Preprints
Filtering by Subject: Earth Sciences
Duration and nature of the end-Cryogenian (Marinoan) glaciation
Published: 2017-11-05
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics, Stratigraphy
The end-Cryogenian glaciation (Marinoan) is portrayed commonly as the archetype of snowball Earth, yet its duration and character remain uncertain. Here we report U-Pb zircon ages for two ash beds from widely separated localities of the Marinoan-equivalent Ghaub Formation in Namibia: 639.29 ± 0.26 Ma and 635.21 ± 0.59 Ma. These findings verify, for the first time, the key prediction of the [...]
Precision and Accuracy in Geochronology
Published: 2017-11-05
Subjects: Earth Sciences, Geochemistry, Geology, Paleontology, Physical Sciences and Mathematics, Stratigraphy, Tectonics and Structure, Volcanology
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 [...]
Synchronizing terrestrial and marine records of environmental change across the Eocene–Oligocene transition
Published: 2017-11-05
Subjects: Earth Sciences, Geology, Physical Sciences and Mathematics, Stratigraphy
Synchronizing terrestrial and marine records of environmental change across the Eocene–Oligocene transition
Could the IMS Infrasound Stations Support a Global Network of Small Aperture Seismic Arrays?
Published: 2017-11-05
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
The IMS infrasound arrays have up to 15 sites with apertures up to 3 km. They are distributed remarkably uniformly over the globe, providing excellent coverage of South America, Africa, and Antarctica. Therefore, many infrasound arrays are in regions thousands of kilometers from the closest seismic array. Existing 3-component seismic stations, co-located with infrasound arrays, show how typical [...]
The 2015 MW 7.1 Earthquake on the Charlie-Gibbs Transform Fault: Repeating Earthquakes and Multi-modal Slip on a Slow Oceanic Transform
Published: 2017-11-04
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
The slow spreading rate Charlie-Gibbs Atlantic transform fault slips in large (M~7) quasi-repeating earthquakes. The foreshocks, aftershocks, and unilateral rupture of the 2015 earthquake are similar to a 1974 earthquake on the same transform. The findings of this study are consistent with transform earthquakes starting small near the ridge and large slip asperities nearer to the transform center.
Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines
Published: 2017-11-04
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Aftershock sequences following very large earthquakes present enormous challenges to near‐real‐time generation of seismic bulletins. The increase in analyst resources needed to relocate an inflated number of events is compounded by failures of phase‐association algorithms and a significant deterioration in the quality of underlying, fully automatic event bulletins. Current processing pipelines [...]
How do we understand and visualize uncertainty?
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Geophysicists are often concerned with reconstructing subsurface properties using observations collected at or near the surface. For example, in seismic migration, we attempt to reconstruct subsurface geometry from surface seismic recordings, and in potential field inversion, observations are used to map electrical conductivity or density variations in geologic layers. The procedure of inferring [...]
Three-dimensional variations in Love and Rayleigh wave azimuthal anisotropy for the upper 800 km of the mantle
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We present a new mantle model (YB14SHani) of azimuthal anisotropy for horizontally polarized shear waves (SH) in parallel with our previously published vertically polarized shear wave (SV) anisotropy model (YB13SVani). YB14SHani was obtained from higher mode Love wave phase velocity maps with sensitivity to anisotropy down to ~1200 km depth. SH anisotropy is present down to the mantle transition [...]
Structure and anisotropy of the Mexico subduction zone based on Rayleigh-wave analysis and implications for the geometry of the Trans-Mexican Volcanic Belt
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We develop a three-dimensional model of shear wave velocity and anisotropy for the Mexico subduction zone using Rayleigh wave phase velocity dispersion measurements. This region is characterized by both steep and flat subduction and a volcanic arc that appears to be oblique to the trench. We give a new interpretation of the volcanic arc obliqueness and the location of the Tzitzio gap in volcanism [...]
Radial anisotropy and prior petrological constraints: A comparative study
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Radial seismic anisotropy models are traditionally obtained using empirical constraints based on laboratory experiments and petrological considerations. We tested the hypothesis that such petrological constraints affect the uppermost mantle models of S wave anisotropy using a statistical approach. In addition, we were able to determine which model features are constrained by the data and which [...]
Radial anisotropy in seismic reference models of the mantle
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Sambridges Neighborhood Algorithm was applied to normal mode and surface wave phase velocity data to determine the likelihood of radial anisotropy in mantle reference models. This full model space search technique provides probability density functions for each model parameter and therefore reliable estimates of resolution and uncertainty, without having to introduce unnecessary regularization on [...]
Changes in Seismic Anisotropy Shed Light on the Nature of the Gutenberg Discontinuity
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
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 [...]
Robust Normal Mode Constraints on Inner-Core Anisotropy from Model Space Search
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
A technique for searching full model space that was applied to measurements of anomalously split normal modes showed a robust pattern of P-wave and S-wave anisotropy in the inner core. The parameter describing P-wave anisotropy changes sign around a radius of 400 kilometers, whereas S-wave anisotropy is small in the upper two-thirds of the inner core and becomes negative at greater depths. Our [...]
Seismic anisotropy changes across upper mantle phase transitions
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
The mantle transition zone is believed to play an important role in the thermochemical evolution of our planet and in its deep water cycle. Constraining mantle flow at these depths can help elucidate its nature and better understand mantle dynamics and the history of plate tectonics. Seismic anisotropy, i.e., the directional dependence of seismic wave velocity, provides us with the most direct [...]
Depth constraints on azimuthal anisotropy in the Great Basin from Rayleigh-wave phase velocity maps
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We present fundamental-mode Rayleigh-wave azimuthally anisotropic phase velocity maps obtained for the Great Basin region at periods between 16 s and 102 s. These maps offer the first depth constraints on the origin of the semi-circular shear-wave splitting pattern observed in central Nevada, around a weak azimuthal anisotropy zone. A variety of explanations have been proposed to explain this [...]