaternary faults and conducted paleoseismic trenching, where I found evidence for a mid-late Holocene earthquake on the Twin Lakes maar fault. I suggest that tectonics and not volcanism is responsible for the most recent deformation in the region based on fault geometries and earthquake timings, although more research is needed to tease out finer temporal and genetic relationships between tectonics and volcanism regionally. Second, I investigated the rupture pattern and earthquake history of the Calico fault system in the Eastern California Shear Zone. We mapped ~18 km of continuous rupture, with a mean offset of 2.3 m based on 39 field measurements. We also found evidence for two earthquakes, 0.5 - 1.7 ka and 5.5 - 6.6 ka through paleoseismic trenching. We develop a number of different multifault rupture scenarios using our rupture mapping and rupture scaling relationships to conduct Coulomb stress change modeling for the most recent earthquake on the Calico fault system. We find that the most recent event places regions adjacent to the fault in a stress shadow and may have both delayed the historic Landers and Hector Mine ruptures and prevented triggering of the Calico fault system during those events. Last, I studied the spatial distribution of the southern transition zone of the creeping section of the San Andreas fault at Parkfield, CA to determine if it shifted in response to the M6 2004 Parkfield earthquake. I used an Iterative Closest Point algorithm to find the displacement between two lidar datasets acquired 13 years apart. I compared creep rates measured before the 2004 earthquake to creep rates calculated from my lidar displacement results and found that there is not a discernible change in the overall pattern or distribution of creep as a response to the 2004 earthquake. Peaks within the lidar displacement results indicate complexity in the geometry of fault locking. Doctor of Philosophy Fault behavior varies widely across different regions, depending on the type of fault and local geology. In this dissertation I examine three regions with different mechanisms controlling deformation within them. First, I study the relationship between volcanic and tectonic induced faulting in the La Pine graben in the Oregon Cascades. While volcanoes and tectonics can both produce faults within a region, the surface expression of those faults changes depending on the underlying driver. I map > 20 new faults in the La Pine graben. I also conduct paleoseismic trenching on one of the newly identified faults, the Twin Lakes maar fault, and find that its most recent rupture occurred < 7.6 ka. I conclude that tectonism is the dominant driver of faulting within the La Pine graben based on the fault geometries and timing between identified regional earthquakes and volcanism. Second, I explore recent rupture on the Calico fault system in the Eastern California Shear Zone, which is a wide region across eastern California where deformation is distributed among many faults. Faulting in this region is complex, with some earthquakes occurring on multiple connected faults. I conducted a paleoseismic survey to determine the timing of the most recent earthquake(s) on the Calico fault system. This trenching effort found evidence for 1-2 earthquakes, the most recent occurring 0.5 – 1.7 ka. I use the rupture mapping and earthquake timing to develop a number of various rupture scenarios. I use these scenarios as inputs for computer modeling to explore the regional stress changes from these events and find that they reduce the overall stress in the area, elongating the amount of time between regional earthquakes. Last, I examine how creeping fault behavior on the San Andreas fault near Parkfield, CA changes as a response to an earthquake. Creeping behavior is where the two sides of a fault are continuously moving past one another. I examine the spatial distribution of where the San Andreas fault transitions from creeping to locked behavior by differencing two high-resolution lidar topographic datasets taken after the M6 2004 Parkfield earthquake. I compare my displacement results to pre-2004 datasets and conclude that the transition zone did not appreciably change as a result of the earthquake.

Modern geodynamic modeling is more complex than ever, and has been used to answer questions about Earth pertaining to the dynamics of the convecting mantle and core, layers humans have never directly interacted with. While the insights gleaned from these models cannot be argued, it is important to ensure calculations are understood and behaving correctly according to known math and physics. Here I perform several thermal 3-D spherical shell tests using the geodynamic code ASPECT, and compare the results against the legacy code CitcomS. I find that these two codes match to within 1.0% using a number of parameters. The application of geodynamic modeling is also traditionally to expand our understanding of Earth; however, even with a scarcity of data modern methods can provide insight into other planetary bodies. I use machine learning to show that coronae, circular features on the surface of the planet Venus, are not randomly distributed. I suggest the idea of coronae being fed by secondary mantle plumes in connected clusters. The entirety of the Venusian surface is poorly understood as well, with a large percentage being topographically smooth and much younger than the planet's hypothesized age. I use modeling to test the hypothesis of a large impact being responsible for a major resurfacing event in Venus's history, and find three distinct scenarios following impact: relatively little change, some localized change evolving into resurfacing through geologic time, or large-scale overturn and injection of heat deep into the Venusian mantle. Doctor of Philosophy Modern geodynamic modeling has been used to answer questions about Earth in wide-ranging fields. Despite technological improvements, it is important to ensure the calculations are understood and behaving correctly. Here I perform several tests using a code called ASPECT and compare the results against another code, CitcomS. I find that the two codes are in good agreement. Application of these techniques is also traditionally done for Earth, but modern methods can provide insight into other planets or moons as well. Coronae are circular features on the surface of Venus that are poorly understood. I use machine learning to show that these are not randomly distributed, and suggest a mechanism for the formation of clusters of coronae. The surface of Venus is also strange: it is both too flat and too young based on current ideas in planetary science. I use modeling to test whether a large impact could cause the details of Venus's surface we see today.

California has experienced an unusually dry past two decades punctuated by three intense multi-year droughts from 2007-2010, 2012-2015, and 2020-2022. A portion of the water lost during these two decades is due to intense groundwater overdraft of the Central Valley Aquifer. This groundwater overdraft has led to poroelastic compaction of the aquifer system and subsidence of the land surface. Water mass loss also causes elastic deformation of the solid Earth, an opposite and smaller amplitude response than the poroelastic deformation of aquifer systems. These mass changes can disturb the regional stress field, which may influence earthquake activity. Both the elastic and poroelastic deformation responses can be observed using satellite-based geodetic tools including Global Navigation Satellite System (GNSS) station displacements and Interferometric Synthetic Aperture Radar (InSAR). In this dissertation, I model aquifer-system compaction at depth using InSAR-based vertical land motion during the 2007-2010 drought and evaluate hazards related to Earth fissures, tensional cracks that form at the edges of subsidence zones. Next, I forward-calculate the predicted elastic deformation response to groundwater mass loss over the same period and calculate crustal stress change to evaluate what, if any, impact this has on seismicity in California. In addition to modeling deformation caused by water storage change, I also introduce a new method to jointly invert elastic vertical displacements at GNSS stations with water storage anomalies from the Gravity Recovery and Climate Experiment (GRACE) to solve for water storage changes from 2003-2016 over California. Finally, I expand on this joint inversion framework to include poroelastic deformation measured using InSAR over the Central Valley aquifer-system to solve for a change in water storage and groundwater storage over water years 2020-2021, the most recent drought period in California. Doctor of Philosophy Changes in the hydrologic system can have wide-reaching societal, geopolitical, economic, ecological, and agricultural impacts. Proper water management, particularly in places that have water scarcity concerns due to overuse, water pollution, or recurrent drought conditions, is essential to ensure this resource is available to future generations. Current projections of climate change scenarios point to more intense and frequent extreme hydroclimate events. With accelerating population growth in many urban centers across the world, measuring water storage changes has never been more important to ensure resiliency of our cities, energy sector, and agricultural systems. Furthermore, water storage changes deform the Earth, which may create or alter geophysical hazards such as subsidence, the development of Earth fissures, and seismicity. Today, a multitude of space-based geodetic tools allow us to monitor changes in the Earth system, including changes in terrestrial water content and associated deformation, with higher spatial and temporal resolution than ever before. These datasets have provided an unprecedented understanding of hydroclimatic hazards and have resolved constraints arising from sparse and infrequent in-situ measurements. Here, I use space-based geodetic tools and geophysical models to measure water storage fluctuations, deformation, and evaluate associated hazards in California, a region that has experienced an unprecedented nearly continuous two-decades long drought. In general, I find that 21st century droughts have caused significant water storage loss, especially groundwater storage loss, in California, which has exacerbated some geophysical hazards including land subsidence and Earth fissure hazards.

Continental rifting is an important geodynamic process during which the Earth's outer-most rigid shell undergoes continuous stretching resulting in continental break-up and theformation of new oceanic basins. The East African Rift System, which has two continentalsegments comprising largely of the East African Rift (EAR) to the West and the easternmostsegment Madagascar, is the largest narrow rift on Earth. However, the driving mechanismsof continental rifting remain poorly understood due to a lack of numerical infrastructure tosimulate rifting, the lack of knowledge of the underlying mantle dynamics, and poor knowl-edge of mantle rheology. Here, we use state-of-art computational modeling of the upper660 km of the Earth to: 1) provide a better understanding of mantle flow patterns and themantle rheology beneath Madagascar, 2) to elucidate the main driving forces of observedpresent-day∼E-W opening in the EAR, and 3) to investigate the role of multiple plumesor a superplume in driving surface deformation in the EAR. In chapter 1, we simulate EdgeDriven convection (EDC), constrained by a lithospheric thickness model beneath Madagas-car. The mantle flow associated with the EDC is used to calculate induced olivine aggregates'Lattice Preferred Orientation (LPO), known as seismic anisotropy. The predicted LPO isthen used to calculate synthetic seismic anisotropy, which were compared with observationsacross the island. Through a series of comparisons, we found that asthenospheric flow result-ing from undulations in lithospheric thickness variations is the dominant source of the seismicanisotropy, but fossilized structures from an ancient shear zone may play a role in southern Madagascar. Our results suggest that the rheological conditions needed for the formationof seismic anisotropy, dislocation creep, dominates the upper asthenosphere beneath Mada-gascar and likely other continental regions. In chapter 2, we use a 3D numerical model ofthe lithosphere-asthenosphere system to simulate instantaneous lithospheric deformation inthe EAR and surroundings. We test the hypothesis that the∼E-W extension of the EAR isdriven by large scale forces arising from topography and internal density gradients, known aslithospheric buoyancy forces. We calculate surface deformation solely driven by lithosphericbuoyancy forces and compare them with surface velocity observations. The lithosphericbuoyancy forces are implemented by imposing observed topography at the model surfaceand lateral density variations in the crust and mantle down to a compensation depth of 100km. Our results indicate that the large-scale∼E-W extension across East Africa is driven bylithospheric buoyancy forces, but not along-rift surface motions in deforming zones. In chap-ter 3, we test the hypothesis that the anomalous northward rift-parallel deformation observedin the deforming zones of the EAR is driven by viscous coupling between the lithosphereand deep upwelling mantle material, known as a superplume, flowing northward. We testtwo end-member plume models including a multiple plumes model simulated using high res-olution shear wave tomography-derived thermal anomaly and a superplume model (Africansuperplume) simulated by imposing a northward mantle-wind on the multiple plumes model.Our results suggest that the horizontal tractions from northward mantle flow associated withthe African Superplume is needed to explain observations of rift-parallel surface motions indeforming zones from GNSS/GPS data and northward oriented seismic anisotropy beneaththe EAR. Overall, this work yields a better understanding of the geodynamics of Africa. Doctor of Philosophy Continental rifting is an important geodynamic process during which the Earth's outer-most rigid shell undergoes continuous stretching resulting in continental break-up and theformation of new oceanic basins. The East African Rift System, which has two continentalsegments comprising largely of the East African Rift (EAR) to the West and the easternmostsegment Madagascar, is the largest narrow rift on Earth. However, the driving mechanismsof continental rifting remain poorly understood due to a lack of numerical infrastructure tosimulate rifting, the lack of knowledge of the underlying mantle dynamics, and poor knowl-edge of mantle rheology. Here, we use state-of-art computational modeling of the upper660 km of the Earth to: 1) provide a better understanding of mantle flow patterns and themantle rheology beneath Madagascar, 2) to elucidate the main driving forces of observedpresent-day∼E-W opening in the EAR, and 3) to investigate the role of multiple plumesor a superplume in driving surface deformation in the EAR. In chapter 1, we simulate EdgeDriven convection (EDC), constrained by a lithospheric thickness model beneath Madagas-car. The mantle flow associated with the EDC is used to calculate induced olivine aggregates'Lattice Preferred Orientation (LPO), known as seismic anisotropy. The predicted LPO isthen used to calculate synthetic seismic anisotropy, which were compared with observationsacross the island. Through a series of comparisons, we found that asthenospheric flow result-ing from undulations in lithospheric thickness variations is the dominant source of the seismicanisotropy, but fossilized structures from an ancient shear zone may play a role in southern Madagascar. Our results suggest that the rheological conditions needed for the formationof seismic anisotropy, dislocation creep, dominates the upper asthenosphere beneath Mada-gascar and likely other continental regions. In chapter 2, we use a 3D numerical model ofthe lithosphere-asthenosphere system to simulate instantaneous lithospheric deformation inthe EAR and surroundings. We test the hypothesis that the∼E-W extension of the EAR isdriven by large scale forces arising from topography and internal density gradients, known aslithospheric buoyancy forces. We calculate surface deformation solely driven by lithosphericbuoyancy forces and compare them with surface velocity observations. The lithosphericbuoyancy forces are implemented by imposing observed topography at the model surfaceand lateral density variations in the crust and mantle down to a compensation depth of 100km. Our results indicate that the large-scale∼E-W extension across East Africa is driven bylithospheric buoyancy forces, but not along-rift surface motions in deforming zones. In chap-ter 3, we test the hypothesis that the anomalous northward rift-parallel deformation observedin the deforming zones of the EAR is driven by viscous coupling between the lithosphereand deep upwelling mantle material, known as a superplume, flowing northward. We testtwo end-member plume models including a multiple plumes model simulated using high res-olution shear wave tomography-derived thermal anomaly and a superplume model (Africansuperplume) simulated by imposing a northward mantle-wind on the multiple plumes model.Our results suggest that the horizontal tractions from northward mantle flow associated withthe African Superplume is needed to explain observations of rift-parallel surface motions indeforming zones from GNSS/GPS data and northward oriented seismic anisotropy beneaththe EAR. Overall, this work yields a better understanding of the geodynamics of Africa.

Our understanding of how magma-poor rifts accommodate strain remains limited largely due to sparse geophysical observations from these rift systems. To better understand magma-poor rifting processes, chapter 1 of this dissertation is focused on investigating the lithosphere-asthenosphere interactions beneath the Malawi Rift, a segment of the magma-poor Western Branch of the East African Rift (EAR). Chapter 2 and 3 are focused on investigating the sources of melt beneath the Rungwe Volcanic Province (RVP), an anomalous volcanic center located at the northern tip of the Malawi Rift. In chapter 1, we use the lithospheric structure of the Malawi Rift derived from the World Gravity Model 2012 to constrain three-dimensional (3D) numerical models of lithosphere-asthenosphere interactions, which indicate ~3 cm/yr asthenospheric upwelling beneath the thin lithosphere (115-125 km) of the northern Malawi Rift and the RVP from lithospheric modulated convection (LMC) that is decoupling from surface motions. We suggest that the asthenospheric upwelling may generate decompression melts which weakens the lithosphere thereby enabling extension. The source of asthenospheric melt for the RVP is still contentious. Some studies suggest the asthenospheric melt beneath the RVP arises from thermal perturbations in the upper mantle associated with plume head materials, while others propose decompression melting from upwelling asthenosphere due to LMC where the lithosphere is thin. Chapter 2 of this dissertation is focused on testing the hypothesis that asthenospheric melt feeding the RVP can be generated from LMC using realistic constraints on the mantle potential temperature (Tp). We develop a 3D thermomechanical model of LMC beneath the RVP and the entire Malawi Rift that incorporates melt generation. We find decompression melt associated with LMC upwelling (~3 cm/yr) occurs at a maximum depth of ~150 km localized beneath the RVP. Studies of volcanic rock samples from the RVP indicate plume signatures which are enigmatic since the RVP is highly localized, unlike the large igneous provinces in the Eastern Branch of the EAR. In chapter 3, we test the hypothesis that the melt beneath the RVP is generated from plume materials. We investigate melt generation from plume-lithosphere interactions (PLI) beneath the RVP by developing a 3D seismic tomography-based convection (TBC) model beneath the RVP. The seismic constraints indicate excess temperatures of ~250 K in the sublithospheric mantle beneath the RVP suggesting the presence of a plume. We find a relatively fast upwelling (~10 cm/yr) beneath the RVP which we interpret as a rising plume. The TBC upwelling generates decompression melt (~0.25 %) at a maximum depth of ~200 km beneath the RVP where the lithosphere is thinnest (~100 km). Our results demonstrate that an excess heat source from may be plume materials is necessary for melt generation in the sublithospheric mantle beneath the RVP because passive asthenospheric upwelling of ambient mantle will require a higher than normal Tp to generate melt. Studies of volcanic rock samples from the RVP indicate plume signatures which are enigmatic since the RVP is highly localized, unlike the large igneous provinces in the Eastern Branch of the EAR. In chapter 3, we test the hypothesis that the melt beneath the RVP is generated from plume materials. We investigate melt generation from plume-lithosphere interactions (PLI) beneath the RVP by developing a 3D seismic tomography-based convection (TBC) model beneath the RVP. The seismic constraints indicate excess temperatures of ≈ 250K in the sublithospheric mantle beneath the RVP suggesting the presence of a plume. We find a relatively fast upwelling (≈10 cm/yr) beneath the RVP which we interpret as a rising plume. The TBC upwelling generates decompression melt (≈0.25 %) at a maximum depth of ≈200 km beneath the RVP where the lithosphere is thinnest (≈100 km). Our results demonstrate that an excess heat source from may be plume materials is necessary for melt generation in the sublithospheric mantle beneath the RVP because passive asthenospheric upwelling of ambient mantle will require a higher than normal Tp to generate melt. Doctor of Philosophy Studies suggest the presence of hot, melted rock deep in the continents makes them weaker and easier to break apart, however, our understanding of how continents with less melted rock break apart remains limited largely due to sparse geophysical observations from these dry areas. To better understand how continents with less melted rock break apart, chapter 1 of this dissertation is focused on investigating the interactions between the rigid part of the Earth, called lithosphere, and the underlying lower viscosity rock layer called asthenosphere beneath the Malawi Rift, a segment of the magma-poor Western Branch of the East African Rift (EAR). Chapter 2 and 3 are focused on investigating the sources of melt beneath the Rungwe Volcanic Province (RVP), an anomalous volcanic center located at the northern tip of the Malawi Rift. In chapter 1, we use the lithospheric structure of the Malawi Rift derived from gravity data to constrain three-dimensional (3-D) numerical models of lithosphere-asthenosphere interactions, which indicate ~3 cm/yr asthenospheric upwelling beneath the thin lithosphere (115-125 km) of the northern Malawi Rift and the RVP that does not seem to drive movements at the surface. We suggest that the asthenospheric upwelling may generate melted rock which weakens the lithosphere thereby enabling extension. However, the source of asthenospheric melt for the RVP is still contentious. Some studies suggest the asthenospheric melt beneath the RVP arises from thermal perturbations in the upper mantle associated with rising mantle rocks or plume head materials, while others propose melting occurs from upwelling asthenosphere due to lithospheric modulated convection (LMC) where the lithosphere is thin. Chapter 2 of this dissertation is focused on testing the hypothesis that asthenospheric melt feeding the RVP can be generated from LMC. We develop a 3D thermomechanical model of LMC beneath the RVP and the entire Malawi Rift that incorporates melt generation. We find decompression melt associated with LMC upwelling (~3 cm/yr) occurs at a maximum depth of ~150 km localized beneath the RVP. Studies of volcanic rock samples from the RVP indicate plume signatures which are enigmatic since the RVP is highly localized, unlike the large igneous provinces in the Eastern Branch of the EAR. In chapter 3, we investigate melt generation from plume-lithosphere interactions (PLI) beneath the RVP. We develop a 3D model of convection using information from seismology we call tomography-based convection (TBC) beneath the RVP. The seismic data indicate excess temperatures of ~250 K beneath the RVP suggesting the presence of a plume. We find a relatively fast upwelling (~10 cm/yr) beneath the RVP which we interpret as a rising plume. The TBC upwelling generates decompression melt at a maximum depth of ~200 km beneath the RVP. Our results demonstrate that an excess heat source from may be plume materials is necessary for melt generation in the sublithospheric mantle beneath the RVP because passive asthenospheric upwelling of ambient mantle will require a higher than normal mantle potential temperatures to generate melt.

The use of tsunami models for applications of 'now-casting', which is the prediction of the present and near future behavior, has limited exploration, and could potentially be of significant usefulness. Tsunamis are most often caused by earthquakes in subduction zones, which generates coupled uplift and subsidence, and displaces the water column. The behavior of the fault failure is difficult to describe in the short term, often requiring seismic waveform inversion, which takes a length of time on the order of weeks to months to properly model, and is much too late for any use in a now-casting sense. To expedite this length of time, a series of source models are created with variable fault geometry behaviors, using fault parameters from Northern Oceanic and Atmospheric Administration's Short-term Inundation and Forecasting of Tsunamis (SIFT) database, in order to model a series of potential tsunami behaviors using the numerical modelling package, GeoClaw. The implementation of modeling could identify areas of interest for further study that are sensitive to fault failure geometry. Initial results show that by varying the geometry of sub-faults of a given earthquake, the resulting tsunami models behave fairly differently with different wave dispersion behavior, both in pattern and magnitude. While there are shortcomings of the potential geometries the code created in this study, and there are significant improvements that can be made, this study provides a good starting point into now-casting of tsunami models, with future iterations likely involving statistical probability in the fault failure geometries. Master of Science Short term modeling of tsunamis generated by earthquakes is poorly explored. If an earthquake causes movement in a fault located underwater, and this movement will then cause the water column above it to be displaced. Tsunami models are sensitive to how the fault moves, and an accurate representation of this movement often takes much more time that the duration of a tsunami. This lengthy process is ineffective for short term modeling. This study instead estimates several possible scenarios of how the fault will behave, and model each of them. This will show how different locations of interest are sensitive to different geometries of fault failure. Initial results show that by varying this geometry, the tsunami wave behaves very differently, and will cause different amounts of run-up in the same location depending on which particular geometry is modeled. The automation of distinctly different earthquake sources serve as a good starting point for future work to be conducted to generate more accurate models.

The Caribbean and Central America region (CCAR) undergoes the entire spectrum of earthquake types due to its complex tectonic setting comprised of transform zones, young oceanic spreading ridges, and subduction along its eastern and western boundaries. CCAR is, therefore, an ideal setting in which to study the impacts of long-term tectonic deformation on the distribution of present-day seismic activity. In this work, we develop a revised continuous tectonic strain rate model based on interseismic, secular geodetic data. We compare it with its predecessor, the Global Strain Rate Model v2.1 (GSRM). Specifically, we compare predicted fault types with known active faults and evaluate the style of predicted fault types with present-day earthquake focal mechanism data. We first create a 0.25$^{circ}$ x 0.25$^{circ}$ finite element grid that is comprised of block geometries defined from previous studies. Second, we isolate and remove anomalous signals that are inconsistent with rigid block motion from the latest open access community Global Navigation Satellite System (GNSS) velocity solution from UNAVCO and combine it with GNSS data compiled for the GSRM. In a third step, we delineate zones of deformation and rigidity by creating a buffer around the boundary of each block that varies depending on the size of the block and the expected deformation zone, which are based on locations of GNSS data consistent with rigid block motion. Fourth, we assign the regions within the buffer of zero for the deforming areas and a plate index outside the buffer to constrain plate rigidity. Finally, we calculate a tectonic strain rate and continuous velocity model for CCAR using the Haines and Holt finite element approach to fit bicubic Bessel splines to the GNSS data assuming block rotation for zones of rigidity. Our model of the CCAR is consistent with compression along subduction zones, extension across the East Pacific Rise, and a combination of compression and extension across the North America - Caribbean plate boundary with a few exceptions due to limitations with the modeling approach. Modeling results are then used to calculate expected faulting behaviors that we compare with seismic activity, the GSRM, and mapped geologic faults. We find the accumulation of strain rates in areas near the Middle American Trench, Hispaniola, the northeastern Caribbean, and northern South America indicate tectonic deformation that may result in seismic events. We conclude the tectonic deformation plays a critical role in explaining present-day seismicity along land masses adjacent to the subduction zone and the Hispaniola block. Master of Science Central America and the Caribbean are areas with high occurrences of earthquakes. This is due to the various types of tectonic plate boundaries that occur in the region. When plates move in relation to each other, they can accumulate strain, which plays a role in the size and type of earthquakes that occur. In this work, we aim to determine the effects on strain on earthquakes. To do this, we utilize an inversion method to calculate strain rates from Global Navigation Satellite System (GNSS) data. In our model, we first create a grid of points and a geometry of the regional tectonic blocks. We then gather data from public and published sources. The model also requires that we define where the plates are allowed to deform (accumulate strain) and where they remain rigid. Using the Haines and Holt method, we invert the GNSS velocities for strain rates and velocities. We find long-term tectonic deformation dominates the present-day seismic activity in three key regions: along the Middle America Trench and across the Hispaniola block.