© 2024 Seismological Society of America.
\n\nThe authors thank Hiroo Kanamori for helpful discussions about energy and magnitude, Jackie Caplan\u2010Auerbach for interesting discussions about the concert signals, Jim Meyer for very detailed information about stadium concert sound systems, and Rafael Sabelli and Mark Waggoner for useful information about stadium structural response parameters. The authors also appreciate helpful comments from the anonymous reviewers and the editors. The authors thank Dave Branum for retrieving data from the CE station that is usually only archived for triggered earthquakes. The Southern California Seismic Network (G. T. and I. S.) is funded by the U.S. Geological Survey (USGS) and the California Office of Emergency Services, the latter of which motivated interest for this study. The authors thank the California Geological Survey, the Terrestrial Hazard Observation and Reporting (THOR) Center at Caltech, and the Divisions of Geological and Planetary Science, and Engineering and Applied Science at Caltech for funding research connected with the Community Seismic Network. The Southern California Earthquake Data Center (SCEDC) is funded through USGS Grant G10AP00091 and the Southern California Earthquake Center, which is funded by National Science Foundation (NSF) Cooperative Agreement EAR-0529922 and USGS Cooperative Agreement 07HQAG0008.
\nThe Hough line and frequency peak analyses were done using built\u2010in functions in MATLAB. These analyses, as well as the particle motion analysis, also used the GISMO toolbox for MATLAB (https://github.com/geoscience-community-codes/GISMO, last accessed February 2024). For the energy analysis, waveform processing was done with the Seismic Analysis Code (SAC) using Standard for the Exchange of Earthquake Data (SEED) volume instrument response (RESP) files. Waveform data and metadata for the CI and NP network stations and the temporary ZY.CIT\u2010E station can be accessed through the Southern California Earthquake Data Center (SCEDC; scedc.caltech.edu, last accessed February 2024). Data from the CE station can be obtained by request from the California Strong Motion Instrument Program (CSMIP). Non\u2010earthquake data from the Community Seismic Network (CSN) stadium sensors cannot be released to the public without prior approval from SoFi Stadium officials. Structural and geotechnical CSMIP data are from www.strongmotioncenter.org (last accessed February 2024), station number 14M33. The station map was created using Plotly Express with basemap data contributed by Carto and OpenStreetMap, licensed under the Open Data Commons Open Database License (ODbL). Stadium map drawings are adapted from www.sofistadium.com (last accessed February 2024) (seating maps). Concert setlist data were obtained from https://www.setlist.fm (last accessed October 2023). The duration and beat rate values were obtained from https://songbpm.com (last accessed October 2023). The supplemental material includes more details about the stadium construction and speaker system experiment, additional figures, the concert analysis data tables, and the speaker experiment waveform data.
\nThe authors acknowledge that there are no conflicts of interest recorded.
\nLarge music festivals and stadium concerts are known to produce unique vibration signals that resemble harmonic tremor, particularly at frequencies around 1–10 Hz. This study investigates the seismic signals of a Taylor Swift concert performed on 5 August 2023 (UTC) as part of a series at SoFi Stadium in Inglewood, California, with an audience of ∼70,000. Signals were recorded on regional seismic network stations located within ∼9 km of the stadium, as well as on strong\u2010motion sensors placed near and inside the stadium prior to the concert series. We automatically identified the seismic signals from spectrograms using a Hough transform approach and characterized their start times, durations, frequency content, particle motions, radiated energy, and equivalent magnitudes. These characteristics allowed us to associate the signals with individual songs and explore the nature of the seismic source. The signal frequencies matched the song beat rates well, whereas the signal and song durations were less similar. Radiated energy was determined to be a more physically relevant measure of strength than magnitude, given the tremor\u2010like nature of the signals. The structural response of the stadium showed nearly equal shaking intensities in the vertical and horizontal directions at frequencies that match the seismic signals recorded outside the stadium. In addition, we conducted a brief experiment to further evaluate whether the harmonic tremor signals could be generated by the speaker system and instruments, audience motions, or something else. All evidence considered, we interpret the signal source as primarily crowd motion in response to the music. The particle motions of the strongest harmonics are consistent with Rayleigh waves influenced by scattered body waves and likely reflect how the crowd is moving. Results from three other musical performances at SoFi in summer 2023 were similar, although differences in the signals may relate to the musical genre and variations in audience motions.
\n\nPublished - Kohler_SMIP21.pdf
", "abstract": "The Community Seismic Network (CSN) is a cloud-based, strong-motion network of seismic stations deployed in the greater Los Angeles area. The sensors report three-component acceleration time series data and peak acceleration scalar data for use in assessments of earthquake shaking intensity in buildings and on the ground level, monitoring structural health of instrumented buildings, zonation maps of future shaking potential, and the ShakeAlert earthquake early warning system. The hardware and software behind CSN's client and server architecture are described, as well as network subarrays deployed at Los Angeles Unified School District campuses, the NASA-JPL campus, and in mid-rises and high-rises.", "date": "2021-10-21", "date_type": "published", "publisher": "California Department of Conservation", "id_number": "CaltechAUTHORS:20220128-214417127", "official_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220128-214417127", "rights": "No commercial reproduction, distribution, display or performance rights in this work are provided.", "funders": { "items": [ { "agency": "Caltech" }, { "agency": "UCLA" }, { "agency": "Conrad N. Hilton Foundation" }, { "agency": "Computers and Structures, Inc." }, { "agency": "Gordon and Betty Moore Foundation" }, { "agency": "NSF" } ] }, "local_group": { "items": [ { "id": "Community-Seismic-Network" } ] }, "corp_creators": { "items": [ "Community Seismic Network Team" ] }, "primary_object": { "basename": "Kohler_SMIP21.pdf", "url": "https://authors.library.caltech.edu/records/x54b6-0gm84/files/Kohler_SMIP21.pdf" }, "pub_year": "2021", "author_list": "Kohler, Monica" } ]