bluuebunny/crossref_metadata_2025 huggingface dataset:
Collinearity assessment of geocentre coordinates derived from multi-satellite SLR data
Authors: Spatar Ciprian , Moore Philip , Clarke Peter
Published: July 2018

Of the three satellite geodetic techniques contributing to the International Terrestrial Reference Frame (ITRF), Satellite Laser Ranging (SLR) is generally held to provide the most reliable time series of geocentre coordinates and exclusively defines the ITRF origin. Traditionally, only observations to the two LAser GEOdynamics Satellite (LAGEOS) and Etalon pairs of satellites have been used for the definition of the ITRF origin. Previous simulation studies using evenly sampled LAGEOS-like data have shown that only the Z component of geocentre motion suffers minor collinearity issues, which may explain its lower quality compared to the equatorial components. Using collinearity diagnosis, this study provides insight into the actual capability of SLR to sense geocentre motion using the existing geographically unbalanced ground network and real observations to eight spherical geodetic satellites. We find that, under certain parameterisations, observations to the low Earth orbiters (LEOs) Starlette, Stella, Ajisai and LAser RElativity Satellite (LARES) are able to improve the observability of the geocentre coordinates in multi-satellite solutions compared to LAGEOS-only solutions. The higher sensitivity of LEOs to geocentre motion and the larger number of observations are primarily responsible for the improved observability. Errors in the modelling of Starlette, Stella and Ajisai orbits may contaminate the geocentre motion estimates, but do not disprove the intrinsic strength of LEO tracking data. The sporadically observed Etalon satellites fail to make a significant beneficial contribution to the observability of the geocentre coordinates derived via the network shift approach and can be safely omitted from SLR data analyses for terrestrial reference frame (TRF) determination.
Structural signatures of igneous sheet intrusion propagation
Authors: Magee Craig , Muirhead James , Schofield Nick , Walker Richard , Galland Olivier , Holford Simon , Spacapan Juan , Jackson Christopher , McCarthy William
Published: July 2018

The geometry and distribution of planar igneous bodies (i.e. sheet intrusions), such as dykes, sills, and inclined sheets, has long been used to determine emplacement mechanics, define melt source locations, and reconstruct palaeostress conditions to shed light on various tectonic and magmatic processes. Since the 1970’s we have recognised that sheet intrusions do not necessarily display a continuous, planar geometry, but commonly consist of segments. The morphology of these segments and their connectors is controlled by, and provide insights into, the behaviour of the host rock during emplacement. For example, tensile brittle fracturing leads to the formation of intrusive steps or bridge structures between adjacent segments. In contrast, brittle shear faulting, cataclastic and ductile flow processes, as well as heat-induced viscous flow or fluidization, promotes magma finger development. Textural indicators of magma flow (e.g., rock fabrics) reveal that segments are aligned parallel to the initial sheet propagation direction. Recognising and mapping segment long axes thus allows melt source location hypotheses, derived from sheet distribution and orientation, to be robustly tested. Despite the information that can be obtained from these structural signatures of sheet intrusion propagation, they are largely overlooked by the structural and volcanological communities. To highlight their utility, we briefly review the formation of sheet intrusion segments, discuss how they inform interpretations of magma emplacement, and outline future research directions.
Rainfall-Runoff modelling using Long Short-Term Memory (LSTM) networks
Authors: Kratzert Frederik , Klotz Daniel , Brenner Claire , Schulz Karsten , Herrnegger Mathew
Published: July 2018

Rainfall-runoff modelling is one of the key challenges in the field of hydrology. Various approaches exist, ranging from physically based over conceptual to fully data driven models. In this paper, we propose a novel data driven approach, using the Long-Short-Term-Memory (LSTM) network, a special type of recurrent neural networks. The advantage of the LSTM is its ability to learn long-term dependencies between the provided input and output of the network, which are essential for modelling storage effects in e.g. catchments with snow influence. We use 241 catchments of the freely available CAMELS data set to test our approach and also compare the results to the well-known Sacramento Soil Moisture Accounting Model (SAC-SMA) coupled with the Snow-17 snow routine. We also show the potential of the LSTM as a regional hydrological model, in which one model predicts the discharge for a variety of catchments. In our last experiment, we show the possibility to transfer process understanding, learned at regional scale, to individual catchments and thereby increasing model performance when compared to a LSTM trained only on the data of single catchments. Using this approach, we were able to achieve better model performance as the SAC-SMA + Snow-17, which underlines the potential of the LSTM for hydrological modelling applications.
Changes in Seismic Anisotropy Shed Light on the Nature of the Gutenberg Discontinuity
Authors: Beghein Caroline , Yuan Kaiqing , Schmerr Nicholas , Xing Zheng
Published: July 2018

The boundary between the lithosphere and asthenosphere is associated with a plate-wide high seismic velocity “lid” overlying lowered velocities, consistent with thermal models. Seismic body waves also intermittently detect a sharp velocity reduction at similar depths, the Gutenberg (G) discontinuity, which cannot be explained by temperature alone. We compared an anisotropic tomography model with detections of the G to evaluate their context and relation to the lithosphere-asthenosphere boundary (LAB). We find that the G is primarily associated with vertical changes in azimuthal anisotropy and lies above a thermally controlled LAB, implying the two are not equivalent interfaces. The origin of the G is a result of frozen-in lithospheric structures, regional compositional variations of the mantle, or dynamically perturbed LAB.
Morphological expressions of crater infill collapse: model simulations of Chaotic Terrains on Mars
Authors: Roda Manuel , Govers Rob , Westerweel Jan , Marketos George
Published: July 2018

Martian chaotic terrains are characterized by deeply depressed intensively fractured areas that contain a large number of low-strain tilted blocks. Stronger deformation (e.g. higher number of fractures) is generally observed in the rims when compared to the middle regions of the terrains. The distribution and number of fractures and tilted blocks are correlated with the size of the chaotic terrains. Smaller chaotic terrains are characterized by few fractures between undeformed blocks. Larger terrains show an elevated number of fractures uniformly distributed with single blocks. We investigate whether this surface morphology may be a consequence of the collapse of the infill of a crater. We perform numerical simulations with the Discrete Element Method and we evaluate the distribution of fractures within the crater and the influence of the crater size, infill thickness and collapsing depth on the final morphology. The comparison between model predictions and the morphology of the Martian chaotic terrains shows strong statistical similarities in terms of both number of fractures and correlation between fractures and crater diameters. No or very weak correlation is observed between fractures and the infill thickness or collapsing depth. The strong correspondence between model results and observations suggests that the collapse of an infill layer within a crater is a viable mechanism for the peculiar morphology of the martian chaotic terrains.
Quantifying closed-basin lake temperature and hydrology by inversion of oxygen isotope and trace element paleoclimate records
Authors: Ibarra Daniel , Chamberlain C.
Published: July 2018

Lake systems are important paleoclimate archives that preserve ecosystem and hydrologic responses to critical periods in Earth history, such as carbon cycle perturbations and glacial-interglacial cycles. Geochemical measurements of biogenic carbonate (for example, δ18O, δ13C, 87Sr/86Sr, [Li], [U], [Sr], and [Mg]) are indicators of hydrologic variability in lake systems throughout the geologic record. In this study, we present a new closed-basin lake modeling approach, HyBIM (the Hydrologic Balance Inverse Model), that employs a system of total differential equations and uses the measured δ18O, Sr/Ca, and Mg/Ca of biogenic carbonate to determine changes in temperature, runoff, and lake evaporation. Using equally-spaced time steps, these equations are simultaneously solved to constrain the hydrologic parameters of the lake as recorded in biogenic carbonate. We use a Monte Carlo approach to account for uncertainty in the input parameters, such as δ18O temperature relationships, partition coefficient uncertainty, and watershed solute chemistry. For illustrative purposes, we apply the model to two ostracod valve datasets covering different timescales: (1) the Cretaceous Songliao Basin, northeast China, and (2) Holocene Lake Miragoane, Haiti. Modern water measurements of water isotopes and cation concentrations from each location are required as model inputs. We compare our modeling results with author interpretations and geologic observations. The modeling approach presented in this study can be applied to other closed-basin lake records, can be modified for other calcifying species (for example, gastropods or mollusks) or with calibration to inorganic lacustrine carbonate. In addition, this approach holds promise for extension with additional proxy measurements (that is, δD, U/Ca or Li/Ca) and changing source area on tectonic timescales using proxies that reflect changing source lithology (that is, Sr and Pb isotopes). Future incorporation of age model uncertainty in the Monte Carlo approach will also provide utility by quantifying temporal uncertainty on the hydrologic response recorded by lake sediments.
Synchronizing terrestrial and marine records of environmental change across the Eocene–Oligocene transition
Authors: Sahy Diana , Condon Daniel , Terry Dennis , Fischer Anne , Kuiper Klaudia
Published: July 2018

Synchronizing terrestrial and marine records of environmental change across the Eocene–Oligocene transition
Different frequencies and triggers of canyon filling and flushing events in Nazaré Canyon, offshore Portugal
Authors: Allin Joshua , Hunt James , Talling Peter , Clare Michael , Pope Ed
Published: July 2018

Submarine canyons are one of the most important pathways for sediment transport into ocean basins. For this reason, understanding canyon architecture and sedimentary processes has importance for sediment budgets, carbon cycling, and geohazard assessment. Despite increasing knowledge of turbidity current triggers, the down-canyon variability in turbidity current frequency within most canyon systems is not well constrained.NewAMS radiocarbon chronologies from canyon sediment cores illustrate significant variability in turbidity current frequency within Nazaré Canyon through time. Generalised linear models and Cox proportional hazardsmodels indicate a strong influence of global sea level on the frequency of turbidity currents that fill the canyon.Radiocarbon ages from basin sediment cores indicate that larger, canyon-flushing turbidity currents reachingthe Iberian Abyssal Plain have a significantly longer average recurrence interval than turbidity currents that fillthe canyon. The recurrence intervals of these canyon-flushing turbidity currents also appear to be unaffectedby long-term changes in global sea level. Furthermore, canyon-flushing and canyon-filling have very differentstatistical distributions of recurrence intervals. This indicates that the factors triggering, and thus controllingthe frequency of canyon-flushing and canyon-filling events are very different. Canyon-filling appears to be predominantly triggered by sediment instability during sea level lowstand, and by storm and nepheloid transportduring the present day highstand. Canyon-flushing exhibits time-independent behaviour. This indicates that atemporally random process, signal shredding, or summation of non-random processes that cannot be discerned from a random signal, are triggering canyon flushing events.
2-D numerical study of hydrated wedge dynamics from subduction to post-collisional phases
Authors: Regorda Alessandro , Roda Manuel , Marotta Anna , Spalla Maria
Published: July 2018

We developed a 2-D finite element model to investigate the effect of shear heating and mantle hydration on the dynamics of the mantle wedge area. The model considers an initial phase of active oceanic subduction, which is followed by a post-collisional phase characterized by pure gravitational evolution. To investigate the impact of the subduction velocity on the thermomechanics of the system, three models with different velocities prescribed during the initial subduction phase were implemented. Shear heating and mantle hydration were then systematically added into the models. We then analysed the evolution of the hydrated area during both the subduction and post-collisional phases, and examined the difference in Pmax–T (maximum pressure–temperature) and P–Tmax (pressure–maximum temperature) conditions for the models with mantle hydration. The dynamics that allow for the recycling and exhumation of subducted material in the wedge area are strictly correlated with the thermal state at the external boundaries of the mantle wedge, and the size of the hydrated area depends on the subduction velocity when mantle hydration and shear heating are considered simultaneously. During the post-collisional phase, the hydrated portion of the mantle wedge increases in models with high subduction velocities. The predicted P–T configuration indicates that contrasting P–T conditions, such as Barrovian- to Franciscan-type metamorphic gradients, can contemporaneously characterize different portions of the subduction system during both the active oceanic subduction and post-collisional phases and are not indicative of collisional or subduction phases.
Multiphase flow characteristics of heterogeneous rocks from CO2 storage reservoirs in the United Kingdom
Authors: Reynolds Catriona , Blunt Martin , Krevor Sam
Published: July 2018

We have studied the impact of heterogeneity on relative permeability and residual trapping for rock samples from the Bunter sandstone of the UK Southern North Sea, the Ormskirk Sandstone of the East Irish Sea, and the Captain Sandstone of the UK Northern North Sea. Reservoir condition CO2-brine relative permeability measurements were made while systematically varying the ratio of viscous to capillary flow potential, across a range of flow rates, fractional flow, and during drainage and imbibition displacement. This variation resulted in observations obtained across a range of core-scale capillary number 0.2 < Nc < 200. Capillary pressure heterogeneity was quantitatively inferred from 3D observations of the fluid saturation distribution in the rocks. For each of the rock samples a threshold capillary number, 5 < Nc < 30, was found, below which centimetre-scale layering resulted in a heterogeneous distribution of the fluid phases and a commensurate impact on flow and trapping. The threshold was found to be dependent on the capillary number alone, irrespective of the displacement path (drainage or imbibition) and average fluid saturation in the rock. The impact of the heterogeneity on the relative permeability varied depending on the characteristics of the heterogeneity in the rock sample, whereas heterogeneity increased residual trapping in all samples above what would be expected from the pore-scale capillary trapping mechanism alone. Models of subsurface CO2 injection should use properties that incorporate the impacts of heterogeneity at the flow regime of interest or risk significant errors in estimates of fluid flow and trapping.
Pre-Cadomian to late-Variscan odyssey of the eastern Massif Central, France: Formation of the West European crust in a nutshell
Authors: Chelle-Michou Cyril
Published: July 2018

The East Massif Central (EMC), France, is part of the internal zone of the Variscan belt where late Carboniferous crustal melting and orogenic collapse have largely obliterated the pre- to early-Variscan geological record. Nevertheless, parts of this history can be reconstructed by using in-situ U-Th-Pb-Lu-Hf isotopic data of texturally well-defined zircon grains from different lithological units. All the main rock units commonly described in the EMC are present in the area of Tournon and include meta-sedimentary and meta-igneous rocks of the Upper Gneiss Unit (UGU) and of the Lower Gneiss Unit (LGU), as well as cross-cutting Variscan granitoid dikes and a heterogeneous granite coring the major Velay dome. Herein we demonstrate that the UGU and the LGU have markedly distinct zircon records. The results of this study are consistent with deposition of the protoliths of the paragneisses within a back-arc basin that was located adjacent to the Arabian-Nubian shield and/or the Saharan Metacraton during the late Ediacaran and collected detritus from the Gondwana continent. At ~ 545 Ma some of these sedimentary rocks were affected by a first melting event that formed the protoliths of the LGU orthogneisses, those of which subsequently remelted at ca. 308 Ma to form the Velay granite-migmatite dome. Protoliths of the UGU result mainly from a bimodal rift-related magmatism at ~ 480 Ma, corresponding to melting of the Ediacaran sediments and depleted mantle. Zircon rims from the UGU additionally provide evidence for a metamorphic/migmatitic overprint during the Lower Carboniferous (~ 350–340 Ma). Finally, several generations of granite dikes of which inherited zircons display characteristics of both the UGU and the LGU were protractedly emplaced from ~ 322 Ma to ~ 308 Ma, the youngest of which being coeval with the formation of the Velay dome. Our data further show that the vast majority of crustal material ultimately involved in the Variscan orogeny, which forms the present-day basement in the EMC, was derived from a sedimentary mixture of various components from the Gondwana continent deposited in Ediacaran times, with no evidence for the involvement of an older autochthonous crust.
Non-crossing nonlinear regression quantiles by monotone composite quantile regression neural network, with application to rainfall extremes
Authors: Cannon Alex
Published: July 2018

The goal of quantile regression is to estimate conditional quantiles for specified values of quantile probability using linear or nonlinear regression equations. These estimates are prone to "quantile crossing", where regression predictions for different quantile probabilities do not increase as probability increases. In the context of the environmental sciences, this could, for example, lead to estimates of the magnitude of a 10-yr return period rainstorm that exceed the 20-yr storm, or similar nonphysical results. This problem, as well as the potential for overfitting, is exacerbated for small to moderate sample sizes and for nonlinear quantile regression models. As a remedy, this study introduces a novel nonlinear quantile regression model, the monotone composite quantile regression neural network (MCQRNN), that (1) simultaneously estimates multiple non-crossing, nonlinear conditional quantile functions; (2) allows for optional monotonicity, positivity/non-negativity, and generalized additive model constraints; and (3) can be adapted to estimate standard least-squares regression and non-crossing expectile regression functions. First, the MCQRNN model is evaluated on synthetic data from multiple functions and error distributions using Monte Carlo simulations. MCQRNN outperforms the benchmark models, especially for non-normal error distributions. Next, the MCQRNN model is applied to real-world climate data by estimating rainfall Intensity-Duration-Frequency (IDF) curves at locations in Canada. IDF curves summarize the relationship between the intensity and occurrence frequency of extreme rainfall over storm durations ranging from minutes to a day. Because annual maximum rainfall intensity is a non-negative quantity that should increase monotonically as the occurrence frequency and storm duration decrease, monotonicity and non-negativity constraints are key constraints in IDF curve estimation. In comparison to standard QRNN models, the ability of the MCQRNN model to incorporate these constraints, in addition to non-crossing, leads to more robust and realistic estimates of extreme rainfall.
The shape and distribution of Maar craters using the MaarVLS database.
Authors: Graettinger Alison
Published: July 2018

A maar crater is the top of a much larger subsurface diatreme structure produced by phreatomagmatic explosions and the size and shape of the crater reflects the growth history of that structure during an eruption. Recent experimental and geophysical research has shown that crater complexity can reflect subsurface complexity. Morphometry provides a means of characterizing a global population of maar craters in order to establish the typical size and shape of features. A global database of Quaternary maar crater planform morphometry indicates that maar craters are typically not circular and frequently have compound shapes resembling overlapping circles. Maar craters occur in volcanic fields that contain both small volume and complex volcanoes. The global perspective provided by the database shows that maars are common in many volcanic and tectonic settings producing a similar diversity of size and shape within and between volcanic fields. A few exceptional populations of maars were revealed by the database, highlighting directions of future research to improve our understanding on the geometry and spacing of subsurface explosions that produce maars. These outlying populations, such as anomalously large craters (> 3000 m), chains of maars, and volcanic fields composed of mostly maar craters each represent a small portion of the database, but provide opportunities to reinvestigate fundamental questions on maar formation. Maar crater morphometry can be integrated with structural, hydrological studies to investigate lateral migration of phreatomagmatic explosion location in the subsurface. A comprehensive database of intact maar morphometry is also beneficial for the hunt for maar-diatremes on other planets.
Spatially explicit spectral analysis of point clouds and geospatial data
Authors: Buscombe Daniel
Published: July 2018

The increasing use of spatially explicit analyses of high-resolution spatially distributed data (imagery and point clouds) for the purposes of characterising spatial heterogeneity in geophysical phenomena necessitates the development of custom analytical and computational tools. In recent years, such analyses have become the basis of, for example, automated texture characterisation and segmentation, roughness and grain size calculation, and feature detection and classification, from a variety of data types. In this work, much use has been made of statistical descriptors of localised spatial variations in amplitude variance (roughness), however the horizontal scale (wavelength) and spacing of roughness elements is rarely considered. This is despite the fact that the ratio of characteristic vertical to horizontal scales is not constant and can yield important information about physical scaling relationships. Spectral analysis is a hitherto under-utilised but powerful means to acquire statistical information about relevant amplitude and wavelength scales, simultaneously and with computational efficiency. Further, quantifying spatially distributed data in the frequency domain lends itself to the development of stochastic models for probing the underlying mechanisms which govern the spatial distribution of geological and geophysical phenomena. The software package PySESA (Python program for Spatially Explicit Spectral Analysis) has been developed for generic analyses of spatially distributed data in both the spatial and frequency domains. Developed predominantly in Python, it accesses libraries written in Cython and C++ for efficiency. It is open source and modular, therefore readily incorporated into, and combined with, other data analysis tools and frameworks with particular utility for supporting research in the fields of geomorphology, geophysics, hydrography, photogrammetry and remote sensing. The analytical and computational structure of the toolbox is described, and its functionality illustrated with an example of a high-resolution bathymetric point cloud data collected with multibeam echosounder.
The Applicability of Incoherent Array Processing to IMS Seismic Arrays
Authors: Gibbons Steven
Published: July 2018

The seismic arrays of the International Monitoring System (IMS) for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) are highly diverse in size and configuration, with apertures ranging from under 1 km to over 60 km. Large and medium aperture arrays with large inter-site spacings complicate the detection and estimation of high-frequency phases lacking coherence between sensors. Pipeline detection algorithms often miss such phases, since they only consider frequencies low enough to allow coherent array processing, and phases that are detected are often attributed qualitatively incorrect backazimuth and slowness estimates. This can result in missed events, due to either a lack of contributing phases or by corruption of event hypotheses by spurious detections. It has been demonstrated previously that continuous spectral estimation can both detect and estimate phases on the largest aperture arrays, with arrivals identified as local maxima on beams of transformed spectrograms. The estimation procedure in effect measures group velocity rather than phase velocity, as is the case for classical f–k analysis, and the ability to estimate slowness vectors requires sufficiently large inter-sensor distances to resolve time-delays between pulses with a period of the order 4–5 s. Spectrogram beampacking works well on five IMS arrays with apertures over 20 km (NOA, AKASG, YKA, WRA, and KURK) without additional post-processing. Seven arrays with 10–20 km aperture (MJAR, ESDC, ILAR, KSRS, CMAR, ASAR, and EKA) can provide robust parameter estimates subject to a smoothing of the resulting slowness grids, most effectively achieved by convolving the measured slowness grids with the array response function for a 4 or 5 s period signal. Even for medium aperture arrays which can provide high-quality coherent slowness estimates, a complementary spectrogram beampacking procedure could act as a quality control by providing non-aliased estimates when the coherent slowness grids display significant sidelobes. The detection part of the algorithm is applicable to all IMS arrays, with spectrogram-based processing offering a potential reduction in the false alarm rate for high-frequency signals. Significantly, the local maxima of the scalar functions derived from the transformed spectrogram beams are robust estimates of the signal onset time. High-frequency energy is of greater importance for lower event magnitudes and in the cavity decoupling detection evasion scenario. There is a need to characterize both propagation paths with low attenuation of high-frequency energy and situations in which parameter estimation on array stations fails.
Estimating geological CO2 storage security to deliver on climate mitigation
Authors: Alcalde Juan , Flude Stephanie , Wilkinson Mark , Johnson Gareth , Edlmann Katriona , Bond Clare , Scott Vivian , Gilfillan Stuart , Ogaya Xènia , Haszeldine R.
Published: July 2018

Carbon capture and storage (CCS) can help nations meet their Paris CO2 reduction commitments cost-effectively. However, lack of confidence in geologic CO2 storage security remains a barrier to CCS implementation. Here we present a numerical program that calculates CO2 storage security and leakage to the atmosphere over 10,000 years. This combines quantitative estimates of geological subsurface CO2 retention, and of surface CO2 leakage. We calculate that realistically well-regulated storage in regions with moderate well densities has a 50% probability that leakage remains below 0.0008% per year, with over 98% of the injected CO2 retained in the subsurface over 10,000 years. An unrealistic scenario, where CO2 storage is inadequately regulated, estimates that more than 78% will be retained over 10,000 years. Our modelling results suggest that geological storage of CO2 can be a secure climate change mitigation option, but we note that long-term behaviour of CO2 in the subsurface remains a key uncertainty.
Comparison of roving-window and search-window techniques for characterising landscape morphometry
Authors: Grohmann Carlos
Published: July 2018

Neighbourhood analysis in a Geographical Information System (GIS) calculates the value of a given raster cell from the values of its neighboring cells. Common operations include filtering (high-pass, low-pass, etc) and smoothing (mean, mode) of data, operations that can be done by means of roving-windows or search-windows. Digital terrain analysis (or geomorphometry) relies on neighbourhood operations to calculate morphometric variables such as slope, aspect, local relief or surface roughness (among many others) at scales ranging from local (i.e., single landforms) to regional (entire mountain chains).The intent of this paper is to compare both techniques in a multi-scale study of geomorphometry, in central-eastern Brazil.
vonHagke_etal_2016_Geology_Subduction_Polarity_Reversal
Authors: von Hagke Christoph , Philippon Melody , Avouac Jean-Philippe , Gurnis Michael
Published: July 2018

We present a regional model of plate geometry and kinematics of southeast Asia since the Late Cretaceous, embedded in a global plate model. The model involves subduction polarity reversals and sheds new light on the origin of the subduction polarity reversal presently observed in Taiwan. We show that this subduction zone reversal is inherited from subduction of the Proto South China Sea plate and owes its current location to triple junction migration and slab rollback. This analysis sheds new light on the plate tectonic context of the Taiwan orogeny and questions the hypothesis that northern Taiwan can be considered as an older, more mature equivalent, of southern Taiwan.
Upscaling permeability in anisotropic volcanic systems
Authors: Farquharson Jamie , Wadsworth Fabian
Published: July 2018

Permeability is an increasingly prevalent metric included in volcano modelling; however, it is a property that can exhibit anisotropy in volcanic environments. Permeability of a layered medium can be described by the arithmetic or harmonic means of the permeabilities of the constituent units, depending on the orientation of flow with respect to layering (i.e. flow parallel or perpendicular to layering, respectively). We outline the theory underlying these formulations, and provide experimental permeability data measured on anisotropic volcanic materials in order to demonstrate this point. We highlight that permeability measured parallel to layering or bedding must be higher than that measured perpendicular to layering. Moreover, we emphasise that the choice of averaging method used to upscale permeability data (i.e.to calculate the equivalent permeability of a system) has important consequences on the validity of the derived values. We anticipate that these points will help move towards more realistic models of pressure evolution behaviour in volcanoes, and increase the utility of laboratory-derived data for volcano-scale modelling.
Strain analysis of a seismically-imaged mass-transport complex, offshore Uruguay
Authors: Steventon Michael , Jackson Christopher , Hodgson David , Johnson Howard
Published: July 2018

Strain style, magnitude, and distribution within mass-transport complexes (MTCs) is important for understanding the process evolution of submarine mass flows and for estimating their runout distances. Structural restoration and quantification of strain in gravitationally-driven passive margins have been shown to approximately balance between updip extensional and downdip compressional domains; such an exercise has not yet been attempted for MTCs. We here interpret and structurally restore a shallowly buried (c. 1500 mbsf) and well-imaged MTC, offshore Uruguay using a high-resolution (12.5 m vertical and 15x12.5 m horizontal resolution) 3D seismic-reflection survey. This allows us to characterise and quantify vertical and lateral strain distribution within the deposit. Detailed seismic mapping and attribute analysis shows that the MTC is characterised by a complicated array of kinematic indicators, which vary spatially in style and concentration. Seismic-attribute extractions reveal several previously undocumented fabrics preserved in the MTC, including internal shearing in the form of sub-orthogonal shear zones, and fold-thrust systems within the basal shear zone beneath rafted-blocks. These features suggest multiple phases of flow and transport directions during emplacement. The MTC is characterised by a broadly tripartite strain distribution, with extensional (e.g. normal faults), translational and compressional (e.g. folds and thrusts) domains, along with a radial frontally emergent zone. We also show how strain is preferentially concentrated around intra-MTC rafted-blocks due to kinematic interaction between these features and the underlying basal shear zone. Overall, and even when volume loss within the frontally emergent zone is excluded, a strain difference between extension (1.6-1.9 km) and contraction (6.7-7.3 km) is calculated. We attribute this to a combination of distributed, sub-seismic, ‘cryptic’ strain, likely related to de-watering, grain-scale deformation, and related changes in bulk sediment volume. This work has implications for assessing MTCs strain distribution and provides a practical approach for evaluating structural interpretations within such deposits.
Protected Places: A Survey of Laws on Archaeological Site and Cave Location Confidentiality and Their Potential Impact on Library Reference Policies and Services
Authors: Zellmer Linda
Published: July 2018

Librarians who work with maps and other forms of spatial information are often asked for information about the location of a place. These questions can range from the location of a village or farm where an ancestor lived to more cryptic questions, such as the location of the Garden of Eden based on its Biblical description. Most librarians will attempt to answer locational questions by directing users to resources such as gazetteers, atlases, maps and plat books. However, the locations of archaeological sites and caves are protected by Federal and state laws. This article provides a summary of Federal and state laws protecting archaeological sites and caves, the reasons for the laws, issues to consider when asked for locations of archaeological sites and caves, and additionally suggests a policy for dealing with users requesting information about archaeological sites and caves.
Precision and Accuracy in Geochronology
Authors: Schoene Blair , Condon Daniel , Morgan Leah , McLean Noah
Published: July 2018

Geochronology in Earth and Solar System science is increasingly in demand, and this demand is not only for more results, but for more precise, more accurate, and more easily interpreted temporal constraints. Because modern research often requires multiple dating methods, scrupulous inter- and intramethod calibration in absolute time is required. However, improved precision has highlighted systematic analytical biases and uncovered geologic complexity that affects mineral dates. At the same time, both enhanced spatial resolution through microbeam geochronology and creative uses of disparate data sets to inform age interpretations have helped explain complexities in age data. Quantifying random and systematic sources of instrumental and geological uncertainty is vital, and requires transparency in methodology, data reduction, and reporting. Community efforts toward inter- and intracalibration of chronometers will continue to help achieve the highest possible resolving power for integrative geochronology.
A new global mode of Earth deformation: seasonal cycle detected
Authors: Blewitt Geoffrey , Lavallee David , Clarke Peter , Nurutdinov Konstantin
Published: July 2018

We have detected a global mode of Earth deformation that is predicted by theory. Precise positioning of GPS sites distributed worldwide reveals that in February to March the northern hemisphere compresses (and the southern hemisphere expands), such that sites near the North Pole move downward by 3.0 mm, and sites near the equator are pulled northwards by 1.5 mm. The opposite pattern of deformation occurs in August to September. We identify this pattern as the degree-one spherical harmonic response of an elastic Earth to increased winter loading of soil moisture, snow cover, and atmosphere. Data inversion shows the load moment’s trajectory as a great circle traversing the continents, peaking at 6.9e22 kg m near the North Pole in winter, indicating inter-hemispheric mass exchange of 1.0±0.2e16 kg.
New analogue materials for nonlinear lithosphere rheology, with an application to slab break-off
Authors: Broerse Taco , Norder Ben , Govers Rob , Sokoutis Dimitrios , Willingshofer Ernst , Picken Stephen
Published: July 2018

Stress-dependent nonlinear upper mantle rheology has a firm base in rock mechanical tests, where this nonlinearity results from dislocation creep of minerals. In the last few decades there has been some attention to nonlinear, power-law, materials for application in scaled analogue experiments for tectonic processes. However, studies describing the rheology of analogue materials with the same nonlinear dependency on stress as observed for lithospheric mantle materials at relevant stress levels, are still lacking. In this study we have developed and rheologically tested materials based on combinations of silicone polymers and plasticine, with the aim of obtaining a material that can serve as a laboratory analogue to the power-law rheology of olivine aggregates at lithospheric mantle conditions. From our steady-state creep tests we find that it is possible to obtain such a power-law material, with effective viscosities over relevant model stress ranges [5-4000 Pa] that allow for nonlinear deformation at laboratory time scales. We apply the developed material to a process where localized deformation of the lithosphere can be expected: slab break-off. We study this process using analogue models, where we apply the new nonlinear material to the lithospheric mantle domains, while we use Newtonian glucose to represent the low viscous asthenosphere. Now that we properly manage power-law behavior in our analogue lithosphere materials, we are able to model localized lithospheric tearing.
The impact of earthquake cycle variability on neotectonic and paleoseismic slip rate estimates
Authors: Styron Richard
Published: July 2018

Because of the natural variability (aleatoric uncertainty) in earthquake recurrence intervals and coseismic displacements on a fault, cumulative slip on a fault does not increase linearly or perfectly step-wise with time; instead, some amount of variability in shorter-term slip rates results. Though this variability could greatly affect the accuracy of neotectonic (i.e., late Quaternary) and paleoseismic slip rate estimates, these effects have not been quantified. In this study, idealized faults with four different, representative earthquake recurrence distributions are created with equal mean recurrence intervals (1,000 years) and coseismic slip distributions, and the variability in slip rate measurements over 500 to 100,000 year measurement windows is calculated for all faults through Monte Carlo simulations. The recurrence distributions used are quasi-periodic, unclustered and clustered lognormal distributions, and an unclustered exponential distribution. The results demonstrate that the most important parameter is the coefficient of variation (COV = standard deviation/mean) of the recurrence distributions rather than the shape of the distribution itself. Slip rate variability over short time scales (< 10,000 years or 10 mean earthquake cycles) is quite high, but decreases with time and is close to stable after ~ 40,000 years (40 mean earthquake cycles). This variability is higher for recurrence distributions with a higher COV. The natural variability in the slip rate estimates compared to the true value is then used to estimate the epistemic uncertainty in a single slip rate measurement (as one would make in a geological study) in the absence of any measurement uncertainty. This epistemic uncertainty is very high (a factor of 2 or more) for measurement windows of a few mean earthquake cycles (as in a paleoseismic slip rate estimate), but decreases rapidly to a factor of 1–2 with > 5 mean earthquake cycles (as in a neotectonic slip rate study). These uncertainties are independent of, and should be propagated with uncertainties in fault displacement and geochronologic measurements used to estimate slip rates. They may then aid in the comparison of slip rates from different methods or the evaluation of potential slip rate changes over time.
Effects of shoal margin collapses on the morphodynamics of a sandy estuary
Authors: van Dijk Wout , Hiatt Matthew , van der Werf Jebbe , Kleinhans Maarten
Published: July 2018

Shoal margin collapses of several Mm3 have occurred in the Western Scheldt estuary, the Netherlands, on average five times a year over the last decades. While these collapses involve significant volumes of material, their effect on the channel‐shoal morphology is unknown. We hypothesize that collapses dynamicise the channel‐shoal interactions, which could impact the ecological functioning, flood safety and navigation in the estuary. The objective is to investigate how locations, probability, type, and volume of shoal margin collapse affect the channel‐shoal dynamics. We implemented an empirically‐validated parameterization for shoal margin collapses and tested its effect on simulated estuary morphological development in a Delft3D schematization of the Western Scheldt. Three sets of scenarios were analyzed for near‐field and far‐field effects on flow pattern and channel‐shoal morphology: 1) an observed shoal margin collapse of 2014, 2) initial large collapses on 10 locations, and 3) continuous collapses predicted by our novel probabilistic model over a time span of decades. Results show that a single shoal margin collapse only affects the local dynamics in the longitudinal flow direction and dampen out within a year for typical volumes, whereas larger disturbances that reach the seaward or landward sill at tidal channel junctions grow. The direction of the strongest tidally‐averaged flow determined the redistribution of the collapsed sediment. We conclude that adding the process of shoal margin collapses increases the channel‐shoal interactions and that in intensively dredged estuaries shoal margins oversteepen, amplifying the number of collapses, but because of dredging the natural morphological response is interrupted.
Accurate relative location estimates for the North Korean nuclear tests using empirical slowness corrections
Authors: Gibbons Steven , Pabian Frank , Näsholm Sven , Kværna Tormod , Mykkeltveit Svein
Published: July 2018

Declared North Korean nuclear tests in 2006, 2009, 2013 and 2016 were observed seismically at regional and teleseismic distances. Waveform similarity allows the events to be located relatively with far greater accuracy than the absolute locations can be determined from seismic data alone. There is now significant redundancy in the data given the large number of regional and teleseismic stations that have recorded multiple events, and relative location estimates can be confirmed independently by performing calculations on many mutually exclusive sets of measurements. Using a 1-D global velocity model, the distances between the events estimated using teleseismic P phases are found to be approximately 25 per cent shorter than the distances between events estimated using regional Pn phases. The 2009, 2013 and 2016 events all take place within 1 km of each other and the discrepancy between the regional and teleseismic relative location estimates is no more than about 150 m. The discrepancy is much more significant when estimating the location of the more distant 2006 event relative to the later explosions with regional and teleseismic estimates varying by many hundreds of metres. The relative location of the 2006 event is challenging given the smaller number of observing stations, the lower signal-to-noise ratio and significant waveform dissimilarity at some regional stations. The 2006 event is however highly significant in constraining the absolute locations in the terrain at the Punggye-ri test-site in relation to observed surface infrastructure. For each seismic arrival used to estimate the relative locations, we define a slowness scaling factor which multiplies the gradient of seismic traveltime versus distance, evaluated at the source, relative to the applied 1-D velocity model. A procedure for estimating correction terms which reduce the double-difference time residual vector norms is presented together with a discussion of the associated uncertainty. The modified velocity gradients reduce the residuals, the relative location uncertainties and the sensitivity to the combination of stations used. The traveltime gradients appear to be overestimated for the regional phases, and teleseismic relative location estimates are likely to be more accurate despite an apparent lower precision. Calibrations for regional phases are essential given that smaller magnitude events are likely not to be recorded teleseismically. We discuss the implications for the absolute event locations. Placing the 2006 event under a local maximum of overburden at 41.293°N, 129.105°E would imply a location of 41.299°N, 129.075°E for the January 2016 event, providing almost optimal overburden for the later four events.
Unphysical properties of the rotation tensor estimated by least squares optimization with specific application to biomechanics
Authors: Rubin MB , Solav Dana
Published: July 2018

Analysis of the transformation of one data set into another is a ubiquitous problem in many fields of science. Many works approximate the transformation of a reference cluster of n vectors Xi (i=1,2,..,n) into another cluster of n vectors xi by a translation and a rotation using a least squares optimization to obtain the rotation tensor Q. The objective of this work is to prove that this rotation tensor Q exhibits unphysical dependence on the shape and orientation of the reference cluster. In contrast, when the transformation is approximated by a translation and a general non-singular tensor F, which includes deformations, then the associated rotation tensor R does not exhibit these unphysical properties. An example in biomechanics quantifies the errors of these unphysical properties.