Preprints

Filtering by Subject: Geophysics and Seismology

On the Evolution of Thermally Stratified Layers at the top of Earth’s Core

Sam Greenwood, Jonathan Mound, Christopher J. Davies

Published: 2020-08-17
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Stable stratification at the top of the Earth’s outer core has been suggested based upon seismic and geomagnetic observations, however, the origin of the layer is still unknown. In this paper we focus on a thermal origin for the layer and conduct a systematic study on the thermal evolution of the core. We develop a new numerical code to model the growth of thermally stable layers beneath the CMB, [...]

Rapid finite-frequency microseismic noise source inversion at regional to global scales

Jonas Karl Hans Igel, Laura Ermert, Andreas Fichtner

Published: 2020-08-17
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Ambient noise cross-correlations can be used as self-consistent observables, opening novel possibilities for investigating ambient noise sources. To optimise the forward- modelling of global ambient cross-correlations for any given noise distribution of noise sources in the microseismic frequency range up to 0.2 Hz, we implement (i) pre-computed wavefields and (ii) spatially variable grids. This [...]

Bridging the gap between geophysics and geology with Generative Adversarial Networks (GANs)

Suihong Song, Tapan Mukerji, Jiagen Hou

Published: 2020-08-17
Subjects: Artificial Intelligence and Robotics, Computer Sciences, Databases and Information Systems, Earth Sciences, Environmental Monitoring, Environmental Sciences, Geology, Geomorphology, Geophysics and Seismology, Natural Resource Economics, Oil, Gas, and Energy, Other Earth Sciences, Physical Sciences and Mathematics, Sedimentology, Water Resource Management

Inverse mapping from geophysics to geology is a difficult problem due to the inherent uncertainty of geophysical data and the spatially heterogeneous patterns (structure) in geology. We describe GANSim, a type of generative adversarial networks (GANs) that discovers the mapping between remotely-sensed geophysical information and geology with realistic patterns, with a specially designed loss [...]

Stress, rigidity and sediment strength control megathrust earthquake and tsunami dynamics

Thomas Ulrich, Alice-Agnes Gabriel, Elizabeth Madden

Published: 2020-08-17
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Megathrust faults host the largest earthquakes on Earth which can trigger cascading hazards such as devastating tsunamis. Determining characteristics that control subduction zone earthquake and tsunami dynamics is critical to mitigate megathrust hazards, but is impeded by structural complexity, large spatio-temporal scales, and scarce or asymmetric instrumental coverage. Here we show that [...]

A Source Clustering Approach for Efficient Inundation Modeling and Regional Scale PTHA

Amy Williamson, Donsub Rim, Loyce Adams, Randall J LeVeque, Diego Melgar, Frank Gonzalez

Published: 2020-08-15
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

For coastal regions on the margin of a subduction zone, near-field megathrust earthquakes are the source of the most extreme tsunami hazards, and are important to handle properly as one aspect of any Probabilistic Tsunami Hazard Assessment (PTHA). Typically, great variability in inundation depth at any point is possible due to the extreme variation in extent and pattern of slip over the fault [...]

Isotropic and Azimuthally Anisotropic Rayleigh Wave Dispersion Across the Juan de Fuca and Gorda Plates and U.S. Cascadia from Earthquake Data and Ambient Noise Two- and Three-Station Interferometry

Shane Zhang, Hongda Wang, Mengyu Wu, Michael H. Ritzwoller

Published: 2020-08-09
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics, Physics

We use data from the Cascadia Initiative (CI) amphibious array and the USArray Transportable Array to construct and compare Rayleigh wave isotropic and azimuthally anisotropic phase speed maps across the Juan de Fuca and Gorda Plates extending onto the continental northwestern U.S. Results from both earthquakes (28--80~s) as well as ambient noise two- and three-station interferometry (10--40~s) [...]

Principal component analysis of seismic facies

Thilo Wrona, Indranil Pan, Rebecca E. Bell, Haakon Fossen, Robert Gawthorpe

Published: 2020-08-06
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Seismic facies analyses are fundamental to the study of sedimentary, tectonic and magmatic systems using seismic reflection data. These analyses generally assume that seismic facies are: (1) well defined, (2) distinct and (3) prevalent patterns in the data. Here, we examine these assumptions critically. First, we demonstrate how to extract the main seismic facies from conventional industry [...]

Seismic diffraction imaging to better characterise mass-transport complexes: examples from the Gulf of Cadiz, south west Iberian Margin

Jonathan Ford, Roger Urgeles, Angelo Camerlenghi, Eulàlia Gràcia

Published: 2020-08-04
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Mass‐transport complexes (MTCs) are often characterised by small‐scale, discontinuous internal structure, such as slide blocks, rough interfaces, faults and truncated strata. Seismic images may not properly resolve such structure because seismic reflections are fundamentally limited in lateral resolution by the source bandwidth. The relatively weak seismic diffractions, instead, encode [...]

Notes on Seismic Source Models in Elastostatics

Deyu Ming

Published: 2020-08-01
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Seismic source models in elastostatics lay the foundations for the popular earthquake deformation formula derived in Okada (1992), which forms key components for many studies in earthquake displacement simulations, earthquake source inversions and ground-motion predictions. However,despite of their importance, we found that the assumptions and proofs of some important theorems about the topic are [...]

Inferring Interseismic Coupling along the Lesser Antilles Arc: a Bayesian Approach

Elenora van Rijsingen, Eric Calais, Romain Jolivet, Jean Bernard de Chabalier, Jorge Jara, Steeve Symithe, Richard Robertson, Graham A. Ryan

Published: 2020-08-01
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

The Lesser Antilles subduction zone is a challenging region when it comes to unraveling its seismogenic behavior. Over the last century, the subduction megathrust has been seismically quiet, with no large thrust event recorded, which raises the question whether this subduction zone is able to produce large interplate earthquakes or not. However, two historical earthquakes in the 19th century, a M [...]

Robust Q estimation using surface seismic data

Joakim Oscar Blanch

Published: 2020-07-30
Subjects: Applied Mathematics, Computational Engineering, Earth Sciences, Engineering, Geophysics and Seismology, Numerical Analysis and Computation, Physical Sciences and Mathematics

Direct wave arrivals are the most robust signals to determine velocity and consequently they have been used for almost a century in hydrocarbon exploration. The reason is simple as the arrivaltime is explicitly available and provide a direct measurement of the average velocity of the sub-surface ray-path. These signals have not been extensively used to estimate attenuation or Q. One reason may [...]

Energetic Rupture and Tsunamigenesis during the 2020 Mw 7.4 La Crucecita, Mexico Earthquake

Diego Melgar, Angel Ruiz-Angulo, Xyoli Pérez-Campos, Brendan W. Crowell, Xiaohua Xu, Enrique Cabral-Cano, Michael R Brudzinski, Luis Rodriguez-Abreu

Published: 2020-07-21
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

The La Crucecita earthquake ruptured on the megathrust generating strong shaking and a modest, long-lived tsunami. This is a significant earthquake that illuminates important aspects of the behavior of the megathrust as well as the potential related hazards. The rupture is contained within 15-30km depth, ground motions are elevated and the energy to moment ratio is high. We argue that it [...]

Whats down there? The structures, materials and environment of deep-seated tremor and slip

Whitney Maria Behr, Roland Bürgmann

Published: 2020-07-16
Subjects: Earth Sciences, Geochemistry, Geology, Geophysics and Seismology, Physical Sciences and Mathematics, Tectonics and Structure

Episodic tremor and slow slip (ETS) events occur downdip of the seismogenic zone of numerous subduction megathrusts and plate boundary strike-slip faults. These events represent a fascinating and perplexing mode of fault failure that has greatly broadened our view of earthquake dynamics. In this contribution, we review constraints on the ETS deformation process from both geophysical observations [...]

Precursory slow slip and foreshocks on rough faults

Camilla Cattania, Paul Segall

Published: 2020-07-16
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Foreshocks are not uncommon prior to large earthquakes, but their physical mechanism controversial. Two interpretations have been put forward: 1. foreshocks are driven by aseismic nucleation; 2. foreshocks are cascades, with each event triggered by earlier ones. Here we study seismic cycles on faults with fractal roughness at wavelengths exceeding the nucleation length. We perform 2-D [...]

Bayesian inference for fault slip distributions based on ensemble modeling of the uncertainty of underground structure

Ryoichiro Agata, Amato Kasahara, Yuji Yagi

Published: 2020-07-16
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

The prediction errors that originate from the uncertainty of underground structure is often a major contributor of the errors between the data and the model predictions in fault slip estimation using geodetic or seismic waveform data. However, most studies on slip inversions either neglect the model prediction errors or do not distinguish them from observation errors. Several methods that [...]

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