Journal: The Seismic Record

Abbreviation

Publisher

Seismological Society of America

Journal Volumes

ISSN

2694-4006

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2022 - 20258
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Publications 1 - 8 of 8
  • Waveform Tomography Improves Far-Regional Distance Simulations of Underground Nuclear Explosions and Earthquakes from the Former Nuclear Test Site, Western United States
    Item type: Journal Article
    Rodgers, Arthur James (2024)
    The Seismic Record
    We investigated the efficacy of seismic Earth models to simulate complete regional distance waveforms from underground nuclear explosions and earthquakes on and near the former Nevada Test Site in Nevada, western United States. We focused on two far-regional stations (∼1000 km) in two period bands 20–50 and 15–40 s, for which path propagation effects over many wavelengths accumulate and pose challenges to low-mag-nitude nuclear explosion monitoring (NEM). Four seismic models were considered: two average radially symmetric 1D and two fully 3D models. Model performance was evaluated with metrics of waveform phase (cross-correlation delay time), shape (correlation coefficient), and amplitude (variance reduction with delay time shift) and averaged into a summary score. We found that a recent 3D model based on full waveform inversion (FWI) tomography including radial anisotropy and crustal thickness variations performs on average better than the alternatives. Results suggest that FWI based on crustal depth earthquakes can provide useful 3D models for NEM. Such models can be used for the simulation of Green’s functions for source characterization including moment tensor inversion and source type characterization (e.g., explosion–earthquake–collapse identification, moment and yield estimation).
  • Revisiting the Seismicity in the Eagle Ford Shale: The Overlooked Role of Wastewater Disposal
    Item type: Journal Article
    Grigoratos, Iason; Savvaidis, Alexandros; Wiemer, Stefan (2025)
    The Seismic Record
    The seismicity in the Eagle Ford play has increased dramatically over the last decade. Past studies identified hydraulic fracturing (HF) as the only driving force in this area. We conclude that although HF is the dominant causal factor, wastewater disposal (SWD) was also a triggering mechanism in certain zones. Notably, in the center of the shale, there is a small area where both causal factors overlap. Furthermore, a cluster of earthquakes on the Mexican side of the national border is almost certainly triggered by SWD within Texas. To our knowledge, this is the first such documented case globally. Next, our analysis investigated the causal factors of the 2011 M$_w$ 4.8 Fashing earthquake and of two recent M$_w$ 3.9 events, while also confirming that HF was the key driving force behind the 2018 M$_w$ 4.0 rupture. We employed new earthquake catalogs, established physics-based principles, and a robust hypothesis testing framework.
  • Fiber-Optic Observation of Volcanic Tremor through Floating Ice Sheet Resonance
    Item type: Journal Article
    Fichtner, Andreas; Klaasen, Sara; Thrastarson, Sölvi; et al. (2022)
    The Seismic Record
    Entirely covered by the Vatnajökull ice cap, Grímsvötn is among Iceland’s largest and most hazardous volcanoes. Here we demonstrate that fiber-optic sensing technology deployed on a natural floating ice resonator can detect volcanic tremor at the level of few nanostrain/s, thereby enabling a new mode of subglacial volcano monitoring under harsh conditions. A 12.5 km long fiber-optic cable deployed on Grímsvötn in May 2021 revealed a high level of local earthquake activity, superimposed onto nearly monochromatic oscillations of the caldera. High data quality combined with dense spatial sampling identify these oscillations as flexural gravity wave resonance of the ice sheet that floats atop a subglacial lake. Although being affected by the ambient wavefield, the time–frequency characteristics of observed caldera resonance require the presence of an additional persistent driving force with temporal variations over several days, that is most plausibly explained in terms of low-frequency volcanic tremor. In addition to demonstrating the logistical feasibility of installing a large, high-quality fiber-optic sensing network in a sub arctic environment, our experiment shows that ice sheet resonance may act as a natural amplifier of otherwise undetectable (volcanic) signals. This suggests that similar resonators might be used in a targeted fashion to improve monitoring of ice-covered volcanic systems.
  • The Far Side of Mars: Two Distant Marsquakes Detected by InSight
    Item type: Journal Article
    Horleston, Anna C.; Clinton, John Francis; Ceylan, Savas; et al. (2022)
    The Seismic Record
    For over three Earth years the Marsquake Service has been analyzing the data sent back from the Seismic Experiment for Interior Structure—the seismometer placed on the surface of Mars by NASA’s InSight lander. Although by October 2021, the Mars seismic catalog included 951 events, until recently all these events have been assessed as lying within a radius of 100° of InSight. Here we report two distant events that occurred within days of each other, located on the far side of Mars, giving us our first glimpse into Mars’ core shadow zone. The first event, recorded on 25 August 2021 (InSight sol 976), shows clear polarized arrivals that we interpret to be PP and SS phases at low frequencies and locates to Valles Marineris, 146° ± 7° from InSight. The second event, occurring on 18 September 2021 (sol 1000), has significantly more broadband energy with emergent PP and SS arrivals, and a weak phase arriving before PP that we interpret as Pdiff. Considering uncertain pick times and poorly constrained travel times for Pdiff, we estimate this event is at a distance between 107° and 147° from InSight. With magnitudes of MMaw 4.2 and 4.1, respectively, these are the largest seismic events recorded so far on Mars.
  • Seismic Node Arrays for Enhanced Understanding and Monitoring of Geothermal Systems
    Item type: Journal Article
    Hudson, Thomas; Kettlety, Tom; Kendall, John-Michael; et al. (2024)
    The Seismic Record
    Harnessing geothermal energy will likely play a critical role in reducing global emissions. However, exploration, development, and monitoring of geothermal systems remain challenging. Here, we explore how recent low‐cost seismic node instrumentation advances might enhance geothermal exploration and monitoring. We show the results from 450 nodes deployed at a geothermal prospect in Cornwall, United Kingdom. First, we demonstrate how the nodes can be used to monitor the spatiotemporal and size distribution of induced seismicity. Second, we use focal mechanisms, shear‐wave source polarities, and anisotropy to indicate how the dense passive seismic observations might provide enhanced insight into the stress state of the geothermal systems. All the methods are fully automated, essential for processing the data from many receivers. In our example case study, we find that the injection‐site fracture orientations significantly differ from that of the crust above and the regional stress state. These observations agree well with fracture orientations inferred from independent well‐log data, exemplifying how the nodes can provide new insight for understanding the geothermal systems. Finally, we discuss the limitations of nodes and the role they might play in hybrid seismic monitoring going forward. Overall, our results emphasize the important role that low‐cost, easy‐to‐deploy dense nodal arrays can play in geothermal exploration and operation.
  • Fiber-Optic Airplane Seismology on the Northeast Greenland Ice Stream
    Item type: Journal Article
    Fichtner, Andreas; Hofstede, Coen; Kennett, Brian L.N.; et al. (2023)
    The Seismic Record
    We present distributed fiber-optic sensing data from an airplane landing near the EastGRIP ice core drilling site on the Northeast Greenland Ice Stream. The recordings of exceptional clarity contain at least 15 easily visible wave propagation modes corresponding to various Rayleigh, pseudoacoustic, and leaky waves. In the frequency range from 8 to 55 Hz, seven of the modes can be identified unambiguously. Based on an a priori firn and ice model that matches P-wave dispersion and the fundamental Rayleigh mode, a Backus–Gilbert inversion yields an S-wavespeed model with resolution lengths as low as a few meters and uncertainties in the range of only 10 m/s. An empirical scaling from S wavespeed to density leads to a depth estimate of the firn–ice transition between 65 and 71 m, in agreement with direct firn core measurements. This work underlines the potential of distributed fiber-optic sensing combined with strong unconventional seismic sources in studies of firn and ice properties, which are critical ingredients of ice core cli-matology, as well as ice sheet dynamics and mass balance calculations.
  • Uncertainty in Ground-Motion-to-Intensity Conversions Significantly Affects Earthquake Early Warning Alert Regions
    Item type: Journal Article
    Saunders, Jessie K.; Annemarie S.Baltay, Annemarie S.; Minson, Sarah E.; et al. (2024)
    The Seismic Record
    We examine how the choice of ground-motion-to-intensity conversion equations (GMICEs) in earthquake early warning (EEW) systems affects resulting alert regions. We find that existing GMICEs can underestimate observed shaking at short rupture distances or overestimate the extent of low-intensity shaking. Updated GMICEs that remove these biases would improve the accuracy of alert regions for the ShakeAlert EEW system for the West Coast of the United States. ShakeAlert uses ground-motion prediction equations (GMPEs), which calculate spatial distributions of peak ground acceleration (PGA) and peak ground velocity (PGV) from earthquake source estimates, combined with GMICEs to translate GMPE output into modified Mercalli intensity (MMI). We find significant episte-mic uncertainty in alert distances; near-source MMI estimates from different GMICEs can differ by over 1 MMI unit, and MMI extents used for public EEW alerts can differ by hundreds of kilometers for larger magnitude earthquakes (M ∼6.5+). We use a catalog of “Did You Feel It?” shaking reports to evaluate how well GMICEs predict observed shak-ing. Our preferred GMICE is the one that computes MMI using PGV for high intensities and transitions to using PGA for nondamaging intensities. These results motivate updating GMICE relationships more generally, including in ShakeMap applications.
  • Constraints on Midmantle Discontinuities in Mars from Analysis of InSight Seismic Data
    Item type: Journal Article
    Duran, Andrea Cecilia; Khan, Amir; Helffrich, George; et al. (2025)
    The Seismic Record
    The structure and nature of Earth’s transition zone, which is delineated by the transformation of olivine to its higher-pressure polymorphs, exerts a strong influence on material transfer between upper and lower mantle. Mars, however, because of its relatively large core, is only expected to exhibit the equivalent of Earth’s uppermost transition zone seismic discontinuity. We searched the InSight seismic data for marsquakes and impacts located in an epicentral distance range favorable for detection of seismic phases that have interacted with Mars’s olivine transition (midmantle) discontinuity. Through application of careful data selection criteria and processing schemes, we found 13 events in the distance range in which body waves are expected to refract through the midmantle of Mars. Although triplicated body waves are potentially present in seven events, the distance distribution is insufficient to allow for unambiguous detection of the triplicated waveform pattern associated with the midmantle discontinuity. Comparison of travel times of the observed waveforms with predictions from recent Mars models indicates the possible presence of a midmantle discontinuity located between 987 and 1052 km or 1075 and 1122 km depth, in which the uncertainty comes from our inability to reliably distinguish first from secondary arrivals.
Publications 1 - 8 of 8