Frequency and distance changes in the apparent P-wave radiation pattern (0.75–12 Hz) are investigated using velocity seismograms of shallow strike-slip earthquakes occurring in Chugoku region, southwestern Japan. Data from a dense seismic monitoring network revealed that the four-lobe apparent P-wave radiation pattern was gradually distorted with increasing frequency and propagation distance.…

We investigate the capability of Time Reversal Mirror (TRM) algorithm to image local acoustic sources (<3.5 km) associated with complex, sustained volcanic eruptions. Accurate source localization for volcano infrasound (low-frequency acoustic waves) is often challenging due to pronounced volcanic topography and emergent arrivals of infrasound signals. While the accuracy of the conventional app…

The solution of the geophysical electromagnetic (EM) modelling problem on unstructured tetrahedral-Vorono¨ı grids using EM potentials is investigated. Unstructured grids enable accurate representation of geological structures and interfaces and allow local refinements that can be beneficial in the mesh, for example, at the observation points and at the source. The time-harmonic Helmholtz…

The scattering of seismic waves travelling in the Earth is not only caused by random velocity heterogeneity but also by surface topography. Both factors are known to strongly affect groundmotion complexity even at relatively short distance from the source. In this study, we simulate ground motion with a 3-D finite-difference wave propagation solver in the 0–5 Hz frequency band using three to…

A new method of fully nonlinear waveform fitting to measure interstation phase speeds and amplitude ratios is developed and applied to USArray. The Neighbourhood Algorithm is used as a global optimizer, which efficiently searches for model parameters that fit two observed waveforms on a common great-circle path by modulating the phase and amplitude terms of the fundamental-mode surface waves. W…

In the complex action theory whose path runs over not only past but also future, we study a normalized matrix element of an operator ˆO defined in terms of the future state at the latest time TB and the past state at the earliest time TA with a proper inner product that makes normal a given Hamiltonian that is non-normal at first. We present a theorem that states that, provided that the operat…

In most numerical simulations of the Earth’s core the dynamo resides outside the tangent cylinder and may be crudely classified as being of the α2 type. In this region the flow comprises a sea of thin columnar vortices aligned with the rotation axis, taking the form of alternating cyclones and anticyclones. The dynamo is thought to be driven by these columnar vortices within which the f…

Previous studies of Earth rotation perturbations due to ice-age loading have predicted a slow secular drift of the rotation axis relative to the surface geography (i.e. true polar wander, TPW) of order of several degrees over the Plio-Pleistocene. It has been argued that this drift and the change in the geographic distribution of solar insolation that it impliesmay have been responsible for imp…

A molecular dynamics simulation with a new-application potential model has been explored for melting temperature, radial distribution of iron–copper bimetallic nanoclusters, and their bulk for the first time. At low copper weight percentages, the melting temperature changes a little for the bulk structures; however, for nanostructures, the variation of melting temperature is significant. At m…

A computational method is given for solving the forward modelling problem for transient electromagnetic exploration. Its key features are the discretization of the quasi-static Maxwell’s equations in space using the first-kind family of curl-conforming N´ed´elec elements combined with time integration using rational Krylov methods. We show how rational Krylov methods can also be used to sol…