Newly discovered moonquakes from Apollo short-period seismometer data

The beginning of planetary seismology dates back to the Apollo lunar seismic observations (1969 – 1977), where two types of seismometers were deployed at four places on the nearside of the Moon. The seismic observation package consisted of (i) two horizontal and one vertical long-period (LP) sensors and (ii) one vertical short-period (SP) sensor. About 8 years of observation brought us 13000 seismic events and contributed to the understanding of the internal structure and the seismicity of the Moon (see Nunn et al., 2020 and Garcia et al., 2019 for the recent review).

On the other hand, because the existing moonquake catalog by Nakamura et al. (1981) builds on the LP data, it has been expected that there are potential events only observable in the SP data (Nakamura, 2021, pers. comm.). Referring to the already cataloged events, shallow moonquakes and thermal moonquakes excite the energy at a high-frequency range more sensible with the SP sensor (> 1-2 Hz). Especially, shallow moonquakes being used to define the lunar seismicity (Banerdt et al., 2020), it is of great importance to investigate the SP data for re-evaluating the current seismic activities on the Moon.

In this study, utilizing the re-archived Apollo lunar seismic data by Nunn et al. (2022), we searched for undetected moonquakes by looking into the coherence between the reference moonquakes and the SP time series. As a result, we succeeded in discovering seismic events that were not cataloged before. A new SP event catalog will be released with our future publication. 

In the presentation, we will show the newly detected moonquakes and describe their characteristics.

 

References

• Banerdt et al. (2020), Nat. Geosci.,13, 183–189.
• Garcia et al. (2019), Space Sci. Rev., 215, 50.
• Nakamura et al. (1981), UTIG Technical Report, 18.
• Nunn et al. (2020), Space Sci. Rev., 216, 89.
• Nunn et al. (2022), Planet. Sci. J., 3 219.