More Like this

1. Spatiotemporal evaluation of Rayleigh surface wave estimated from roadside dark fiber DAS array and traffic noise

   https://doi.org/10.26443/seismica.v2i2.247  

   Czarny, Rafał; Zhu, Tieyuan; Shen, Junzhu (August 2023, Seismica)

   Seismic imaging and monitoring of the near-surface structure are crucial for the sustainable development of urban areas. However, standard seismic surveys based on cabled or autonomous geophone arrays are expensive and hard to adapt to noisy metropolitan environments. Distributed acoustic sensing (DAS) with pre-existing telecom fiber optic cables, together with seismic ambient noise interferometry, have the potential to fulfill this gap. However, a detailed noise wavefield characterization is needed before retrievingcoherent waves from chaotic noise sources. We analyze local seismic ambient noise by tracking five-month changes in signal-to-noise ratio (SNR) of Rayleigh surface wave estimated from traffic noise recorded by DAS along the straight university campus busy road. We apply the seismic interferometry method to the 800 m long part of the Penn State Fiber-Optic For Environment Sensing (FORESEE) array. We evaluate the 160 virtual shot gathers (VSGs) by determining the SNR using the slant-stack technique. We observe strong SNR variations in time and space. We notice higher SNR for virtual source points close to road obstacles. The spatial noise distribution confirms that noise energy focuses mainly on bumps and utility holes. We also see the destructive impact of precipitation, pedestrian traffic, and traffic along main intersections on VSGs. A similar processing workflow can be applied to various straight roadside fiber optic arrays in metropolitan areas. 

   more » « less
2. Active-Source Environmental Seismology

   https://doi.org/10.1785/0220260046  

   Holbrook, W Steven; Bemis, Sean P; Burgett, Denise; Eppinger, Benjamin J; Gupta, Anya; Mangal_Gupta, Shiv; Rabak, Ivan (May 2026, Seismological Research Letters)

   Abstract Environmental seismology is a rapidly growing field that is providing new insights into many surficial and near-surface Earth processes, largely through passive detection of events (e.g., landslides and sediment movement) and subsurface velocity changes that reflect changes in saturation (e.g., water table changes). Recent advances in instrumentation (e.g., distributed acoustic sensing) and analysis techniques (e.g., machine learning and artificial intelligence) are expanding the use cases and data volumes of passive environmental seismology. However, despite these successes, passive environmental seismology has two disadvantages that may limit the usefulness of the data. First, passive-source studies that rely on surface-wave observations usually produce S-wave velocity without accompanying P-wave velocity measurements, thus incompletely characterizing subsurface elastic properties. Second, passive-source studies often do not provide subsurface structure at the resolution necessary to distinguish the near-surface units that host and control environmental processes (e.g., soil, saprolite, and fractured bedrock). We suggest that these limitations can be surmounted by incorporating active-source seismic imaging of the critical zone (CZ). Active-source data records the entire wavefield, thus providing detailed P- and S-velocity structure that can contextualize passive-source measurements. Active-source CZ seismology is a rapidly changing field, with notable recent advances in instrumentation (e.g., small, autonomous nodes) and analysis techniques (e.g., wider adoption of full-waveform inversion). As a result, new types of surveys (e.g., three-component, 3D, and time-lapse) are imaging the CZ in novel ways and with unprecedented resolution. Here, we review the state of the art in active-source CZ seismology and provide several examples demonstrating that active-source environmental seismology can achieve meter-scale resolution of CZ structure and processes. 

   more » « less
3. An Open-Access Data Set of Active-Source and Passive-Wavefield DAS and Nodal Seismometer Measurements at the Newberry Florida Site

   https://doi.org/10.1785/0220230216  

   Abbas, Aser; Cox, Brady R; Tran, Khiem T; Corey, Isabella; Dawadi, Nishkarsha (January 2024, Seismological Research Letters)

   Abstract This article documents a comprehensive subsurface imaging experiment using seismic waves in a well-studied outdoor laboratory at Newberry, Florida, which is known for significant spatial variability, karstic voids, and underground anomalies. The experiment used approximately two kilometers of distributed acoustic sensing (DAS) fiber-optic cable, forming a dense 2D array of 1920 horizontal-component channels, and a 2D array of 144 SmartSolo three-component nodal seismometers, to sense active-source and passive-wavefield seismic waves. The active-source data were generated using a powerful, triaxial vibroseis shaker truck (T-Rex) and impact sources (accelerated weight drop and an eight-pound sledgehammer) that were simultaneously recorded by both the DAS and nodal seismometers. The vibroseis truck was used to excite the ground in three directions (two horizontal and one vertical) at 260 locations inside and outside the instrumented array, whereas the impact sources were used at 268 locations within the instrumented array. The passive-wavefield data recorded using the nodal seismometers comprised 48 hr of ambient noise collected over a period of four days in four 12-hour time blocks, whereas the passive wavefield data collected using DAS consisted of four hours of ambient noise recordings. This article aims to provide a comprehensive overview of the testing site, experiment layout, the DAS and nodal seismometer acquisition parameters, and implemented raw data processing steps. Although potential use cases, such as surface-wave testing, full-waveform inversion, and ambient noise tomography, are discussed relative to example data, the focus of this article is on documenting this unique data set and presenting its initial data quality rather than on generating subsurface imaging results. The raw and processed data, along with detailed documentation of the experiment and Python tools to aid in visualizing the DAS data set, have been made publicly available. 

   more » « less
4. Monitoring Spatiotemporal Seismic Velocity Changes Using Seismic Interferometry and Distributed Acoustic Sensing in Mexico City

   https://doi.org/10.1029/2024JB030697  

   Li, Yang; Perton, Mathieu; Ermert, Laura A; Sánchez‐Sesma, Francisco J; Escobar_Maya, Leobardo I; Spica, Zack J (August 2025, Journal of Geophysical Research: Solid Earth)

   Abstract Distributed Acoustic Sensing (DAS) offers a transformative solution for dense, high‐resolution seismic monitoring to address the challenges of traditional seismometers in urban seismic surveys. Here, we employ seismic interferometry of the ambient noise field and the trace stretching method to monitor seismic velocity variations in Mexico City. We present spatiotemporal variations in relative Rayleigh wave group velocity calculated over two frequency bands (0.4–1.2 Hz and 1.2–3.6 Hz) using DAS data collected over a year. To investigate these variations, we model the impacts resulting from the 2022 Mw7.6 earthquake, along with the effects of precipitation and temperature on the calculated in the 0.4–1.2 Hz frequency band, which is primarily dominated by the fundamental mode of the Rayleigh waves. Our results indicate that the earthquake‐induced velocity drop differs in certain fiber sections, likely due to their non‐linear soil behaviors and co‐seismic stress changes but without relation to the maximum local deformation registered during the earthquake. Additionally, our modeling indicates that the velocity changes are influenced by seasonal temperature variations, and the impact of precipitation is relatively minor, at least for the depth range (50 m) examined in this study. This study highlights the capability of DAS to enhance spatiotemporal monitoring in urban environments, providing valuable insights into both seismic and environmental responses. 

   more » « less
5. Comparison of methods for coupled earthquake and tsunami modelling

   https://doi.org/10.1093/gji/ggad053  

   Abrahams, Lauren S; Krenz, Lukas; Dunham, Eric M; Gabriel, Alice-Agnes; Saito, Tatsuhiko (February 2023, Geophysical Journal International)

   SUMMARY Tsunami generation by offshore earthquakes is a problem of scientific interest and practical relevance, and one that requires numerical modelling for data interpretation and hazard assessment. Most numerical models utilize two-step methods with one-way coupling between separate earthquake and tsunami models, based on approximations that might limit the applicability and accuracy of the resulting solution. In particular, standard methods focus exclusively on tsunami wave modelling, neglecting larger amplitude ocean acoustic and seismic waves that are superimposed on tsunami waves in the source region. In this study, we compare four earthquake-tsunami modelling methods. We identify dimensionless parameters to quantitatively approximate dominant wave modes in the earthquake-tsunami source region, highlighting how the method assumptions affect the results and discuss which methods are appropriate for various applications such as interpretation of data from offshore instruments in the source region. Most methods couple a 3-D solid earth model, which provides the seismic wavefield or at least the static elastic displacements, with a 2-D depth-averaged shallow water tsunami model. Assuming the ocean is incompressible and tsunami propagation is negligible over the earthquake duration leads to the instantaneous source method, which equates the static earthquake seafloor uplift with the initial tsunami sea surface height. For longer duration earthquakes, it is appropriate to follow the time-dependent source method, which uses time-dependent earthquake seafloor velocity as a forcing term in the tsunami mass balance. Neither method captures ocean acoustic or seismic waves, motivating more advanced methods that capture the full wavefield. The superposition method of Saito et al. solves the 3-D elastic and acoustic equations to model the seismic wavefield and response of a compressible ocean without gravity. Then, changes in sea surface height from the zero-gravity solution are used as a forcing term in a separate tsunami simulation, typically run with a shallow water solver. A superposition of the earthquake and tsunami solutions provides an approximation to the complete wavefield. This method is algorithmically a two-step method. The complete wavefield is captured in the fully coupled method, which utilizes a coupled solid Earth and compressible ocean model with gravity. The fully coupled method, recently incorporated into the 3-D open-source code SeisSol, simultaneously solves earthquake rupture, seismic waves and ocean response (including gravity). We show that the superposition method emerges as an approximation to the fully coupled method subject to often well-justified assumptions. Furthermore, using the fully coupled method, we examine how the source spectrum and ocean depth influence the expression of oceanic Rayleigh waves. Understanding the range of validity of each method, as well as its computational expense, facilitates the selection of modelling methods for the accurate assessment of earthquake and tsunami hazards and the interpretation of data from offshore instruments. 

   more » « less