Preprints
Filtering by Subject: Earth Sciences
A tutorial introduction to the Hamiltonian Monte Carlo solution of weakly nonlinear inverse problems
Published: 2018-06-11
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We present an introduction to Hamiltonian Monte Carlo (HMC) sampling of high-dimensional model spaces with focus on linear and weakly nonlinear inverse problems. This includes the theoretical foundations, intuitive examples, as well as applications to linear and nonlinear, adjoint-based traveltime tomography. HMC rests on the construction of an artificial Hamiltonian system where a model is [...]
New analogue materials for nonlinear lithosphere rheology, with an application to slab break-off
Published: 2018-06-07
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics, Tectonics and Structure
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 [...]
Detrital Zircons from the Amazon river-to-fan system reveal base level controls on land-to-sea sediment transfer
Published: 2018-06-06
Subjects: Earth Sciences, Geology, Geomorphology, Physical Sciences and Mathematics, Sedimentology
Large tropical sediment routing systems have relatively stable output fluxes over observable timescales. However, the functioning of sediment transfer in these systems across Pleistocene climate and sea-level fluctuations is not well documented. Here, we use new U-Pb detrital zircon (DZ) geochronology from the Pleistocene Amazon submarine fan (n=1,362 grains) to investigate provenance signatures [...]
Field evidence for the lateral emplacement of igneous dykes: Implications for 3D mechanical models and the plumbing beneath fissure eruptions.
Published: 2018-06-06
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics, Tectonics and Structure, Volcanology
Seismological and geodetic data from modern volcanic systems strongly suggest that magma is transported significant distance (tens of kilometres) in the subsurface away from central volcanic vents. Geological evidence for lateral emplacement preserved within exposed dykes includes aligned fabrics of vesicles and phenocrysts, striations on wall rocks and the anisotropy of magnetic susceptibility. [...]
Do Geology Field Courses Improve Penetrative Thinking?
Published: 2018-06-05
Subjects: Earth Sciences, Education, Geology, Physical Sciences and Mathematics
Spatial thinking skills are important for geoscientists, and field courses play an important role in using and developing those skills. This study examines the development of spatial perception and geoscience-specific penetrative thinking skills, as measured by paired pre- and post-tests using the water-level test and the Geologic Block Cross-sectioning Test, in a sophomore field mapping course. [...]
Insights into agricultural influences and weathering processes from major ion patters
Published: 2018-06-04
Subjects: Chemistry, Earth Sciences, Environmental Chemistry, Environmental Sciences, Geochemistry, Hydrology, Physical Sciences and Mathematics, Water Resource Management
Karst areas and their catchments pose a great challenge for protection because fast conduit flow results in low natural attenuation of anthropogenic contaminants. Studies of the hydrochemistry of karst sources and river solutes are an important tool for securing and managing water resources. A study of the geochemical downriver evolution of the Wiesent River and its tributaries, located in a [...]
Off-fault Focal Mechanisms not Representative of Interseismic Fault Loading Suggest Deep Creep on the Northern San Jacinto Fault
Published: 2018-06-01
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics, Tectonics and Structure
Within the San Bernardino basin, some focal mechanisms show normal slip that is inconsistent with the expected interseismic strike-slip loading of the region. The discrepancy may owe to deep (> 10 km depth), creep along the nearby northern San Jacinto fault. The enigmatic normal slip microseismicity occurs to the northeast of the fault and primarily below 10 km depth, consistent with off-fault [...]
Coulomb pre-stress and fault bends: ignored yet vital factors for earthquake triggering
Published: 2018-06-01
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics, Tectonics and Structure
Successive locations of individual large earthquakes (Mw>5.5) over years to centuries can be difficult to explain with simple Coulomb stress transfer (CST), because seismicity can miss out nearest-neighbour along-strike faults where coseismic CST increases are greatest. We show that “Coulomb pre-stress” may explain this, because magnitudes are >±50 bars if interseismic loading and local [...]
Micromorphological report of Tour Anneessens
Published: 2018-05-30
Subjects: Earth Sciences, Environmental Sciences, Geology, Physical Sciences and Mathematics, Soil Science, Stratigraphy
Micromorphological description of the thin sections retrieved from the Tour Anneesseens site (Brussels, Belgium)
The impact of earthquake cycle variability on neotectonic and paleoseismic slip rate estimates
Published: 2018-05-28
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
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 [...]
Origin and time evolution of subduction polarity reversal from plate kinematics of Southeast Asia
Published: 2018-05-28
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics, Tectonics and Structure
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 [...]
Vibrational modes of hydraulic fractures: Inference of fracture geometry from resonant frequencies and attenuation
Published: 2018-05-27
Subjects: Earth Sciences, Environmental Sciences, Geophysics and Seismology, Glaciology, Physical Sciences and Mathematics, Volcanology
Oscillatory seismic signals arising from resonant vibrations of hydraulic fractures are observed in many geologic systems, including volcanoes, glaciers and ice sheets, and hydrocarbon and geothermal reservoirs. To better quantify the physical dimensions of fluid‐filled cracks and properties of the fluids within them, we study wave motion along a thin hydraulic fracture waveguide. We present a [...]
Crack models of repeating earthquakes predict observed moment-recurrence scaling
Published: 2018-05-24
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Small repeating earthquakes are thought to represent rupture of isolated asperities loaded by surrounding creep. The observed scaling between recurrence interval and seismic moment, Tr ~ M^(1/6), contrasts with expectation assuming constant stress drop and no aseismic slip (Tr ~ M^(1/3)). Here we demonstrate that simple crack models of velocity-weakening asperities embedded in a [...]
Pervasive iron limitation at subsurface chlorophyll maxima of the California Current
Published: 2018-05-24
Subjects: Biogeochemistry, Earth Sciences, Oceanography, Oceanography and Atmospheric Sciences and Meteorology, Physical Sciences and Mathematics
Subsurface chlorophyll maximum layers (SCMLs) are nearly ubiquitous in stratified water columns and exist at horizontal scales ranging from the submesoscale to the extent of oligotrophic gyres. These layers of heightened chlorophyll and/or phytoplankton concentrations are generally thought to be a consequence of a balance between light energy from above and a limiting nutrient flux from below, [...]
Time scales of shallow magma chamber replenishment at Campi Flegrei caldera.
Published: 2018-05-23
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics, Volcanology
Ascent of primitive magmas from depth into shallow, partially degassed reservoirs is commonly assumed to be a viable eruption trigger. The resulting processes of convection and mixing have played an important role both in pre- and syn-eruptive stages in many eruptions of different sizes at the unrest Campi Flegrei caldera in Southern Italy. We performed numerical simulations of magma chamber [...]