Seismica

Changes in seismic anisotropy at Ontake volcano: a tale of two eruptions

Mon, 28 Apr 2025 00:00:00 -0400

The interaction of faults, fractures, and hydromagmatic systems of volcanoes can lead to complicated stress patterns that vary over short spatial and temporal scales. Here we study stress-induced anisotropy using observations of shear-wave splitting at 12 stations across Ontake volcano, Japan. The results reveal a complicated pattern of anisotropy indicating that the volcano perturbs the local stress field. In 2007, a minor phreatic eruption (VEI 0) occurred at Ontake, but there is little evidence of changes in splitting parameters during this eruption. In contrast, the much large eruption of 2014 (VEI 3) shows clear temporal changes in splitting parameters following the eruption. The average background magnitude of anisotropy, as described by the delay time between the fast and slow shear wave, doubles to nearly 0.2 second at the onset of the 2014 eruption, but the percent anisotropy increases dramatically from 3% to 20%. Contemporaneously, the polarisation of the fast shear wave rotates towards s_Hmax. We interpret these observations in terms of basal heating of the hydrothermal system. We suggest that a lack of temporal variation in anisotropy parameters during the 2007 eruption indicates that a critical stress or crack density threshold must be overcome to exhibit a change in anisotropy, which may be indicative of a more significant eruption.

An analysis of the dynamic range of Distributed Acoustic Sensing for Earthquake Early Warning

Martijn van den Ende, Alister Trabattoni, Marie Baillet, Diane Rivet — Thu, 24 Apr 2025 00:00:00 -0400

Owing to its deployment and sensing characteristics, Distributed Acoustic Sensing (DAS) has been touted as a promising technology for low-cost and low-latency Earthquake Early Warning (EEW). While preliminary experiments conducted by several research groups have yielded encouraging results, it must be acknowledged that these EEW feasibility studies were performed only on low-magnitude events. When exposed to the wavefield of a large magnitude earthquake (being the prime subject of EEW), the DAS strain rate recordings are likely to become highly distorted ("saturated") due to cycle skipping of the optical phase measurements, to an extent that the recorded data start to degrade to uniform random noise. This clearly poses a major challenge to EEW, as neither amplitude nor phase information can be readily extracted from saturated DAS data. In this study, we perform a detailed analysis of the dynamic range of DAS, both from theoretical and practical perspectives. We offer a set of criteria that need to be met for matching the DAS dynamic range with EEW targets, and we propose a computationally convenient method to quantify the information content of saturated recordings. We apply these methods to DAS data recorded offshore Chile, and identify several avenues for future research to improve the feasibility of DAS for EEW.

Monitoring Time Variations in Seismic Noise Amplitude at Permanent Seismic Networks

Mon, 07 Apr 2025 00:00:00 -0400

The quality control process usually followed at broad-band seismic networks includes the calculation of the power spectral density and their probability density functions. These results do not make possible a quick estimation of temporal variations that can result from non-continuous sources of noise, meteorologic phenomena, etc. We propose the use of the SeismoRMS package, originally developed to analyze the seismic amplitude variations associated with the COVID19 lockdown, to monitor the time evolution of seismic noise sources in a permanent network, using as a case example the dataset collected during 2023 by the CA network in NE Iberia. Frequencies above 1 Hz show remarkable differences between the stations, despite sharing similar installation settings. Most of the sites show day/night and working day/weekend variations, suggesting a relevant contribution of anthropic sources, but the amplitude of such variations differs strongly among the sites. Our study allows us to identify specific sources of noise affecting some sites during short and regular time periods, an aspect that needs to be taken into account when evaluating the overall quality of each site. We conclude that a systematic analysis of the amplitude variations at different frequency bands can be a tool of interest for the management of a broad-band seismic network.

Using citizen science Raspberry Shake seismometers to enhance earthquake location and characterization: a case study from Wellington, New Zealand

Wed, 05 Feb 2025 00:00:00 -0500

The recent development of low-cost citizen seismometers has opened new avenues for earthquake analysis. We explore the integration of Raspberry Shake citizen seismometers with the national GeoNet seismic network to improve the precision of earthquake locations in Wellington, New Zealand. We use a dataset of 19 earthquakes between magnitudes 1.1 and 3.5 and between hypocentral distances of 22 km and 102 km. Our findings demonstrate that using Raspberry Shake seismometers in conjunction with the GeoNet network is effective for both the locating and characterisation of earthquakes. Notably, we find that precise station locations are less critical for precise earthquake location, a significant factor given that the publicly available Raspberry Shake locations are obfuscated to protect user privacy. These results suggest that, dependent on network geometry, citizen seismometer data can be a valuable tool in seismic monitoring and improve earthquake location capability, whilst remaining cost-effective.

Unlocking DAS amplitude information through coherency coupling quantification

Tom Hudson, Anna Stork, Jack Muir, Andreas Fichtner — Tue, 11 Mar 2025 00:00:00 -0400

Distributed Acoustic Sensing (DAS) allows one to measure strain at metre-resolution along a fibreoptic cable, increasing the density of spatial sampling of a seismic wavefield compared to conventional instrumentation. However, the challenge of measuring DAS-derived strain amplitude currently limits applications of this technology. Amplitude measurements are required in passive seismology for estimating earthquake magnitudes, moment tensor inversion and attenuation tomography, for example. For active seismic studies, amplitude information is essential for methods such as Amplitude Versus Offset (AVO) analysis. Central to this challenge is quantifying how well the fibre is coupled to the subsurface. Here, we present a method using coherency to pragmatically estimate coupling of fibre to the medium. We first introduce a theoretical justification relating coherency to relative coupling between channels and calibrating this to obtain absolute coupling coefficients, before evidencing the performance of the method using various examples from glaciers to downhole geothermal deployments. We apply the method to estimate earthquake magnitudes, comparing values to independent geophone estimates. The results allow us to explore whether quantifying coupling is possible or indeed necessary to account for in certain instances. We find that although coupling of fibre to the medium is important, results suggest that practically in many cases, it may be appropriate to simply make the binary first-order assumption that fibre is either approximately perfectly coupled or too poorly coupled for any amplitude analysis. While our findings do not comprehensively solve the fibre-optic coupling problem, the theory and results provide a practical foundation with which to start using DAS-derived amplitude information in earnest.

Distributed Acoustic Sensing for aftershock monitoring: the case of the 2019 Mw 4.9 Le Teil earthquake

Mon, 03 Mar 2025 00:00:00 -0500

Recent developments in Distributed Acoustic Sensing (DAS) have greatly expanded our capabilities for dense geophysical instrumentation by tapping into existing (but unused) fibre-optic telecommunication networks. Leveraging these so-called "dark fibres" permits an extremely rapid deployment of thousands of vibration sensors over distances of several tens of kilometres, which is ideal for rapid postseismic response efforts. Here we report on the use of dark-fibre DAS for monitoring of the aftershock sequence of the 2019-11-11 Mw 4.9 Le Teil, France earthquake. Through comparison with the local seismometer network, we assess the capabilities of the DAS array to detect and locate small-magnitude seismic events. Likely owing to cable deployment and DAS sensing characteristics, we find that the DAS noise floor is up to 3 orders of magnitude higher than that of nearby seismometers, which greatly inhibits the detection and analysis of the low-energy events. However, locating a selected aftershock with DAS yields an accuracy and precision that is comparable to that of the seismic network, even though the DAS array has a relatively unfavourable geometry. Based on these observations we provide a number of recommendations for routinely incorporating DAS into postseismic response protocols, and for optimal use of DAS alongside conventional seismic instrumentation.

An unexplained tsunami: Was there megathrust slip during the 2020 Mw7.6 Sand Point, Alaska, earthquake?

Wed, 12 Feb 2025 00:00:00 -0500

On October 19, 2020, the M_w7.6 Sand Point earthquake struck south of the Shumagin Islands in Alaska. Moment tensors indicate the earthquake was primarily strike-slip, yet the event produced an enigmatic tsunami that was larger and more widespread than expected for an earthquake of that magnitude and mechanism. Using a suite of hydrodynamic, seismic, and geodetic modeling techniques, we explore plausible causes of the tsunami. We find that strike-slip models consistent with the moment tensor orientation cannot produce the observed tsunami. Hydrodynamic inversion of sea surface deformation from deep ocean and tide gauge data suggest seafloor deformation more closely matches a megathrust, rather than a strike-slip, source. Static slip inversions, using sea level and Global Navigation Satellite System data, allow for a portion of co-seismic megathrust slip that can explain tsunamigenesis. Combining all available geophysical datasets to model the kinematic rupture, we show that considerable, relatively slow, megathrust slip is allowable in the Shumagin segment, concurrent with strike-slip faulting. We hypothesize that the slow megathrust rupture does not contribute much seismic radiation allowing it to previously go unnoticed with traditional seismic monitoring.

On single-station, six degree-of-freedom observations of local to regional seismicity at the Piñon Flat Observatory in Southern California

Tue, 06 May 2025 00:00:00 -0400

In September 2022, a portable, three-component rotational rate sensor, namely a blueSeis-3A gyroscope, has been deployed at the underground vault of the Pinon Flat Observatory (PFO) in southern California. A three-component, broadband seismometer is co-located, jointly forming a six degree-of-freedom (DoF) station for long-term observations of local and regional seismicity and multi-component wavefield studies. The seismic recordings are available online via IRIS FDSN services as PY.BSPF (BlueSeis at Pinon Flat). The instrumentation at PFO additionally provides high-quality strain observations, allowing now to study translation, rotations and strain of the seismic wavefield in a low noise and high seismicity area (e.g. San Andreas fault zone). The seismic array at PFO is used to compute array derived rotations and validate the direct observations of rotational ground motions. We show results of 6-DoF processing applied to a local Mw 4.1 and a regional Mw 6.2 event to obtain backazimuth estimates, which we validate with array beamforming, and estimates of local seismic phase velocities. For observed events between October 2022 and October 2023, we detect more than 400 events of which 118 are triggered on all six components. Peak rotation rate amplitudes are used to derive empirical peak amplitude relations for vertical and horizontal rotation rates to provide valuable insights towards resolvability for comparable 6~DoF campaigns. We find the dominating limitations for rotational motion observations currently to be set by the self-noise level of the blueSeis-3A rotation sensor and encourage further instrumental development.

Near-real-time design of experiments for seismic monitoring of volcanoes

Dominik Strutz, Andrew Curtis — Fri, 14 Feb 2025 00:00:00 -0500

Monitoring the seismic activity of volcanoes is crucial for hazard assessment and eruption forecasting. The layout of each seismic network determines the information content of recorded data about volcanic earthquakes, and experimental design methods optimise sensor locations to maximise that information. We provide a code package that implements Bayesian experimental design to optimise seismometer networks to locate seismicity at any volcano, and a practical guide to make this easily and rapidly implementable by any volcano seismologist. This work is the first to optimise travel-time, amplitude and array source location methods simultaneously, making it suitable for a wide range of volcano monitoring scenarios. The code-package is designed to be straightforward to use and can be adapted to a wide range of scenarios, and automatically links to existing global databases of topography and properties of volcanoes worldwide to allow rapid deployment. Any user should be able to obtain an initial design within minutes using a combination of generic and volcano-specific information to guide the design process, and to refine the design for their specific scenario within hours, if more specific prior information is available.

Picking first arrivals in hydroacoustic seismograms from MERMAID floats

Fri, 25 Apr 2025 00:00:00 -0400

Floating seismometers (‘MERMAIDs’) operating in the noisy environment of the world’s oceans pose a challenge for picking the time of earthquake first arrivals. We report on an experiment to estimate the errors in picked arrivals from 49 MERMAIDS operating in the South Pacific, using two independent strategies. For 15 events, the same arrivals were redundandly picked by several analysts, allowing for a direct estimate of error distributions. Standard errors in times from MERMAID seismograms vary from 0.2 s for close events at mantle depths in the Kermadec subduction zone to more than 2 s for crustal events at large epicentral distance. In a second experiment we analysed the a posteriori misfits after tomographically inverting all events. The residual traveltime misfit is consistent with the error estimates from the first experiment, but also shows inconsistencies with arrival times from the ISC-EHB and NEIC catalogues, which we attribute to errors in the published hypocentres and/or origin times.

Migration of Seismicity from the Mantle to the Upper Crust Beneath Harrat Lunayyir Volcanic Field, Saudi Arabia

Alexander Blanchette, Simon Klemperer, Walter Mooney, Turki Sehli — Thu, 27 Feb 2025 00:00:00 -0500

Harrat Lunayyir is a volcanic field in Saudi Arabia that experienced a Mw~5.4 earthquake driven by an upper-crustal dike intrusion in May 2009. This volcanic field has exhibited numerous forms of volcanic seismicity both prior to and since the 2009 dike intrusion. Significantly, earthquakes within the lithospheric mantle and, rarely, the lower crust are present in the two-decade long seismicity catalog of Harrat Lunayyir. Here we analyze 24 years of volcanic seismicity at Harrat Lunayyir from 1998 to 2022. We find that: 1) precursory seismicity began at least eight years prior to the 2009 event, with a particularly notable seismic episode one year prior; 2) lithospheric mantle seismicity is highly localized in space and in time, largely occurring in discrete sequences lasting on the order of a few hours to a few days; 3) one seismic sequence clearly migrates upward from the lithospheric mantle to the upper crust, including seismicity within the nominally ductile lower crust; 4) crustal seismicity has been slowly declining over time; and 5) lithospheric-mantle seismicity does not show any apparent decline with time. From these observations we infer that the seismicity is driven by magmatic fluids or volatiles, and seismic monitoring of this volcanic field should continue into the future.

Qseek: A data-driven Framework for Automated Earthquake Detection, Localization and Characterization

Wed, 19 Feb 2025 00:00:00 -0500

We introduce a data-driven method and software for detecting and locating earthquakes in large seismic datasets. By combining seismic phase arrival annotations, delivered by neural network phase pickers, and waveform stacking with an adaptive octree search, we can automatically detect and locate seismic events even in noise-dominant seismic data. The resolution of the search volume is iteratively refined toward the seismic source location; this strategy facilitates an efficient, fast, and accurate search. We present a user-friendly and high-performance open-source software framework based on established frameworks, featuring event detection in layered 1D and complex 3D velocity models and event feature extraction capabilities, such as moment and local magnitude calculation from peak ground motions. We incorporated station-specific corrections and source-specific station terms into the search to enhance the location accuracy. We demonstrate and validate our approach by extracting extensive earthquake catalogs from large seismic datasets in different regions and geological settings: (1) Reykjanes Peninsula, Iceland; (2) Eifel volcanic region, Germany; and (3) Utah FORGE, USA. We capture seismic events from tectonic activity, volcanic swarms, and induced microseismic activity with magnitudes ranging from -1 to 5. Such precise and complete earthquake catalogs contribute to the interpretation and understanding of otherwise hidden subsurface processes.

Performance of Automatic Detector & Locator Tested on Synthetic Seismograms

Eva Káldy, Tomáš Fischer — Wed, 09 Apr 2025 00:00:00 -0400

Seismic network sensitivity and event detection performance are critical for assessing earthquake risks, particularly in regions susceptible to induced seismicity. In seismically inactive zones, the network monitoring presents unique challenges, even when adapting automated detection and location systems originally designed for active zones.

In this study, we evaluate the capabilities of the seismic network deployed in the Litoměřice region of the Czech Republic, where a geothermal project is underway and no seismicity was recorded in years of monitoring. Using synthetic seismograms, we simulate a potential earthquake in the geothermal well to assess the network's detection efficiency at the most exposed area. PEPiN, an automated earthquake picker and locator which was originally designed for the West Bohemia region, is employed to analyze the synthetic dataset with real background seismicity.

Our results demonstrate that PEPiN detects and localizes 82% of the synthetic events with magnitude of completeness M_L-0.5, slightly above the value predicted by our previous research. Overall, our findings provide valuable insights into the seismic monitoring capabilities of the Litoměřice network, shedding light on the potential strengths and limitations of seismic surveillance systems in similar geothermal and underground operation settings.

Mapping finite-fault earthquake slip using spatial correlation between seismicity and point-source Coulomb failure stress change

Anthony Lomax — Mon, 03 Mar 2025 00:00:00 -0500

Most earthquake energy release arises during fault slip many kilometers below the Earth’s surface. Understanding earthquakes and their hazard requires mapping the geometry and distribution of this slip. Such finite-fault maps are typically derived from surface phenomena, such as seismic and geodetic ground motions. Here we introduce an imaging procedure for mapping finite-fault slip directly from seismicity and aftershocks—phenomena occurring at depth around an earthquake rupture. For specified source and receiver faults, we map source-fault slip in 3D by correlation of point-source Coulomb failure stress change (ΔCFS) kernels across the distribution of seismicity around the source. These seismicity-stress maps show relative, static fault slip compatible with the surrounding seismicity given the physics of ΔCFS; they can aid other slip inversions, aftershock forecasting, and study of early instrumental earthquakes and volcanic intrusions. We verify this procedure recovers synthetic fault slip which matches independent estimates of slip for the 2004 Mw 6.0 Parkfield and 2021 Mw 6.0 Antelope Valley California earthquakes. For the 2018 Mw 7.1 Anchorage Alaska intra-slab earthquake, seismicity-stress maps, combined with multi-scale precise hypocenter relocation, resolve the enigma of which mainshock faulting plane ruptured (the gently east-dipping plane), and clarify slab structures activated in the energetic aftershock sequence.

Picking Regional Seismic Phase Arrival Times with Deep Learning

Albert Leonardo Aguilar Suarez, Gregory Beroza — Wed, 30 Apr 2025 00:00:00 -0400

Sparse instrumental coverage for much of the Earth requires working with regional seismic phases for effective seismic monitoring. Machine learning phase pickers to date have focused on local earthquake recordings. Here we present deep learning models designed and trained to be effective at picking the arrival times of earthquake phases at distances up to 20 degrees. We trained our models on the CREW dataset, which includes 1.6 million earthquake waveforms with over 3.2 million labeled arrivals on 5 minute long three component seismograms. We present models that accurately pick the first arriving P and S waves and models that pick and classify Pn, Pg, Sn, and Sg phase arrivals. We apply these models in a variety of settings and compare their performance to established machine learning models that were trained on local earthquake recordings. We demonstrate the abilities of our models by finding new earthquakes in the Gorda plate offshore northern California. Finally, we use our multiple phase picker to find new examples with secondary arrivals from our massive training dataset. The goal of this method is to improve automatic earthquake monitoring in regions of sparse instrumental coverage and seismicity in remote regions far from instrumentation.

A new consistent and high-precision earthquake catalogue for the Taupō Volcanic Zone, New Zealand

Finnigan Illsley-Kemp, Eleanor Mestel — Fri, 02 May 2025 00:00:00 -0400

The Taupō Volcanic Zone is a ~300 km long, volcanically active region in the North Island of Aotearoa New Zealand. As well as hosting numerous active volcanoes, it is also one of the most seismically active parts of the country. In this study, we present a new consistent and high-precision earthquake catalogue for the Taupō Volcanic Zone from 2007 to 2023. This catalogue was produced through the detection of earthquake phase arrivals, association of these arrivals, and finally earthquake location and relocation using a three-dimensional velocity model. The final catalogue contains 86,579 individual earthquakes, 65% of which also have a high-precision relative relocation hypocentre. The catalogue contains a huge amount of information on multiple volcanic, geothermal, and tectonic events. We make the catalogue freely available in the hope that it will be used for future research and development in the Taupō Volcanic Zone.

Evidence for Far-Field Wastewater Disposal Causing Recent Increases in Seismicity in Central and Northern Kansas

Shannon Fasola, Mike Brudzinski, Noel Jackson — Tue, 06 May 2025 00:00:00 -0400

The rate of felt earthquakes in Kansas increased dramatically in 2014, where most seismicity initially occurred in southern Kansas, and was attributed to large-volume wastewater disposal (WD) near the Oklahoma-Kansas border. Interestingly, 9 of 10 magnitude 4+ earthquakes from 2019-2022 occurred in northern and central Kansas, where the nature of seismicity has not been explored. We investigated seismicity near the recent M4+ earthquakes using waveform cross-correlation and carefully assembled injection and extraction volumes, well stimulations, and pressure measurements. Waveform cross-correlation reveals earthquakes occur via swarms with low b-values implying a stress state that is closer to failure. Relative volumes and temporal trends indicate seismicity was primarily induced by WD into the Arbuckle. However, the large coefficient of variation of interevent times suggests primarily far-field pressure influences. In particular, Jewell County seismicity provides strong evidence of far-field forcing as it occurs >50 km from any WD wells and ~100 km from large volume WD wells, one of the largest distances of WD-induced seismicity documented. The heterogenous locations of seismicity relative to WD wells is likely controlled by preexisting unknown structures and prestresses. These results imply a large spatial influence from proposed large volume carbon sequestration in the Arbuckle and similar formations.

Scaled seismotectonic models of megathrust seismic cycles through the lens of dynamical system theory

Fabio Corbi, Adriano Gualandi, Giacomo Mastella, Francesca Funiciello — Tue, 25 Feb 2025 00:00:00 -0500

We investigate the physics of laboratory earthquakes in scaled seismotectonic models of megathrust seismic cycles. We study models of different sizes, materials, deformation rates, and frictional configurations. We use nonlinear time-series analysis tools to characterize the dynamics of the models. Observations are described, on average, by a low-dimension (<5), similar to slow slip episodes in nature and friction experiments performed with quartz powder. Results seem insensitive to the along-strike frictional segmentation of the megathrust. Using displacement as an input variable, the instantaneous dimension and the instantaneous extremal index vary through the seismic cycles. We notice the highest values of the instantaneous dimension associated with slip phases. Under specific circumstances, clear drops of the instantaneous extremal index can serve as an early indicator of slip episodes. Prediction horizons in the order of slip duration mirror similar predictability as for slow slip episodes in nature. We conclude that seismotectonic models are effective tools to study frictional physics despite their different spatio-temporal scales.

Magmatic activity at the slowest spreading rates: insights from a high-resolution earthquake catalog obtained from Gakkel Ridge Deep (Arctic Ocean)

David Essing, Annika Hellbrück, Vera Schlindwein — Thu, 06 Mar 2025 00:00:00 -0500

At the eastern end of Gakkel Ridge, Arctic Ocean, spreading rates drop below 5 mm/y near the termination of the active mid-ocean ridge in the Laptev Sea. A small-scale ocean bottom seismometer network deployed for one year at a volcanic center near Gakkel Ridge Deep in sea ice covered waters revealed abundant microseismicity despite the low spreading rate. In order to reveal spreading processes, we analyze a manually picked earthquake catalog refined by low-magnitude events detected by template matching. We attribute seismicity occurring randomly in time and space to tectonic stress release along the ridge. During short time periods of hours to days, seismicity is organized in time and densely clustered in space with signs of migration away from an aseismic area. In analogy to volcanic centers at Knipovich Ridge and in Iceland, we interpret the seismicity as signs of ongoing localized magmatism occurring even at the slowest spreading rates.

Can Earthquake Locations Be Improved for Real-time Monitoring? Revisiting the 1995 seismicity at Soufri`ere Hills Volcano, Montserrat

Jade Eyles, Jessica Johnson, Jenni Barclay, Paddy Smith, Victoria Miller — Thu, 01 May 2025 00:00:00 -0400

Volcanic earthquakes provide a wealth of information about the magmatic system. Monitoring volcanic seismicity is one of the primary methods used by volcano observatories globally, including at Soufri`ere Hills Volcano, Montserrat. Computed earthquake locations represent the optimal solution given the information available, and vary depending on the chosen location method and seismic velocity model, but rarely are these parameters tested for suitability in each region. We propose a new method that utilises synthetic earthquakes to evaluate whether the calculated hypocenters and their associated errors accurately represent the true source locations. We define this evaluation as a confidence parameter that highlights events we can 'trust'. By comparing several location methods and seismic velocity models for Montserrat we show the current setup is not optimal, and suggest an alternative location method. Analysis using new 'trusted' relocations focuses on four seismic clusters distal from Soufriere Hills in 1995. Our results highlight differences in hypocenters during this period, suggesting alternative interpretations of the distal seismicity. We propose a WNW dyke orientation supporting previous studies, and local fault complexes in the region. Overall, this paper highlights the importance of using a robust location method suitable for the region to ensure that calculated hypocenters are trustworthy and accurate. Use of sub-optimal methods can influence apparent spatial earthquake trends, impacting interpretations and our understanding of volcanic systems.

Application of Neural Networks for Estimating Coseismic Slip Distribution Using Synthetic GNSS Data

Sun, 18 May 2025 00:00:00 -0400

Accurately and rapidly estimating coseismic slip is crucial for characterizing the rupture and magnitude of earthquakes and improving early warning systems. However, slip inversions often involve hyperparameters related to prior information, whose selection significantly affects solution efficiency and quality. In this study, we present a novel method for estimating fault slip distributions from GNSS displacements using neural networks. The method was initially developed with synthetic models to define an optimal architecture for accurately recovering target slip. This approach demonstrated exceptional computational efficiency, delivering accurate slip distribution predictions in just 0.07 seconds without specialized hardware. The method was then validated with real-world data from the 2015 M_w 8.3 Illapel earthquake, achieving a GNSS displacement RMSE of 0.07 m and yielding a slip distribution consistent with published solutions. Compared to Regularized Least Squares (RLS) inversion, the neural network estimated slip closer to the trench, aligning with tsunami observations despite slightly higher residuals. Additionally, hyperparameter exploration revealed that using the GELU activation function and a 35% dropout rate provided the best balance. Model performance improved with larger datasets, and while reducing GNSS stations increased uncertainty, more data enhanced accuracy. These findings highlight the importance of hyperparameter tuning and data selection in improving slip estimations, offering insights for future improvements.

Nondestructive testing of railway embankments by measuring multi-modal dispersion of surface waves induced by high-speed trains with linear geophone arrays

Mon, 13 Jan 2025 00:00:00 -0500

To effectively address engineering challenges and risks, it is crucial to characterize mechanical properties of near-surface environments. The Multichannel Analysis of Surface Waves (MASW) has proven to be a valuable active seismic imaging technique by providing near-surface shear (S)-wave velocities estimations. However, its application to urban areas requires further development. This study leverages well-constrained experimental sites to assess the viability of a passive-MASW technique, utilizing seismic waves induced by high-speed train traffic instead of conventional active sources. We suggest employing short 96-geophone uniform linear arrays to capture surface waves in a broad frequency band (10-200 Hz). Train passages are automatically detected and categorized regarding to the train travel direction. Seismic interferometry and phase-weighted stack techniques are applied to generate virtual shot-gathers that are transformed into high-resolution multi-modal dispersion images. Our results demonstrate a strong coherence between the picked dispersion curves from the passive-MASW approach and those obtained through traditional active MASW with a hammer source. We discuss the validity of higher modes and explore array density limits to ensure reliable results. Our findings highlight that seismic interferometry, coupled with a high phase-weighted stack power, effectively recovers energy at high frequencies, enhancing the characterization of multi-modal surface-wave dispersion associated with thin near-surface layers.

Volcanic eruption tremor from particle impacts and turbulence using conduit flow models

Katherine Coppess, Fredric Lam, Eric Dunham — Fri, 03 Jan 2025 00:00:00 -0500

The intensity of explosive volcanic eruptions is correlated with the amplitude of eruption tremor, a ubiquitously observed seismic signal during eruptions. Here we expand upon a recently introduced theoretical model that attributes eruption tremor to particle impacts and dynamic pressure changes in the turbulent flow above fragmentation (Gestrich et al., 2020). We replace their point source model with Rayleigh wave Green's functions with full Green's functions and account for depth variation of input fields using conduit flow models. The latter self-consistently capture covariation of input fields like particle velocity, particle volume fraction, and density. Body wave contributions become significant above 2-3 Hz, bringing the power spectral density (PSD) closer to observations. Conditions at the vent are not representative of flow throughout the tremor source region and using these values overestimates tremor amplitude. Particle size and its depth distribution alter the PSD and where dominant source contributions arise within the conduit. Solutions with decreasing mass eruption rate, representing a waning eruption, reveal a shift in the dominant tremor contribution from turbulence to particle impacts. Our work demonstrates the ability to integrate conduit flow modeling with volcano seismology studies of eruption tremor, providing an opportunity to link observations to eruptive processes.

The InSAR lookbook: an illustrated guide to earthquake deformation interferograms

Israporn Sethanant, Edwin Nissen — Wed, 23 Apr 2025 00:00:00 -0400

Interferometric Synthetic Aperture Radar (InSAR) is the prevalent method for mapping earthquake deformation and is seeing ever-increasing popularity through a new generation of satellite missions. Nowadays, following any large onshore earthquake, InSAR images (interferograms) are quickly disseminated across the community and media, but outside of InSAR specialists there remains a lack of general understanding of how to interpret them. We begin our study by describing how InSAR fringe patterns are determined by the combination of horizontal and vertical ground motions and ascending or descending satellite viewing geometries. In our "lookbook", we synthesize interferograms for a comprehensive suite of faulting styles, including strike-slip, reverse, normal, low-angle thrust, low-angle normal, and oblique-slip faults. This highlights the most common InSAR fringe patterns and demonstrates how strike-slip, dip-slip, and oblique-slip earthquakes produce distinct fringe patterns controlled primarily by their strike angles. We offer guidelines for utilizing the lookbook to assess earthquake mechanisms visually and to pick the causative fault plane from two nodal planes. Lastly, by comparing modelled interferograms and real-world earthquakes, we showcase the broad applicability of the lookbook, even for complex multiple segment ruptures.

Seismicity acceleration and clustering before the 2015 Mw 7.9 Gorkha earthquake, Nepal

Tue, 06 May 2025 00:00:00 -0400

In the last decade, several observations of peculiar seismic and geodetic phases preceding large earthquakes have been documented. Despite being a posteriori, these observations provide a better understanding of the processes involved in the nucleation of earthquakes. In this study, we investigate the foreshocks and the pre-seismic phase of the M$_w$7.9 25 April 2015, Gorkha earthquake in Nepal by applying a matched-filter technique to its nucleation zone. We use the seismic signals of 1851 local earthquakes and the continuous signal recorded at the nearest station for the 6 years preceding the mainshock. The pre-seismic phase depicts a long-term increase of seismicity rate and several seismic swarms less than 20 km away from the mainshock epicenter. The longest swarm occurs one month before the Gorkha earthquake, lasts two weeks and consists of 38 repetitive earthquakes located at the northwestern edge of the rupture zone. Another increase in seismicity rate starts six days before the mainshock and includes small foreshocks that develop less than 10 kilometers from the future earthquake hypocenter. These observations suggest that the Gorkha earthquake was preceded by a pre-seismic phase related to a possible initiation of a slow slip with fluids involved at the northwestern boundary of the rupture zone.

On the location uncertainty of early-instrumental earthquakes

Mon, 24 Feb 2025 00:00:00 -0500

Uncertainty in reported body-wave arrival times is a key contributor to earthquakes location error estimates, especially in the early-instrumental period (e.g., prior to the early 1960s). As such, a reliable assessment of the observational errors in the early-instrumental period is an important element of the earthquake location problem. Standard location procedures at the International Seismological Centre assume seismic arrival time picking errors defined for the most recent decades of instrumental seismology (i.e., from the early 1960s). However, the error measurements currently used fail to capture the uncertainty in the seismic arrival time pickings of earthquakes occurred before the early 1960s (early-instrumental period). The larger observational uncertainty in the early-instrumental period is due to a range of error sources arising from reading arrival times on analogue seismographs. Such errors have been drastically reduced since the 1960s thanks to the significant improvements in seismometry and time keeping as well as the migration from analogue to digital stations worldwide. Since observational errors play a key role in the uncertainty estimations of an earthquake location, it follows that error ellipses for early-instrumental earthquakes are underestimated in our current procedures. To address this feature, we modify the error assumptions used in the early-instrumental period with a time dependent term enabling more reliable error ellipses for early-instrumental earthquakes.

Seismica's Data and Code Policy in Action

Sam Teplitzky — Mon, 05 May 2025 00:00:00 -0400

Seismica launched in July 2022 with a strong policy in support of data and code sharing. Two years later, the journal has upheld the policy while guiding authors toward successful compliance. Our authors are engaged and willing to share and cite their generated data and code, as well as reuse and cite others’ data and code. Notable achievements include the consistent use of Data and Code Availability Statements (DCAS), which ensure transparency and reproducibility. Authors also cite software, with a preference for open source options, and frequently use shared infrastructure such as GitHub and Zenodo for data and code archiving. Beyond mere citation, authors prioritize persistence, utilizing generalist, institutional, and disciplinary repositories to ensure the longevity of research outputs. However, challenges remain. While compliance with the data and code sharing policy is high, the lack of standardization in Data and Code Availability Statement (DCAS) formatting and acknowledgment practices can lead to inconsistencies in Seismica’s articles. Authors often usea mix of informal acknowledgments or web links over formal citations with DOIs, complicating attribution for organizations that rely on citations to bolster support. Moreover, software packages often lack clear citation guidance which may necessitate journal-level recommendations. Infrastructure limitations further hinder the seamless hosting and integration of data and code. As we move forward, Seismica should consider how to stay aligned with best practices in the field, and potentially offer standardized templates or examples to facilitate simplified and consistent data and code citation practices for authors.

Real-Time Loss Tools: Open-Source Software for Time- and State-Dependent Seismic Damage and Loss Calculations – Features and Application to the 2023 Türkiye-Syria Sequence

Cecilia I. Nievas, Helen Crowley, Graeme Weatherill, Fabrice Cotton — Fri, 28 Mar 2025 00:00:00 -0400

During a seismic sequence, the action of each earthquake has the potential to damage and weaken exposed structures, causing their fragility to change, and increasing their likelihood of being further damaged by subsequent earthquakes. At the same time, building occupants that need to be hospitalised after an earthquake will not be present in the buildings whose damage led to their hospitalisation during any subsequent events, for as long as they remain in hospital. These changes in the fragility of buildings and the location of building occupants during a seismic sequence have an impact on the estimation of damage and losses throughout the sequence, but are often not accounted for in rapid loss assessments or when estimating future damage associated with time-dependent short-term seismicity forecasts. While knowledge and modelling capabilities for individual components have advanced in this direction in recent years, there has been, up to this point, no publicly available open-source software able to account for damage accumulation and the displacement of building occupants during seismic sequences. Building upon OpenQuake, we have developed the Real-Time Loss Tools software to address this limitation and present its main features herein, together with a case-study application focused on the 2023 Türkiye-Syria earthquakes.

Unveiling midcrustal seismic activity at the front of the Bolivian altiplano, Cochabamba region

Wed, 29 Jan 2025 00:00:00 -0500

Located in the heart of the Bolivian orocline, the Cochabamba department and its two million inhabitants are exposed to frequent seismic activity. However, the tectonic structures causing these earthquakes remain poorly identified. Indeed, Bolivia’s national seismological network does not optimally cover the area and the hypocentral locations of local earthquakes are therefore subject to large uncertainties which hinder their association with specific faults. We established a regional network consisting of 11 broadband and short-period seismic stations, spaced approximately 20 km apart. This study highlights the initial 6-month seismic bulletin made by manual and automated deep-neural-network based seismic phase picking. We also test the network's ability to resolve focal mechanisms of moderate to small events with a combined inversion of waveforms and polarities. Our preliminary results document midcrustal microseismicity located in the Main Thrust fault shear zone, and in its hangingwall, in a region affected by tectonic slivers and transverse faults impacting the sedimentary cover. These outcomes provide fresh insights into the fault system’s seismogenic behavior and potential across the Bolivian orocline.

DOI, licence and citation uptake for seismological waveform data after 10 years of implementation effort

Tue, 01 Apr 2025 00:00:00 -0400

The International Federation of Digital Seismic Networks (FDSN) has championed online open access to seismological waveform data for almost four decades. In 2014, FDSN recommended using DataCite Digital Object Identifiers (DOIs) for seismic networks to enhance data attribution, citation, and impact metrics. This study evaluates the level of adoption of DOIs and licences across FDSN-registered networks, analyzing their influence on data citation and compliance with FAIR (Findability, Accessibility, Interoperability, and Reusability) principles. 73% of seismic networks that have an assigned FDSN network code have adopted DOIs, with more than 80% DOI coverage for networks created after 2014. Licence adoption, not covered by present FDSN recommendations, remains low (8%), with significant regional variations. The main challenges are presently barriers to systematic data citation, whether on scientist or publisher side. Citations have increased substantially, but improvements are needed to support and implement correct data citation across all levels, including networks, data centers, scientists and journals. Of specific concern is the limitation on references set by some journals, which renders proper attribution impossible for studies using data from many seismic networks. This work highlights best practices and provides a set of recommendations for improving attribution, citation, and FAIRness of seismological waveform data, the latter including that FDSN should recommend licence on waveform data and a limited set of recommended licences. It also explores emerging ethical considerations, like the CARE principles, for Indigenous Data Governance. These insights aim to guide future FDSN strategies and foster enhanced alignment with FAIR and CARE principles. An added value of the assessment was that many minor errors and inconsistencies were identified and fixed at FDSN and in the seismological metadata.

WMSAN Python Package: From Oceanic Forcing to Synthetic Cross-correlations of Microseismic Noise

Fri, 11 Apr 2025 00:00:00 -0400

Seismic ambient noise spectra ubiquitously show two amplitude peaks corresponding to distinct oceanic wave interaction mechanisms called primary (seismic period (T) ~ 14 s) and secondary (T ~ 7 s) microseism. Seismic noise records are used in a wide range of applications including crustal monitoring, imaging of the Earth's deep interior using noise correlations, and studies on the coupling between oceans and solid Earth. All of these applications could benefit from a robust knowledge of spatiotemporal dynamics of microseismic sources. Consequently, seismologists have been studying how to model microseismic sources of ambient noise with the recent improvements in ocean wave models. Global sea state and its derivative products are now covering the past decades in models such as the WAVEWATCHIII hindcast. This paper introduces the Wave Model Sources of Ambient Noise (WMSAN, pronounced [wam-san]) Python package. This modular package uses standardized wave model outputs to visualize ambient noise source maps and efficiently compute synthetics of seismic spectrograms and cross-correlations for surface waves (Rayleigh) and body waves (P, SV), in a user-friendly way.

FINNSIP - The mobile Finnish Seismic Instrument Pool

Mon, 14 Apr 2025 00:00:00 -0400

We report on establishing the mobile Finnish Seismic Instrument Pool (FINNSIP) that is owned and operated by Finnish academic and research institutions. The pool supports domestic and international collaborative seismic research. At the conclusion of the 2020 to 2024 build-up stage, the instrumentation includes 46 broadband seismometers and digitizers, 5 accelerometers, and 1216 and 71 Geospace and SmartSolo autonomous geophone units, respectively, making FINNSIP one of the largest and most coherent mobile seismic instrument pools in Europe in the public sector. We explain the utilization of the pool instruments and discuss the equipment, facilities, ownership and governance structure, fees, and the management and support system. Through Finland's membership in the Observatories and Research Facilities for European Seismology (ORFEUS) and the Finnish European Plate Observing System (EPOS) node, FINNSIP endorses and implements international data management standards and best practices as promoted in Europe. The importance of appropriate data and computing systems is highlighted by the ~90 TB volume of formatted data that has been collected in 25 large-N projects between October 2021 and December 2024. We summarize a checklist for building, operating, and managing this extensive seismic pool that can inform the planning and establishment of other research infrastructure.

The propagation of seismic waves, misinformation, and disinformation from the 2024-10-05 M 4.5 Iran earthquake

Tue, 04 Feb 2025 00:00:00 -0500

The 2024-10-05 Iran M 4.5 earthquake took place at a time of heightened tensions in the Middle East. We perform a discrimination and moment tensor analysis and identify a shallow-dipping, reverse fault source commensurate with the compressional setting of the Iranian interior. Nonetheless, the event's aftermath saw widespread dissemination of misinformation, and potentially active disinformation, concluding that it was in fact a test of an Iranian nuclear weapon. The `evidence' for many of these claims was based on inaccurate interpretation of seismic data. In this paper, we analyse how geophysical `fake news' propagated through social media (mainly Twitter/X) following this event, eventually gaining traction in mainstream, earned media. This event is an illustrative warning of how seismic data can be misinterpreted and/or manipulated in public discourse.

The 2024–2025 seismic sequence in the Santorini-Amorgos region: Insights into volcano-tectonic activity through high-resolution seismic monitoring

Ioannis Fountoulakis, Christos P. Evangelidis — Thu, 29 May 2025 00:00:00 -0400

The 2024–2025 seismic sequence in the Santorini-Amorgos region demonstrates a complex evolution revealing the interaction between tectonic and volcanic processes. In this study, a detailed seismic catalog is presented, generated for operational monitoring using machine-learning-based phase picking and high-precision relocation methods. By late summer 2024, seismic activity emerged beneath Santorini and within the caldera. By late January 2025 the seismicity appeared at around 20 km beneath the Kolumbo volcano before migrating northeastward and shallower around Anydros island, aligning with southwest-northeast tectonic structures. The relocation process confirmed a diffuse back-and-forth migration along this trend, with some distinct shallow events. Non-double couple moment tensor solutions show predominantly positive isotropic components suggesting crack-opening processes driven by magmatic and fluid involvement. Spectral analysis metrics also support this, highlighting earthquake spatial variations with different frequency content linked to alternative source mechanisms. The results show a complex interaction between tectonic and magmatic processes, potentially indicating the upward migration of magmatic fluids from deep reservoirs or dike injection. Overall, during this intense seismovolcanic activity, we established an operational workflow to provide the authorities with updates on the ongoing evolution of this earthquake sequence. This high quality seismic catalog is now openly available for future studies.

A multiple asymmetric bilateral rupture sequence derived from the peculiar tele-seismic P-waves of the 2025 Mandalay, Myanmar earthquake

Tue, 20 May 2025 00:00:00 -0400

A large strike-slip earthquake occurred in central Myanmar on March 28, 2025. The aftershock distribution suggests that the rupture of the mainshock propagated mainly to the south. However, a large-amplitude phase lasting 20 s, followed by a short-period pulse-like phase, were observed at the stations on the north side of the source, while on the south side, tremor-like phases with multiple peaks continued for 90 s. Using the potency density tensor inversion method, we explain the "unusual" waveform signature of the Myanmar earthquake by a multiple, asymmetric bilateral rupture, involving boomerang-like back-rupture propagation and supershear.