Subduction Duration and Slab Dip

The dip angles of slabs are among the clearest characteristics of subduction zones, but the factors that control them remain obscure. Here, slab dip angles and subduction parameters, including subduction duration, the nature of the overriding plate, slab age, and convergence rate, are determined for 153 transects along subduction zones for the present day. We present a comprehensive tabulation of subduction duration based on isotopic ages of arc initiation and stratigraphic, structural, plate tectonic and seismic indicators of subduction initiation. We present two ages for subduction zones, a long‐term age and a reinitiation age. Using cross correlation and multivariate regression, we find that (1) subduction duration is the primary parameter controlling slab dips with slabs tending to have shallower dips at subduction zones that have been in existence longer; (2) the long‐term age of subduction duration better explains variation of shallow dip than reinitiation age; (3) overriding plate nature could influence shallow dip angle, where slabs below continents tend to have shallower dips; (4) slab age contributes to slab dip, with younger slabs having steeper shallow dips; and (5) the relations between slab dip and subduction parameters are depth dependent, where the ability of subduction duration and overriding plate nature to explain observed variation decreases with depth. The analysis emphasizes the importance of subduction history and the long‐term regional state of a subduction zone in determining slab dip and is consistent with mechanical models of subduction

Studying subduction zone dynamics and continental evolution in South America using data-oriented geodynamic models

Among all continental plates, South America remains one of the least explored regarding its geological evolution. This continent possesses the longest subduction zone, the second highest continental plateau and tremendous amounts of volcanic eruption on its western coast. On the eastern coast, the Brazilian highlands that reach more than 1 km above the sea level were once submerged by shallow ocean in Mid-Cretaceous. All these magnificent landscapes and the associated dramatic geologic events are potentially linked to the underlying restless mantle convection that has persisted for billions of years. The purpose of my dissertation is to understand the causes and consequences of the major geological events in South America and evaluate the potential role of mantle convection in driving subduction zone dynamics and continental evolution. Yet, these geological events usually have distinct characteristics. Some of them are extreme events that occur within several minutes to days and have great impact on local societies, such as earthquakes and volcanic eruptions; while others may span a long geological period and exert gradual but significant influence in Earth evolution, such as mountain building and surface uplifts. Modern observations have contributed a lot to the study of the tectonics in South America, but they usually have limited spatial or temporal coverage. For example, seismic tomography reveals the present mantle structure which is only a snapshot of Earth's history. Thermochronology can tell us the exhumation history of a rock that may span tens to hundreds of millions of years, but the inference is spatially restricted to the sampling area. While numerical modeling can largely overcome these shortcomings, it is affected by uncertain model parameters. As a result, many tectonic questions remain open, with little consensus from decades' of dedicated research. One promising way to further investigate the tectonics of South America is through the cutting-edge multi-disciplinary research. In this dissertation, we apply numerical modeling with sequential data assimilation that progressively incorporates the paleo-reconstructions of plate kinematics and seafloor ages. The outputs are calibrated by multiple observations, including seismic tomography, earthquake source properties, distribution of volcanisms, seismic anisotropy, topography and gravity, mineral physics, as well as geological data such as mountain shortening and paleo-altimetry. The synergy among all these disciplines not only increases the spatial and temporal coverage of the research topics, but also narrows down the intrinsic uncertainties in each discipline. In practice, we tailor our multi-disciplinary models for two research topics, subduction zone dynamics and continental evolution. For the first topic, we use geodynamic models with plate kinematics and seafloor ages as boundary conditions to reproduce the history of South American subduction since the Late Cretaceous. With this model and the constraints mentioned above, we attempt to investigate the dynamic causes (Chapter 2) and consequences (Chapter 3) of flat subduction, as well as seismic anisotropy caused by subduction-induced mantle flow (Chapter 4). Our model reveals that the flat slabs in South America are caused by the synergy of dynamic suction from the overriding plate and the extra buoyancy provided by subducting oceanic plateau and aseismic ridges. The broken flat slab configuration due to the subduction of aseismic ridges better explains the abnormal distribution of intermediate-depth earthquakes and volcanisms as well as the intra-slab stress patterns than earlier models. This model also suggests that the mantle flow is controlled by the subducting slabs, with Poiseuille flow dominating the sub-continental region and Couette flow dominating the sub-oceanic region. Such a flow pattern best matches the observed patterns of surface wave anisotropy and shear wave splitting. For the second topic, we further combine this well-established geodynamic model with observations from other disciplines, including residual topography, residual gravity, reconstructed hotspot tracks, and surface geology, to study the temporal evolution of the cratonic lithosphere (Chapter 5). We find that lowermost cratonic lithosphere is compositionally denser than the asthenospheric mantle and can be episodically removed when perturbed by underlying mantle dynamics, while the shallower buoyant lithosphere helps to stabilize cratonic crust over billions of years. We further show that zones where the lithosphere was lost would take tens of millions of years to recover thermally, but the density of the new thermal root would remain less than that of the intact root. This new model challenges the traditional view on the density profile and tectonic stability of cratons, and thus have important implications on continental evolution. Overall, this dissertation shows that modern multi-disciplinary research that combines data-assimilation numerical modeling with various geological and geophysical observations, could greatly help us understand the tectonic driving forces in continents like South America

Cracked modeling and vibration analysis of pipe with a part-through crack

Pipeline is an important transportation facility in the oil and gas industries. But cracks inevitably appear in the pipe body due to various factors. Mechanical analysis of cracked pipe structures based on local flexibility has received increased attention in the last three decades. However, few reports exist on the local flexibility of pipes with an arbitrary angled crack. In this paper, the general solution of the local flexibility equations of a pipe with a part through-crack subjected to axial force, shearing force, and bending moment is deduced with respect to an arbitrary angled crack. The proposed equations consider the influence of the crack orientation on the local flexibility coefficient. An adaptive Simpson method is used to calculate the local flexibility coefficients of a cracked pipe. The results of testing by Naniwadekar’s and Authors’ are used to validate the proposed method. The results demonstrate that the proposed method is accurate for calculating local flexibility and can be applied for vibration analysis in a pipe-like structure

Nonlinear dynamic response analysis of a cantilever beam with a breathing crack

The nonlinear dynamic characteristics of plane cracked beam subjected to a harmonic load at the tip are researched. A crack opens and closes during vibration that is simulated as a frictionless plane contact problem, and a finite element contact model for a cantilever cracked beam is established. The quarter-point element is used to describe the crack tip singularity. Based on the proposed finite element contact model, the influence of excitation frequency, crack depth and crack position on nonlinear dynamic characteristics are discussed in detail. Relative amplitude of frequency spectrum with respect to different factors is analyzed to realize sub-harmonics or super-harmonics of cracked beam. The research results demonstrate that there is obvious nonlinear dynamic behavior for plane beam with a fatigue crack, and the different feature of frequency spectrum can be used to identify the beam damage in structure. Meanwhile, the strategy of experimental validation to the FEM results is discussed

VoxDet: Voxel Learning for Novel Instance Detection

Detecting unseen instances based on multi-view templates is a challenging problem due to its open-world nature. Traditional methodologies, which primarily rely on 2D representations and matching techniques, are often inadequate in handling pose variations and occlusions. To solve this, we introduce VoxDet, a pioneer 3D geometry-aware framework that fully utilizes the strong 3D voxel representation and reliable voxel matching mechanism. VoxDet first ingeniously proposes template voxel aggregation (TVA) module, effectively transforming multi-view 2D images into 3D voxel features. By leveraging associated camera poses, these features are aggregated into a compact 3D template voxel. In novel instance detection, this voxel representation demonstrates heightened resilience to occlusion and pose variations. We also discover that a 3D reconstruction objective helps to pre-train the 2D-3D mapping in TVA. Second, to quickly align with the template voxel, VoxDet incorporates a Query Voxel Matching (QVM) module. The 2D queries are first converted into their voxel representation with the learned 2D-3D mapping. We find that since the 3D voxel representations encode the geometry, we can first estimate the relative rotation and then compare the aligned voxels, leading to improved accuracy and efficiency. Exhaustive experiments are conducted on the demanding LineMod-Occlusion, YCB-video, and the newly built RoboTools benchmarks, where VoxDet outperforms various 2D baselines remarkably with 20% higher recall and faster speed. To the best of our knowledge, VoxDet is the first to incorporate implicit 3D knowledge for 2D tasks.Comment: 17 pages, 10 figure

Cracked modeling and vibration analysis of pipe with a part-through crack

Pipeline is an important transportation facility in the oil and gas industries. But cracks inevitably appear in the pipe body due to various factors. Mechanical analysis of cracked pipe structures based on local flexibility has received increased attention in the last three decades. However, few reports exist on the local flexibility of pipes with an arbitrary angled crack. In this paper, the general solution of the local flexibility equations of a pipe with a part through-crack subjected to axial force, shearing force, and bending moment is deduced with respect to an arbitrary angled crack. The proposed equations consider the influence of the crack orientation on the local flexibility coefficient. An adaptive Simpson method is used to calculate the local flexibility coefficients of a cracked pipe. The results of testing by Naniwadekar’s and Authors’ are used to validate the proposed method. The results demonstrate that the proposed method is accurate for calculating local flexibility and can be applied for vibration analysis in a pipe-like structure

Damage modeling and simulation of vibrating pipe with part-through circumferential crack

A new finite element model is developed to perform vibration analysis of a cracked pipe. To formulate the method, the local flexibility coefficients of a part-through circumferential crack in a pipe that is subjected to axial force, shear force and bending moment are analytically derived using linear fracture mechanics. In particular, an adaptive Simpson method is utilized to carry out the numerical integration for calculating the flexibility coefficients. With the flexibility coefficients, a finite element model is established to study the vibration characteristics of the cracked pipe, with particular emphasis on the crack effect represented by change in natural frequency. As an illustrative application, the finite element model is utilized to identify a crack in a pipe by contour plots of frequency ratio as function of crack location and crack depth, with the crack location and depth identified accurately. The proposed method is effective in characterizing the vibration behavior of a pipe with a crack

Multi-scale assessment of the economic impacts of flooding: evidence from firm to macro-level analysis in the Chinese manufacturing sector

We present an empirical study to systemically estimate flooding impacts, linking across scales from individual firms through to the macro levels in China. To this end, we combine a detailed firm-level econometric analysis of 399,356 firms with a macroeconomic input-output model to estimate flood impacts on China's manufacturing sector over the period 2003-2010. We find that large flooding events on average reduce firm outputs (measured by labor productivity) by about 28.3% per year. Using an input-output analysis, we estimate the potential macroeconomic impact to be a 12.3% annual loss in total output, which amounts to 15,416 RMB billion. Impacts can propagate from manufacturing firms, which are the focus of our empirical analysis, through to other economic sectors that may not actually be located in floodplains but can still be affected by economic disruptions. Lagged flood effects over the following two years are estimated to be a further 5.4% at the firm level and their associated potential effects are at a 2.3% loss in total output or 2,486 RMB billion at the macro-level. These results indicate that the scale of economic impacts from flooding is much larger than microanalyses of direct damage indicate, thus justifying greater action, at a policy level and by individual firms, to manage flood risk