Preprints
Filtering by Subject: Earth Sciences
How do we understand and visualize uncertainty?
Published: 2017-11-04
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: 2017-11-04
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: 2017-11-04
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: 2017-11-04
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: 2017-11-04
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: 2017-11-04
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: 2017-11-04
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: 2017-11-04
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: 2017-11-04
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 [...]
Probability density functions for radial anisotropy: implications for the upper 1200 km of the mantle
Published: 2017-11-04
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
The presence of radial anisotropy in the upper mantle, transition zone and top of the lower mantle is investigated by applying a model space search technique to Rayleigh and Love wave phase velocity models. Probability density functions are obtained independently for S-wave anisotropy, P-wave anisotropy, intermediate parameter η, Vp, Vs and density anomalies. The likelihoods for P-wave and S-wave [...]
A Bayesian approach to assess the importance of crustal corrections in global anisotropic surface wave tomography
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Several recent studies have demonstrated the importance of crustal corrections when inverting surface wave data to model lateral variations in mantle radial anisotropy. It has also been shown that the choice of the prior crustal model to correct the data can strongly influence the anisotropy model and potentially lead to different geodynamic interpretations. In comparing tomographic models of [...]
Surface wave array tomography in SE Tibet from ambient seismic noise and two-station analysis - II. Crustal and upper-mantle structure
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We determine the 3-D shear wave speed variations in the crust and upper mantle in the southeastern borderland of the Tibetan Plateau, SW China, with data from 25 temporary broad-band stations and one permanent station. Interstation Rayleigh wave (phase velocity) dispersion curves were obtained at periods from 10 to 50 s from empirical Greens function (EGF) derived from (ambient noise) [...]
The signal of mantle anisotropy in the coupling of normal modes
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We investigate whether the coupling of normal mode (NM) multiplets can help us constrain mantle anisotropy.We first derive explicit expressions of the generalized structure coefficients of coupled modes in terms of elastic coefficients, including the Love parameters describing radial anisotropy and the parameters describing azimuthal anisotropy (Jc, Js, Kc, Ks, Mc, Ms, Bc, Bs, Gc, Gs, Ec, Es, Hc, [...]
Probability density function for radial anisotropy from fundamental mode surface wave data and the Neighbourhood Algorithm,
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We applied Sambridges Neighbourhood Algorithm (NA) to degree-8 fundamental mode Love and Rayleigh wave phase velocity maps between 40 and 150 s to find models of radial anisotropy in the upper 220 km of the mantle. The NA is a powerful tool to explore a multidimensional model space and retrieve an ensemble of models from which statistical inferences (posterior probability density functions [...]
P and S tomography using normal-mode and surface waves data with a neighbourhood algorithm
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Traditionally P- and S-wave tomography has been based on the inversion of data that are sensitive to the desired Earth structure, and model covariance is estimated from imperfect resolution and data error propagation. This analysis ignores the usually large null-spaces, and hence the significant non-uniqueness of the solution encountered in seismic tomography problems. Here we perform a model [...]