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Induced polarization applied to landslides. Part 3: The case of rock glaciers

Geophysical Journal International - Thu, 11/06/2025 - 00:00

SUMMARYRock glaciers are specific landforms consisting of a mixture of rock debris, ice, liquid water, and air. In the Alps, active rock glaciers are generally found at high elevations above 2500 m. Active rock glaciers creep and can develop anomalous slide-like behaviors called destabilization. Induced polarization is a non-intrusive geophysical method that has proven to be sensitive to the hydrogeological properties of porous media. In August 2023, we performed four induced polarization profiles at Plan-du-Lac (Vanoise, France), on a multi-unit rock glacier complex with a front located at a low altitude of 2200 m). Our goal was to determine its architecture and its water and ice contents in relation with its activity rate. The survey included two transverse high-resolution profiles with a 5 m spacing between the electrodes and two other longitudinal profiles with a 20 m spacing between the electrodes allowing a depth of investigation of roughly 200 m to image the rock glacier from its terminal front up to its root. The conductivity and normalized chargeability tomograms were inverted and then used to get the water content and cation exchange capacity (a proxy for the clay content) tomograms. In most of the units, ice has disappeared and the landforms associated with the former rock glacier were characterized by low water and clay contents with respect to the basement. This was consistent with these units being mostly formed by rock debris with a low water saturation except at their bases, which are water-saturated. Ice remains were found at the roots of the rock glacier, with a volume content up to ∼10 per cent (vol. per cent) for profile P2 and 16 per cent for profile P4. The roots of the rock glacier complex were still creeping as shown by InSAR data. This case study demonstrates the usefulness of the induced polarization method to quantitatively characterize gravitational instabilities associated with coarse materials and transitional rock glaciers.

Co- and Early Post-seismic InSAR Observations Reveal Complex Rupture of the 2023 Herat Earthquake Sequence, NW Afghanistan

Geophysical Journal International - Thu, 11/06/2025 - 00:00

SUMMARYIn October 2023, an earthquake sequence comprising four ∼ MW 6.0 events struck Herat Province in northwestern Afghanistan, causing severe casualties and property losses. The geometry of seismogenic faults and the mechanisms of the earthquake sequence are essential for regional seismic hazard assessment, but still remain poorly constrained. With Interferometric Synthetic Aperture Radar (InSAR) techniques, we extracted high-resolution co- and early post-seismic deformations of the events. Through a two-step inversion method, we inferred the geometry of the causative faults and the distributed slip models. The earthquake sequence ruptured two intersecting low-dip thrust faults, indicating that the complex geometry may have played a key role in controlling the propagation of the events. The ruptures of the four major events are clearly imaged at depths of 1-10 km without reaching the surface, showing a pattern of first spreading westwards, then jumping eastwards to the bend segment, and finally rupturing an adjacent fault. Post-seismic deformation further reveals reactivation of a secondary fault splay which underwent afterslip. Shallow afterslip up-dip of the co-seismic rupture dominates post-seismic deformation during 10 months following the earthquake sequence. Relying on the evolution of afterslip, we infer that significant rate-strengthening property in the shallow bend section may have hindered further co-seismic rupture propagation. Combining obtained results and the complex geological setting of the Herat region, we suggest that the earthquake sequence reflects N-S crustal shortening between two branches of the western Herat Fault System.

Induced polarization as a tool to characterize permafrost 1. Theory and laboratory experiments

Geophysical Journal International - Thu, 11/06/2025 - 00:00

SUMMARYIn the last decade, the Dynamic Stern Layer (DSL) model has proven to be a reliable petrophysical model to comprehend induced polarization data at various scales from the representative elementary volume of a porous rock to the interpretation of field data. Preliminary works have demonstrated that such model can be extended to understand the induced polarization properties of ice-bearing rocks and to interpret field-acquired induced polarization data in the context of permafrost. That being said, the direct effect of ice was let aside. We first review the DSL model in presence of ice and discuss the role of ice as an interfacial protonic dirty semi-conductor in the complex conductivity spectra with an emphasis on the role of the complex-valued surface conductivity of ice crystals above 1 Hz. We propose a new combined polarization model including indirect and direct ice effects. By direct effects, we mean the effects associated with change in the liquid water content and salinity of the pore water. By direct effect, we mean the role of the interfacial properties of the ice surface and liquid water is still present in the pore space of the porous composite. In this case, the electrical current is not expected to cross the ice crystals. Instead, it would polarize the surface of the ice crystals and generate a very high chargeability that can reach one depending on the value of the volumetric content of ice. We apply the DSL model to a new set of complex conductivity spectra obtained in the frequency range 10 mHz-45 kHz using a collection of 25 rock samples including metamorphic and sedimentary rocks in the temperature range + 15/+20°C to -10/-15°C. We observe that the model explains very well the observed data in the low-frequency range (10 mHz-1 Hz) without any direct contribution of ice. In the high frequency range (above 1 Hz), we observe a weak contribution possibly associated with the contribution of ice crystals. We establish under what conditions the direct contribution of ice can be neglected. We also investigate the role of porosity, cation exchange capacity, and freezing curve parameters on the complex conductivity spectra of crystalline and non-crystalline rocks during freezing. Laboratory experiments demonstrate that in most field conditions including permafrost conditions, surface conductivity associated with conduction on the surface of clay minerals (and alumino-silicates in general) is expected to dominate the overall conductivity response. Therefore Archie’s law cannot be used as a conductivity equation in this context because of the contribution of surface conductivity. A large experimental and field dataset at the Aiguille du Midi (3842 m a.s.l., French Alps) for the resistivity versus temperature data of granitic rocks demonstrates the role of surface conductivity in the overall conductivity of the rock.

Researchers improve marine aerosol remote sensing accuracy using multiangular polarimetry

Phys.org: Earth science - Wed, 11/05/2025 - 21:39

A research group led by Prof. Sun Xiaobing from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, investigated the impact of multiangular polarimetry on the quantification of marine aerosol remote sensing applications.

Tiny diatoms, big climate impact: How microscopic skeletons rapidly shape ocean chemistry

Phys.org: Earth science - Wed, 11/05/2025 - 21:37

If you know what diatoms are, it's probably because of their beauty. These single-celled algae found on the ocean floor have ornate glassy shells that shine like jewels under the microscope.

Simulations show Antarctic meltwater slows warming but drives uneven sea level rise

Phys.org: Earth science - Wed, 11/05/2025 - 21:20

Melting of the Antarctic ice sheet due to global warming has long-term, irreversible societal impacts with important implications for people around the world. Spatial patterns of sea level change from ice sheet mass loss vary in cause, and have worldwide impacts.

East African Rift study uncovers why breaking up is hard for some continents

Phys.org: Earth science - Wed, 11/05/2025 - 20:59

Tulane University researchers, collaborating with an international team of scientists, have discovered why some parts of Earth's crust remain strong while others give way, overturning long-held assumptions about how continents break apart.

The 'blue forest' in figures: First global inventory of carbon stored by seagrass meadows

Phys.org: Earth science - Wed, 11/05/2025 - 20:40

An international study presents the first global assessment of blue carbon accumulated in the living parts of seagrass plants. According to the results, their leaves, rhizomes and roots store up to 40 million tons of carbon worldwide.

Helheim Glacier's massive calving events don't behave the way scientists assumed

Phys.org: Earth science - Wed, 11/05/2025 - 19:50

For nearly a decade, Leigh Stearns and collaborators aimed a laser scanner system at Greenland's Helheim Glacier. Their long-running survey reveals that Helheim's massive calving events don't behave the way scientists once thought, reframing how ice loss contributes to sea-level rise.

When irrigation backfires: Global farming practices are driving heat stress and water strain, research warns

Phys.org: Earth science - Wed, 11/05/2025 - 19:31

Three new high-profile studies led by Dr. Yi Yao (Vrije Universiteit Brussel and ETH Zurich) show that while irrigation may be seen as a tool to dampen heat extremes, its benefits will come with adverse impacts.