Geophysical Research Letters

Journal: Geophysical Research Letters

Abbreviation

Geophys. Res. Lett.

Publisher

American Geophysical Union

ISSN

0094-8276
1944-8007

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Publications 1 - 10 of 735

Sedimentation of Snow Particles in Still Air in Stokes Regime
Zeugin, Till; Krol, Quirine; Fouxon, Itzhak; et al. (2020)
Geophysical Research Letters
We compute the resistance matrices of realistic 3-D snow particle shapes obtained from microcomputed tomography data of snowpack samples and a phase field model. Using these resistance matrices, we calculate the sedimentation of the particles in still air in Stokes regime. We find that particles attain preferred orientations and the mode of motion is either drifting or spiraling. Simple laws, relating average drag and rotation torque coefficients to the particles' sphericity, are established which lead to a new formulation of a snow particle's average terminal velocity. The presented models are valid in Stokes regime in still air, corresponding to particle sizes up to ∼100 μm but can reasonably be extended to moderately higher Reynolds numbers (∼1 mm) and used for estimating mean settling velocity in turbulent conditions. Though not all relevant atmospheric conditions are covered, our study provides the basis for addressing more complex conditions in the future. © 2020 American Geophysical Union.
Maximum Magnitude Forecast in Hydraulic Stimulation Based on Clustering and Size Distribution of Early Microseismicity
Afshari Moein, Mohammad J.; Tormann, Thessa; Valley, Benoît; et al. (2018)
Geophysical Research Letters
We interpreted the spatial clustering and size distribution of induced microseismicity observed during the stimulation of an enhanced geothermal system beneath Basel by comparison with scale-invariant synthetic data derived from discrete fracture network models. We evaluated microseimic specific influential factors including the effect of hypocentral location uncertainties, existence of a fractured zone and repeating events on the observed spatial organization. Using a dual power-law model originally developed in the context of discrete fracture network modeling, we developed theoretically the relationships among spatial clustering and magnitude distributions. We applied this model to the Basel data set and showed that the spatial clustering characteristics presented stationary properties during the hydraulic stimulation. Based on this observation, we proposed a statistical seismicity model calibrated on the scaling of early stimulation spatial patterns that is capable of forecasting the maximum magnitude of induced events with increasing injection time and stimulated volume.
Secondary Plumes Formation Controlled by Interaction of Thermochemical Mantle Plumes With the Mantle Transition Zone
Zhu , Xiaoxi; Balázs, Attila; Gerya , Taras; et al. (2025)
Geophysical Research Letters
The causes and global distribution of intraplate volcanism remain poorly understood, particularly the occurrence of scattered magmatism unrelated to large igneous provinces (LIPs). In this study, high-resolution numerical simulations are employed to examine the interaction between deep thermochemical mantle plumes and the mantle transition zone (MTZ) to clarify its role in plume ascent and surface magmatism. Results demonstrate that the MTZ exerts a significant control on plume behavior, with some plumes ascending directly while others stall and generate secondary upwellings (“baby plumes”), which may contribute to scattered, localized magmatism. The transition from direct ascent to stagnation of the primary (“parent”) thermochemical plume is influenced by temperature, plume volume, Clapeyron slopes, and compositional heterogeneities. Our results highlight the crucial role of the MTZ in how mantle plumes evolve and drive surface magmatism. This provides new insights into why some deep mantle plumes fail to generate LIPs, instead producing widely scattered volcanism.
Are short-term evacuations warranted? Case of the 2009 L'Aquila earthquake
van Stiphout, Thomas; Wiemer, Stefan; Marzocchi, Warner (2010)
Geophysical Research Letters
The disastrous earthquake in L'Aquila Italy (Mw 6.3, 6 April 2009) again highlights the issue of potentially reducing seismic risk by releasing warnings or initiating mitigation actions. Earthquakes cluster strongly in space and time, leading to periods of increased seismic hazard. During such seismic crises, seismologists typically convey their knowledge of earthquake clustering based on past experience, basic statistics and “gut feeling.” However, this information is often not quantitative nor reproducible and difficult for decision-makers to digest. We define a novel interdisciplinary approach that combines probabilistic seismic hazard and risk assessment with cost-benefit analysis to allow objective risk-based decision-making. Our analysis demonstrates that evacuation as mitigation action is rarely cost-effective. Future mitigation strategies should target the weakest buildings and those on the poorest soil.
Very high resolution paleosecular variation record for the last similar to 1200 years from the Aral Sea
Nourgaliev, Danis K.; Heller, Friedrich; Borisov, Anatoly S.; et al. (2003)
Geophysical Research Letters
A record of geomagnetic paleosecular variation (PSV) spanning the last ∼1200 years has been obtained from two lacustrine sediment cores from the north part of Aral Sea (Kazakhstan). Magnetic susceptibility and NRM intensity have been used for correlating between cores and reconstructing composite core data. The main swings and fine details of declination and inclination records correlate well between both cores. A very high sedimentation rate (up to 25 mm per year) due to recent tectonic activity of the region provides a very high resolution PSV record for the interval from 450 ± 100 years BP to 655 ± 65 years BP. The results which have been dated by eight AMS radiocarbon age determinations, suggest that a 200–400 years secular variation period with amplitudes in declination and inclination up to 10–15° existed regularly during the time interval 0–1200 BP. Amplitudes of the PSV record from Aral Sea are not reduced and smoothed by postdetrital magnetization processes. They adjoin to the historical data model and are considered to represent a reliable paleosecular variation record for the Aral Sea region for the last ∼1200 years.
Interplay of Loading and Adsorption Controls Elastic Deformation of Clastic and Crystalline Rocks
Wu , Rui; Kang , Hongpu; Gao , Fuqiang; et al. (2025)
Geophysical Research Letters
Rock elasticity varies with both mechanical loading and moisture content. Studies to date have only examined each effect independently, although moisture interactions with pore walls are likely coupled to mechanical stress. Here, we present experimental data specifically collected in sandstone and granite under simultaneous control of cyclic loading alongside ambient humidity approaching saturated vapor. Adsorption can account for 40% reduction in Young's modulus, which reduces to (Formula presented.) 10% as uniaxial stress increases from below 1 MPa to below the elastic limit. The observation is explained by a micromechanical model linking grain-scale contact stiffness to pore-scale vapor adsorption, quantitatively capturing coupled stress-induced stiffening and adsorption-induced softening. The coupled behavior is interpreted as adsorption-induced softening becoming inhibited under greater mechanical loads. Our results suggest the coupled effects are strongest at overburden stresses between 3.3 and 10.6 MPa (140–450 m) in sandstone and 6–30.3 MPa (235–1,200 m) in granite.
Importance of aerosols in satellite-derived estimates of surface shortwave irradiance over China
Hayasaka, Tadahiro; Kawamoto, Kazuaki; Shi, Guangyu; et al. (2006)
Geophysical Research Letters
Pyranometer measurements and two satellite-derived data sets were used to evaluate surface downward shortwave irradiance over China. Compared to pyranometer measurements, the satellite-derived data overestimated surface shortwave irradiance, particularly over large cities. These positive biases can be attributed to aerosols with absorptive properties; aerosols especially in the sub-cloud layer impact surface shortwave irradiance determinations under cloudy conditions. Satellite-derived radiation data sets are useful. However, aerosols strongly affect surface shortwave irradiance, creating discrepancies between satellite-derived data and pyranometer measurements.
Divergent causes of terrestrial water storage decline between drylands and humid regions globally
An, Linli; Wang, Jida; Huang, Jianping; et al. (2021)
Geophysical Research Letters
Declines in terrestrial water storage (TWS) exacerbate regional water scarcity and global sea level rise. Increasing evidence has shown that recent TWS declines are substantial in ecologically fragile drylands, but the mechanism remains unclear. Here, by synergizing satellite observations and model simulations, we quantitatively attribute TWS trends during 2002–2016 in major climate zones to three mechanistic drivers: climate variability, climate change, and direct human activities. We reveal that climate variability had transitory and limited impacts (<20%), whereas warming-induced glacier loss and direct human activities dominate the TWS loss in humid regions (∼103%) and drylands (∼64%), respectively. In non-glacierized humid areas, climate variability generated regional water gains that offset synchronous TWS declines. Yet in drylands, TWS losses are enduring and more widespread with direct human activities, particularly unsustainable groundwater abstraction. Our findings highlight the substantive human footprints on the already vulnerable arid regions and an imperative need for improved dryland water conservation.
Mantle transition zone variations beneath the Ethiopian Rift and Afar
Cornwell, D.G.; Hetényi, György; Blanchard, T.D. (2011)
Geophysical Research Letters
The mantle transition zone (MTZ) structure beneath the Ethiopian Rift and Afar is mapped using receiver functions. The 410 discontinuity is flat and regionally depressed by 30–40 km, most likely due to a hot (≥+250 °C) and slow (average δVₛ > 3 %) upper mantle. The 660 discontinuity is shown to have variations in depth (665–705 km) over short length scales (<200 km). This results in a MTZ with a ‘normal’ average thickness of 244 km, (i.e., within error of the observed global average). However, local thickness variations (<230 km to >260 km) indicate possible compositional/chemical heterogeneities and elevated ambient temperatures near the base of the MTZ. These observations provide evidence for a link between the low velocity anomalies of the Ethiopian upper mantle and the African Superplume in the lower mantle.
Nonlocal Effects Dominate the Global Mean Surface Temperature Response to the Biogeophysical Effects of Deforestation
Winckler, Johannes; Lejeune, Quentin; Reick, Christian H.; et al. (2019)
Geophysical Research Letters

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