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Abstract The devastating 6 February 2023 Kahramanmaraş earthquake sequence in southeastern Türkiye started with a moment magnitude (Mw) 7.8 earthquake, for which the initial rupture broke the Sakçagöz segment near Nurdağı and then jumped into a bilateral rupture along multiple segments of the Eastern Anatolian fault zone (EAFZ). This complicated rupture was followed nine hours later by an Mw 7.6 event near Ekinözü. To better understand the spatiotemporal evolution of aftershocks, site amplification, and the structural and tectonic framework of the EAFZ in this diffuse triple junction, we deployed a dense seismometer array covering both aftershock zones for nearly four months. The main Eastern Anatolian Seismic Temporary (EAST) array includes 125 nodal, 10 broadband, and 6 strong-motion seismic stations distributed around the rupture zone. An additional linear array of 73 nodal stations was also installed across the Pazarcık segment of the EAFZ and the Sakçagöz segment near the Mw 7.8 epicenter to record fault-zone waves for ∼30 days. This article shows example recordings and the EAST array geometry, preliminary research results, and the metadata related to all of the stations in this array. A deep-learning-based phase picking for one month of continuous recording yielded millions of seismic phase readings and tens of thousands of aftershock locations after phase associations. We also give examples of both local and teleseismic waveforms recorded by the nodal arrays, which can be used for subsequent high-resolution earthquake relocation, imaging of crustal structures, and fault-zone imaging.
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Active and Passive Seismic Surveys over the Grounding Zone of Eastwind Glacier, Antarctica
Abstract The grounding zone of a marine-terminating glacier, where ice begins to float, is a key control on glacier stability and ice discharge. Seismic deployments are a powerful means of studying both the geometry and processes of grounding zones; however, these regions are frequently inaccessible and dangerous for field work, and as a result are underrepresented in field studies. We report new data sets acquired at Eastwind Glacier, Antarctica, a relatively accessible grounding zone near McMurdo Station and Scott Base, as part of the Eastwind Glacier Geophysical Surveys on Top of an Antarctic Ice Shelf Transition, EGGS on TOAST, project. These data sets comprise a deployment of three-component seismic nodes and distributed acoustic sensing. The nodal deployment consisted of 330 nodes crossing the grounding zone, with all 330 nodes continuously recording for at least nine days, and 150 nodes recording for 19 days, in the austral summer of 2022/2023. Hammer-and-plate sources were recorded, with densely spaced shots along flow through the center of the array and shots located at every node. In 2023/2024, a 2.2 km fiber-optic cable was deployed for active source imaging by distributed acoustic sensing along and across flow, immediately downstream of the grounding line, for a period of 2 hr. Analysis of active source data recorded by the nodal array locates the point of flotation within the grounding zone and provides ice thickness estimates. We present initial analyses of passive source data, including icequake detection and location, and ambient noise analysis. We expect this data set to be of significant value to provide insight into fundamental grounding zone processes and as an event-rich cryoseismological data set on which to test novel methods of seismic analysis.
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- Award ID(s):
- 1739027
- PAR ID:
- 10674562
- Publisher / Repository:
- The Seismological Society of America
- Date Published:
- Journal Name:
- Seismological Research Letters
- Volume:
- 97
- Issue:
- 1
- ISSN:
- 0895-0695
- Page Range / eLocation ID:
- 591 to 605
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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
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SUMMARY In this study, I demonstrate that distributed acoustic sensing (DAS) raw strain rate data can directly be used to estimate spectral source parameters through an Empirical Green's Function (EGF) deconvolution analysis. Previously, DAS had been widely used in passive seismology to image the subsurface and analyze ground motion variations by converting strain or strain rate to particle velocity or acceleration prior to analysis. In this study, spectral analysis is applied to the PoroTomo joint DAS and seismic Nodal array in the Brady Hot Springs geothermal field to obtain source parameters for two M4 earthquakes via EGF analysis, where nearly collocated smaller events are used as an EGF to remove path and site effects. The EGF workflow is applied to raw DAS strain rate data without conversion to particle velocities and raw Nodal seismic data. The DAS and Nodal results are very consistent with similar features of spectral ratios, corner frequencies and moment ratios for the same event pairs. The uncertainty due to stacked spectral measurement is much lower on the DAS array, suggesting better stability of spectral shape measurement, possibly due to the much denser spatial sampling. The uncertainty due to model fitting is similar between DAS and Nodal arrays with slightly lower uncertainty on the DAS array. These observations demonstrate potential for directly using the strain rate measurements from DAS arrays for earthquake source characterizations.more » « less
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Abstract Geolocalization of distributed acoustic sensing (DAS) array channels represents a crucial step whenever the technology is deployed in the field. Commonly, the geolocalization is performed using point-wise active-source experiments, known as tap tests, conducted in the vicinity of the recording fiber. However, these controlled-source experiments are time consuming and greatly diminish the ability to promptly deploy such systems, especially for large-scale DAS experiments. We present a geolocalization methodology for DAS instrumentation that relies on seismic signals generated by a geotracked vehicle. We demonstrate the efficacy of our workflow by geolocating the channels of two DAS systems recording data on dark fibers stretching approximately 100 km within the Long Valley caldera area in eastern California. Our procedure permits the prompt calibration of DAS channel locations for seismic-related applications such as seismic hazard assessment, urban-noise monitoring, wavespeed inversion, and earthquake engineering. We share the developed set of codes along with a tutorial guiding users through the entire mapping process.more » « less
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ABSTRACT The recorded seismic waveform is a convolution of event source term, path term, and station term. Removing high-frequency attenuation due to path effect is a challenging problem. Empirical Green’s function (EGF) method uses nearly collocated small earthquakes to correct the path and station terms for larger events recorded at the same station. However, this method is subject to variability due to many factors. We focus on three events that were well recorded by the seismic network and a rapid response distributed acoustic sensing (DAS) array. Using a suite of high-quality EGF events, we assess the influence of time window, spectral measurement options, and types of data on the spectral ratio and relative source time function (RSTF) results. Increased number of tapers (from 2 to 16) tends to increase the measured corner frequency and reduce the source complexity. Extended long time window (e.g., 30 s) tends to produce larger variability of corner frequency. The multitaper algorithm that simultaneously optimizes both target and EGF spectra produces the most stable corner-frequency measurements. The stacked spectral ratio and RSTF from the DAS array are more stable than two nearby seismic stations, and are comparable to stacked results from the seismic network, suggesting that DAS array has strong potential in source characterization.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1785/0220250024
