Seismica https://seismica.library.mcgill.ca/ <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="https://seismica.library.mcgill.ca/article/view/255">our first editorial</a>. Thank you to all the members of the Seismica community who contributed to this editorial!</p> <p><strong>[May 2024] Seismica is recruiting! We are looking for people who share Seismica's key values to join our Editorial Board. For more information on specific positions and the application, see the <a href="https://seismica.library.mcgill.ca/announcement/view/20">recruitment announcement</a>.</strong></p> <p><strong>[November 2023] Seismica is soliciting submissions for a special issue, "<a href="https://seismica.library.mcgill.ca/announcement/view/17">The Cascadia Subduction Zone: Grand Challenges and Research Frontiers</a>" For more information on submitting a paper, see the <a href="https://seismica.library.mcgill.ca/announcement/view/17">issue announcement</a>.</strong></p> McGill University Library en-US Seismica 2816-9387 Feasibility of Deep Learning in Shear Wave Splitting analysis using Synthetic-Data Training and Waveform Deconvolution https://seismica.library.mcgill.ca/article/view/1124 <p>Teleseismic shear-wave splitting analyses are often performed by reversing the splitting process through the application of frequency- or time-domain operations aimed at minimizing the transverse-component energy of waveforms. These operations yield two splitting parameters, ɸ (fast-axis orientation) and δt (delay time). In this study, we investigate the applicability of a baseline recurrent neural network, SWSNet, for determining the splitting parameters from pre-selected waveform windows. Due to the scarcity of sufficiently labelled real waveform data, we generate our own synthetic dataset to train the model. The model is capable of determining ɸ and δt with a root mean squared error (RMSE) of 9.7° and 0.14 s on a noisy synthetic test data. The application to real data involves a deconvolution step to homogenize the waveforms. When applied to data from the USArray dataset, the results exhibit similar patterns to those found in previous studies with mean absolute differences of 9.6° and 0.16 s in the calculation of ɸ and δt respectively.</p> Megha Chakraborty Georg Rümpker Wei Li Johannes Faber Nishtha Srivastava Frederik Link Copyright (c) 2024 Megha Chakraborty, Georg Rümpker, Wei Li, Johannes Faber, Nishtha Srivastava, Frederik Link https://creativecommons.org/licenses/by/4.0 2024-03-23 2024-03-23 3 1 10.26443/seismica.v3i1.1124 Monitoring urban construction and quarry blasts with low-cost seismic sensors and deep learning tools in the city of Oslo, Norway https://seismica.library.mcgill.ca/article/view/1166 <p>The aim of this study is to collect information about events in the city of Oslo, Norway, that produce a seismic signature. In particular, we focus on blasts from the ongoing construction of tunnels and under-ground water storage facilities under populated areas in Oslo. We use seismic data recorded simultaneously on up to 11 Raspberry Shake sensors deployed between 2021 and 2023 to quickly detect, locate, and classify urban seismic events. We present a deep learning approach to first identify rare events and then to build an automatic classifier from those templates. For the first step, we employ an outlier detection method using auto-encoders trained on continuous background noise. We detect events using an STA/LTA trigger and apply the auto-encoder to those. Badly reconstructed signals are identified as outliers and subsequently located using their surface wave (Rg) signatures on the seismic network. In a second step, we train a supervised classifier using a Convolutional Neural Network to detect events similar to the identified blast signals. Our results show that up to 87% of about 1,900 confirmed blasts are detected and locatable in challenging background noise conditions. We demonstrate that a city can be monitored automatically and continuously for explosion events, which allows implementing an alert system for future smart city solutions.</p> Andreas Köhler Erik Myklebust Anna Maria Dichiarante Volker Oye Copyright (c) 2024 Andreas Köhler, Erik Myklebust, Anna Maria Dichiarante, Volker Oye https://creativecommons.org/licenses/by/4.0 2024-06-17 2024-06-17 3 1 10.26443/seismica.v3i1.1166 Discontinuous transtensional rupture during the Mw 7.2 1995 Gulf of Aqaba earthquake https://seismica.library.mcgill.ca/article/view/1135 <p>The Gulf of Aqaba earthquake occurred on 22 November 1995 in the Northern Red Sea and is the largest instrumentally recorded earthquake in the region to date. The event was extensively studied during the initial years following its occurrence. However, it remained unclear which of the many faults in the gulf were activated during the earthquake. We present results from multi-array back projection that we use to inform Bayesian kinematic rupture models constrained by geodetic and teleseismic data. Our results indicate that most of the moment release was on the Aragonese fault via left-lateral strike slip and shallow normal faulting that may have been dynamically triggered by an early rupture phase on the Arnona fault. We also identified a predominantly normal fault-segment on the eastern shore of the gulf that was activated in the event. We dismiss the previously proposed hypothesis of a co-seismic sub-event on the western shore of the gulf and confirm that observed deformation can be rather attributed to post-seismic activity. In conclusion, the gulf shows many signs of active tectonic extension. Therefore, more events close to the shorelines are to be expected in the future and should be considered conducting infrastructure projects in the region.</p> Hannes Vasyura-Bathke Andreas Steinberg Frank Krüger Guangcai Feng P. Martin Mai Sigurjón Jónsson Copyright (c) 2024 Hannes Vasyura-Bathke, Andreas Steinberg, Frank Krüger, Guangcai Feng, P. Martin Mai, Sigurjón Jónsson https://creativecommons.org/licenses/by/4.0 2024-02-20 2024-02-20 3 1 10.26443/seismica.v3i1.1135 Extensional failure in a weak slab under slab pull -- the 2023 Mw 6.4 Quiché, Guatemala, earthquake https://seismica.library.mcgill.ca/article/view/1190 <p>The 2023 Mw 6.4 Quiché earthquake is the deepest recorded major (Mw &gt; 6) earthquake to have occurred in the Cocos slab beneath Central America, at a depth of ~ 255 km. Here, we refine the source parameters of both the Quiché earthquake, and the only other event at comparable depths (the 1997 Mw 5.5 Jutiapa earthquake), confirming both their exceptional depth within the downgoing slab, and their down-dip extensional mechanism. That the Cocos slab remains capable of hosting major intraslab earthquakes, with mechanisms consistent with down-dip extension, near, or at, the tip of the contiguous slab, suggests that the slab itself is weak, such that the minimal stresses derived from supporting the negative buoyancy of the short section of slab down-dip from this earthquake are still sufficient to lead to brittle failure of the slab.</p> Timothy Craig Amber Hull Copyright (c) 2024 Timothy Craig, Amber Hull https://creativecommons.org/licenses/by/4.0 2024-05-28 2024-05-28 3 1 10.26443/seismica.v3i1.1190 Dispersive Elastic Moduli and Frequency-Dependent Attenuation due to Wave-Induced Fluid Flow in Metapelite https://seismica.library.mcgill.ca/article/view/624 <p>Seismic waves are used to interpret geologic structure, composition, and environmental conditions in the Earth. However, rocks are not perfectly elastic and their viscoelasticity can dissipate energy during wave propagation. Wave-induced fluid flow mechanisms can cause viscoelasticity resulting in frequency-dependent attenuation, velocities, and elastic moduli (dispersion) in saturated rocks. Dispersion and attenuation are hypothesized to be important in subduction zones, where regions of high fluid content are interpreted below the seismogenic zone. However, this has not been well-tested because of a lack of measurements on relevant lithologies and under saturated conditions. We measured the Young's and shear moduli and the attenuation of a greenschist facies metapelite with the forced oscillation technique at frequencies between 2 x 10<sup>-5</sup> and 30 Hz. The moduli and attenuation are frequency-dependent under saturated conditions and depend on the effective pressure. At relatively low effective pressure, the Young's and shear moduli increase by over 50 % between 2 x 10<sup>-5</sup> and 30 Hz. We use Standard Linear Solid viscoelastic models to investigate the relationship between the attenuation and dispersion in the Orocopia schist. The models are consistent with the experimental data and demonstrate that viscoelasticity can cause significant dispersion and attenuation in subduction zones.</p> Celine Fliedner Melodie French Copyright (c) 2024 Celine Fliedner, Melodie French https://creativecommons.org/licenses/by/4.0 2024-01-29 2024-01-29 3 1 10.26443/seismica.v3i1.624 Insights on the dip of fault zones in Southern California from modeling of seismicity with anisotropic point processes https://seismica.library.mcgill.ca/article/view/1092 <p>Accurate models of fault zone geometry are important for scientific and hazard applications. While seismicity can provide high-resolution point measurements of fault geometry, extrapolating these measurements to volumes may involve making strong assumptions. This is particularly problematic in distributed fault zones, which are commonly observed in immature faulting regions. In this study, we focus on characterizing the dip of fault zones in Southern California with the goal of improving fault models. We introduce a novel technique from spatial point process theory to quantify the orientation of persistent surficial features in seismicity, even when embedded in wide shear zones. The technique makes relatively mild assumptions about fault geometry and is formulated with the goal of determining the dip of a fault zone at depth. The method is applied to 11 prominent seismicity regions in Southern California. Overall, the results compare favorably with the geometry models provided by the SCEC Community Fault Model and other focused regional studies. More specifically, we find evidence that the Southern San Andreas and San Jacinto fault zones are both northeast dipping at seismogenic depths at the length scales of 1.0–4.0 km. In addition, we find more limited evidence for some depth dependent variations in dip that suggest a listric geometry. The developed technique can provide an independent source of information from seismicity to augment existing fault geometry models.</p> Zachary Ross Copyright (c) 2024 Zachary Ross https://creativecommons.org/licenses/by/4.0 2024-06-18 2024-06-18 3 1 10.26443/seismica.v3i1.1092 ScS shear-wave splitting in the lowermost mantle: Practical challenges and new global measurements https://seismica.library.mcgill.ca/article/view/1128 <p>Many regions of the Earth's mantle are seismically anisotropic, including portions of the lowermost mantle, which may indicate deformation due to convective flow. The splitting of ScS phases, which reflect once off the core-mantle boundary (CMB), is commonly measured to identify lowermost mantle anisotropy, although some challenges exist. Here, we use global wavefield simulations to evaluate commonly used approaches to inferring a lowermost mantle contribution to ScS splitting. We show that due to effects of the CMB reflection, only the epicentral distance range between 60° and 70° is appropriate for ScS splitting measurements. For this distance range, splitting is diagnostic of deep mantle anisotropy if no upper mantle anisotropy is present; however, if ScS is also split due to upper mantle anisotropy, the reliable diagnosis of deep mantle anisotropy is challenging. Moreover, even in the case of a homogeneously anisotropic deep mantle region sampled from a single azimuth by multiple ScS waves with different source polarizations (in absence of upper mantle anisotropy), different apparent fast directions are produced. We suggest that ScS splitting should only be measured at "null" stations and conduct such an analysis worldwide. Our results indicate that seismic anisotropy is globally widespread in the deep mantle.</p> Jonathan Wolf Maureen D. Long Copyright (c) 2024 Jonathan Wolf, Maureen D. Long https://creativecommons.org/licenses/by/4.0 2024-04-25 2024-04-25 3 1 10.26443/seismica.v3i1.1128 What does my technology facilitate? A toolbox to help researchers understand the societal impact of a technology in the context of disasters https://seismica.library.mcgill.ca/article/view/1144 <p>Disaster risk is increasing globally. Emerging technologies – Artificial Intelligence, Internet of Things, and remote sensing – are becoming more important in supporting disaster risk reduction and enhancing safety culture. Despite their presumed benefits, most research focuses on their technological potential, whereas societal aspects are rarely reflected. Taking a societal perspective is vital to ensure that these technologies are developed and operated in ways that benefit societies’ resilience, comply with ethical standards, are inclusive, and address potential risks and challenges. Therefore, we were particularly interested in understanding how societal impacts can be considered and leveraged throughout the development process. Based on an explorative literature review, we developed a toolbox for professionals working on emerging technologies in disaster risk reduction. By applying a Delphi study with experts on AI in seismology, we iteratively adapted and tested the toolbox. The results show that there is a need for guided reflection in order to foster discussion on the societal impacts. They further indicate a gap in the common understanding that is crucial for developing inclusive technologies or defining regulations. Our toolbox was found to be useful for professionals in reflecting on their developments and making technologies societally relevant, thereby enhancing societies’ resilience.</p> Lorena Daphna Kuratle Irina Dallo Michèle Marti Michael Stauffacher Copyright (c) 2024 Lorena Daphna Kuratle, Irina Dallo , Michèle Marti, Stauffacher Michael https://creativecommons.org/licenses/by/4.0 2024-03-01 2024-03-01 3 1 10.26443/seismica.v3i1.1144 Deep learning detects uncataloged low-frequency earthquakes across regions https://seismica.library.mcgill.ca/article/view/1185 <p>Documenting the interplay between slow deformation and seismic ruptures is essential to understand the physics of earthquakes nucleation. However, slow deformation is often difficult to detect and characterize. The most pervasive seismic markers of slow slip are low-frequency earthquakes (LFEs) that allow resolving deformation at minute-scale. Detecting LFEs is hard, due to their emergent onsets and low signal-to-noise ratios, usually requiring region-specific template matching approaches. These approaches suffer from low flexibility and might miss LFEs as they are constrained to sources identified a priori. Here, we develop a deep learning-based workflow for LFE detection and location, modeled after classical earthquake detection with phase picking, phase association, and location. Across three regions with known LFE activity, we detect LFEs from both previously cataloged sources and newly identified sources. Furthermore, the approach is transferable across regions, enabling systematic studies of LFEs in regions without known LFE activity.&nbsp;</p> Jannes Münchmeyer Sophie Giffard-Roisin Marielle Malfante William Frank Piero Poli David Marsan Anne Socquet Copyright (c) 2024 Jannes Münchmeyer, Sophie Giffard-Roisin, Marielle Malfante, William B. Frank, Piero Poli, David Marsan, Anne Socquet https://creativecommons.org/licenses/by/4.0 2024-05-10 2024-05-10 3 1 10.26443/seismica.v3i1.1185 Ocean Bottom Seismometer Clock Correction using Ambient Seismic Noise https://seismica.library.mcgill.ca/article/view/367 <p>Ocean-bottom seismometers (OBSs) are equipped with seismic sensors that record acoustic and seismic events at the seafloor, which makes them suitable for investigating tectonic structures capable of generating earthquakes offshore. One critical parameter to obtain accurate earthquake locations is the absolute time of the incoming seismic signals recorded by the OBSs. It is, however, not possible to synchronize the internal clocks of the OBSs with a known reference time, given that GNSS signals are unable to reach the instrument at the sea bottom. To address this issue, here we introduce a new method to synchronize the clocks of large-scale OBS deployments. Our approach relies on the theoretical time-symmetry of time-lapse (averaged) crosscorrelations of ambient seismic noise. Deviations from symmetry are attributed to clock errors. This implies that the recovered clock errors will be obscured by lapse crosscorrelations' deviations from symmetry that are not due to clock errors. Non-uniform surface wave illumination patterns are arguably the most notable source which breaks the time symmetry. Using field data, we demonstrate that the adverse effects of non-uniform illumination patterns on the recovered clock errors can be mitigated by means of a weighted least-squares inversion that is based on station-station distances. In addition, our methodology permits the recovery of timing errors at the time of deployment of the OBSs. This error can be attributed to either: i) a wrong initial time synchronization of the OBS or ii) a timing error induced by changing temperature and pressure conditions while the OBS is sunk to the ocean floor. The methodology is implemented in an open-source Python package named OCloC, and we applied it to the OBS recordings acquired in the context of the IMAGE project in and around Reykjanes, Iceland. As expected, most OBSs suffered from clock drift. Surprisingly, we found incurred timing errors at the time of deployment for most of the OBSs.</p> David Naranjo Laura Parisi Sigurjón Jónsson Philippe Jousset Dieter Werthmüller Cornelis Weemstra Copyright (c) 2024 David Naranjo, Laura Parisi, Sigurjón Jónsson, Philippe Jousset, Dieter Werthmüller, Cornelis Weemstra https://creativecommons.org/licenses/by/4.0 2024-01-19 2024-01-19 3 1 10.26443/seismica.v3i1.367 The Impact of the Three-Dimensional Structure of a Subduction Zone on Time-dependent Crustal Deformation Measured by HR-GNSS https://seismica.library.mcgill.ca/article/view/887 <p>Accurately modeling time-dependent coseismic crustal deformation as observed on high-rate Global Navigation Satellite System (HR-GNSS) lends insight into earthquake source processes and improves local earthquake and tsunami early warning algorithms. Currently, time-dependent crustal deformation modeling relies most frequently on simplified 1D radially symmetric Earth models. However, for shallow subduction zone earthquakes, even low-frequency shaking is likely affected by the many strongly heterogeneous structures such as the subducting slab, mantle wedge, and the overlying crustal structure. We demonstrate that including 3D structure improves the estimation of key features of coseismic HR-GNSS time series, such as the peak ground displacement (PGD), the time to PGD (t<sub>PGD</sub>), static displacements (SD), and waveform cross-correlation values. We computed synthetic 1D and 3D, 0.25 Hz and 0.5 Hz waveforms at HR-GNSS stations for four M7.3+ earthquakes in Japan using MudPy and SW4, respectively. From these synthetics, we computed intensity-measure residuals between the synthetic and observed GNSS waveforms. Comparing 1D and 3D residuals, we observed that the 3D simulations show better fits to the PGD and SD in the observed waveforms than the 1D simulations for both 0.25 Hz and 0.5 Hz simulations. We find that the reduction in PGD residuals in the 3D simulations is a combined effect of both shallow and deep 3D structures; hence incorporating only the upper 30 km of 3D structure will still improve the fit to the observed PGD values. Our results demonstrate that 3D simulations significantly improve models of GNSS waveform characteristics and will not only help understand the underlying processes, but also improve local tsunami warning.</p> Oluwaseun Fadugba Valerie Sahakian Diego Melgar Arthur Rodgers Roey Shimony Copyright (c) 2024 Oluwaseun Fadugba, Valerie Sahakian, Diego Melgar, Arthur Rodgers, Roey Shimony https://creativecommons.org/licenses/by/4.0 2024-05-03 2024-05-03 3 1 10.26443/seismica.v3i1.887 Comparison of geodetic slip-deficit and geologic fault slip rates reveals that variability of elastic strain accumulation and release rates on strike-slip faults is controlled by the relative structural complexity of plate-boundary fault systems https://seismica.library.mcgill.ca/article/view/1119 <p>Comparison of geodetic slip-deficit rates with geologic fault slip rates on major strike-slip faults reveals marked differences in patterns of elastic strain accumulation on tectonically isolated faults relative to faults that are embedded within more complex plate-boundary fault systems. Specifically, we show that faults that extend through tectonically complex systems characterized by multiple, mechanically complementary faults (that is, different faults that are all accommodating the same deformation field), which we refer to as high-Coefficient of Complexity (or high-CoCo) faults, exhibit ratios between geodetic and geologic rates that vary and that depend on the displacement scales over which the geologic slip rates are averaged. This indicates that elastic strain accumulation rates on these faults change significantly through time, which in turn suggests that the rates of ductile shear beneath the seismogenic portion of faults also vary through time. This is consistent with models in which mechanically complementary faults trade off slip in time and space in response to varying mechanical and stress conditions on the different component faults. In marked contrast, structurally isolated (or low-CoCo) faults exhibit geologic slip rates that are similar to geodetic slip-deficit rates, regardless of the displacement and time scales over which the slip rates are averaged. Such faults experience relatively constant geologic fault slip rates as well as constant strain accumulation rate (aside from brief, rapid post-seismic intervals). This suggests that low-CoCo faultsd "keep up" with the rate imposed by the relative plate-boundary condition, since they are the only structures in their respective plate-boundary zone that can effectively accommodate the imposed steady plate motion. We hypothesize that the discrepancies between the small-displacement average geologic slip rates and geodetic slip-deficit rates may provide a means of assessing a switch of modes for some high-CoCo faults, transitioning from a slow mode to a faster mode, or vice versa. If so, the differences between geologic slip rates and geodetic slip-deficit rates on high-CoCo faults may indicate changes in a fault's behavior that could be used to refine next-generation probabilistic seismic hazard assessments.</p> Judith Gauriau James Dolan Copyright (c) 2024 Judith Gauriau, James Dolan https://creativecommons.org/licenses/by/4.0 2024-02-22 2024-02-22 3 1 10.26443/seismica.v3i1.1119 Realtime Selection of Optimal Source Parameters Using Ground Motion Envelopes https://seismica.library.mcgill.ca/article/view/1142 <p>It is increasingly common for seismic networks to operate multiple independent automatic algorithms to characterise earthquakes in real-time, such as in earthquake early warning (EEW) or even standard network practice. Commonly used methods to select the best solution at a given time are simple and use ad hoc rules. An absolute measure of how well a solution (event origin and magnitude) matches the observations by the goodness-of-fit between the observed and predicted envelopes is a robust and independent metric to select optimal solutions. We propose such a measure that is calculated as a combination of amplitude and cross-correlation fit. This metric can be used to determine when a preferred solution reaches an appropriate confidence level for alerting, or indeed to compare two (or more) different event characterisations directly. We demonstrate that our approach can also be used to suppress false alarms commonly seen at seismic networks. Tests using the 10 largest earthquakes in Switzerland between 2013 and 2020, and events that caused false alarms demonstrate that our approach can effectively prefer solutions with small errors in location and magnitude, and can clearly identify and discard false origins or incorrect magnitudes, at all time scales, starting with the first event characterisation.</p> Dario Jozinović John Clinton Frédérick Massin Maren Böse Carlo Cauzzi Copyright (c) 2024 Dario Jozinović, John Clinton, Frédérick Massin, Maren Böse, Carlo Cauzzi https://creativecommons.org/licenses/by/4.0 2024-05-09 2024-05-09 3 1 10.26443/seismica.v3i1.1142 Apparent Non-Double-Couple Components as Artifacts of Moment Tensor Inversion https://seismica.library.mcgill.ca/article/view/1157 <p>Compilations of earthquake moment tensors from global and regional catalogs find pervasive non-double-couple (NDC) components<br />with a mean deviation from a double-couple (DC) source of around 20%. Their distributions vary only slightly with magnitude, faulting mechanism, or geologic environments. This consistency suggests thatfor most earthquakes, especially smaller ones whose rupture processes are expected to be simpler, the NDC components are largely artifacts of the moment tensor inversion procedure. This possibility is also supported by the fact that NDC components for individual earthquakes with Mw&lt;6.5 are only weakly correlated between<br />catalogs. We explore this possibility by generating synthetic seismograms for the double-couple components of earthquakes around the<br />world using one Earth model and inverting them with a different Earth model. To match the waveforms with a different Earth model, the inversion changes the mechanisms to include a substantial NDC component while largely preserving the fault geometry (DC component). The resulting NDC components have a size and distribution similar to those reported for the earthquakes in the Global Centroid Moment Tensor (GCMT) catalog. The fact that numerical experiments replicate general features of the pervasive NDC components reported in moment tensor catalogs implies that these components are largely artifacts of the inversions not adequately accounting for the effects of laterally varying Earth structure.</p> Boris Rösler Seth Stein Adam Ringler Jiří Vackář Copyright (c) 2024 Boris Rösler, Seth Stein, Adam T. Ringler, Jiří Vackář https://creativecommons.org/licenses/by/4.0 2024-04-04 2024-04-04 3 1 10.26443/seismica.v3i1.1157 Virtual Shake Robot: Simulating Dynamics of Precariously Balanced Rocks for Overturning and Large-displacement Processes https://seismica.library.mcgill.ca/article/view/692 <p> Understanding the dynamics of precariously balanced rocks (PBRs) is important for seismic hazard analysis and rockfall prediction. Utilizing a physics engine and robotic tools, we develop a virtual shake robot (VSR) to simulate the dynamics of PBRs during overturning and large-displacement processes. We present the background of physics engines and technical details of the VSR, including software architecture, mechanical structure, control system, and implementation procedures. Validation experiments show the median fragility contour from VSR simulation is within the 95% prediction intervals from previous physical experiments, when PGV/PGA is greater than 0.08 s. Using a physical mini shake robot, we validate the qualitative consistency of fragility anisotropy between the VSR and physical experiments. By overturning cuboids on flat terrain, the VSR reveals the relationship between fragility and geometric dimensions (e.g., aspect and scaling ratios). The ground motion orientation and lateral pedestal support affect PBR fragility. Large-displacement experiments estimate rock trajectories for different ground motions, which is useful for understanding the fate of toppled PBRs. Ground motions positively correlate with large displacement statistics such as mean trajectory length, mean largest velocity, and mean terminal distance. The overturning and large displacement processes of PBRs provide complementary methods of ground motion estimation.</p> Zhiang Chen Ramón Arrowsmith Jnaneshwar Das Christine Wittich Chris Madugo Albert Kottke Copyright (c) 2024 Zhiang Chen, Ramón Arrowsmith, Jnaneshwar Das, Christine Wittich, Chris Madugo, Albert Kottke https://creativecommons.org/licenses/by/4.0 2024-01-16 2024-01-16 3 1 10.26443/seismica.v3i1.692 DAS sensitivity to heterogeneity scales much smaller than the minimum wavelength https://seismica.library.mcgill.ca/article/view/1007 <p>Distributed Acoustic Sensing (DAS) is a photonic technology allowing toconvert fiber-optics into long (tens of kilometers) and dense (every few meters) arrays of seismo-acoustic sensors which are basically measuring the strain of the cable all along the cable. The potential of such a distributed measurement is very important and has triggered strong attention in the seismology community for a wide range of applications. In this work, we focus on the interaction of such measurements with heterogeneities of scale much smaller than the wavefield minimum wavelength. With a simple 2-D numerical modeling, we first show that the effect of such small-scale heterogeneities, when located in the vicinity of the instruments, is very different depending on whether we measure particle velocity or strain rate: in the case of velocity, this effect is small but becomes very strong in the case of the strain rate. We then provide a physical explanation of these observations based on the homogenization method showing that indeed, the strain sensitivity to nearby heterogeneities is strong, which is not the case for more traditional velocity measurements. This effect appears as a coupling of the strain components to the DAS measurement. Such effects can be seen as a curse or an advantage depending on the applications.</p> Yann Capdeville Anthony Sladen Copyright (c) 2024 Yann Capdeville, Anthony Sladen https://creativecommons.org/licenses/by/4.0 2024-01-25 2024-01-25 3 1 10.26443/seismica.v3i1.1007 Shear-wave attenuation anisotropy: a new constraint on mantle melt near the Main Ethiopian Rift https://seismica.library.mcgill.ca/article/view/1098 <p>The behaviour of fluids in preferentially aligned fractures plays an important role in a range of dynamic processes within the Earth. In the near-surface, understanding systems of fluid-filled fractures is crucial for applications such as geothermal energy production, monitoring CO2 storage sites, and exploration for metalliferous sub-volcanic brines. Mantle melting is a key geodynamic process, exerting control over its composition and dynamic processes. Upper mantle melting weakens the lithosphere, facilitating rifting and other surface expressions of tectonic processes.<br />Aligned fluid-filled fractures are an efficient mechanism for seismic velocity anisotropy, requiring very low volume fractions, but such rock physics models also predict significant shear-wave attenuation anisotropy. In comparison, the attenuation anisotropy expected for crystal preferred orietation mechanisms is negligible or would only operate outside of the seismic frequency band.<br />Here we demonstrate a new method for measuring shear-wave attenuation anisotropy, apply it to synthetic examples, and make the first measurements of SKS attenuation anisotropy using data recorded at the station FURI, in Ethiopia. At FURI we measure attenuation anisotropy where the fast shear-wave has been more attenuated than the slow shear-wave. This can be explained by the presence of aligned fluids, most probably melts, in the upper mantle using a poroelastic squirt flow model. Modelling of this result suggests that a 1% melt fraction, hosted in aligned fractures dipping ca. 40° that strike perpendicular to the Main Ethiopian Rift, is required to explain the observed attenuation anisotropy. This agrees with previous SKS shear-wave splitting analysis which suggested a 1% melt fraction beneath FURI. The interpreted fracture strike and dip, however, disagrees with previous work in the region which interprets sub-vertical melt inclusions aligned parallel to the Main Ethiopian Rift which only produce attenuation anisotropy where the slow shear-wave is more attenuated. These results show that attenuation anisotropy could be a useful tool for detecting mantle melt, and may offer strong constraints on the extent and orientation of melt inclusions which cannot be achieved from seismic velocity anisotropy alone.</p> Joseph Asplet James Wookey Micheal Kendall Mark Chapman Ritima Das Copyright (c) 2024 Joseph Asplet, James Wookey, Micheal Kendall, Mark Chapman, Ritima Das https://creativecommons.org/licenses/by/4.0 2024-05-15 2024-05-15 3 1 10.26443/seismica.v3i1.1098 PyOcto: A high-throughput seismic phase associator https://seismica.library.mcgill.ca/article/view/1130 <p>Seismic phase association is an essential task for characterising seismicity: given a collection of phase picks, identify all seismic events in the data. In recent years, machine learning pickers have lead to a rapid growth in the number of seismic phase picks. Even though new associators have been suggested, these suffer from long runtimes and sensitivity issues when faced with dense seismic sequences. Here we introduce PyOcto, a novel phase associator tackling these issues. PyOcto uses 4D space-time partitioning and can employ homogeneous and 1D velocity models. We benchmark PyOcto against popular state of the art associators on two synthetic scenarios and a real, dense aftershock sequence. PyOcto consistently achieves detection sensitivities on par or above current algorithms. Furthermore, its runtime is consistently at least 10 times lower, with many scenarios reaching speedup factors above 50.On the challenging 2014 Iquique earthquake sequence, PyOcto achieves excellent detection capability while maintaining a speedup factor of at least 70 against the other models. PyOcto is available as an open source tool for Python on Github and through PyPI.</p> Jannes Münchmeyer Copyright (c) 2024 Jannes Münchmeyer https://creativecommons.org/licenses/by/4.0 2024-01-29 2024-01-29 3 1 10.26443/seismica.v3i1.1130 Spatiotemporal characteristics and earthquake statistics of the 2020 and 2022 adjacent earthquake sequences in North Aegean Sea (Greece) https://seismica.library.mcgill.ca/article/view/1145 <p>The two moderate earthquakes that occurred close and to the north of the North Aegean Trough (NAT) on 26 September 2020 (M<span class="annotation subscript" data-id="subscript_1">w</span>5.3) and 16 January 2022 (M<span class="annotation subscript" data-id="subscript_2">w</span>5.4), both followed by aftershock activity, are examined. Seismic activity along the NAT and its parallel branches is continuous and remarkable, with numerous strong instrumental (M≥6.0) earthquakes. Yet, the frequency of moderate (5.0≤M&lt;6.0) earthquakes outside these major fault branches is rather rare and therefore their investigation provides the optimal means to decipher the seismotectonic properties of the broader area. The temporal and spatial proximity of the two seismic excitations from late September of 2020 through early 2022, intrigues for exhaustive investigation of seismic activity with the employment of earthquake relocation techniques, moment tensor solutions and statistical analysis. Our research revealed that this seismic activity purely falls inside the Mainshock – Aftershock type, with fast aftershock decay rates and moderate productivity. According to our findings, the two seismic sequences, despite their close proximity, exhibit distinctive features as a result of the intricate stress field generated at the western termination of the NAF system in an extensional domain.</p> Pavlos Bonatis Vasileios Karakostas Christos Kourouklas Anastasios Kostoglou Eleftheria Papadimitriou Copyright (c) 2024 Pavlos Bonatis, Vasileios Karakostas, Christos Kourouklas, Anastasios Kostoglou, Eleftheria Papadimitriou https://creativecommons.org/licenses/by/4.0 2024-05-08 2024-05-08 3 1 10.26443/seismica.v3i1.1145 Mapping fault geomorphology with drone-based lidar https://seismica.library.mcgill.ca/article/view/1186 <p>The advent of sub-meter resolution topographic surveying has revolutionized active fault mapping. Light detection and ranging (lidar) collected using crewed airborne laser scanning (ALS) can provide ground coverage of entire fault systems but is expensive, while Structure-from-Motion (SfM) photogrammetry from uncrewed aerial vehicles (UAVs) is popular for mapping smaller sites but cannot image beneath vegetation. Here, we present a new UAV laser scanning (ULS) system which overcomes these limitations to survey fault-related topography cost-effectively, at desirable spatial resolutions, and even beneath dense vegetation. In describing our system, data acquisition and processing workflows, we provide a practical guide for other researchers interested in developing their own ULS capabilities. We showcase ULS data collected over faults from a variety of terrain and vegetation types across the Canadian Cordillera and compare them to conventional ALS and SfM data. Due to the lower, slower UAV flights, ULS offers improved ground return density (~260 points/m<sup>2</sup> for the capture of a paleoseismic trenching site and ~10<span dir="ltr" style="left: 223.965px; top: 566.841px; font-size: 11.1295px; font-family: sans-serif; transform: scaleX(0.946739);" role="presentation">–</span>72 points/m<sup>2</sup> for larger, multi-kilometer fault surveys) over conventional ALS (~3<span dir="ltr" style="left: 223.965px; top: 566.841px; font-size: 11.1295px; font-family: sans-serif; transform: scaleX(0.946739);" role="presentation">–</span>9 points/m<sup>2</sup>) as well as better vegetation penetration than both ALS and SfM. The resulting ~20<span dir="ltr" style="left: 223.965px; top: 566.841px; font-size: 11.1295px; font-family: sans-serif; transform: scaleX(0.946739);" role="presentation">–</span>50 cm-resolution ULS terrain models reveal fine-scale tectonic landforms that would otherwise be challenging to image.</p> Guy Salomon Theron Finley Edwin Nissen Roger Stephen Brian Menounos Copyright (c) 2024 Guy Salomon, Theron Finley, Edwin Nissen, Roger Stephen, Brian Menounos https://creativecommons.org/licenses/by/4.0 2024-06-05 2024-06-05 3 1 10.26443/seismica.v3i1.1186 Influence of outer-rise faults on shallow décollement heterogeneity and sediment flux at the Japan trench https://seismica.library.mcgill.ca/article/view/386 <p>We investigate the impact of outer-rise normal fault subduction on the structural evolution of the décollement and frontal prism in a portion of the Japan trench that hosted the 2011 Tohoku earthquake. We use seismic reflection data to map the relative occurrence of sediment accretion, sediment subduction, and frontal tectonic erosion in the shallow portion of the subduction zone and correlate these deformation styles to the magnitude of outer-rise fault throw and incoming plate sediment thickness. These data reveal spatial heterogeneity in the modes of deformation over distances of 5-10 km that necessitate correlative heterogeneity in the geometry and composition of the shallow décollement over similar length-scales. We find that sediment accretion predominantly occurs in regions where incoming plate sediment thickness is greater than fault throw. In these areas, the décollement appears to be non-planar and compositionally homogenous. Conversely, frontal tectonic erosion and slope failures are predominantly observed in regions where fault throw is greater than sediment thickness. In these areas, the décollement may be planar but compositionally heterogeneous. Additionally, spatial variations in near trench slip appear to correlate with the dominant deformation modes, suggesting that both sediment thickness and outer-rise fault throw may be important controls on shallow megathrust behavior.</p> Emily Schottenfels Christine Regalla Yasuyuki Nakamura Copyright (c) 2024 Emily Schottenfels, Christine Regalla, Yasuyuki Nakamura https://creativecommons.org/licenses/by/4.0 2024-01-15 2024-01-15 3 1 10.26443/seismica.v3i1.386 Detection of slow slip events along the southern Peru - northern Chile subduction zone https://seismica.library.mcgill.ca/article/view/980 <p>Detections of slow slip events (SSEs) are now common along most plate boundary fault systems at the global scale. However, no such event has been described in the south Peru - north Chile subduction zone so far, except for the early preparatory phase of the 2014 Iquique earthquake. We use geodetic template matching on GNSS-derived time series of surface motion in Northern Chile to extract SSEs hidden within the geodetic noise. We detect 33 events with durations ranging from 9 to 40 days and magnitudes from Mw 5.6 to 6.2. The moment released by these aseismic events seems to scale with the cube of their duration, suggesting a dynamic comparable to that of earthquakes. We compare the distribution of SSEs with the distribution of coupling along the megathrust derived using Bayesian inference on GNSS- and InSAR-derived interseismic velocities. From this comparison, we obtain that most SSEs occur in regions of intermediate coupling where the megathrust transitions from locked to creeping or where geometrical complexities of the interplate region have been proposed. We finally discuss the potential role of fluids as a triggering mechanism for SSEs in the area.</p> Jorge Jara Romain Jolivet Anne Socquet Diana Comte Edmundo Norabuena Copyright (c) 2024 Jorge Jara, Romain Jolivet, Anne Socquet, Diana Comte, Edmundo Norabuena https://creativecommons.org/licenses/by/4.0 2024-06-10 2024-06-10 3 1 10.26443/seismica.v3i1.980 Testing the Predictive Power of b Value for Italian Seismicity https://seismica.library.mcgill.ca/article/view/1084 <p>A very efficient method for estimating the completeness magnitude<em> m<sub>c</sub></em> and the scaling parameter <em>b</em> of earthquake magnitude distribution has been thoroughly tested using synthetic seismic catalogues. Subsequently, the method was employed to assess the capability of the <em>b</em>-value in differentiating between foreshocks and aftershocks, confirming previous findings regarding the Amatrice-Norcia earthquake sequence. However, a blind algorithm reveals that the discriminative ability of the <em>b</em>-value necessitates a meticulous selection of the catalogue, thereby reducing the predictability of large events occurring subsequent to a prior major earthquake.</p> Cataldo Godano Anna Tramelli Giuseppe Petrillo Vincenzo Convertito Copyright (c) 2024 Cataldo Godano, Anna Tramelli, Giuseppe Petrillo, Vincenzo Convertito https://creativecommons.org/licenses/by/4.0 2024-02-01 2024-02-01 3 1 10.26443/seismica.v3i1.1084 VIP - Variational Inversion Package with example implementations of Bayesian tomographic imaging https://seismica.library.mcgill.ca/article/view/1143 <p>Bayesian inference has become an important methodology to solve inverse problems and to quantify uncertainties in their solutions. Variational inference is a method that provides probabilistic, Bayesian solutions efficiently by using optimisation. In this study we present a Python Variational Inversion Package (VIP), to solve inverse problems using variational inference methods. The package includes automatic differential variational inference (ADVI), Stein variational gradient descent (SVGD) and stochastic SVGD (sSVGD), and provides implementations of 2D travel time tomography and 2D full waveform inversion including test examples and solutions. Users can solve their own problems by supplying an appropriate forward function and a gradient calculation code. In addition, the package provides a scalable implementation which can be deployed easily on a desktop machine or using modern high performance computational facilities. The examples demonstrate that VIP is an efficient, scalable, extensible and user-friendly package, and can be used to solve a wide range of low or high dimensional inverse problems in practice.</p> Xin Zhang Andrew Curtis Copyright (c) 2024 Xin Zhang, Andrew Curtis https://creativecommons.org/licenses/by/4.0 2024-05-29 2024-05-29 3 1 10.26443/seismica.v3i1.1143 The First Network of Ocean Bottom Seismometers in the Red Sea to Investigate the Zabargad Fracture Zone https://seismica.library.mcgill.ca/article/view/729 <p>In the last decades, the slow-spreading Red Sea rift has been the objective of several geophysical investigations to study the extension of the oceanic crust, the thickness of the sedimentary cover, and the formation of transform faults. However, local seismology datasets are still lacking despite their potential to contribute to the understanding of the tectonic evolution of the Red Sea. The Zabargad Fracture Zone is located in the Northern Red Sea and significantly offsets the rift axis to the East. Thus, it is considered a key tectonic element to understand better the formation of the Red Sea rift. To fill the gap in the dataset availability, we deployed the first passive seismic network in the Red Sea, within the Zabargad Fracture Zone. This network included 12 Lobster OBSs from the DEPAS pool, 2 OBS developed and deployed by Fugro, and 4 portable seismic land stations deployed on islands and onshore on the Saudi Arabian coast. Our data-quality analysis confirms that the head-buoy cable free to strum, as well as other additional elements of the DEPAS OBSs, generate seismic noise at frequencies $&gt;$ 10 Hz. However, the Fugro OBSs show high-frequency disturbances even if they lack vibrating elements. Comparison between land and OBS stations reveals that noise between 1 and 10 Hz is due to ocean-generated seismic noise, and not due to resonance of the OBS elements. We also found that waveforms of teleseismic earthquakes recorded by the Fugro OBSs, islands, and onshore stations have comparable signal-to-noise ratios. Instead, differences in signal-to-noise ratio for local earthquakes are affected more by site and path effects than instrument settings.</p> Laura Parisi Nico Augustin Daniele Trippanera Henning Kirk Anke Dannowski Rémi Matrau Margherita Fittipaldi Adriano Nobile Olaf Zielke Eduardo Valero Cano Guus Hoogewerf Theodoros Aspiotis Sofia Manzo-Vega Armando Espindola Carmona Alejandra Barreto Marlin Juchem Cahli Suhendi Mechita Schmidt-Aursch P. Martin Mai Sigurjón Jónsson Copyright (c) 2024 Laura Parisi, Nico Augustin, Daniele Trippanera, Henning Kirk, Anke Dannowski, Rémi Matrau, Margherita Fittipaldi, Adriano Nobile, Olaf Zielke, Eduardo Valero Cano, Guus Hoogewerf, Theodoros Aspiotis, Sofia Manzo-Vega, Armando Espindola Carmona, Alejandra Barreto, Marlin Juchem, Cahli Suhendi, Mechita Schmidt-Aursch, P. Martin Mai, Sigurjón Jónsson https://creativecommons.org/licenses/by/4.0 2024-04-30 2024-04-30 3 1 10.26443/seismica.v3i1.729 The SCEC/USGS Community Stress Drop Validation Study Using the 2019 Ridgecrest Earthquake Sequence https://seismica.library.mcgill.ca/article/view/1009 <p class="Abstracttext">We introduce a community stress drop validation study using the 2019 Ridgecrest, California, earthquake sequence, in which researchers are invited to use a common dataset to independently estimate comparable measurements using a variety of methods. Stress drop is the change in average shear stress on a fault during earthquake rupture, and as such is a key parameter in many ground motion, rupture simulation, and source physics problems in earthquake science. Spectral stress drop is commonly estimated by fitting the shape of the radiated energy spectrum, yet estimates for an individual earthquake made by different studies can vary hugely. In this community study, sponsored jointly by the U. S. Geological Survey and Southern/Statewide California Earthquake Center, we seek to understand the sources of variability and uncertainty in earthquake stress drop through quantitative comparison of submitted stress drops. The publicly available dataset consists of nearly 13,000 earthquakes of M1 to 7 from two weeks of the 2019 Ridgecrest sequence recorded on stations within 1-degree. As a community study, findings are shared through workshops and meetings and all are invited to join at any time, at any interest level.</p> Annemarie Baltay Rachel Abercrombie Shanna Chu Taka'aki Taira Copyright (c) 2024 Annemarie Baltay, Rachel Abercrombie, Shanna Chu, Taka'aki Taira https://creativecommons.org/licenses/by/4.0 2024-05-22 2024-05-22 3 1 10.26443/seismica.v3i1.1009 SeisMIC - an Open Source Python Toolset to Compute Velocity Changes from Ambient Seismic Noise https://seismica.library.mcgill.ca/article/view/1099 <p>We present SeisMIC, a fast, versatile, and adaptable open-source software to estimate seismic velocity changes from ambient seismic noise. SeisMIC includes a broad set of tools and functions to facilitate end-to-end processing of ambient noise data, from data retrieval and raw data analysis via spectrogram computation, over waveform coherence analysis, to post-processing of the final velocity change estimates. A particular highlight of the software is its ability to invert velocity change time series onto a spatial grid, making it possible to create maps of velocity changes. To tackle the challenge of processing large continuous datasets, SeisMIC can exploit multithreading at high efficiency with an about five-time improvement in compute time compared to MSNoise, probably the most widespread ambient noise software. In this manuscript, we provide a short tutorial and tips for users on how to employ SeisMIC most effectively. Extensive and up-to-date documentation is available online. Its broad functionality combined with easy adaptability and high efficiency make SeisMIC a well-suited tool for studies across all scales.</p> Peter Makus Christoph Sens-Schönfelder Copyright (c) 2024 Peter Makus, Christoph Sens-Schönfelder https://creativecommons.org/licenses/by/4.0 2024-02-04 2024-02-04 3 1 10.26443/seismica.v3i1.1099 Seismoacoustic measurements of the OSIRIS-REx re-entry with an off-grid Raspberry PiShake https://seismica.library.mcgill.ca/article/view/1154 <p>Hypersonic re-entries of spacecraft are valuable analogues for the identification and tracking of natural meteoroids re-entering the Earth's atmosphere. We report on the detection of seismic and acoustic signals from the OSIRIS-REx landing sequence, acquired near the point of peak capsule heating and recorded using a fully off-grid Raspberry PiShake sensor. This simple setup is able to record all the salient features of both the seismic and acoustic wavefields; including the primary shockwave, later reverberations, and possible locally induced surface waves. Peak overpressures of 0.7 Pa and ground velocities of 2x10<sup>-6</sup>m/s yield lower bound on the air-to-ground coupling factor between 3 and 44 Hz of 1.4x10<sup>-6</sup> m/s/Pa, comparable to results from other re-entries</p> Benjamin Fernando Constantinos Charalambous Christelle Saliby Eleanor Sansom Carene Larmat David Buttsworth Daniel Hicks Roy Johnson Kevin Lewis Meaghan McCleary Giuseppe Petricca Nick Schmerr Fabian Zander Jennifer Inman Copyright (c) 2024 Benjamin Fernando, Constantinos Charalambous, Christelle Saliby, Eleanor Sansom, Carene Larmat, David Buttsworth, Daniel Hicks, Roy Johnson, Kevin Lewis, Meaghan McCleary, Giuseppe Petricca, Nick Schmerr, Fabian Zander, Jennifer Inman https://creativecommons.org/licenses/by/4.0 2024-03-26 2024-03-26 3 1 10.26443/seismica.v3i1.1154 History and activities of the European-Mediterranean Seismological Centre https://seismica.library.mcgill.ca/article/view/981 <p>The European-Mediterranean Seismological Centre (EMSC) provides rapid information on earthquakes and their effects, but does not operate seismic stations. It collects and merges parametric earthquake data from seismological agencies and networks around the world and collects earthquake observations from global earthquake eyewitnesses. Since its creation in 1975, it has developed strategies to complement earthquake monitoring activities of national agencies and coordinated its activities in Europe with its sister organisations ORFEUS and EFEHR as well as with global actors, while being part of the transformative EPOS initiative. The purpose of this article is to give a brief history of the EMSC and describe its activities, services and coordination mechanisms.</p> Rémy Bossu Florian Haslinger Hélène Hébert Copyright (c) 2024 Rémy Bossu, Florian Haslinger, Hélène Hébert https://creativecommons.org/licenses/by/4.0 2024-01-16 2024-01-16 3 1 10.26443/seismica.v3i1.981 Curated Regional Earthquake Waveforms (CREW) Dataset https://seismica.library.mcgill.ca/article/view/1049 <p>We have assembled CREW, the Curated Regional Earthquake Waveforms Dataset, which is a dataset of earthquake arrivals recorded at local and regional distances. CREW was assembled from millions of waveforms with quality control through semi-supervised learning. CREW includes 1.6 million waveforms that have global coverage. Each waveform consists of a 5 minute three component seismogram with labels for both a P and S arrival. CREW provides a high quality labelled waveform data set that can be used to develop and test machine learning models for the analysis of earthquakes recorded at regional distances.</p> Albert Leonardo Aguilar Suarez Greg Beroza Copyright (c) 2024 Albert Leonardo Aguilar Suarez, Greg Beroza https://creativecommons.org/licenses/by/4.0 2024-05-23 2024-05-23 3 1 10.26443/seismica.v3i1.1049