Azimuthal Coverage Research Articles

Crust and uppermost mantle S-wave velocity structure of the Wudalianchi volcanic belt from direct surface-wave tomography

The Wudalianchi volcanic belt is located at the junction among the Greater Xing’an range, the Lesser Xing’an range, and the Songliao basin. Investigation of detailed crustal velocity structure under the Wudalianchi volcanic belt is of great significance to better understand the deep geodynamics of Northeast Asia. Applying the direct surface-wave tomography method to ambient noise records of our newly deployed dense WAVESArray stations from 2015 to 2019, we aim to determine a high-resolution three-dimensional (3-D) S-wave velocity (Vs) model of the crust and uppermost mantle down to 45 km depth beneath the Wudalianchi volcanic belt and surrounding areas. The WAVESArray stations have good azimuthal coverage around the Wudalianchi volcano. Our high-resolution tomographic model reveals low-Vs anomalies in the upper crust and the uppermost mantle beneath the Wudalianchi volcano and high-Vs anomalies in the mid-lower crust, indicating the presence of hot mantle upwelling and lower crust cooling solidification. This upwelling process is related to the complex dynamics of the big mantle wedge that has developed above the subducted Pacific slab that is stagnant in the mantle transition zone beneath East Asia. In addition, low-Vs anomalies are visible beneath the Erkeshan, Wudalianchi, Keluo, and Xunke volcanoes in the upper crust and they are connected with a low-Vs layer in the mid-lower crust, which provides a new piece of seismological evidence for the homology of these volcanoes, suggesting that there might be exchanges of material and energy between these volcanoes.

A quantitative assessment of GeoNet earthquake location quality in Aotearoa New Zealand

ABSTRACT Tens of thousands of earthquakes are located by GeoNet across Aotearoa every year. However, spatial variability – both in station coverage and earthquake distributions – produce heterogeneity in earthquake location quality throughout the GeoNet catalogue. Here we consider simple, established criteria (including station azimuthal coverage, minimum station distance, phase arrival coverage and fixed location criteria) to score earthquakes on a network location Quality Score (QS) scale of QS0 (unconstrained) to QS6 (best constrained). Significant variation in QS exists nationwide; 48% and 20% of earthquakes score QS6 for the North and South Islands respectively. The Hawkes Bay region scores highest (68% QS6) closely followed by other Hikurangi regions. However, several regions score extremely poorly, with Fiordland, West Coast, Nelson, Otago-Southland and Auckland-Northland regions having ≤5% QS6 events and >75% of events scoring QS3 or lower. Low QS mostly arises from the failure of minimum distance criteria, whereby the closest station is too far from the earthquake to provide sufficient depth control. Our analysis quantitatively assesses the impact of network heterogeneity on GeoNet earthquake catalogue location quality to inform end users. This work also provides motivation for the expansion of the weak-motion network in critically under-instrumented regions, especially those with high seismic hazard.

The Korean infrasound catalogue (1999–2022)

SUMMARY The Korean infrasound catalogue (KIC) covers 1999–2022 and characterizes a rich variety of source types as well as document the effects of the time-varying atmosphere on event detection and location across the Korean Peninsula. The KIC is produced using data from six South Korean infrasound arrays that are cooperatively operated by Southern Methodist University and Korea Institute of Geoscience and Mineral Resources. Signal detection relies on an Adaptive F-Detector that estimates arrival time and backazimuth, which draws a distinction between detection and parameter estimation. Detections and associated parameters are input into a Bayesian Infrasonic Source Location procedure. The resulting KIC contains 38 455 infrasound events and documents repeated events from several locations. The catalogue includes many anthropogenic sources such as an industrial chemical explosion, explosions at limestone open-pit mines and quarries, North Korean underground nuclear explosions and other atmospheric or underwater events of unknown origin. Most events in the KIC occur during working hours and days, suggesting a dominance of human-related signals. The expansion of infrasound arrays over the years in South Korea and the inclusion of data from the International Monitoring System infrasound stations in Russia and Japan increase the number of infrasound events and improve location accuracy because of the increase in azimuthal station coverage. A review of selected events and associated signals at multiple arrays provides a location quality assessment. We quantify infrasound events that have accompanying seismic arrivals (seismoacoustic events) to support the source type assessment. Ray tracing using the Ground-to-Space (G2S) atmospheric model generally predicts observed arrivals when strong stratospheric winds exist, although the predicted arrival times have significant discrepancies. In some cases, local atmospheric data better captures small-scale variations in the wind velocity of the shallow atmosphere and can improve arrival time predictions that are not well matched by the G2S model. The analysis of selected events also illustrates the importance of topographic effects on tropospheric infrasound propagation at local distances. The KIC is the first infrasound catalogue compiled in this region, and it can serve as a valuable data set in developing more robust infrasound source localization and characterization methods.

A Low-Profile Pattern and Polarization Diversity Dual-Band MIMO Antenna with Full Azimuth Coverage for Indoor Access Points

A Low-Profile Pattern and Polarization Diversity Dual-Band MIMO Antenna with Full Azimuth Coverage for Indoor Access Points

Characteristics of Earthquake Mechanisms Along the Andaman - Nicobar Region derived from Bayesian Moment Tensor Inversion

Abstract Earthquake activities in the Andaman - Nicobar region are generated mainly by several active faults and an active subduction zone that can activate multiple hypocenter clusters. Therefore, studying the seismotectonic process from source mechanism analysis using moment tensor inversion is essential. In this research, we applied a stochastic Bayesian inversion using Grond, a framework tool for moment tensor (MT) inversion, to characterize the earthquake mechanisms and the most appropriate centroid locations. Procedurally, several of the largest earthquakes with a moment magnitude Mw > 5.5 from 2007 to 2023 were analyzed using the regional and teleseismic networks up to 2000 km from the epicenter based on 1 Hz green function model and azimuthal gap coverage. We applied 10,000-30,000 iterations of inversions with 300 bootstrap chains for a stable result. The low-frequency bandpass with a range of 0.007 - 0.03 Hz was chosen for the inversion process. There were 17 solutions for earthquake mechanisms with good misfit values of < 0.65. Based on the division of the 5 clusters with the highest seismicity, the selected earthquakes’ source mechanism is dominated by strike-slip and oblique faulting. The results were compared with existing data catalogs showing differences in hypocentre and fault orientation direction, particularly for strike-slip earthquakes in the shallow crust and mantle zones.

Simultaneous magnitude and slip distribution characterization from high-rate GNSS using deep learning: case studies of the 2021 Mw 7.4 Maduo and 2023 Turkey doublet events

SUMMARY Rapid and accurate characterization of earthquake sources is crucial for mitigating seismic hazards. In this study, based on 18 000 scenario ruptures ranging from Mw 6.4 to Mw 8.3 and corresponding synthetic high-rate Global Navigation Satellite System (HR-GNSS) waveforms, we developed a multibranch neural network framework, the continental large earthquake agile response (CLEAR), to simultaneously determine the magnitude and slip distributions. We apply CLEAR to recent large strike-slip events, including the 2021 Mw 7.4 Maduo earthquake and the 2023 Mw 7.8 and Mw 7.6 Turkey doublet. The model generally estimates the magnitudes successfully at 32 s with errors of less than 0.15, and predicts the slip distributions acceptably at 64 s, requiring only approximately 30 ms on a single CPU (Central Processing Unit). With optimal azimuthal coverage of stations, the system is relatively robust to the number of stations and the time length of the received data.

Empirical Green’s function analysis of some induced earthquake pairs from the Groningen gas field

We have applied the empirical Green’s function (EGF) method to 53 pairs of earthquakes, with magnitudes ranging from M = 0.4 to M = 3.4, induced by gas production from the Groningen field in the Netherlands. For a subset of the events processed, we find that the relative source time functions obtained by the EGF deconvolution show clear indications of a horizontal component of rupture propagation. The earthquake monitoring network used has dense azimuthal coverage for nearly all events such that wavelet duration times can be picked as a function of source-station azimuth and inverted using the usual Doppler broadening model to estimate rupture propagation strike, distance, and velocity. Average slip velocities have also been estimated and found to be in agreement with typical published values. We have used synthetic data, from both a simple convolutional model of the seismogram and more sophisticated finite difference rupture simulations, to validate our data processing workflow and develop kinematic models which can explain the observed characteristics of the field data. Using a measure based on the L1-norm to discriminate results of differing quality, we find that the highest quality results show very good alignment of the rupture propagation with directions of the detailed fault map, obtained from the full-field 3D seismic data. The dip direction rupture extents were estimated from the horizontal rupture propagation distances and catalogue magnitudes showing that, for all but the largest magnitude event (the M = 3.4 event of 8th January 2018), the dip-direction extent is sufficiently small to be contained wholly within the reservoir.

A low-profile high-isolation endfire MIMO antenna based on spoof surface plasmon polaritons for X-band applications

This work proposes a three-port, low-profile, coplanar endfire multiple-input-multiple-output (MIMO) antenna based on spoof surface plasmon polaritons (SSPPs). The proposed antenna comprises a coplanar waveguide (CPW)-fed SSPPs transmission line (TL). A transition to transform the CPW quasi-TEM mode to the SSPPs mode. The radiator section with asymmetric discontinuities converts the bounded SSPPs waves into radiating waves. The proposed MIMO antenna exploits the inherent feature of high isolation in the SSPPs TL due to its strong field confinement competency. Wider beamwidths for ample azimuth and elevation coverage with a stable pattern in the endfire direction are achieved in the 9.52–11.23 GHz operating band. In the operating band, the MIMO antenna has an average realized gain of 6 dBi. Mainly, it has high isolation below -35 dB (measured) in the operating range, a maximum envelope correlation coefficient (ECC) of 1.5 × 10−3, and a total active reflection coefficient (TARC) value below 0.3. The measured results are closely matched with the simulated ones in terms of S-parameters, radiation pattern, ECC, TARC, and CCL.

Two-dimensional kinematics and dynamical modelling of the ‘Jackpot’ gravitational lens from deep MUSE observations

ABSTRACT We present results from the first spatially resolved kinematic and dynamical modelling analysis of the unique SDSSJ0946+1006 (‘Jackpot’) triple-source lens system, where a single massive foreground $z\, =\, 0.222$ galaxy multiple-images three background sources at different redshifts. Deep integral field unit spectroscopic data were obtained using the MUSE instrument on the VLT, which, compared to previous single-slit observations, provides full azimuthal area coverage, high sensitivity (5 h integration) and high angular resolution (0.5 arcsec full width at half-maximum). To account for the strong continuum contributions from the $z\, =\, 0.609$ source, a multiple-component stellar template fitting technique is adopted to fit to the spectra of both the lens galaxy and the bright lensed background arc simultaneously. Through this, we robustly measure the first and second moments of the 2D stellar kinematics out to about 10 kpc from the centre of the lens, as well as resolving the inner profile inwards to ∼1 kpc. The 2D kinematic maps show a steep velocity dispersion gradient and a clear rotational component. We constrain the characteristic properties of the stellar and dark matter (DM) mass components with a sufficiently flexible parametrised dynamical model and an imposed lensing mass and find a DM density slope of $\gamma \, =\, 1.73\substack{+0.17 \\ -0.26}$, i.e. significantly steeper than an unmodified NFW profile ($\gamma \, =\, 1$) and consistent with a contracted DM halo. Our fitted models have a lensing-equivalent density slope of $\eta \, =\, 0.96\pm 0.02$, and thus we confirm most pure lensing results in finding a near isothermal profile for this galaxy.

CANVAS: An Adjoint Waveform Tomography Model of California and Nevada

AbstractWe present the California‐Nevada Adjoint Simulations (CANVAS) model, an adjoint waveform tomography model of the crust and uppermost mantle of the states of California and Nevada. We used WUS256 (Rodgers et al., 2022, https://doi.org/10.1029/2022jb024549) as the starting model and iteratively decreased the minimum period of CANVAS from 30 to 12 s. CANVAS was iterated in two distinct stages: the first stage with source mechanisms from the Global Centroid Moment Tensor (GCMT) catalog and the second stage with inverted moment tensors (MT) using the CANV_WUS model (Doody et al., 2023, https://doi.org/10.1029/2023jb026463). We show that updating the MTs with 3D Green's functions improved waveform fits and azimuthal coverage of windowed data used to calculate the gradients. As for the model itself, we improved waveform fits over WUS256, particularly in the dispersed surface waves. CANVAS resolved tectonic features seen in other models and accurately defined the depth to basement of major basins, including the Central Valley and the Ventura Basin. We propose CANVAS as a starting model for crustal tomography models on smaller scales.

Adjoint Inversion of Near‐Field Pressure Gauge Recordings for Rapid and Accurate Tsunami Source Characterization

AbstractWe explore the potential of the adjoint‐state tsunami inversion method for rapid and accurate near‐field tsunami source characterization using S‐net, an array of ocean bottom pressure gauges. Compared to earthquake‐based methods, this method can obtain more accurate predictions for the initial water elevation of the tsunami source, including potential secondary sources, leading to accurate water height and wave run‐up predictions. Unlike finite‐fault tsunami source inversions, the adjoint method achieves high‐resolution results without requiring densely gridded Green's functions, reducing computation time. However, optimal results require a dense instrument network with sufficient azimuthal coverage. S‐net meets these requirements and reduces data collection time, facilitating the inversion and timely issuance of tsunami warnings. Since the method has not yet been applied to dense, near‐field data, we test it on synthetic waveforms of the 2011 Mw 9.0 Tohoku earthquake and tsunami, including triggered secondary sources. The results indicate that with a static source model without noise, using the first 5 min of the waveforms yields a favorable performance with an average accuracy score of 93%, and the largest error of predicted wave amplitudes ranges between −5.6 and 1.9 m. Using the first 20 min, secondary sources were clearly resolved. We also demonstrate the method's applicability using S‐net recordings of the 2016 Mw 6.9 Fukushima earthquake. The findings suggest that lower‐magnitude events require a longer waveform duration for accurate adjoint inversion. Moreover, the estimated stress drop obtained from inverting our obtained tsunami source, assuming uniform slip, aligns with estimations from recent studies.

Hydraulic fracturing distributed acoustic sensing monitoring data source mechanism inversion: A Hessian-based method

Distributed acoustic sensing (DAS) microseismic monitoring during hydraulic fracturing provides microseismic data with high spatial samplings for fracturing zones. However, sources located perpendicular to the single horizontal well of the DAS acquisition system have limited source-receiver geometries with extremely poor azimuthal coverage, resulting in high uncertainty in source mechanism inversion. To address this problem, we introduce the Hessian matrix, which governs the blurring effect caused by the source-receiver geometry, into the DAS microseismic source mechanism inversion. Our Hessian-based source mechanism inversion method consists of three main steps: (1) construct the Hessian matrix of the source mechanism based on the source-receiver geometry, (2) obtain an initial source mechanism using a conventional source mechanism inversion method, and (3) update the initial source mechanism using a Hessian-based [Formula: see text]-regularized least-squares algorithm. We assess the robustness of our method using synthetic DAS microseismic data with the consideration of noise, source location error, and different regularization parameters, and we compare the results with those of the conventional method. The results demonstrate that the Hessian-based method has a remarkable ability to mitigate the blurring effect of the Hessian matrix caused by limited DAS source-receiver geometry with poor azimuthal coverage, thereby reducing the uncertainty of the inverted source mechanism even in the presence of real noise and/or source location error. Finally, we use our method to invert the source mechanism of a real DAS microseismic event acquired during hydraulic fracturing. Our Hessian-based method provides low uncertainty in the source mechanism inversion of the real DAS microseismic data.

Directional Resonant MEMS Acoustic Sensor and Associated Acoustic Vector Sensor.

This paper reports on the design, modeling, analysis, and evaluation of a micro-electromechanical systems acoustic sensor and the novel design of an acoustic vector sensor array (AVS) which utilized this acoustic sensor. This research builds upon previous work conducted to develop a small, lightweight, portable system for the detection and location of quiet or distant acoustic sources of interest. This study also reports on the underwater operation of this sensor and AVS. Studies were conducted in the lab and in the field utilizing multiple acoustic sources (e.g., generated tones, gun shots, drones). The sensor operates at resonance, providing for high acoustic sensitivity and a high signal-to-noise ratio (SNR). The sensor demonstrated a maximum SNR of 88 dB with an associated sensitivity of -84.6 dB re 1 V/μPa (59 V/Pa). The sensor design can be adjusted to set a specified resonant frequency to align with a known acoustic signature of interest. The AVS demonstrated an unambiguous, 360-degree, in-plane, azimuthal coverage and was able to provide an acoustic direction of arrival to an average error of within 3.5° during field experiments. The results of this research demonstrate the potential usefulness of this sensor and AVS design for specific applications.

Outskirts of Abell 1795: Probing gas clumping in the intracluster medium

Contact. The outskirts of galaxy clusters host complex interactions between the intracluster and circumcluster media. During the evolution of clusters, ram-pressure stripped gas clumps from infalling substructures break the uniformity of the gas distribution, potentially leading to observational biases at large radii. However, assessing the contribution of gas clumping poses observational challenges and requires robust X-ray measurements in the background-dominated regime of the cluster outskirts. Aims. The main objectives of this study are to isolate faint gas clumps from field sources and from the diffuse emission in the Abell 1795 galaxy cluster, then to probe their impact on the observed surface brightness and thermodynamic profiles. Methods. We performed an imaging analysis on deep Chandra ACIS-I observations of the Abell 1795 cluster outskirts, extending out to ∼1.5r200 with full azimuthal coverage. We built the 0.7 − 2.0 keV surface brightness distribution from the adaptively binned image of the diffuse emission and looked for clumps in the form of > + 2σ surface brightness outliers. Our classification of the clump candidates was based primarily on Chandra and SDSS data. Benefiting from the point source list resolved by Chandra, we extracted the thermodynamic profiles of the intracluster medium from the associated Suzaku XIS data out to r200 using multiple point source and clump candidate removal approaches. Results. We identified 24 clump candidates in the Abell 1795 field, most of which are likely to be associated with background objects, including active galactic nuclei, galaxies, and clusters or groups of galaxies, as opposed to intrinsic gas clumps. These sources had minimal impact on the surface brightness and thermodynamic profiles of the cluster emission. After correcting for clump candidates, the measured entropy profile still deviates from a pure gravitational collapse, suggesting complex physics at play in the outskirts, which may include potential electron–ion non-equilibrium and non-thermal pressure support.

Forge ahead in acquisition and model building via full-waveform inversion: Gulf of Mexico case study

Full-waveform inversion (FWI) has proven itself an essential tool for velocity model building using seismic data. In recent years, the geophysical community has made substantial progress in developing FWI to overcome some long-standing limitations, such as handling cycle skipping, better using reflection energy, including more physics in the inversion algorithms, and increasing inverted frequencies to achieve higher resolution. FWI does not only target the larger and midscale model updates, more and more FWI examples were presented with increased resolution which allows for extraction of FWI derived reflectivity. Interrogating the FWI kernel with given geology and acquisition geometry can provide critical information on how the acquisition design should be optimized to provide FWI a better opportunity to update the velocity model at target depth, especially in the deep part of the model. When the acquisition geometry is different in terms of offsets, azimuthal coverage, and the minimum frequency in the recording, it can be analyzed to design workflows to enable FWI to optimally update the model parameters. Obviously, recent ocean-bottom node acquisitions that record long offsets, full azimuth, and low frequencies have made FWI shine in the seismic industry. Modifying and reshaping a complex salt geometry is one of the ultimate goals of FWI. In addition to the salt boundary being an issue, there is a potential cycle-skipping problem associated with uncertainties of large salt bodies missing or misplaced even though the frequencies used to start FWI are becoming lower due to the advancement in seismic acquisition and FWI algorithms. Furthermore, if the FWI-predicted data are simulated with an acoustic engine, it could pose amplitude and phase discrepancies at high-velocity contrast interfaces. Elastic FWI alone has been proposed as a means of overcoming these challenges associated with salt and regions with high-velocity contrast. We determine the FWI progress of the past few decades with the latest examples from different acquisition geometries.

A High-Gain Dual-Band Multibeam Antenna System for MIMO Wi-Fi Application

A compact dual-band multibeam antenna system with high gain is presented for multiple-input-multiple-output (MIMO) Wi-Fi application. The antenna system is composed of four rotationally symmetric antenna panels occupying a compact size of 60 × 200 × 7.2 mm3. Two series-fed microstrip patch antenna (MPA) arrays are proposed to operate at the 5-GHz band. They are fed with ±90° phase difference signals for two directional radiation patterns with about 45° horizontal 3-dB beamwidth and distinct radiation directions. Two dual-function metasurface based on periodically loaded parallel lines is designed and compactly placed between the two MPA arrays. The metasurface works as a 2.4-GHz antenna with about 90° 3-dB beamwidth in the azimuth. Besides, the application of metasurface improves the gains at the 5-GHz band. Then, four antenna panels are placed in a rotating arrangement with an electric size of 0.59λL × 0.59λL × 1.57λL (λL is the free-space wavelength at the lowest operating frequency). The antenna system was manufactured and demonstrated the characteristics of 360° pattern coverage in azimuth and high gain. The measured average gains are respectively higher than 8 dB and 12 dB at the 2.4-and 5-GHz bands.

Earthquake focal mechanisms with distributed acoustic sensing

Earthquake focal mechanisms provide critical in-situ insights about the subsurface faulting geometry and stress state. For frequent small earthquakes (magnitude< 3.5), their focal mechanisms are routinely determined using first-arrival polarities picked on the vertical component of seismometers. Nevertheless, their quality is usually limited by the azimuthal coverage of the local seismic network. The emerging distributed acoustic sensing (DAS) technology, which can convert pre-existing telecommunication cables into arrays of strain/strain-rate meters, can potentially fill the azimuthal gap and enhance constraints on the nodal plane orientation through its long sensing range and dense spatial sampling. However, determining first-arrival polarities on DAS is challenging due to its single-component sensing and low signal-to-noise ratio for direct body waves. Here, we present a data-driven method that measures P-wave polarities on a DAS array based on cross-correlations between earthquake pairs. We validate the inferred polarities using the regional network catalog on two DAS arrays, deployed in California and each comprising ~ 5000 channels. We demonstrate that a joint focal mechanism inversion combining conventional and DAS polarity picks improves the accuracy and reduces the uncertainty in the focal plane orientation. Our results highlight the significant potential of integrating DAS with conventional networks for investigating high-resolution earthquake source mechanisms.

A Circularly Polarized Heterogeneous Antenna Array for Wide Elevation Angle Scanning and Full Azimuthal Coverage

A Circularly Polarized Heterogeneous Antenna Array for Wide Elevation Angle Scanning and Full Azimuthal Coverage

A Planar Orbicular Rectenna Array System With 3-D Uniform Coverage for Wireless Powering of IoT Nodes

Microwave power transfer (MPT) is a revolutionary technique for charging batteries of wireless sensor nodes in smart applications. However, sensor nodes can be positioned at any arbitrary orientation and location with respect to the microwave transmitter (Tx). Therefore, harvested DC power depends on the node’s position and orientation. Thus, to reduce this reliance, a novel, fully integrated planar multisector rectenna (Rx) array is designed to achieve a nearly uniform 3-D spherical DC coverage. To realize orientation insensitive azimuth and elevation plane coverage, the proposed Rx features eight radially arranged endfire Rx (EFR-antenna) elements, and a bore-sight Rx (BSR-antenna) element with multiarms for inherent DC combining is used at the center with orthogonally polarized ports. Furthermore, direct conjugate matching of antenna and rectifier circuit with integrated operation is applied to realize a fully integrated design. This reduces insertion losses and achieves the desired 3-D coverage along with miniaturization, shaping it suitable for deployment at space-constrained IoT sensor nodes for orientation oblivion wireless powering.

Ranking Earthquake Sources Using Spatial Residuals of Seismic Scenarios: Methodology Application to the 1909 Benavente Earthquake

ABSTRACT Historical earthquakes are of major importance in the analysis of seismic hazards, in particular for stable continental regions. In this article, we propose a methodology that uses seismic scenarios to provide constraints on the location of the seismic source of historical earthquakes. Our methodology involves generating seismic scenarios for the proposed seismic sources and comparing the results to the observed intensity field of the earthquake. To avoid the bias related to strongly heterogeneously distributed datasets, we focus on data points that are useful in discriminating between competing ruptures. These data are identified by the spatial patterns of residuals between seismic scenarios produced for each source. We apply this methodology to a test event—the 1999 Athens earthquake—for which both the magnitude and location are constrained by independent data, and to the 1909 Benavente earthquake, for which the magnitude is constrained by seismological studies, but the location is uncertain due to the very poor azimuthal coverage available. Within its application limits, the proposed methodology was capable of identifying the source of the Athens earthquake amongst different ruptures located few kilometers apart. The analysis performed for the 1909 Benavente earthquake suggests that the eastern strand of the lower Tagus Valley fault zone is the most likely seismic source for earthquake, amongst those proposed in the literature.