Preprints
Filtering by Subject: Geophysics and Seismology
101 Geodynamic modelling: How to design, interpret, and communicate numerical studies of the solid Earth
Published: 2021-01-27
Subjects: Geophysics and Seismology
Geodynamic modelling provides a powerful tool to investigate processes in the Earth's crust, mantle, and core that are not directly observable. However, numerical models are inherently subject to the assumptions and simplifications on which they are based. In order to use and review numerical modelling studies appropriately, one needs to be aware of the limitations of geodynamic modelling as well [...]
Observational estimates of dynamic topography through space and time
Published: 2021-01-24
Subjects: Biogeochemistry, Cosmochemistry, Earth Sciences, Geochemistry, Geology, Geomorphology, Geophysics and Seismology, Paleobiology, Physical Sciences and Mathematics, Sedimentology, Stratigraphy, Tectonics and Structure, Volcanology
Earth's mantle undergoes convection on million-year timescales as heat is transferred from depth to the surface. Whilst this flow has long been linked to the large-scale horizontal forces that drive plate tectonics and supercontinent cycles, geologists are increasingly recognising the signature of convection through transient vertical motions in the rock record, known as "dynamic topography". A [...]
Earthquake rupture on multiple splay faults and its effect on tsunamis
Published: 2021-01-16
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Detailed imaging of accretionary wedges reveals splay fault networks that could pose a significant tsunami hazard. However, the dynamics of multiple splay fault activation during megathrust earthquakes and the consequent effects on tsunami generation are not well understood. We use a 2-D dynamic rupture model with complex topo-bathymetry and six curved splay fault geometries constrained from [...]
Integrated magnetotelluric and petrological analysis of felsic magma reservoirs: Insights from Ethiopian rift volcanoes
Published: 2021-01-16
Subjects: Earth Sciences, Geochemistry, Geophysics and Seismology, Volcanology
Geophysical and petrological probes are key to understanding the structure and the thermochemical state of active magmatic systems. Recent advances in laboratory analyses, field investigations and numerical methods have allowed increasingly complex data-constraint models with new insights into magma plumbing systems and melt evolution. However, there is still a need for methods to quantitatively [...]
Time to Depth Seismic Reprocessing of Vintage Data: a Case Study in the Otranto Channel (South Adriatic Sea)
Published: 2021-01-14
Subjects: Earth Sciences, Geology, Geophysics and Seismology, Physical Sciences and Mathematics
In this chapter, we present a case study focused on the reprocessing of marine seismic line MS-29, acquired in 1971 in the Otranto Channel, in the South Adriatic Sea (Italy). This line crosses the channel between South Italy and Albania, a key location for understanding the geodynamics of the North Adria Plate. The work is divided into two steps. The first step consists of a modern broadband [...]
LASIF: LArge-scale Seismic Inversion Framework, an updated version
Published: 2021-01-07
Subjects: Geophysics and Seismology, Numerical Analysis and Scientific Computing, Software Engineering
Recent methodological advances and increases in computational power have made it feasible to perform full-waveform inversions (FWI) of large domains while using more sources. This trend, along with the increasing availability of seismic data has led to an explosion of the data volumes that can, and should, be used within an inversion. Similar to machine learning problems, the incorporation of [...]
Comments on “On the reported magnetic precursor of the 1989 Loma Prieta earthquake” by J.N. Thomas, J.J. Love, and M.J.S. Johnston
Published: 2021-01-06
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Thomas et al. (2009) (hereafter TLJ09) attempt to cast doubt upon the report by FraserSmith et al. (1990) (hereafter FS90) of unusual large-amplitude ultra-low frequency (ULF; f < 10 Hz) magnetic fields preceding the M ~7 Loma Prieta earthquake. TLJ09 suggest there are instrumental problems with FS90’s data that we, the designers, builders and long-term operators of the equipment, are presumed to [...]
2-D P-SV and SH spectral element modelling of seismic wave propagation in non-linear media with pore-pressure effects
Published: 2021-01-06
Subjects: Earth Sciences, Engineering, Geophysics and Seismology, Geotechnical Engineering
It has long been recognized that the effects of superficial geological layers, or site effects, can play a major role on the seismic ground motion at the free surface. In this study, we compute wave propagation in a 2-D asymmetrical basin considering both soil non-linearity and pore- pressure effects. Equations of elastodynamics of wave propagation are solved using the spectral element method [...]
Spectral element modelling of seismic wave propagation in visco-elastoplastic media including excess-pore pressure development
Published: 2021-01-06
Subjects: Earth Sciences, Engineering, Geophysics and Seismology, Geotechnical Engineering
Numerical modelling of seismic wave propagation, considering soil nonlinearity, has become a major topic in seismic hazard studies when strong shaking is involved under particular soil conditions. Indeed, when strong ground motion propagates in saturated soils, pore pressure is another important parameter to take into account when successive phases of contractive and dilatant soil behaviour are [...]
Joint event location and 3D Poisson’s ratio tomography for downhole microseismic monitoring
Published: 2021-01-02
Subjects: Geophysics and Seismology, Physical Sciences and Mathematics
Passive seismic tomography plays a significant role in monitoring subsurface structures and properties during hydraulic fracturing. In this study, we develop a new passive seismic tomography approach to jointly invert for event locations, 3D P-wave velocity (Vp), and Poisson’s ratio models, for downhole microseimic monitoring The method enables to directly obtain the 3D Poisson’s ratio or Vp/Vs [...]
Evaluation of the Grillo sensor, a low-cost accelerometer for IoT-based Real-time seismology
Published: 2021-01-02
Subjects: Geophysics and Seismology
Micro-Electro-Mechanical (MEMS) accelerometers are useful for real-time seismology due to their ability to record strong, unsaturated seismic signals. Recent advances in MEMS technologies enable design of instruments with improved capabilities that also allow recording of small signals. As a result, MEMS can be useful across a broad dynamic range and for both major earthquakes and smaller [...]
Identifying shale sweet spots by 3D microseismic imaging
Published: 2021-01-02
Subjects: Geophysics and Seismology, Physical Sciences and Mathematics
Several studies suggest that shale sweet spots are likely associated with low Poisson’s ratio in the shale layer. Compared with conventional geophysical techniques with active seismic data, it is straightforward and cost effective to delineate the distribution of 3D Poisson’s ratio using microseismic data. In this study, we develop a method for determining microseismic event locations, 3D P-wave [...]
Bayesian Seismic Tomography using Normalizing Flows
Published: 2020-12-28
Subjects: Geophysics and Seismology, Physical Sciences and Mathematics
We test a fully non-linear method to solve seismic tomographic problems using data consisting of observed travel times of first-arriving waves. We use variational inference to calculate the posterior probability distribution which describes the solution to the Bayesian tomographic inverse problem. The variational method is an efficient alternate to Monte Carlo methods, which seeks the best [...]
Evolution of a sand-rich submarine channel-lobe system and impact of mass-transport and transitional flow deposits on reservoir heterogeneity: Magnus Field, northern North Sea
Published: 2020-12-19
Subjects: Geology, Geophysics and Seismology, Sedimentology, Stratigraphy
The geometry, distribution, and rock properties (i.e. porosity and permeability) of turbidite reservoirs, and the processes associated with turbidity current deposition, are relatively well known. However, less attention has been given to the equivalent properties resulting from laminar sediment gravity-flow deposition, with most research limited to cogenetic turbidite-debrites (i.e. transitional [...]
Small-scale lithospheric heterogeneity characterization using Bayesian inference
Published: 2020-12-18
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Observations from different disciplines have shown that our planet is highly heterogeneous at multiple scale lengths. Still, many seismological Earth models tend not to include any small-scale heterogeneity or lateral velocity variations, which can affect measurements and predictions based on these homogeneous models. In this study, we describe the lithospheric small-scale heterogeneity structure [...]