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The 15 January 2022 climactic eruption of Hunga volcano, Tonga, produced an explosion in the atmosphere of a size that has not been documented in the modern geophysical record. The event generated a broad range of atmospheric waves observed globally by various ground-based and spaceborne instrumentation networks. Most prominent was the surface-guided Lamb wave (≲0.01 hertz), which we observed propagating for four (plus three antipodal) passages around Earth over 6 days. As measured by the Lamb wave amplitudes, the climactic Hunga explosion was comparable in size to that of the 1883 Krakatau eruption. The Hunga eruption produced remarkable globally detected infrasound (0.01 to 20 hertz), long-range (~10,000 kilometers) audible sound, and ionospheric perturbations. Seismometers worldwide recorded pure seismic and air-to-ground coupled waves. Air-to-sea coupling likely contributed to fast-arriving tsunamis. Here, we highlight exceptional observations of the atmospheric waves.

In an ongoing effort to improve 3D seismic-wave propagation modeling for frequencies up to 10 Hz, we used cross correlations between vertical-component waveforms from an underground chemical explosion to estimate the statistical properties of small-scale velocity heterogeneities. The waveforms were recorded by a dense 2D seismic array deployed during the Source Physics Experiments for event number 5 (SPE-5) in a series of six underground chemical explosions, conducted at the Nevada National Security Site. The array consisted of 996 geophones with a 50–100 m grid spacing, deployed at the SPE site at the north end of the Yucca Flat basin. The SPE were conducted to investigate the generation and propagation of seismic and acoustic waves from underground explosions.Comparisons of decay rates of waveform cross correlations as function of interstation distance, computed for observed and synthetic seismograms from the SPE-5 chemical explosion, were used to constrain statistical properties of correlated stochastic velocity perturbations representing small-scale heterogeneities added to a geology-based velocity model of the Yucca Flat basin. Using comparisons between recorded and simulated waveform cross correlations, we were able to recover sets of statistical properties of small-scale velocity perturbations in the velocity model that produce the best-fit between the recorded and simulated ground motion. The stochastic velocity fluctuations in the velocity model that produced the smallest misfits have a horizontal correlation distance of between 400 and 800 m, a vertical correlation distance between 100 and 200 m, and a standard deviation of 10% from the nominal model velocity in the alluvium basin layers. They also have a horizontal correlation distance of 1000 m, a vertical correlation distance of 250 m, and a standard deviation of 6% in the underlying and consolidated sedimentary layers, up to a depth of 4 km.Comparisons between observed and simulated wavefields were used to assess the proposed small-scale heterogeneity enhancements to the Yucca Flat basin model. We found that adding a depth-resolved stochastic variability to the geology-based velocity model improves the overall performance of ground-motion simulations of an SPE-5 explosion in the modeled frequency range up to 10 Hz. The results may be applicable to other similar basins.

The Source Physics Experiment (SPE) consists of a series of chemical explosions at the Nevada National Security Site. The goal of the SPE is to understand and model seismic‐wave generation and propagation from these explosions. To achieve this goal, we need an accurate velocity model of the SPE site. A large‐N seismic array deployed at the SPE site during one of the chemical explosions (SPE‐5) provides great data for this purpose. The array consists of 996 geophones and covers an area of approximately 2×2.5 km. In addition to the SPE‐5 explosion, the array recorded 53 large weight drops. Using the large‐N seismic array recordings, we perform first‐arrival analysis and obtain a 2D P‐wave velocity model of the SPE site. We image a sharp transition from high‐velocity Cretaceous granite to low‐velocity Quaternary alluvium. Other geological units such as the Tertiary volcanic rocks and Paleozoic sedimentary rocks are also clearly shown. The results of this work provide important local geological information and will be incorporated into the larger 3D modeling effort of the SPE program to validate the predictive models developed for the site.

Fiber-based interferometry with entangled photons can provide sub-shot-noise resolution, which is ideal for photon-starved applications. Simulations demonstrate that measurements with realistic losses and other imperfections show quantum-enhanced phase resolution for practical applications.

There are benefits from the addition of rotational motions to translational displacements for moment tensor (MT) inversions. The rotational radiation pattern is orthogonal to the shear radiation pa...

Harrat Rahat volcanic field lies along the Makkah-Madinah-Nafud active volcanic line. It has extensive linear weak zones of wrench faults that could provide ideal conduits for upwelling magma and hydrothermal fluids as well. Passive seismic data recorded by seismic stations installed within and around Harrat Rahat has been processed for the detection of microseismic events. Moreover, ambient noise was also gathered and analyzed to construct a subsurface velocity model. This model indicates low velocity zone in Harrat Rahat, and two areas with coincident basement faults and possibly with enhanced subsurface temperatures were identified. It is concluded that Harrat Rahat has high geothermal potential and promising for geothermal renewable power.

Arabian Shield offers a strong potential for geothermal energy. However, only a limited amount of exploration effort has taken place. Harrat Rahat is a recent volcanic area located along the Makkah-Madinah-Nafud volcanic line in western Saudi Arabia. This study is oriented to identify the geothermal potential of Harrat Rahat. The geologic data was collected and processed. In the current study, we focus on evaluating the potential sources of subsurface heat and groundwater. Subsurface heat is based on the age of erupted volcanoes and the expected volume of subsurface magma chambers. An analogy with an existing geothermal field in a similar setting as Mexico suggests that the faults and the coincident seismicity may be associated with higher permeability. It is concluded that Harrat Rahat is characterized by a good geothermal potential for future geothermal energy source production.

© 2017 The Author(s) At Brady Hot Springs, a geothermal field in Nevada, heated fluids have been extracted, cooled, and re-injected to produce electrical power since 1992. Analysis of daily pumping records and catalogs of microseismicity between 2010 and 2015 indicates a statistically significant correlation between days when the daily volume of production was at or above its long-term average rate and days when no seismic event was detected. Conversely, shutdowns in pumping for plant maintenance correlate with increased microseismicity. We hypothesize that the effective stress in the subsurface has adapted to the long-term normal operations (deep extraction) at the site. Under this hypothesis, extraction of fluids inhibits fault slip by increasing the effective stress on faults; in contrast, brief pumping cessations represent times when effective stress is decreased below its long-term average, increasing the likelihood of microseismicity.

Using fiber-optic cables as distributed sensors to monitor the subsurface is one of the fastest growing acquisition technologies in the hydrocarbon energy sector. Since the first exploration and production downhole field trial of a Distributed Acoustic Sensing (DAS) system for seismic monitoring in 2009, the technology has boomed. It has already proven to be an effective tool for acquiring vertical seismic profiles (VSP), performing passive interferometric measurements, and monitoring of microseismic earthquakes. DAS cables record seismo-acoustic wavefields and ground motions because ground-motion-induced changes in strain on the fiber affect the phase of back-scattered light in the fiber. Commercially available systems already provide sub-meter spatial resolution in sensing fibers up to 50 km in length with a frequency response up to several kHz. This exceeds the frequency range and spatial coverage of conventional seismic sensors. As a result, surface and borehole monitoring with DAS in addition to traditional sensors will most likely form a central component of future Measurement, Monitoring and Verification (MMV) systems for CO2 storage. DAS, however, does possess some key disadvantages in that it only provides a single component measurement which is most sensitive to motions in line with the fiber. DAS also measures linear strain rather than particle motion, meaning the recorded signals are not directly comparable to conventional sensors. In order to better understand the response of DAS it is therefore necessary to understand the seismic source, path, site and instrument effects. The ACT DIGIMON project aims to develop and demonstrate an affordable, flexible and societally embedded Digital Monitoring early-warning system, for monitoring CO2 storage sites. Within the DIGIMON concept fiber-optic monitoring will form a key component, therefore a thorough understanding of the response of DAS systems, including the transfer function, is a fundamental issue to be addressed. In this paper we present our modeling approach for the DAS response for a fictive CO2 storage site. The workflow exploits geometrical models of different complexity which in the end are representative of North Sea geology. Using ray tracing techniques and the seismic waveform modelling packages: SW4 and SPECFEM3D, we were able to analyze and compare these modeling approaches in relation to the response of a DAS system. With varying model complexity, we accurately capture and analyze the DAS response for realistic cable geometries. These geometries represent both vertical and horizontal deployments, which replicate fiber placed in wells and deployed on the seabed and or in shallow trenches.

The role of gamification in Australian higher educational learning has gained increasing currency in recent years, with many proponents promoting its usefulness for improving the university student experience by increasing progression and lowering attrition, particularly among first year students (Charles, Charles, McNeill, Bustard, & Black, 2011). However, some students express reservations that the inherently competitive nature of some gamified learning activities negatively impact their learning experience, especially when compared to classic instructional methods (Charles et al., 2011). This discussion and instructional paper undertakes a review of the gamification literature within the Australian higher education context, concurrently exploring what it means and how to use gamification to enhance student learning. The paper provides a short biographic summary of the positive impact selected popular gamified activities has had on improving student engagement, participation and retention in tertiary settings.

Low-dimensional spinel ferrites have recently attracted increasing attention because their tunable magnetic properties make them attractive candidates as spin-filtering tunnel barriers in spintronic devices and as magnetic components in artificial multiferroic heterostructures. Although we know that the distribution of cations (Fe3+ and Co2+) in a spinel structure governs its magnetic properties, their distribution in the so-called ideal inverse spinel structure of a ferrite, CoFe2O4, has not yet been imaged with sub-angstrom resolution. In this work, we fill this gap in evidence by reporting a direct observation of the distribution of cations in an ideal inverse spinel structure of CoFe2O4 nanofibres using aberration-corrected transmission electron microscopy (TEM). The ordering of Co2+ and Fe3+ at the octahedral sites imaged along either [001], [011] or [-112] orientation was identified as 1 : 1, in accordance with the ideal inverse spinel structure. The saturation magnetisation calculated based on the crystal structure as determined from the TEM image is in good agreement with that measured experimentally on the spinel CoFe2O4 nanofibres, further confirming results from TEM.

One challenging task in explosion seismology is the development of physical models for explaining the generation of S waves during underground explosions. Recent analysis of ground motion from chemical explosions during the Source Physics Experiment (Pitarka et al. , 2015) suggests that, although a large component of shear motion was generated directly at the source, additional scattering from heterogeneous velocity structure and topography is necessary to better match the recorded data. In our study, we used a stochastic representation of small‐scale velocity variability to produce high‐frequency scattering and to analyze its implication on shear‐motion generation during underground explosions. In our stochastic velocity model, the key parameters that affect scattering are the correlation length and the relative amplitude of velocity perturbations. Based on finite‐difference simulations of elastic wave propagation from an isotropic explosion source, we find that higher velocity perturbations result in larger shear motion, whereas the correlation length, which controls the scatterers size, affects the frequency range at which relative transverse motion is larger.

In this study, we analyzed the performance of a preliminary three-dimensional (3D) velocity model of the Eastern Caucasus covering most of the Azerbaijan. The model was developed in support to long-period ground motion simulations and seismic hazard assessment from regional earthquakes in Azerbaijan. The model’s performance was investigated by simulating ground motion from the damaging Mw 5.9, 2012 Zaqatala earthquake, which was well recorded throughout the region by broadband seismic instruments. In our simulations, we use a parallelized finite-difference method of fourth-order accuracy. The comparison between the simulated and recorded ground motion velocity in the modeled period range of 3–20 s shows that in general, the 3D velocity model performs well. Areas in which the model needs improvements are located mainly in the central part of the Kura basin and in the Caspian Sea coastal areas. Comparisons of simulated ground motion using our 3D velocity model and corresponding 1D regional velocity model were used to locate areas with strong 3D wave propagation effects. In areas with complex underground structure, the 1D model fails to produce the observed ground motion amplitude and duration, and spatial extend of ground motion amplification caused by wave propagation effects.

© 2016 The Authors. We analyze interferometric synthetic aperture radar (InSAR) data acquired between 2004 and 2014, by the ERS-2, Envisat, ALOS and TerraSAR-X/TanDEM-X satellite missions to measure and characterize time-dependent deformation at the Brady Hot Springs geothermal field in western Nevada due to extraction of fluids. The long axis of the ~4 km by ~1.5 km elliptical subsiding area coincides with the strike of the dominant normal fault system at Brady. Within this bowl of subsidence, the interference pattern shows several smaller features with length scales of the order of ~1 km. This signature occurs consistently in all of the well-correlated interferometric pairs spanning several months. Results from inverse modeling suggest that the deformation is a result of volumetric contraction in shallow units, no deeper than 600 m, likely associated with damaged regions where fault segments mechanically interact. Such damaged zones are expected to extend downward along steeply dipping fault planes, providing a high permeability conduit to the production wells. Using time series analysis, we test the hypothesis that geothermal production drives the observed deformation. We find a good correlation between the observed deformation rate and the rate of production in the shallow wells. We also explore mechanisms that could potentially cause the observed deformation, including thermal contraction of rock, decline in pore pressure and dissolution of minerals over time.

Saudi Arabia offers a strong potential for geothermal energy, but only a limited amount of exploration efforts has taken place. We conducted a preliminary, low-cost, reconnaissance level evaluation of the western volcanic areas (harrats) based on mapped geology and existing seismic data. The emphasis is on the Harrat Rahat volcanic area in western Saudi Arabia although a survey of other major harrats is conducted using geologic data. The goal is to test the procedure and identify areas for future, more intensive study.

Imaging subsurface rock formations or geological objects like oil and gas reservoirs, mineral deposits, cavities or even magmatic plumbing systems under active volcanoes has been for many years a major quest of geoscientists. Since these subsurface objects cannot be observed directly, different indirect methods have been developed. These methods are all based on variations of certain physical properties of the subsurface materials that can be detected from the ground surface or from boreholes. To determine the density distribution, a new imaging technique using cosmic-ray muon detectors deployed in a borehole has been developed and a first prototype of a borehole muon detector successfully tested. In addition to providing a static image of the subsurface density in three dimensions (or three-dimensional tomography), borehole muography can also inform on the variations of density with time, which recently became of major importance with the injection of large volumes of fluids, mainly water and CO 2 , in porous subsurface reservoirs (e.g. aquifer storage and recovery, wastewater disposal, enhanced oil recovery and carbon sequestration). This raises several concerns about the risk of leakage and the mechanical integrity of the reservoirs. Determining the field scale induced displacement of fluids by geophysical methods like muography is thus a priority. This article is part of the Theo Murphy meeting issue ‘Cosmic-ray muography'.

We investigate the excitation and propagation of far‐field seismic waves from the 905 kg trinitrotoluene equivalent underground chemical explosion SPE‐3 recorded during the Source Physics Experiment (SPE) at the Nevada National Security Site. The recorded far‐field ground motion at short and long distances is characterized by substantial shear‐wave energy, and large azimuthal variations in P ‐ and S ‐wave amplitudes. The shear waves observed on the transverse component of sensors at epicentral distances