Thermal Moonquake Characterization and Cataloging Using Frequency‐Based Algorithms and Stochastic Gradient Descent
Abstract
Thermal moonquakes are recurring seismic signals detected on the lunar surface that are temporally correlated with the lunar day‐night cycle, although their precise mechanism is not known. The Lunar Seismic Profiling Experiment (LSPE) was a deployment of four geophones during the Apollo 17 mission to characterize the near‐surface structure of the landing site using explosive shots. The array was reactivated in passive recording mode several times after the mission was completed and recorded thousands of thermal moonquakes. In this study, we expand on an initial detection catalog and determine waveform parameters and source information for the seismic signals. We used a spectrogram‐based approach to obtain fine‐tuned arrival times, quantify the envelope length using emergence, and compute peak‐ground‐velocity. We obtain the incident azimuth direction by applying stochastic gradient descent to a travel‐time misfit equation. We found that thermal moonquakes are split into two main classes: (a) impulsive, high‐amplitude events that are produced by the lunar module descent vehicle located east of the LSPE array in response to rapid temperature transitions during sunrise and sunset and (b) emergent events, that are natural responses to incident sunlight whose duration is directly linked to the temperature of the regolith. We hypothesize that the correlation between temperature and emergence could be due to changes in regolith scattering or higher energy daytime events occurring further away.
Copyright and License
© 2023 American Geophysical Union. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.
Acknowledgement
This study was funded in part by a grant awarded through the NASA SMD 2021 Lunar Data Analysis Program (80NSSC22K1033). Thanks to Nick Schmerr, Mark Panning, Ceri Nunn, and Deanna Phillips for helpful discussions. Many thanks to Yosio Nakamura for his thorough explanation of the Apollo 17 instrumentation, manuscript review, and suggestion that larger seismic events during the day might be causing the observed emergence pattern. The feedback from editor Laurent Montési and an anonymous reviewer greatly helped improve the manuscript.
Data Availability
The initial catalog of seismic detections can be found in the online Supporting Information of Civilini et al. (2021). A GitHub repository containing all code used to process the data and conduct the analysis was published through Zenodo (Civilini et al., 2023a). The codes can be used to reproduce the catalog and every result and figure displayed in the manuscript. The original Apollo 17 LSPE seismic data in Exabyte binary tape format are available upon email request from the NASA NSSDCA as part of the PSPG-00739 archive (Nakamura, 1992). These data were originally converted to daily ASCII files by Yosio Nakamura, which were the starting point for this study. These daily ASCII files, hourly despiked SAC data in decompressed volts (processing described in Section 3.2), hourly despiked SAC data in nm/s (processing described in Section 3.3), final catalog, and data products for each analysis step are published in a CaltechData repository (Civilini et al., 2023b).
Errata
In the originally published version of this article, the first author's affiliation should have been "Now at NASA Goddard Space Flight Center, Greenbelt, MD, USA" rather than "Now at NASA Marshall Space Flight Center, Greenbelt, MD, USA," and the second author's affiliation should have been "NASA Marshall Space Flight Center, Huntsville, AL, USA" rather than "NASA Marshall Space Flight Center, Greenbelt, MD, USA." The affiliations have been corrected, and this may be considered the authoritative version of record.
Attached Files
JGR Planets - 2023 - Civilini.pdf - published article
2022je007704-sup-0001-supporting information si-s01(1).pdf - supplementary information
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Additional details
- ISSN
- 2169-9100
- National Aeronautics and Space Administration
- 80NSSC22K1033
- Accepted
-
2023-08-23Accepted
- Available
-
2023-09-05Published Online
- Updated
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2023-09-15Published with corrections
- Caltech groups
- Division of Geological and Planetary Sciences, Seismological Laboratory