Hasil untuk "Dynamic and structural geology"

Rachael S. Skye, Erin G. Teich

Many tools and techniques measure local structure in materials in contexts ranging from biology to geology. We provide a survey of those tools and metrics that are especially useful for analyzing particulate soft matter. The metrics we discuss can all be computed from the positions of particles, and are thus most useful when there is access to this information, either from simulation or experimental imaging. For each metric, we provide derivations, intuition regarding its implications, example uses, and references to software packages that compute the metric. Our survey encompasses characterization techniques ranging from the simplest to the most complex, and will be useful for students getting started in the structural characterization of particle systems.

Raphael M. Tromer, Isaac M. Felix, Rafael Besse et al.

In materials science, the selection of structural descriptors for machine learning protocols strongly influences predictive performance and the degree of physical interpretability that can be achieved from the derived models. Although more complex descriptors may improve numerical accuracy, they often represent extra computational load, also reducing transparency into the underlying structural information. A framework called the Dynamic Collision Fingerprint (DCF) was recently proposed with the goal of producing concise, physically significant representations, generating descriptors via dynamical probing of atomic structures. In this work, we benchmark DCF using a dataset composed of 120 two-dimensional carbon allotropes and compare its performance with the widely considered Matminer library. The analysis employs three regression models, linear regression, decision tree, and XGBoost, evaluated over train and test partitions ranging from 10\% to 90\% and repeated over multiple random seeds in order to characterize statistical variability. The obtained results demonstrate that DCF easily matches Matminer in terms of predicting accuracy across all learning algorithms. However, it accomplishes this using descriptors that are significantly lower dimensional, pointing to manageable computing costs. Moreover, compared to the rather technical Matminer descriptions, the DCF exhibits considerably clearer physical interpretability. These findings suggest that DCF is a significant substitute for high-dimensional descriptor libraries as structural representation since it is both computationally flexible and physically grounded.

Aniketh Iyengar, Jiaqi Han, Pengwei Sun et al.

Generating molecular dynamics (MD) trajectories using deep generative models has attracted increasing attention, yet remains inherently challenging due to the limited availability of MD data and the complexities involved in modeling high-dimensional MD distributions. To overcome these challenges, we propose a novel framework that leverages structure pretraining for MD trajectory generation. Specifically, we first train a diffusion-based structure generation model on a large-scale conformer dataset, on top of which we introduce an interpolator module trained on MD trajectory data, designed to enforce temporal consistency among generated structures. Our approach effectively harnesses abundant structural data to mitigate the scarcity of MD trajectory data and effectively decomposes the intricate MD modeling task into two manageable subproblems: structural generation and temporal alignment. We comprehensively evaluate our method on the QM9 and DRUGS small-molecule datasets across unconditional generation, forward simulation, and interpolation tasks, and further extend our framework and analysis to tetrapeptide and protein monomer systems. Experimental results confirm that our approach excels in generating chemically realistic MD trajectories, as evidenced by remarkable improvements of accuracy in geometric, dynamical, and energetic measurements.

Ka Lok Chan, Susana Lopez-Querol, Pedro Martin-Moreta

The increasing global demand for renewable energy has resulted in a high interest in wind power, with offshore wind farms offering better performance than onshore installations. Coastal nations are thus, actively developing offshore wind turbines, where monopiles are the predominant foundation type. Despite their widespread use, the effects of monopile installation methods on the overall foundation behaviour are not sufficiently yet understood. This study investigates how different pile installation procedures—jacked and impact-driven—affect the lateral capacity of monopile foundations under both monotonic and dynamic lateral loads, by comparing them with wished-in-place monopiles, the usual assumption in design, for which no soil disturbance due to installation is considered. Three finite element 3D models were employed to simulate these cases, i.e., wished-in-place monopile, jacked, and impact-driven pile, incorporating soil zoning in the latter cases to replicate the effects of the installation methods. Comparisons between all these models, when subject to lateral monotonic and cyclic loads, are presented and discussed in terms of displacements in the soil and horizontal normal stresses. Results reveal that these installation methods significantly influence soil reactions, impacting the lateral performance of monopiles under both monotonic and dynamic conditions. The impact-driven pile demonstrated the most significant influence on the monopile behaviour. These findings highlight the need for engineers to account for installation effects in the design of monopile foundations to enhance performance and reliability, as well as the optimisation of their design.

J. Leinauer, M. Dietze, M. Dietze et al.

<p>The anticipation of massive rock slope failures is a key mitigation strategy in a changing climate and environment requiring a precise understanding of pre-failure process dynamics. Here we exploit <span class="inline-formula">&gt;4</span> years of multi-method high-resolution monitoring data from a large rock slope instability close to failure. To quantify and understand the effect of possible drivers (water from rain and snowmelt, internal rock fracturing, and earthquakes), we correlate slope displacements with environmental data, local seismic recordings, and earthquake catalogues. During the snowmelt phase, displacements are controlled by meltwater infiltration with high correlation and a time lag of 4–9 d. During the snow-free summer, rainfall induces accelerations with a time lag of 1–16 h for up to several days without a minimum activation rain sum threshold. Rock fracturing, linked to temperature and freeze–thaw cycles, is predominantly near the surface and unrelated to displacement rates. A classic Newmark analysis of recent and historic earthquakes indicates a low potential for immediate triggering of a major failure at the case site, unless it is already very close to failure. Seismic topographic amplification of the peak ground velocity (PGV) at the summit ranges from a factor of 2–11 and is spatially heterogeneous, indicating a high criticality of the slope. The presented in-depth monitoring data analysis enables a comprehensive rockfall driver evaluation and indicates where future climatic changes, e.g. in precipitation intensity and frequency, may alter the preconditioning of major rock slope failures.</p>

Min Tang, Xi Mei, Yanna Li et al.

With the continuous development of the oblique photography technique, it has been used more and more widely in the field of geological disasters. It can quickly obtain the three-dimensional (3D) real scene model of dangerous mountainous areas under the premise of ensuring the safety of personnel while restoring the real geographic information as much as possible. However, geological disaster areas are often accompanied by many adverse factors such as cliffs and dense vegetation. Based on this, the paper introduced the flight line design of oblique photogrammetry, analyzed the multi-platform data fusion processing, studied the multi-period data dynamic evaluation technology and proposed the application methods of data acquisition, early warning, disaster assessment and decision management suitable for geological disaster identification through the analysis of actual cases, which will help geologists to plan and control geological work more scientifically and rationally, improve work efficiency and reduce the potential personnel safety hazards in the process of geological survey, to offer technical support to the application of oblique photogrammetry in geological disaster identification and decision making and provide the scientific basis for personal and property safety protection and later-stage geological disaster management in disaster areas.

M. Righi, J. Hendricks, S. Brinkop

<p>A global aerosol–climate model is applied to quantify the impact of the transport sectors (land transport, shipping, and aviation) on aerosol and climate. Global simulations are performed for the present day (2015), based on the emission inventory of the Climate Model Intercomparison Project Phase 6 (CMIP6), and for near-term (2030) and mid-term (2050) future projections, under the Shared Socioeconomic Pathways (SSPs). The results for the present day show that land transport emissions have a large impact on near-surface concentrations of black carbon and aerosol nitrate over the most populated areas of the globe, but with contrasting patterns in terms of relative contributions between developed and developing countries. In spite of the recently introduced regulations to limit the fuel sulfur content in the shipping sector, shipping emissions are still responsible for a considerable impact on aerosol sulfate near-surface concentrations, about 0.5 to 1 <span class="inline-formula">µ</span>g m<span class="inline-formula">⁻³</span> in the most travelled regions, with significant effects on continental air pollution and in the northern polar regions as well. Aviation impacts on aerosol mass are found to be quite small, of the order of a few nanograms per cubic metre, while this sector considerably affects particle number concentrations, contributing up to 20 %–30 % of the upper-tropospheric particle number concentration at the northern mid-latitudes. The transport-induced impacts on aerosol mass and number concentrations result in a present-day radiative forcing of <span class="inline-formula">−164</span>, <span class="inline-formula">−145</span>, and <span class="inline-formula">−64</span> mW m<span class="inline-formula">⁻²</span> for land transport, shipping, and aviation, respectively, with a dominating contribution by aerosol–cloud interactions. These forcings represent a marked offset to the CO<span class="inline-formula">₂</span> warming from the transport sectors and are therefore very relevant for climate policy. The projections under the SSPs show that the impact of the transport sectors on aerosol and climate are generally consistent with the narratives underlying these scenarios: the lowest impacts of transport on both aerosol and climate are simulated under SSP1, especially for the land transport sector, while SSP3 is generally characterized by the largest effects. Notable exceptions to this picture, however, exist, as the emissions of other anthropogenic sectors also contribute to the overall aerosol concentrations and thus modulate the relevance of the transport sectors in the different scenarios, not always consistently with their underlying storyline. On a qualitative level, the results for the present day mostly confirm the findings of our previous assessment for the year 2000, which used a predecessor version of the same model and the CMIP5 emission data. Some important quantitative differences are found, which can mostly be ascribed to the improved representation of aerosol background concentrations in the present study.</p>

Ambrosios-Antonios Savvides, Andreas A. Antoniou, Leonidas Papadopoulos et al.

Rock mechanics and the estimation of their material properties through field tests are important aspects and challengees in civil and geotechnical engineering. However, this procedure is expensive and difficult to attain, while the machine learning and neural network theory provide a computational tool for estimating the material properties with limited data. In this work, an estimation of the Young Modulus and the cohesion of a clayey-originated rock through feed-forward neural networks constructed from in situ data measurements is given. The input values come from the Geological Strength Index (GSI) proposed values of the point load index <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>I</mi><mrow><mi>s</mi><mn>50</mn></mrow></msub></semantics></math></inline-formula>, the uniaxial compression strength <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>σ</mi><mi>s</mi></msub></semantics></math></inline-formula>, as well as the specific gravity <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula> of the rock mass. The convergence analysis revealed that the convergence occurs at approximately 2000 epochs, with the largest <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>L</mi><mn>2</mn></msub></semantics></math></inline-formula> mean square error norm being no greater than <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></semantics></math></inline-formula>. In addition, it is demonstrated that augmenting <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula> results in the estimation of rock that is stiffer and stronger. The aforementioned increase in the specific site may be up to 20% for the stiffness and up to 25% for the cohesion. This model, aside from readability and accuracy, offers the convenience of enriching it with more in situ data, thereby enhancing the flexibility of the proposed numerical tool proposed. However, its applicability is limited to the specific data acquired from the particular site, so a more general estimation requires a substantially larger dataset. Finally, the justification of the proposed model has been carried out based on suggestions from the literature for common values of clayey-oriented rock, which is fairly disintegrated as seen in the field.

Palak Patel, Mohit Sharma, Sarika Maitra Bhattacharyya

In polydisperse systems, describing the structure and any structural order parameter (SOP) is not trivial as it varies with the number of species we use to describe the system, M . Depending on the degree of polydispersity, there is an optimum value of M = M0 where we show that the mutual information of the system increases. However, surprisingly the correlation between a recently proposed SOP and the dynamics is highest for M = 1. This effect increases with polydispersity. We find that the SOP at M = 1 is coupled with the particle size, σ, and this coupling increases with polydispersity and decreases with an increase in M . Careful analysis shows that at lower polydispersity the SOP is a good predictor of the dynamics. However, at higher polydispersity, the dynamics is strongly dependent on σ. Since the coupling between the SOP and σ is higher for M = 1 thus, it appears to be a better predictor of the dynamics. We also study the Vibrality an order parameter independent of structural information. Compared to SOP, at high polydispersity we find Vibrality to be a marginally better predictor of the dynamics. However, this high predictive power of Vibrality, which is not there at lower polydispersity, appears to be due to its stronger coupling with σ. Thus our study suggests that for systems with high polydispersity, the correlation of any order parameter and σ will affect the correlation between the order parameter and dynamics and need not project a generic predictive power of the order parameter.

Yubing Du, Guoshuai Du, Hongliang Dong et al.

The modern very large-scale integration systems based on silicon semiconductor are facing the unprecedented challenges especially when transistor feature size lowers further, due to the excruciating tunneling effect and thermal management. Besides the common diamond cubic silicon, numerous exotic silicon allotropes with outstanding properties can emerge under high pressure, such as the metastable BC8 and metallic \b{eta}-tin structures. Despite much effort on the controlled synthesis in experiment and theory, the effective approach to rationally prepare Si phases with desired purity is still lacking and their transition mechanism remains controversial. Herein, we systematically investigated on the complicated structural transformations of Si under extreme conditions, and efficiently enriched BC8-Si phase via dynamic decompression strategy. The splendid purity of BC8-Si was achieved up to ~95%, evidently confirmed by Raman spectroscopy and synchrotron X-ray diffraction. We believe these results can shed a light on the controlled preparation of Si metastable phases and their potential applications in nanoelectronics.

Y. Wang, Y. Wang, M. E. Oskin et al.

<p>Located at the transition between monsoon- and westerly-dominated climate systems, major rivers draining the western North Qilian Shan incise deep, narrow canyons into latest Quaternary foreland basin sediments of the Hexi Corridor. Field surveys and previously published geochronology show that the Beida River incised 130 m at the mountain front over the Late Pleistocene and Holocene at an average rate of 6 m kyr<span class="inline-formula">⁻¹</span>. We hypothesize that a steep knickzone, with 3 % slope, initiated at the mountain front and has since retreated to its present position, 10 km upstream. Additional terrace dating suggests that this knickzone formed around the mid-Holocene, over a duration of less than 1.5 kyr, during which incision accelerated from 6 m kyr<span class="inline-formula">⁻¹</span> to at least 25 m kyr<span class="inline-formula">⁻¹</span>. These incision rates are much faster than the uplift rate across the North Qilian fault, which suggests a climate-related increase in discharge drove rapid incision over the Holocene and formation of the knickzone. Using the relationship between incision rates and the amount of base level drop, we show the maximum duration of knickzone formation to be <span class="inline-formula">∼700</span> years and the minimum incision rate to be 50 m kyr<span class="inline-formula">⁻¹</span>. We interpret that this period of increased river incision corresponds to a pluvial lake-filling event at the terminus of the Beida River and correlates with a wet period driven by strengthening of the Southeast Asian Monsoon.</p>

K. Worou, H. Goosse, T. Fichefet et al.

<p>The Guinea Coast is the southern part of the West African continent. Its summer rainfall variability mostly occurs on interannual timescales and is highly influenced by the sea surface temperature (SST) variability in the eastern equatorial Atlantic, which is the centre of action of the Atlantic Niño mode. Using both historical and scenario (SSP5–8.5) simulations from 31 general circulation models (GCMs) participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we first show that these models present a wet bias during boreal summer. This bias is associated with overly high mean boreal summer SSTs in the eastern equatorial and south Atlantic regions. Next, we analyse the near-term, mid-term and long-term changes of the Atlantic Niño relative to the present-day situation, in a climate with a high anthropogenic emission of greenhouse gases. We find a gradual decrease in the equatorial Atlantic SST anomalies associated with the Atlantic Niño in the future. This result reflects a possible reduction of the Atlantic Niño variability in the future due to a weakening of the Bjerknes feedback over the equatorial Atlantic. In a warmer climate, an anomalous higher sea level pressure in the western equatorial Atlantic relative to the eastern equatorial Atlantic weakens the climatological trade winds over the equatorial Atlantic. As a result, the eastern equatorial Atlantic thermocline is deeper and responds less to the Atlantic Niño events. Among the models that simulate a realistic rainfall pattern associated with the Atlantic Niño in the present-day climate, there are 12 GCMs which project a long-term decrease in the Guinea Coast rainfall response related to the Atlantic Niño. In these models, the zonal 850 hPa wind response to the Atlantic Niño over the equatorial Atlantic is strongly attenuated in the future climate. We also find that 12 other GCMs show no robust change in the patterns associated with the Atlantic Niño. There is a higher confidence in the mid-term and long-term reduction of the rainfall associated with the Atlantic Niño over the Atlantic Ocean than over the Guinea Coast. We also found a projected decrease in the convection associated with the Atlantic Niño in the majority of the models.</p>

T. Kempka, T. Kempka, S. Steding et al.

<p>Many types of geologic subsurface utilisation are associated with fluid and heat flow as well as simultaneously occurring chemical reactions. For that reason, reactive transport models are required to understand and reproduce the governing processes. In this regard, reactive transport codes must be highly flexible to cover a wide range of applications, while being applicable by users without extensive programming skills at the same time. In this context, we present an extension of the Open Source and Open Access TRANSPORT Simulation Environment, which has been coupled with the geochemical reaction module PHREEQC, and thus provides multiple new features that make it applicable to complex reactive transport problems in various geoscientific fields. Code readability is ensured by the applied high-level programming language Python which is relatively easy to learn compared to low-level programming languages such as C, C++ and FORTRAN. Thus, also users with limited software development knowledge can benefit from the presented simulation environment due to the low entry-level programming skill requirements. In the present study, common geochemical benchmarks are used to verify the numerical code implementation. Currently, the coupled simulator can be used to investigate 3D single-phase fluid and heat flow as well as multicomponent solute transport in porous media. In addition to that, a wide range of equilibrium and nonequilibrium reactions can be considered. Chemical feedback on fluid flow is provided by adapting porosity and permeability of the porous media as well as fluid properties. Thereby, users are in full control of the underlying functions in terms of fluid and rock equations of state, coupled geochemical modules used for reactive transport, dynamic boundary conditions and mass balance calculations. Both, the solution of the system of partial differential equations and the PHREEQC module, can be easily parallelised to increase computational efficiency. The benchmarks used in the present study include density-driven flow as well as advective, diffusive and dispersive reactive transport of solutes. Furthermore, porosity and permeability changes caused by kinetically controlled dissolution-precipitation reactions are considered to verify the main features of our reactive transport code. In future, the code implementation can be used to quantify processes encountered in different types of subsurface utilisation, such as water resource management as well as geothermal energy production, as well as geological energy, <span class="inline-formula">CO₂</span> and nuclear waste storage.</p>

Elsa Abreu, Matteo Savoini, Larissa Boie et al.

We use time-resolved hard x-ray diffraction to investigate the structural dynamics of the multiferroic insulator TbMnO$_3$ in the low temperature antiferromagnetic and ferroelectrically ordered phase. The lattice response following photoexcitation at 1.55 eV is detected by measuring the (0 2 4) and (1 3 -5) Bragg reflections. A 0.02% tensile strain, normal to the surface, is seen to arise within 20 - 30 ps. The magnitude of this transient strain is over an order of magnitude lower than that predicted from laser-induced heating, which we attribute to a bottleneck in the energy transfer between the electronic and lattice subsystems. The timescale for the transient expansion is consistent with that of previously reported demagnetization dynamics. We discuss a possible relationship between structural and demagnetization dynamics in TbMnO$_3$, in which photoinduced atomic motion modulates the exchange interaction, leading to a destruction of the magnetic order in the system.

L. France, M. Lombard, C. Nicollet et al.

At oceanic spreading centers, the interactions between the igneous system that builds the crust, and the hydrothermal system that cools it govern the plumbing system architecture and its thermokinetic evolution. At fast‐spreading centers, most of those interactions occur around the axial magma lens (AML) that feeds the upper crust, and possibly part of the underlying mushy igneous reservoir. Heat extracted from crystallizing AML is transferred through a conductive boundary layer to the overlying hydrothermal system. Quantifying the AML physical and thermal evolutions and its interactions with hydrothermal system is therefore essential to understand oceanic accretion. Those general issues were the rationale of drilling ICDP OmanDP Hole GT3A, and we present herein the geological, structural, and petrological data that were used as a site survey to select its location. GT3 area enables observations in three dimensions of fossilized AMLs and overlying dikes. The new field data and corresponding mineral compositions are used together with thermokinetic and thermodynamic models to deliver an integrated dynamic model for the AML/hydrothermal system interactions. Results attest that the isotropic gabbro interval is composite, with gabbro bodies intruding and reheating both gabbros and dikes (up to 1,040°C). We show that AMLs should be considered as transient igneous bodies that likely crystallize from primitive MORBs in decades, releasing heat to the intruded hosts, and feeding high temperature vents on the seafloor. We show for the first time that the thermal gradient recorded in AML roof is consistent with the heat fluxes reported at active hydrothermal vents.

S. Gautam, D. Cole

Dynamical behavior of fluids under nano-pore confinement is studied extensively as it has important implications for several industrial as well as geological processes. Pore network in many porous materials exhibits a varied degree of inter connections. The extent of this pore connectivity may affect the structural and dynamical behavior of the confined fluid. However, studies of fluid confinement addressing these effects systematically are lacking. Here, we report molecular dynamics simulation studies addressing the effects of pore connectivity on the dynamics of two representative fluids - CO2 and ethane in silicalite by systematically varying the degree of pore connectivity through selectively blocking some pore space with immobile methane molecules. By selectively turning off the pore spaces in the shape of straight, or tortuous zigzag channels, we also probe the effects of pore tortuosity. In general, pore connectivity is found to facilitate both the translational as well as rotational dynamics of both fluids, while the intermolecular modes of vibration in both fluids remain largely unaffected. The effects of providing connections between a set of straight or zigzag channel-like pores are however more nuanced. Pore tortuosity facilitates the rotational motion, but suppresses the translational motion of CO2, while its effects on the rotational and translational motion of ethane are less pronounced. The intermolecular vibrational modes of both fluids shift to higher energies with an increase in the number of tortuous pores. The results reported here provide a detailed molecular level understanding of the effects of pore connectivity on the dynamics of fluids and thus have implications for applications like fluid separation.

M. Groves, J. S. Birnie, M. Creighton et al.

This case study describes a proposed commercial redevelopment at Royal Tunbridge Wells, Kent. The site, located on the Tunbridge Wells Sand and Wadhurst Clay formations, has been affected by major structural faulting as well as by periglacial conditions during the Quaternary. A key aspect of the project was the development of a geological model to inform the engineering design. This study presents the ground model development process, starting with an appreciation of the macro geological setting, understanding the Quaternary landsystem, to focusing on the data from the intrusive ground investigation. The understanding of the primary sedimentary depositional system is critical to the development of a site geological conceptual model. Sediments from highly variable environments of deposition, such as were present in the Early Cretaceous, will present geotechnical and geohazard challenges to a site's development and this first-principles understanding is important in this process. The link from these fundamental geological principles to engineering design, communicated through the ground model, as demonstrated in this paper, is the requirement of the engineering geological appraisal. Locally complex geology demanded a phased site investigation approach, responding to an evolving design and to construction demands, and to meet defined programme requirements for a second-stage tender, to ultimately de-risk key areas with regard to the dynamic ground and groundwater conditions. Thematic collection: This article is part of the Ground models in engineering geology and hydrogeology collection available at: https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology

Jonathan Meddaugh

We demonstrate that there is a large class of compact metric spaces for which the shadowing property can be characterized as a structural property of the space of dynamical systems. We also demonstrate for this class of spaces, that in order to determine whether a system has shadowing, it is sufficient to check that continuously generated pseudo-orbits can be shadowed.

Renas I. Koshnaw, D. Stockli, B. Horton et al.

Apatite (U‐Th)/He (AHe) thermochronometric results are integrated with geologic cross sections, structural relationships, and stratigraphic data to reconstruct the growth of the NW Zagros orogenic belt in the Kurdistan region of Iraq. Prolonged exhumation is documented across the belt with deformation advances and retreats from ~14 Ma onward. After in‐sequence propagation of deformation during middle to late Miocene times, preserved growth strata and AHe data show a deformation retreat by latest Miocene time (~5 Ma). In the NW Zagros, the Phanerozoic succession contains two principal décollements in Lower Triassic and middle Miocene units. The Triassic strata are interpreted as the main décollement for a thin‐skinned system that was dominant during most of the Cenozoic. By ~8–5 Ma, the fold‐thrust belt shifted to basement‐involved deformation in association with growth of the mountain front flexure and reactivation of frontal structures. The shift from thin‐skinned to a hybrid thin‐ and thick‐skinned mode of shortening may reflect variations in the mechanical behavior of the upper crust and the presence of inherited basement discontinuities. On the basis of two NE‐SW balanced cross sections spanning the NW Zagros, the estimated total minimum horizontal shortening is ~18.2 km (6%) in the central and ~16 km (7%) in the southern sectors of the Kurdistan region of Iraq. These findings suggest that the evolution of the NW Zagros orogenic belt was likely driven by the mechanical stratigraphy of the sedimentary cover, inherited basement discontinuities, and the dynamic and thermomechanical effects of potential slab breakoff and lithospheric mantle delamination events.

C. M. Richardson, Margaret A. Zimmer, J. Fackrell et al.

The contributions and composition of baseflow sources across an extended recession period were quantified for six subwatersheds of varying size in a structurally complex watershed in coastal California using endmember mixing analysis and related to catchment characteristics (e.g., topography, geology, land use, and soil characteristics). Both shallow subsurface and deep groundwater reservoirs were important contributors for streamflow during low flow periods, and the composition of baseflow sources across subwatersheds was directly related to geologic indices. A binary classification of underlying bedrock permeability (e.g., low vs. high) best explained the changes in shallow subsurface water and deeper groundwater inputs through the seasonal recession. Dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and specific UV absorbance at 254 nm (SUVA254) were used to provide additional insight into endmember characteristics and their contributions to baseflow. Stream water DIC concentrations were broadly controlled by mixing of groundwater and shallow subsurface water endmembers with relatively constant DIC concentrations, while stream water DOC concentrations reflected both spatial and temporal changes in shallow subsurface water DOC. Results from this study show (1) the importance of considering baseflow as a dynamic mixture of water from multiple sources, (2) the effect of geology on source composition at the subwatershed scale during low flow conditions, and (3) the impact of shifting baseflow sources on stream water dissolved carbon concentrations and the utility of using dissolved carbon concentrations to obtain additional insight into temporal variability in baseflow sources.