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Abstract: We use the two-dimensional (2D) electrical resistivity imaging (ERI) method to detect the contact between sediment and bedrock in a modern fluvial system. We performed eight 2D electrical resistivity surveys along the Peikang River in Kuohsing area, central Taiwan, with a pole–pole array of 1-m electrode spacing to produce a spatial resolution of about 1 m. The resistivity data were inverted into subsurface electrical structures using the least-squares inversion techniques. Then, the contact between the bedrock and sediment was found by using an image processing technique called Laplacian edge detection (LED), which represents an objective approach in interpreting various geophysical images. Numerical modeling demonstrates that isoresistivity lines are not in good agreement with the hypothetical interfaces between the bedrock and sediment, but the zero-lines of the Laplacian operation are strikingly accurate. Our results indicate a well-defined boundary in the resistivity structure that can be used to estimate the quantity of sediments covering bedrock, thus highlighting the utility of this technique in studies of landscape evolution, sediment transport, and sediment budgets. [Copyright &y& Elsevier]

Abstract: We investigated the multifractal structure of magnetic field H measured by magnetotelluric stations installed at three different sites in Taiwan, characterized by different site conditions. Magnetotelluric data include three components of the magnetic field H. We applied the multifractal detrended fluctuation analysis (MF-DFA) to magnetic magnitude time series (evaluated as the L 2 norm). Our findings point out to a significant discrimination among these data in terms of multifractal characteristics of the signals, indicating a strong influence of the environmental settings of the measurement sites on the temporal fluctuations of magnetic field H. Such results highlight the usefulness of the MF-DFA in discriminating dynamics in observational time series of magnetotellurics. [Copyright &y& Elsevier]

Not only direct fault ruptures but also later mass movement may result in complicated frontal deformation of the faults. Consequently, the deformation front or the contacts between the unconsolidated materials from the hanging wall and footwall of the thrust fault may indicate the toe of the mass movement instead of the actual fault zone. In this study, we used a combination of surface electrical resistivity imaging methods and borehole records in order to investigate the geometries of the structures in the frontal deformation zone of the Chihshang Fault at the Dapo elementary school. From the cores, we observed three different geological components at the Dapo site: the conductive Lichi mélange of the hanging wall, the colluvial gravels and the underlying fluvial-gravel layer at the footwall. The resistivity images from two parallel survey lines reveal that the position where the fault trace was thought to be is actually the toe of the slumping body's surface ruptures consisting of materials from the Lichi mélange. On the basis of the resistivity images, we also found that the actual fault plane is located on the southeastern side of the resistivity survey line near the hilltop. As a result, we conclude that mass movement induced by the inter-seismic creeping, not direct faulting, is the main factor affecting the frontal deformation zone of the Chihshang fault at the Dapo site. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Fisher–Shannon method is applied to resistivity time series. [•] The reliability of resistivity estimates is assessed. [•] Day-time resistivity shows higher level of disorder than night-time. [•] The informational methods reveal anthropic source in high frequency band. [Copyright &y& Elsevier]