SummaryExtreme value statistics (EVS) is commonly used to model rare, extreme events such as natural disasters. This study proposes a method that integrates EVS and Bayesian estimation to enable the early forecasting of aftershock-induced ground shaking. The method is applied to continuous seismograms recorded immediately after a large earthquake. The proposed method is based on several key assumptions: the Gutenberg–Richter (G–R) and Omori–Utsu laws, as well as the proportionality between earthquake magnitude and the logarithmic maximum amplitude. Based on these assumptions, two metrics were computed at each seismic station: the exceedance probability of the maximum amplitude (EPMA) and the number of threshold value exceedances (EPNUM). While EPMA follows a long-tailed Fréchet distribution, with uncertainty spanning at least an order of magnitude, EPNUM follows a short-tailed Poisson distribution, with uncertainty typically varying by a factor of two. The performance of the proposed method was evaluated across three different types of aftershock sequences in Japan. The practical forecasting capability was demonstrated within 1 hour of the mainshock and was effective up to 7 days. Compared to conventional methods that rely on incomplete earthquake catalogues, the proposed approach demonstrated faster and more robust results. While the median forecast of maximum amplitude tended to be overestimated, possibly due to the potential nonlinear relationship between magnitude and logarithmic maximum amplitude, the forecast for the number of felt earthquakes did not show such bias. Because the proposed method is based on single-station processing, it can be applied in regions without a dense seismograph network or real-time earthquake monitoring system, as long as continuous ground motion data is available at the target site.
SummaryThe interpretation of subsurface resistivity structures in volcanic areas remains challenging and requires the selection of the most plausible configuration from various geological features that affect the resistivity measurements. A comprehensive physical study of the rocks in the target area is essential for accurate interpretation. A magnetotelluric (MT) survey conducted in the southeast flank of Mt. Ontake volcano detected several kilometres of low resistivity below 30 Ωm. However, the interpretation of resistivity anomalies remains to be verified; borehole data have been used to resolve this problem. In this study, geological, fracture, temperature, and resistivity structures obtained from borehole investigations were analysed using rock physical methods, and core samples were subjected to physical property measurements and microscopic observations. The geology observed in the borehole was sedimentary rock with a porosity of less than a few percent, except for the surface volcanic breccia and some intrusive granites. The borehole wall was poorly fractured. The groundwater temperature in the borehole was aligned with the standard geothermal gradient, 40 °C at a depth of 800 m. These results indicate the absence of a hydrothermal reservoir at the site. In contrast, the core samples contained pyrite-filled microfractures. All the samples had poor porosity and contained a small amount of clay minerals but showed uniformly lower resistivity values than expected for similar porosity. Some samples exhibited robust induced polarization effects. The pyrite contents of the samples were low. A pseudo-high-frequency conductivity model test using electrostatic field analysis on a numerical model of microfractured rock properties reproduced the low resistivity observed in the borehole investigation and MT survey. The specifically low resistivity values observed were appropriately reproduced. The findings of this study indicate that pyrite filling the microfractures can be a major contributor to the low resistivity below 1 Ωm in the study area and suggest that it is necessary to consider the network of microscale veins formed by conductive sulfide minerals, mainly pyrite, for the interpretation of subsurface resistivity in geothermal areas.
Publication date: 15 March 2025
Source: Advances in Space Research, Volume 75, Issue 6
Author(s): Sumanjit Chakraborty, Dibyendu Chakrabarty, Anil K. Yadav, Gopi K. Seemala
Publication date: 15 March 2025
Source: Advances in Space Research, Volume 75, Issue 6
Author(s): C. Cesaroni, M. Pezzopane, E. Zuccheretti, E. Pica, L. Spogli, D. Okoh, A. Pignalberi, J. Olwendo, L. Alfonsi, C. Marcocci, V. Romano, R. Imam, G. De Franceschi, B. Nava, J.B. Habarulema, G. Santilli, A. Di Cecco, J. Munzer
Publication date: 15 March 2025
Source: Advances in Space Research, Volume 75, Issue 6
Author(s): Maocai Wang, Cui Pei, Xiaoyu Chen, Guangming Dai, Zhiming Song, Lei Peng
Publication date: 15 March 2025
Source: Advances in Space Research, Volume 75, Issue 6
Author(s): Carynelisa Haspel, Yoav Yair
NASA research is revealing there's more to flowers than meets the human eye. A recent analysis of wildflowers in California shows how aircraft- and space-based instruments can use color to track seasonal flower cycles. The results suggest a potential new tool for farmers and natural-resource managers who rely on flowering plants.
Global heating over this millennium could exceed previous estimates due to carbon cycle feedback loops. This is the conclusion of a new study by the Potsdam Institute for Climate Impact Research (PIK). The analysis shows that achieving the Paris Agreement's aim of limiting global temperature rise to well below 2°C is only feasible under very low emission scenarios, and if climate sensitivity is lower than current best estimates. The paper is the first to make long-term projections over the next 1,000 years while accounting for currently established carbon cycle feedbacks, including methane.
Around 14,500 years ago, toward the end of the last ice age, melting continental ice sheets drove a sudden and cataclysmic sea level rise of up to 65 feet in just 500 years or less. Despite the scale of the event, known as Meltwater Pulse 1a, scientists still aren't sure which ice sheets were responsible for shedding all that water.
A pair of researchers at the University of Waterloo in Canada, working with a colleague from the Scripps Institution of Oceanography in the U.S., have created a model to visualize how water flows in Antarctica's Aurora Subglacial Basin and how it might flow in coming decades. In their paper published in the journal Nature Communications, Anna-Mireilla Hayden, Tyler Pelle and Christine Dow suggest that water flowing beneath the ice in the Antarctic today may not be reflective of how it might flow in the future.
Freshwater ecosystems require adequate oxygen levels to sustain aerobic life and maintain healthy biological communities. However, both long-term climate warming and the increasing frequency and intensity of short-term heat waves are significantly reducing surface dissolved oxygen (DO) levels in lakes worldwide, according to a study published in Science Advances.
Author(s): Qingbo Luo, Xin Liang, Chengliang Lin, Xinlian Zhang, Jianpeng Liu, Cheng Gao, Yong Hou, and Jianmin Yuan
In hot dense plasma, the interaction between charged particles leads to the ionization potential depression (IPD), which further affects the physical properties of plasma, such as opacity and equation of state. The experiment of IPD of solid-density Al plasma has indicated that present theoretical m…
[Phys. Rev. E 111, 035208] Published Mon Mar 24, 2025
Children are always asking "Why?" As they experience things for the first time, it's natural to want to find out more. But as children grow into adults, they often dismiss something new that challenges their experience and understanding.
SummaryThe intricate architecture of plant root systems is crucial for nutrient and water uptake, significantly influencing plant growth and productivity. Induced polarization (IP) is a promising non-destructive technique for analyzing plant roots in their natural conditions. This study introduces a novel theoretical and numerical model to explain the significant low-frequency polarization of plant root cells observed in previous experiments. Our approach addresses the limitations of existing models by incorporating geometric constraints and internal mechanisms of cell polarization, particularly focusing on interfacial polarization across the cell membrane. Through comprehensive simulations, we investigate various geometries and boundary conditions, demonstrating that densely packed root cells exhibit significant polarization signals within a measurable frequency range due to coupling effects. Our findings align with experimental observations, indicating that the peak frequency is highly sensitive to cell arrangement and membrane properties, while the maximum phase shift remains consistent. This model provides a robust framework for interpreting polarization signals in root systems, offering potential applications for in-situ characterization of plant roots and enhancing the understanding of root dynamics under different environmental conditions.
As Earth continues to warm, more and more of the planet is becoming dry. A 2024 UN report found that in the last three decades, over three-fourths of all the world's land became drier than it had been in the previous 30 years.
By coring the seabed at 850 m water depth in Disko Bay off Greenland's west coast, researchers from the University of Copenhagen have obtained the first historical record of plastic pollution in Greenland. The new data suggest a link to local socio-economic development and represent a step towards developing a common method for analyzing and mapping global microplastic pollution.
Scientists from the University of Sheffield will warn policymakers that the shrinking glaciers of the Andes threaten the water supply of 90 million people on the South American continent at the first-ever World Day for Glaciers hosted by UNESCO in Paris.
SummaryIn the previous papers of this series, we have developed an in-depth analysis of the low-frequency complex conductivity response of volcanic (extrusive) rocks. We showed that the alteration of these rocks plays a key-role in determining their induced polarization properties, especially regarding the formation of smectite in response to the thermo-activated alteration of the volcanic glasses. We also considered the effects associated with the presence of magnetite and pyrite. In the present paper, we look at the induced polarization properties of igneous rocks like granites and granitoids. Usually, the alteration path of these rocks leads to the formation of kaolinite, a clay mineral with a much lower Cation Exchange Capacity (CEC) than smectite. Thirty-three core samples from 3 sites in France are saturated with NaCl solutions at 3 salinities (pore water conductivity of 0.1, 1.0, and 10 S m−1, 25°C) and their complex conductivity spectra are measured in the frequency range 0.01 Hz-45 kHz. As observed for volcanic rocks, the surface conductivity, normalized chargeability, and quadrature conductivity depend strongly on the CEC of the rock, which is independently measured with the cobalt-hexamine method. The (intrinsic) formation factor follows an Archie's type relationship with the connected porosity with a porosity (cementation) exponent of m = 1.70 ± 0.02, much smaller than for volcanic extrusive rocks. Like for volcanic rocks, a dynamic Stern layer model can be used to illustrate the behavior associated with the clay-minerals (mostly kaolinite). A field investigation is conducted in the Vosges (France) using a deep time-domain induced polarization survey reaching at a depth of investigation ∼400 m. We show how the electrical conductivity and the normalized chargeability can be used to image the water content and CEC of the granitic substratum. The conductivity of granite is found to be dominated by surface conductivity rather than by bulk conductivity and therefore Archie's law cannot be used as a conductivity equation to interpret field data as commonly done in ElectroMagnetic (EM) surveys.
SummaryWe present a method for ambient noise cross-correlation modelling and source inversion, which accounts for spatio-spectral variability in noise source distributions. It is based on numerical wavefield simulations in 2-D acoustic media. The source power spectral density is parameterized by a sum of a small number of spatial source distributions, each with a corresponding frequency spectrum held fixed during the inversion. Algorithmically, this is an extension of our previous work which assumed spatially homogeneous source spectra. In this paper, we use it to study the impact of incorrectly estimating source spectra from observed data. This is done using synthetic tests involving sources with closely spaced frequency spectra. The tests demonstrate that when the spatial variability of sources is either partially or wholly unaccounted for, the recovery of true source locations is compromised.
Recent studies have shown that carbon stocks in terrestrial ecosystems are increasing, mitigating around 30% of the CO2 emissions linked to human activities.
