地球科学最新文献

Offset geomorphic markers are commonly used to interpret slip history of strike-slip faults and have played an important role in forming earthquake recurrence models. These data sets are typically analyzed using cumulative probability methods to interpret average amounts of slip in past earthquakes. However, interpretation of the geomorphic record to infer surface slip history is complicated by slip variability, measurement uncertainty, and modification of offset features in the landscape. To investigate how well geomorphic data record surface slip, we use offset measurements from recent strike-slip surface ruptures (n = 39), faults with geomorphic evidence of multiple strike-slip earthquakes (n = 29), and synthetic slip distributions with added noise (n$��>�$10,000) to examine the constraints of the geomorphic record and the underlying assumptions of the cumulative offset probability distribution analysis method. We find that the geomorphic record is unlikely to resolve more than two paleo-slip distributions, except in specific cases with low slip variability, high slip-per-event, and semiarid climate. In cases where site-specific conditions allow for interpretation of more than two earthquakes, lateral extrapolation along a fault is not straightforward because on-fault displacement and distributed deformation may be spatially variable in each earthquake. We also find that average slip in modern earthquakes is adequately recovered by probability methods, but the reported prevalence of strike-slip faults with characteristic slip history is not supported by geomorphic data. We also propose updated methods to interpret slip history and construct uncertainty bounds for paleo-slip distributions.

We present statistical distributions of whistler-mode chorus and hiss waves at frequencies ranging from the local proton gyrofrequency to the equatorial electron gyrofrequency (f_ce,eq) in Jupiter's magnetosphere based on Juno measurements. The chorus wave power spectral densities usually follow the f_ce,eq variation with major wave power concentrated in the 0.05f_ce,eq–f_ce,eq frequency range. The hiss wave frequencies are less dependent on f_ce,eq variation than chorus with major power concentrated below 0.05f_ce,eq, showing a separation from chorus at M < 10. Our survey indicates that chorus waves are mainly observed at 5.5 < M < 13 from the magnetic equator to 20° latitude, consistent with local wave generation near the equator and damping effects. The hiss wave powers extend to 50° latitude, suggesting longer wave propagation paths without attenuation. Our survey also includes the whistler-mode waves at high latitudes which may originate from the Io footprint, auroral hiss, or propagating hiss waves reflected to high M shells.

Ganymede is the only known moon with an active dynamo. No mission has discovered intrinsic magnetism at the other Galilean satellites: Io, Europa, and Callisto. A dynamo requires a large magnetic Reynolds number, which in turn demands, for these moons, a large metallic core that is cooling fast enough for convection. Here we quantify these requirements to construct a regime diagram for the Galilean satellites. We compute the internal heat fluxes that would sustain a dynamo over the wide ranges of plausible radii for their metallic cores. Below a critical radius, no plausible heat flux will sustain a dynamo. Europa likely sits on the opposite side of this limit than Ganymede and Io. We predict that future missions may confirm a small (or absent) core, meaning that Europa could not sustain a dynamo even if its interior were cooling as quickly as Ganymede's core.

Severe convection, responsible for hazards such as tornadoes, flash floods, and hail, is usually preceded by abundant convective available potential energy (CAPE). In this work, we use a Lagrangian approach to study the buildup of anomalously large values of CAPE from 2012 to 2013 in various regions. Nearly all extreme values of CAPE arise from surface fluxes underneath a layer of convective inhibition (the CIN layer) over several diurnal cycles, but the origin of the CIN layer and the diurnal cycle of surface fluxes differ around the world. In some regions, such as North America and Europe, the air above the boundary layer must be much warmer than usual to form this CIN layer, whereas in other regions, especially the Middle East and central Africa, a CIN layer is common. Additionally, high CAPE occurrences that are over land (those in the Americas, Europe, Africa, and Southeast Asia) tend to lose their CIN layers before the time of maximum CAPE due to large diurnal cycles of sensible heating, whereas those that occur over coastal waters (in the Middle East, Northern Australia, South Asia, and the Mediterranean) usually retain substantial convective inhibition. Uniquely, CAPE in Southeast Australia often builds up due to cooling aloft rather than to boundary layer warming. These results show that one hoping to understand or predict CAPE patterns must understand a variety of mechanisms acting in different regions.

The economies and livelihoods of many coastal megacities are at serious risk from flooding, despite investments in flood defenses. For instance, in Ho Chi Minh City, the construction of a large-scale ring-dike has mitigated negative effects from storm surges, yet damage is still frequently caused by high-intensity rainfalls leading to nuisance flooding, which is responsible for the highest proportion of flood losses in the city today. Because sustainable flood risk management requires detailed spatial information, we analyze the local risk and its components based on a chain of novel models previously calibrated and validated for Ho Chi Minh City. Furthermore, we assess the effectiveness of two decentralized adaptation options, namely private precautionary measures and rainwater retention, for mitigating pluvial flooding. Our integrated risk assessment reveals that the approaches are complementary, which is a major advantage for their implementation. Implementation of both approaches has the potential to reduce the expected annual damage and the number of annually affected households by 16% and 56%, respectively. This is also reflected in a significant reduction of annual losses per household, which we propose as an additional, people-centered indicator of flood risk. Moreover, these measures are well-suited to strengthen citizen participation in risk reduction beyond top-down protection schemes. Complementing the ring-dike with decentralized adaptation options can therefore be seen as an effective and generic strategy to alleviate the impacts of nuisance flooding in coastal megacities, such as Ho Chi Minh City, and should be incentivized by decision-makers. Aside from hydrological and metocean site conditions, both the methodology and findings of this study are transferrable to any coastal megacity facing similar challenges.

Coal and gas desorption, as a major form of gas energy release, is a key factor in triggering coal and gas outbursts. Therefore, studying the physical characteristics during coal and gas desorption is essential for understanding the development process of coal and gas outbursts. Based on gas dynamics during coal particle gas desorption, this study established a connection between gas desorption and infrasound signals, elaborating on the generation mechanism of infrasound signals during coal particle gas desorption and validating the feasibility of the theory through experimental data, thereby demonstrating the spontaneous occurrence of subsonic tremors during coal particle gas desorption. Combining observational data, it was found that the peak value of infrasound signals generated during desorption experiments is correlated positively with the initial pressure; while, the dominant frequency of infrasound signals is influenced by the proportion of intergranular pores and fractures within the experimental vessel. To further validate the theory of subsonic generation, a mathematical model describing pressure oscillations within intergranular pores, thereby explaining the mechanism of subsonic tremors, was established. The model confirms that the generation and characteristics of infrasound signals are controlled by the parameters of intergranular pores in coal samples. The model effectively simulates changes in the characteristics of infrasound signal tremors during desorption under different conditions, confirming that the physical properties of intergranular pores are crucial factors influencing the generation of infrasound signals and their characteristics during coal and gas desorption.