Seismica <p>Seismica is a community-driven, <em>Diamond Open Access</em> journal publishing peer-reviewed research in seismology and earthquake science. <em>Diamond Open Access</em> journals are free for all to read, without subscriptions, and do not charge article processing fees to authors.</p> <p>Seismica has been open for submission since July 2022. You can read more about the Seismica initiative in <a href="">our first editorial</a>. Thank you to all the members of the Seismica community who contributed to this editorial!</p> <p><strong>[Holiday break] Seismica's editorial board will take a holiday break from December 11 through January 6th. Any new submissions during this time will be processed after January 6th. Papers submitted prior will also be paused for this time window unless individual editors choose to continue working during the break.</strong></p> <p><strong>[November 2023] Seismica is soliciting submissions for a special issue, "<a href="">The Cascadia Subduction Zone: Grand Challenges and Research Frontiers</a>" For more information on submitting a paper, see the <a href="">issue announcement</a>.</strong><br /><br /><strong>[March 2023] Seismica is soliciting submissions for a special issue, "<a href="">Lessons from the devastating 2023 Kahramanmaraş, Türkiye earthquake sequence.</a>" For more information on submitting a paper, see the <a href="">issue announcement</a>.</strong></p> en-US (Seismica Editorial Team) (Seismica Tech Team) Tue, 01 Aug 2023 10:29:33 -0400 OJS 60 Assessing earthquake rates and b-value given spatiotemporal variation in catalog completeness: Application to Atlantic Canada <p>Spatiotemporal variations in the magnitude of completeness <em>M</em><sub>c</sub> make it challenging to confidently assess seismic hazard or even to simply compare earthquake rates between regions. In this study, we introduce new techniques to correct for heterogeneous <em>M</em><sub>c</sub> in a treatment of the eastern and Atlantic Canada earthquake catalog (1985--2022). We first introduce new methodology to predict <em>M</em><sub>c</sub>(<em>x</em>,<em>t</em>) based on the distribution of seismometers. Second, we introduce a modified maximum-likelihood estimator (MLE) for <em>b</em> (the b-value) that accounts for spatiotemporal <em>M</em><sub>c</sub> variation, allowing the inclusion of more earthquakes. Third, we compute the ratio of detected/predicted <em>M</em>&gt;1 earthquakes as a function of <em>M</em><sub>c</sub> and apply it to create a calibrated <em>M</em>&gt;1 event-rate map. The resulting map has advantages over a moment-rate map, which is effectively sensitive only to the very largest earthquakes in the dataset. The new MLE results in a modestly more precise <em>b</em>&nbsp;when applied to the Charlevoix Seismic Zone, and a substantial increase in precision when applied to the full Atlantic Canada region. It may prove useful in future hazard assessments, particularly of regions with highly heterogeneous <em>M</em><sub>c</sub> and relatively sparse catalogs.</p> Alexandre Plourde Copyright (c) 2023 © His Majesty the King in Right of Canada, as represented by the Minister of Natural Resources, 2023 Wed, 13 Sep 2023 00:00:00 -0400 Inferring rock strength and fault activation from high-resolution in situ Vp/Vs estimates surrounding induced earthquake clusters <p>Fluid injection/extraction activity related to hydraulic fracturing can induce earthquakes. Common mechanisms attributed to induced earthquakes include elevated pore pressure, poroelastic stress change, and fault loading through aseismic slip. However, their relative influence is still an open question. Estimating subsurface rock properties, such as pore pressure distribution, crack density, and fracture geometry can help quantify the causal relationship between fluid-rock interaction and fault activation. Inferring rock properties by means of indirect measurement may be a viable strategy to help identify weak structures susceptible to failure in regions where increased seismicity correlates with industrial activity, such as the Western Canada Sedimentary Basin. Here we present <em>in situ</em> estimates of V<sub>p</sub>/V<sub>s</sub> for 34 induced earthquake clusters in the Kiskatinaw area in northeast British Columbia. We estimate significant changes of up to ±4.5% for nine clusters generally associated with areas of high injection volume. Predominantly small spatiotemporal V<sub>p</sub>/V<sub>s</sub> variations suggest pore pressure increase plays a secondary role in initiating earthquakes. In contrast, computational rock mechanical models that invoke a decreasing fracture aspect ratio and increasing fluid content in a fluid-saturated porous medium that are consistent with the treatment pressure history better explain the observations.</p> Marco Pascal Roth, Alessandro Verdecchia, Rebecca M. Harrington, Yajing Liu Copyright (c) 2023 Marco Pascal Roth, Alessandro Verdecchia, Rebecca M. Harrington, Yajing Liu Thu, 16 Nov 2023 00:00:00 -0500 The July-December 2022 earthquake sequence in the southeastern Fars arc of Zagros mountains, Iran <p style="margin-bottom: 0cm; line-height: 100%;">Within two hours on 01 July 2023, three earthquakes of Mw 5.8-6.0 hit the SE Fars arc, Iran. In the following months, the region characterized by the collision of the Iranian and the Arabian plate, thrust faulting, and salt diapirism was stroke by more than 120 aftershocks of mL 3.1-5.2, of which two of the largest events occurred within one minute on 23 July 2023 in spatial vicinity to each other. We analyzed both the large mainshocks and aftershocks using different techniques, such as the inversion of seismic and satellite deformation data in a joint process and aftershock relocation. Our results indicate the activation of thrust faults within the lower sedimentary cover of the region along with high aftershock activity in significantly larger depth, supporting the controversial model of a crustal strain decoupling during the collision in the Fars Arc. We resolved a magnitude difference of &gt;0.2 magnitude units between seismic and joint seismic and satellite deformation inversions probably caused by afterslip, thereby allowing to bridge between results from international agencies and earlier studies. We also find evidence for an event doublet and triplet activating the same or adjacent faults within the sedimentary cover and the basement</p> Malte Metz, Behnam Maleki Asayesh, Mohammad Mohseni Aref, Mohammadreza Jamalreyhani, Pınar Büyükakpınar, Torsten Dahm Copyright (c) 2023 Malte Metz, Behnam Maleki Asayesh, Mohammad Mohseni Aref, Mohammadreza Jamalreyhani, Pınar Büyükakpınar, Torsten Dahm Wed, 01 Nov 2023 00:00:00 -0400 Seismic Architecture of the Lithosphere-Asthenosphere System in the Western United States from a Joint Inversion of Body- and Surface-wave Observations: Distribution of Partial Melt in the Upper Mantle <p>Quantitative evaluation of the physical state of the upper mantle, including mapping temperature variations and the possible distribution of partial melt, requires accurately characterizing absolute seismic velocities near seismic discontinuities. We present a joint inversion for absolute but discontinuous models of shear-wave velocity (Vs) using 4 types of data: Rayleigh wave phases velocities, P-to-s receiver functions, S-to-p receiver functions, and Pn velocities. Application to the western United States clarifies where upper mantle discontinuities are lithosphere-asthenosphere boundaries (LAB) or mid-lithospheric discontinuities (MLD). Values of Vs below 4 km/s are observed below the LAB over much of the Basin and Range and below the edges of the Colorado Plateau; the current generation of experimentally based models for shear-wave velocity in the mantle cannot explain such low Vs without invoking the presence of melt. Large gradients of Vs below the LAB also require a gradient in melt-fraction. Nearly all volcanism of Pleistocene or younger age occurred where we infer the presence of melt below the LAB. Only the ultrapotassic Leucite Hills in the Wyoming Craton lie above an MLD. Here, the seismic constraints allow for the melting of phlogopite below the MLD.</p> Joseph Byrnes, James Gaherty, Emily Hopper Copyright (c) 2023 Joseph Byrnes, James Gaherty, Emily Hopper Tue, 29 Aug 2023 00:00:00 -0400 Homogenizing instrumental earthquake catalogs – a case study around the Dead Sea Transform Fault Zone <p>The creation of a homogenized earthquake catalog is a fundamental step in seismic hazard analysis. The homogenization procedure, however, is complex and requires a good understanding of the heterogeneities among the available bulletins. Common events within the bulletins have to be identified and assigned with the most suitable origin time and location solution, while all the events have to be harmonized into a single magnitude scale. This process entails several decision variables that are usually defined using qualitative measures or expert opinion, without a clear exploration of the associated uncertainties. To address this issue, we present an automated and data-driven workflow that defines spatio-temporal margins within which duplicate events fall and converts the various reported magnitudes into a common scale. Special attention has been paid to the fitted functional form and the validity range of the derived magnitude conversion relations. The proposed methodology has been successfully applied to a wide region around the Dead Sea Transform Fault Zone (27N-36N, 31E-39E), with input data from various sources such as the International Seismological Centre and the Geophysical Institute of Israel. The produced public catalog contains more than 5500 events, between 1900 and 2017, with moment magnitude Mw above 3. The MATLAB/Python scripts used in this study are also available.</p> Iason Grigoratos, Valerio Poggi, Laurentiu Danciu, Ricardo Monteiro Copyright (c) 2023 Iason Grigoratos, Valerio Poggi, Laurentiu Danciu, Ricardo Monteiro Tue, 07 Nov 2023 00:00:00 -0500 The rupture plane of the February 2022 Mw 6.2 Guatemala, intermediate depth earthquake <p>An intermediate depth intraplate earthquake with Mw 6.2 was generated in the Guatemalan subduction zone on 16 February 2022 with epicenter to Southwest of the department of Escuintla. More than 275 aftershocks were registered, which were relocated with the HypoDD algorithm, being able to identify a fault with an area of ~350 km<sup>2</sup>, which is considerably higher than expected for an earthquake of that magnitude. The moment tensor at the centroid of the main earthquake and the estimation of other focal mechanisms of the largest aftershocks, allowed us to identify extension earthquakes, related to the fault plane, and compression earthquakes that were associated with seismicity on the upper part of the slab. The region of the sequence has presented high seismic activity in recent years. It is proposed that the mainshock nucleated in the lower seismicity layer (LSL) of the double seismicity zone proposed for the region, triggering seismic activity on a pre-existing active fault, also triggering seismic activity in the upper seismicity layer (USL). The separation between these seismicity layers was estimated to be 12.2±5.0 km.</p> Robin Yani-Quiyuch, Ludwing Asturias, Diego Castro Copyright (c) 2023 Robin Yani-Quiyuch, Ludwing Asturias, Diego Castro Thu, 16 Nov 2023 00:00:00 -0500 Rayleigh wave group velocities in North-West Iran: SOLA Backus-Gilbert vs. Fast Marching tomographic methods <p>In this study, we focus on Northwest Iran and exploit a dataset of Rayleigh-wave group-velocity measurements obtained from ambient noise cross-correlations and earthquakes.<br />We build group-velocity maps using the recently developed SOLA Backus-Gilbert linear tomographic scheme as well as the more traditional Fast-marching Surface-wave Tomography method.<br />The SOLA approach produces robust, unbiased local averages of group velocities with detailed information on their local resolution and uncertainty; however, it does not as yet allow ray-path updates in the inversion process. The Fast-marching method, on the other hand, does allow ray-path updates, although it does not provide information on the resolution and uncertainties of the resulting models (at least not without great computational cost) and may suffer from bias due to model regularisation.<br />The core of this work consists in comparing these two tomographic methods, in particular how they perform in the case of strong vs. weak seismic-velocity contrasts and good vs. poor data coverage. <br />We demonstrate that the only case in which the Fast-marching inversion outperforms the SOLA inversion is for strong anomaly contrasts in regions with good path coverage; in all other configurations, the SOLA inversion produces more coherent anomalies with fewer artefacts.</p> Saman Amiri, Alessia Maggi, Mohammad Tatar, Dimitri Zigone, Christophe Zaroli Copyright (c) 2023 Saman Amiri, Alessia Maggi, Mohammad Tatar, Dimitri Zigone, Christophe Zaroli Tue, 05 Dec 2023 00:00:00 -0500 Red-light thresholds for induced seismicity in the UK <p>Induced earthquakes pose a serious hurdle to subsurface energy development. Concerns about induced seismicity led to terminal public opposition of hydraulic fracturing in the UK. Traffic light protocols (TLPs) are typically used to manage these risks, with the red-light designed as the last-possible stopping-point before exceeding a risk tolerance. We simulate trailing earthquake scenarios for the UK, focusing on three risk metrics: nuisance, damage, and local personal risk (LPR) – the likelihood of building collapse fatality for an individual. The severity of these risks can spatially vary (by orders-of-magnitude), depending on exposure. Estimated risks from the Preston New Road earthquakes are used to calibrate our UK earthquake risk tolerances, which we find to be comparable to Albertan (Canadian) tolerances. We find that nuisance and damage concerns supersede those from fatality and that the safest regions for Bowland Shale development would be along the east coast. A retrospective comparison of our TLP result with the Preston New Road case highlights the importance of red-light thresholds that adapt to new information. Overall, our findings provide recommendations for red-light thresholds (<em>M</em><sub>L </sub>2-2.5) and proactive management of induced seismicity – regardless of anthropogenic source.</p> Ryan Schultz, Brian Baptie, Benjamin Edwards, Stefan Wiemer Copyright (c) 2023 Ryan Schultz, Brian Baptie, Benjamin Edwards, Stefan Wiemer Mon, 16 Oct 2023 00:00:00 -0400 False positives are common in single-station template matching <p>Template matching has become a cornerstone technique of observational seismology. By taking known events, and scanning them against a continuous record, new events smaller than the signal-to-noise ratio can be found, substantially improving the magnitude of completeness of earthquake catalogues. Template matching is normally used in an array setting, however as we move into the era of planetary seismology, we are likely to apply template matching for very small arrays or even single stations. Given the high impact of planetary seismology studies on our understanding of the structure and dynamics of non-Earth bodies, it is important to assess the reliability of template matching in the small-n setting. Towards this goal, we estimate a lower bound on the rate of false positives for single-station template matching by examining the behaviour of correlations of totally uncorrelated white noise. We find that, for typical processing regimes and match thresholds, false positives are likely quite common. We must therefore be exceptionally careful when considering the output of template matching in the small-n setting.</p> Jack Muir, Benjamin Fernando, Elizabeth Barrett Copyright (c) 2023 Jack Muir, Benjamin Fernando, Elizabeth Barrett Fri, 11 Aug 2023 00:00:00 -0400 Continuous isolated noise sources induce repeating waves in the coda of ambient noise correlations <div> <div>Continuous excitation of isolated noise sources leads to repeating wave arrivals in cross correlations of ambient seismic noise, including throughout their coda. These waves propagate from the isolated sources. We observe this effect on correlation wavefields computed from two years of field data recorded at the Gräfenberg array in Germany and two master stations in Europe. Beamforming the correlation functions in the secondary microseism frequency band reveals repeating waves incoming from distinct directions to the West, which correspond to well-known dominant microseism source locations in the Northeastern Atlantic Ocean. These emerge in addition to the expected anti-causal and causal correlation wavefield contributions by boundary sources, which are converging onto and diverging from the master station, respectively. Numerical simulations reproduce this observation. We first model a source repeatedly exciting a wavelet, which helps illustrate the fundamental mechanism behind repeated wave generation. Second, we model continuously acting secondary microseism sources and find good agreement with our observations. Our observations and modelling have potentially significant implications for the understanding of correlation wavefields and monitoring of relative velocity changes in particular. Velocity monitoring commonly assumes that only multiply scattered waves, originating from the master station, are present in the coda of the correlation wavefield. We show that repeating waves propagating from isolated noise sources may dominate instead, including the very late coda. Our results imply that in the presence of continously acting noise sources, which we show is the case for ordinary recordings of ocean microseisms, velocity monitoring assuming scattered waves may be adversely affected with regard to measurement technique, spatial resolution, as well as temporal resolution. We further demonstrate that the very late coda of correlation functions contains useful signal, contrary to the common sentiment that it is dominated by instrument noise.</div> </div> Sven Schippkus, Mahsa Safarkhani, Céline Hadziioannou Copyright (c) 2023 Sven Schippkus, Céline Hadziioannou, Mahsa Safarkhani Mon, 09 Oct 2023 00:00:00 -0400 Characterizing High Rate GNSS Velocity Noise for Synthesizing a GNSS Strong Motion Learning Catalog <p>Data-driven approaches to identify geophysical signals have proven beneficial in high dimensional environments where model-driven methods fall short. GNSS offers a source of unsaturated ground motion observations that are the data currency of ground motion forecasting and rapid seismic hazard assessment and alerting. However, these GNSS-sourced signals are superposed onto hardware-, location- and time-dependent noise signatures influenced by the Earth’s atmosphere, low-cost or spaceborne oscillators, and complex radio frequency environments. Eschewing heuristic or physics based models for a data-driven approach in this context is a step forward in autonomous signal discrimination. However, the performance of a data-driven approach depends upon substantial representative samples with accurate classifications, and more complex algorithm architectures for deeper scientific insights compound this need. The existing catalogs of high-rate (<span class="ILfuVd" lang="en"><span class="hgKElc">≥</span></span>1Hz) GNSS ground motions are relatively limited. In this work, we model and evaluate the probabilistic noise of GNSS velocity measurements over a hemispheric network. We generate stochastic noise time series to augment transferred low-noise strong motion signals from within 70 kilometers of strong events (<span class="ILfuVd" lang="en"><span class="hgKElc">≥</span></span> M<sub>W</sub> 5.0) from an existing inertial catalog. We leverage known signal and noise information to assess feature extraction strategies and quantify augmentation benefits. We find a classifier model trained on this expanded pseudo-synthetic catalog improves generalization compared to a model trained solely on a real-GNSS velocity catalog, and offers a framework for future enhanced data driven approaches.</p> Timothy Dittmann, Y. Jade Morton, Brendan Crowell, Diego Melgar, Jensen DeGrande, David Mencin Copyright (c) 2023 Timothy Dittmann, Y. Jade Morton, Brendan Crowell, Diego Melgar, Jensen DeGrande, David Mencin Thu, 05 Oct 2023 00:00:00 -0400 Seismic record of a long duration dispersive signal after the 15 January 2022 Hunga-Tonga eruption <p style="font-weight: 400;">Data acquired by broadband seismic stations distributed around the world are used to document the exceptionally long duration signal from the tsunami-associated gravity wave that followed the January 2022 Hunga-Tonga eruption. The first arrivals of this wave, with a frequency of around 2 mHz, are recorded at the time the tsunami arrives to each station, but the highest recorded frequencies, which reach 40 mHz, arrive 5 days later at some sites, following the prediction of a gravity wave originating at the Hunga-Tonga region and traveling in deep water. This dispersive signal is detected in most of the stations located in the Pacific Ocean basin and its coasts, but also in the Indian Ocean, Antarctica, and some stations in North America located hundreds of kilometers from the coastline. The signal is compared with the data gathered after earthquakes that have produced large tsunamis, showing that the seismic records from the Hunga-Tonga eruption are very different. Following the hypothesis pointed out by Omira et al 2023, we propose that the origin of this exceptional characteristic is due to the interaction between the tsunami and atmospheric waves that travel a little faster.</p> Jordi Diaz Copyright (c) 2023 Jordi Diaz Wed, 29 Nov 2023 00:00:00 -0500 Recent seismicity on the Kerguelen islands <p>The Kerguelen archipelago, one of the largest oceanic archipelagos in the world, was built by an active hotspot interacting with a ridge between 110 and 40 million years ago; since then, the ridge has migrated over 1000~km away and the archipelago's volcanic activity has been steadily decreasing. Despite the lack of recent active tectonics and the quiescent volcanism of the Kerguelen archipelago, there have been several observations of seismic events of unknown origin in its vicinity. The only seismic instrument within 1000~km of the archipelago was installed on Kerguelen's main island in the 1980's. In this study we apply modern earthquake detection techniques to the continuous waveforms recorded by this seismometer over the past 20 years. We reveal that the Kerguelen archipelago islands hosts an abundant seismicity. This seismicity exhibits swarm-like characteristics in several clusters while at other locations the earthquakes appear more steady over time. We locate most events near the largest icecap of the main island. We speculate that the origin of the earthquakes can be linked to residual volcanic, magmatic, or hydrothermal activity at depth, all of which can be favored by flexural stress caused by the documented fast retreat of icecap. This seismicity may also indicate that the Kerguelen hotspot shows signs of unrest.</p> Olivier Lengliné, Joachim Rimpôt, Alessia Maggi, Dimitri Zigone Copyright (c) 2023 Olivier Lengliné, Joachim Rimpôt, Alessia Maggi, Dimitri Zigone Fri, 27 Oct 2023 00:00:00 -0400 Observation of a Synchronicity between Shallow and Deep Seismic Activities during the Foreshock Crisis Preceding the Iquique Megathrust Earthquake <p>We analyze at a broad spatial scale the slab seismicity during one of the longest and best recorded foreshock sequence of a subduction earthquake to date: the M8.1 2014 Iquique earthquake in Chile. &nbsp;We observe the synchronisation of this sequence with seismic events occurring in the deep slab (depth ~100km). This synchronisation supports the existence of long-range seismic bursts already observed in the Japan Trench subduction. It suggests that, like for the 2011 Tohoku earthquake, the deep slab was involved in the nucleation process of the Iquique earthquake.&nbsp; We interpret these observations by the presence of pressure pulses propagating in transient fluid channels linking the deep slab where dehydration occurs to the shallow seismogenic zone before the earthquake. These observations may seem surprising but they are in line with the short-lived pulse-like channelized water escape from the dehydration zone predicted by recent studies in slab mineralogy and geochemistry.</p> Michel Bouchon, Stéphane Guillot, David Marsan, Anne Socquet, Jorge Jara, François Renard Copyright (c) 2023 Michel Bouchon, Stéphane Guillot, David Marsan, Anne Socquet, Jorge Jara, François Renard Tue, 10 Oct 2023 00:00:00 -0400 Optimal Network Design for Microseismic Monitoring in Urban Areas - A Case Study in Munich, Germany <p>Well-designed monitoring networks are crucial for obtaining precise locations, magnitudes and source parameters, both for natural and induced microearthqakes. The performance of a seismic network depends on many factors, including network geometry, signal-to-noise ratio (SNR) at the seismic station, instrumentation and sampling rate. Therefore, designing a high-quality monitoring network in an urban environment is challenging due to the high level of anthropogenic noise and dense building infrastructure, which can impose geometrical limitations and elevated construction costs for sensor siting. To address these challenges, we apply a numerical optimization approach to design a microseismic surveillance network for induced earthquakes in the metropolitan area of Munich (Germany), where several geothermal plants exploit a deep hydrothermal reservoir. First of all, we develop a detailed noise model for the city of Munich, to capture the heterogeneous noise conditions. Then, we calculate the expected location precision for a randomly chosen network geometry from the body-wave amplitudes and travel times of a synthetic earthquake catalog considering the modeled local noise level at each network station. In the next step, to find the optimum network configuration, we use a simulated annealing approach in order to minimize the error ellipsoid volume of the linearized earthquake location problem. The results indicate that a surface station network cannot reach the required location precision (0.5 km in epicentre and 2 km in source depth) and detection capability (magnitude of completeness Mc = 1.0) due to the city´s high seismic noise level. In order to reach this goal, borehole stations need to be added to increase the SNR of the microearthquake recordings, the accuracy of their body-wave arrival times and source parameters. The findings help to better quantify the seismic monitoring requirements for a save operation of deep geothermal projects in urban areas.</p> Sabrina Keil, Joachim Wassermann, Tobias Megies, Toni Kraft Copyright (c) 2023 Sabrina Keil, Joachim Wassermann, Tobias Megies, Toni Kraft Wed, 18 Oct 2023 00:00:00 -0400 Spatiotemporal evaluation of Rayleigh surface wave estimated from roadside dark fiber DAS array and traffic noise <p>Seismic imaging and monitoring of the near-surface structure are crucial for the sustainable development of urban areas. However, standard seismic surveys based on cabled or autonomous geophone arrays are expensive and hard to adapt to noisy metropolitan environments. Distributed acoustic sensing (DAS) with pre-existing telecom fiber optic cables, together with seismic ambient noise interferometry, have the potential to fulfill this gap. However, a detailed noise wavefield characterization is needed before retrieving<br />coherent waves from chaotic noise sources. We analyze local seismic ambient noise by tracking five-month changes in signal-to-noise ratio (SNR) of Rayleigh surface wave estimated from traffic noise recorded by DAS along the straight university campus busy road. We apply the seismic interferometry method to the 800 m long part of the Penn State Fiber-Optic For Environment Sensing (FORESEE) array. We evaluate the 160 virtual shot gathers (VSGs) by determining the SNR using the slant-stack technique. We observe strong SNR variations in time and space. We notice higher SNR for virtual source points close to road obstacles. The spatial noise distribution confirms that noise energy focuses mainly on bumps and utility holes. We also see the destructive impact of precipitation, pedestrian traffic, and traffic along main intersections on VSGs. A similar processing workflow can be applied to various straight roadside fiber optic arrays in metropolitan areas.</p> Rafał Czarny, Tieyuan Zhu, Junzhu Shen Copyright (c) 2023 Rafał Czarny Mon, 14 Aug 2023 00:00:00 -0400 Local station correlation: large N-arrays and DAS <p>The use of cross-correlation between seismic stations has had widespread applications particularly in the exploitation of ambient seismic noise. We here show how the effects of a non-ideal noise distribution can be understood by looking directly at correlation properties and show how the behaviour can be readily visualised for both seismometer and DAS configurations, taking into account directivity effects.&nbsp; For sources lying in a relatively narrow cone around the extension of the inter-station path, the dispersion properties of the correlation relate directly to the zone between the stations.&nbsp; We illustrate the successful use of correlation analysis for both a large-N array perpendicular to a major highway and DAS cable along a busy road.&nbsp; For correlation work, the co-array consisting of the ensemble of inter-station vectors provides an effective means of assessing the behaviour of array layouts, supplementing the standard plane-wave array response. When combined with knowledge of the suitable correlation zones for noise sources, the co-array concept provides a useful way to design array configurations for both seismometer arrays and DAS.</p> Brian Kennett, Chengxin Jiang, Krystyna Smolinski Copyright (c) 2023 Brian Kennett, Chengxin Jiang, Krystyna Smolinski Mon, 18 Sep 2023 00:00:00 -0400 Geocoding Applications for Social Science to Improve Earthquake Early Warning <p>Geocoding is a spatial analysis method that uses address information (e.g., street address, intersection, census tract, zip code, etc.) to determine geographical coordinates (latitude and longitude). In recent decades, geocoding has gone beyond its primary use for census and demographic information to novel applications in disaster risk reduction, even to earthquake early warning. Here I demonstrate the usefulness of geocoding techniques to earthquake early warning systems as applied to case studies that relied on survey response data and crowd-sourced video footage. These datasets were initially collected to understand the efficacy of tests conducted on ShakeAlert<sup>®</sup>, the earthquake early warning system for the West Coast of the United States, and how people behave during earthquakes, respectively. Geocoding these data can improve our overall technical understanding of the system, demonstrate whether individuals take protective actions such as ‘Drop, Cover, and Hold On’, and spotlight community demographics that the system is reaching or unintentionally missing. The combination of these social science datasets with geocoding information deepens our knowledge of these fundamentally human-centered systems, including how to improve the distribution of alerts for people and individuals with access and functional needs. In the future, this work may help verify U.S. Geological Survey ‘Did You Feel It?’ responses and seismic intensity, especially in regions with sparse seismic networks.</p> Danielle Sumy Copyright (c) 2023 Danielle Sumy Mon, 25 Sep 2023 00:00:00 -0400 Unraveling the Evolution of an Unusually Active Earthquake Sequence Near Sheldon, Nevada <p class="Abstracttext" style="line-height: 200%;">One of most universal statistical properties of earthquakes is the tendency to cluster in space and time. Yet while clustering is pervasive, individual earthquake sequences can vary markedly in duration, spatial extent, and time evolution. In July 2014, a prolific earthquake sequence initiated within the Sheldon Wildlife Refuge in northwest Nevada, USA. The sequence produced 26 M4 earthquakes and several hundred M3s, with no clear mainshock or obvious driving force. Here we combine a suite of seismological analysis techniques to better characterize this unusual earthquake sequence. High-precision relocations reveal a clear, east dipping normal fault as the dominant structure that intersects with a secondary, subvertical cross fault. Seismicity occurs in burst of activity along these two structures before eventually transitioning to shallower structures to the east. Inversion of hundreds of moment tensors constrain the overall normal faulting stress regime. Source spectral analysis suggests that the stress drops and rupture properties of these events are typical for tectonic earthquakes in the western US. While regional station coverage is sparse in this remote study region, the timely installation of a temporary seismometer allows us to detect nearly 70,000 earthquakes over a 40-month time period when the seismic activity is highest. Such immense productivity is difficult to reconcile with current understanding of crustal deformation in the region and may be facilitated by local hydrothermal processes and earthquake triggering at the transitional intersection of subparallel fault systems.</p> Daniel T. Trugman, William H. Savran, Christine J. Ruhl, Kenneth D. Smith Copyright (c) 2023 Daniel T. Trugman, William H. Savran, Christine J. Ruhl, Kenneth D. Smith Tue, 26 Sep 2023 00:00:00 -0400 Automated shear-wave splitting analysis for single- and multi- layer anisotropic media <p>Shear-wave velocity anisotropy is present throughout the earth. The strength and orientation of anisotropy can be observed by shear-wave splitting (birefringence) accumulated between earthquake sources and receivers. Seismic deployments are getting ever larger, increasing the number of earthquakes detected and the number of source-receiver pairs. Here, we present a new Python software package, SWSPy, that fully automates shear-wave splitting analysis, useful for large datasets. The software is written in Python, so it can be easily integrated into existing workflows. Furthermore, seismic anisotropy studies typically make a single-layer approximation, but in this work we describe a new method for measuring anisotropy for multi-layered media, which is also implemented. We demonstrate the performance of SWSPy for a range of geological settings, from glaciers to Earth's mantle. We show how the package facilitates interpretation of an extensive dataset at a volcano, and how the new multi-layer method performs on synthetic and real-world data. The automated nature of SWSPy and the discrimination of multi-layer anisotropy will improve the quantification of seismic anisotropy, especially for tomographic applications. The method is also relevant for removing anisotropic effects, important for applications including full-waveform inversion and moment magnitude analysis.</p> Tom Hudson, Joseph Asplet, Andrew M Walker Copyright (c) 2023 Tom Hudson, Joseph Asplet, Andrew M Walker Thu, 19 Oct 2023 00:00:00 -0400 Seismology in the cloud: guidance for the individual researcher <h1>The commercial cloud offers on-demand computational resources that could be revolutionary for the seismological community, especially as seismic datasets continue to grow. However, there are few educational examples for cloud use that target individual seismological researchers. Here, we present a reproducible earthquake detection and association workflow that runs on Microsoft Azure. The Python-based workflow runs on continuous time-series data using both template matching and machine learning. We provide tutorials for constructing cloud resources (both storage and computing) through a desktop portal and deploying the code both locally and remotely on the cloud resources. We report on scaling of compute times and costs to show that CPU-only processing is generally inexpensive, and is faster and simpler than using GPUs. When the workflow is applied to one year of continuous data from a mid-ocean ridge, the resulting earthquake catalogs suggest that template matching and machine learning are complementary methods whose relative performance is dependent on site-specific tectonic characteristics. Overall, we find that the commercial cloud presents a steep learning curve but is cost-effective. This report is intended as an informative starting point for any researcher considering migrating their own processing to the commercial cloud.</h1> Zoe Krauss, Yiyu Ni, Scott Henderson, Marine Denolle Copyright (c) 2023 Zoe Krauss, Yiyu Ni, Scott Henderson, Marine Denolle Fri, 25 Aug 2023 00:00:00 -0400 A Call to Action for a Comprehensive Earthquake Education Policy in Nepal <div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>Earthquakes in Nepal are among the most damaging natural hazards, claiming many lives and causing more widespread destruction than any other natural hazard. Yet, due to other difficulties and challenges, earthquakes are at the forefront of people’s attention only after major events, such as the 1934 or 2015 earthquakes. As a result, current preparedness of the population to earthquakes is far below the optimal level. This calls for an immediate and widespread educational effort to increase awareness and to raise the current young generation responsibly. After describing the current status of earthquake education at various school levels in Nepal, we here propose a series of actions to undertake towards an official education policy, starting from full openness and use of languages, via coordination and teacher's training, to the content, frequency and style of curriculum. We conclude on a timeline of actions, which have various lengths but should start today. We hope that by sharing our researcher and educational experience and thoughts, the actual preparation of the earthquake education policy for Nepal will start being developed under a dedicated team. Elements of the proposal presented here can be used and adapted to other regions at risk around the world.</p> </div> </div> </div> György Hetényi, Shiba Subedi Copyright (c) 2023 György Hetényi, Shiba Subedi Thu, 17 Aug 2023 00:00:00 -0400 The need for open, transdisciplinary, and ethical science in seismology <p>Reducing the seismic risk for societies requires a bridge between scientific knowledge and societal actions. In recent years, three subjects that facilitate this connection gained growing importance: open science, transdisciplinarity, and ethics. We outline their relevance in general and specifically at the example of `'dynamic seismic risk' as explored in a dedicated workshop. We argue that these reflections can be transferred to other research fields for improving their practical and societal relevance. We provide recommendations for scientists at all levels to make science more open, transdisciplinary, and ethical. Only with a transition can we, as scientists, address current societal challenges and increase societies' resilience to disasters.</p> Irina Dallo, Marcus Herrmann, Mariano Supino, José A. Bayona, Asim M. Khawaja, Chiara Scaini Copyright (c) 2023 Irina Dallo, Marcus Herrmann, Mariano Supino, José A. Bayona, Asim M. Khawaja, Chiara Scaini Tue, 01 Aug 2023 00:00:00 -0400 Editorial workflow of a community-led, all-volunteer scientific journal: lessons from the launch of Seismica <p>Seismica is a community-led, volunteer-run, diamond open-access journal for seismology and earthquake science, and Seismica's mission and core values align with the principles of Open Science. This article describes the editorial workflow that Seismica uses to go from a submitted manuscript to a published article. In keeping with Open Science principles, the main goals of sharing this workflow description are to increase transparency around academic publishing, and to enable others to use elements of Seismica's workflow for journals of a similar size and ethos. We highlight aspects of Seismica's workflow that differ from practices at journals with paid staff members, and also discuss some of the challenges encountered, solutions developed, and lessons learned while this workflow was developed and deployed over Seismica's first year of operations.</p> Hannah Mark, Théa Ragon, Gareth Funning, Stephen P. Hicks, Christie Rowe, Samantha Teplitzky, Jaime Convers, Ezgi Karasözen, R. Daniel Corona-Fernandez , Åke Fagereng Copyright (c) 2023 Hannah Mark, Théa Ragon, Gareth Funning, Stephen P. Hicks, Christie Rowe, Samantha Teplitzky, Jaime Convers, Ezgi Karasözen, R. Daniel Corona-Fernandez , Åke Fagereng Wed, 04 Oct 2023 00:00:00 -0400