Under certain geological conditions, low induction number electromagnetic instruments are known to produce negative apparent conductivity responses. This is particularly the case when the subsurface is characterised by highly conductive bodies. We present 3D numerical modelling results of dacite dike intrusions in Sugisawa, Akita Prefecture, Japan.

Based on the Hilbert-Huang transform, a time-frequency analysis method is proposed to obtain stable estimates of the magnetotelluric response function. The response function estimation is performed in the time-frequency domain using instantaneous spectra rather than in the frequency domain, which allows for imaging the response parameter content as a function of time and frequency.

Polarity reversals and cross-talk noises, which degrade the converted wave images (P-S, S-P, and S-S images) of elastic reverse time migration (ERTM), are addressed. To overcome these problems, we derive a new P-S converted wave imaging condition for ERTM based on wavefield separation techniques.

Accuracy and resolution of velocity spectra are very important in seismic data processing, as they have considerable impact on the quality of the final seismic section. We improve the accuracy and resolution of velocity spectra by introducing two weighting functions to the traditional semblance velocity analysis.

We introduce an efficient waveform inversion algorithm using common mid-point gathers. Since we perform both modelling and inversion in the wavenumber-space-time domain, it recovers only a one-dimensional velocity model. However, we can build a two-dimensional velocity model with moderate dips by assuming that reflectors are locally flat.

Rayleigh wave experiments were performed in homogeneous and lateral inhomogeneous models using acoustic and seismoelectric measurements, respectively. The experimental results suggest a potential application of the seismoelectric conversion effect to improve spatial resolution and meet the requirement of dispersion measurement in the laboratory acoustic experiments involving Rayleigh waves.

An analysis of three approaches for estimating 3D PS statics is presented. These include a surface-consistent inversion algorithm, PPS refraction statics, and a robust statistical method. This analysis is achieved through the use of synthetic models, and a coal-scale 3D-3C survey acquired in the Bowen Basin.

We introduce a residual static correction method using first arrivals. Since we fit and smooth the first breaks in a 3D shot–receiver united domain, this method has a lower sensitivity to first arrivals and performs better than traditional methods.

We conducted microtremor array surveys for shallow V_s profiles at strong motion stations in Bursa, Yalova and Kocaeli provinces in Turkey. The V_s profiles to a depth of 100 m were deduced from Rayleigh wave phase velocities in frequencies from 1 to 30 Hz. Site amplification factors were discussed with the profiles.

This study applied a method that uses the H/V spectral ratio of ground motions to analyse site amplification characteristics. Its application was extended to S-waves, coda waves, and background noise. Analysis of data at seismic stations in Korea suggested consistent site amplification characteristics among the three types of seismic energies despite a logarithmic difference in the Fourier transform values.

New comprehensive seismic noise models and 3D seismic noise variation are constructed for Morocco, North Africa, using 23 broadband stations. The results bring a new perception to noise models and can be considered as a significant contribution. This study supplements the Peterson models and allows future permanent stations to be sited in Morocco.

An object program provides hands-on searching through magnetic survey data. The power spectrum is remapped on-screen so that any isolated compact body appears as a straight line in a spectrum of depths. Results are typically noisy, so facilities are provided to change parameters to track down an elusive depth signal.

We describe a new fast gravity inversion method to recover a 3D density model from gravity data. This gravity inversion method introduces a stabiliser model norm with a depth weighting function to produce smooth models and uses a new symmetric successive over-relaxation (SSOR) iterative conjugate gradient (CG) algorithm.

In this paper, we describe the utilisation of numerical models to simulate the downhole application of gravity gradiometry in order to benchmark the impact of a density contrast at depth, with specific application to monitor a density contrast consistent with the sequestration of CO₂ displacing brine water in an abandoned oil reservoir.

Gravity, ground magnetics, DC resistivity and TDEM measurements are used to delineate the near-surface extent of the Okauia Low Temperature Geothermal System, New Zealand. Potential permeable pathways mapped by the geophysical surveys are consistent with the geological environment.

An artificial groundwater recharge experiment was conducted in a pyroclastic plateau in Kagoshima Prefecture in Japan, and time-efficient in-line resistivity surveys were performed along four intersecting lines. The zones of decreased resistivity shifted with time, indicating non-uniform penetration of water from the recharge areas and a horizontal flow of the recharged water.