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Systematic Bias in Shear-Wave Splitting Measurement

Geophysical Journal International - Fri, 01/09/2026 - 00:00

SummaryShear-wave splitting measurement returns two parameters related to the fabric of the upper mantle: the orientation of the fast polarisation (fast direction), and a measure of the intensity and thickness of the fabric known as the split time. Spatial statistics of compiled splitting measurements indicate that the fast direction is spatially coherent, while the split time is not. We show, through modelling large numbers of noisy measurements, that single-earthquake splitting measurements exhibit a prominent upward bias in split time, the degree of which depends on specifics of the measurement process. Averaging single-event splitting parameters over many measurements does not mitigate this bias; however, stacking of error surfaces from individual measurements does, given sufficient back-azimuthal coverage, while also greatly reducing scatter. Published splitting results use a mix of these two averaging techniques, and this inconsistent bias between studies is likely responsible for the lack of spatial coherence in compiled split-time measurements. We demonstrate this in real data by examining a data set from Alberta, Canada and surrounding areas, for which a recent study published parameter-averaged results. By examining a comparable data set using error-surface stacking, we are able to greatly increase the coherence of the split times while obtaining highly similar fast directions. Our coherent split times are mapped to reveal a zone of strong splitting beneath the active Cordillera, and three zones of moderate to low split time within the cratonic lithosphere.

Spectral induced polarization measurements at different mountain permafrost landforms with varying ice contents

Geophysical Journal International - Fri, 01/09/2026 - 00:00

SummaryUnderstanding the spatial variability of ice content in frozen ground is key to design adequate measures to manage different ecosystems in frame of climate change. To-date investigations in frozen ground require the analysis of borehole data or the collection of multiple geophysical data. Here we propose the use of spectral induced polarization (SIP) as a technique that provides in quasi real-time information about changes in ice content in the subsurface. We demonstrate that exploring the frequency dependence in electrical conductivity and polarization (capacitive) properties in the frequency range between 0.1 and 75 Hz provides direct information about their relative variations in ice content. Our study is based on measurements conducted at nine representative permafrost sites in the European Alps with varying landforms and ice contents, including a pure ice and an unfrozen reference. We use the phase frequency effect (ϕFE) parameter as a parameter describing both the amplitude of the polarization and its frequency dependence to compare the response associated to the different sites. Our results show the lowest ϕFE in sites with low ice content, while increases in this parameter are associated with higher ice content. We evaluate the correlation between SIP parameters and validation ground ice contents for all sites and observe a clear correlation between ϕFE and volumetric ice content. The ϕFE results exhibit distinct landform-specific patterns, with the highest values found in rock glaciers, intermediate values in frozen talus slopes, lower values in bedrock permafrost, and the lowest in unfrozen talus slopes, reducing interpretation ambiguities in electrical resistivity results for assessing ice content.

Temperatures are rising, but what about humidity?

Phys.org: Earth science - Thu, 01/08/2026 - 23:10

Heat waves are becoming commonplace, and so too is high humidity, which can strain the electrical grid, hurt the economy, and endanger human health. But the global prevalence of record-breaking humidity events, some of which approach the physiological limit of what humans can safely handle—and all of which go beyond local expectations and adaptations—has not been widely studied.

The Arctic has entered a new era of extreme weather, study suggests

Phys.org: Earth science - Thu, 01/08/2026 - 19:54

Extreme weather events have become significantly more common in the Arctic over recent decades, posing a threat to vital polar ecosystems, according to new research by an international team of scientists.