4:15 PM - 4:30 PM
[PPS09-20] Analysis of Newly Discovered Shallow Moonquakes: Assessment of Lunar Seismicity and Implications for Their Source Mechanism
Keywords:Planetary seismology, Apollo, Moonquake, Seismicity
The installation of seismometers on the Moon in the Apollo missions opened the way to understanding lunar seismicity and the internal structure (e.g., Latham et al., 1969). During the Apollo passive seismic experiments (1969 - 1977), two types of seismometers were operated. One is called a Long-Period (LP) seismometer, which has a high sensitivity at 0.2 – 1.5 Hz, and the other is called a Short-Period (SP) seismometer sensitive at around 1.5 – 10 Hz (e.g., Nunn et al., 2020). Through the Apollo observations, about 13,000 seismic events were identified and cataloged by Nakamura et al. (1981). A noteworthy point here is that these events were discovered by checking the LP data. Therefore, it was suggested that there were many potential events only observable in the SP data (Frohlich & Nakamura, 2006).
Recently, Onodera (2023) analyzed all the SP data and succeeded in discovering more than 22,000 new moonquakes. Most of the new events have similar characteristics to those cataloged, including thermal moonquakes, impact-induced events, and shallow moonquakes. Among them, I pay particular attention to shallow moonquakes because they are the most energy quakes on the Moon, the most similar events to terrestrial quakes, and are used to evaluate lunar seismicity in the context of comparative planetology (e.g., Nakamura et al., 1979; Goins et al., 1981; Banerdt et al., 2020). Although only 28 shallow moonquakes were identified before, the newly discovered 46 shallow moonquakes are expected to contribute to revealing the nature of the most mysterious moonquakes (e.g., spatiotemporal distribution, excitation mechanism) and improving the assessment of lunar seismicity. These topics are important not only for promoting lunar seismology but also for the hazard assessment on the Moon.
In the presentation, I will show the updated lunar seismicity parameters (such as magnitude of completeness, a-value, and b-value) using both cataloged and newly discovered shallow moonquakes. Moreover, referring to the relation between the b-value and the degree of heterogeneity within a medium, I will discuss the source environment of shallow moonquakes, which gives us implications for their excitation mechanism.
References:
•Banerdt et al. (2020), Initial results from the InSight mission on Mars, Nature Geoscience, 13(3), 183-189.
•Frohlich & Nakamura (2006), Possible extra-solar-system cause for certain lunar seismic events, Icarus, 185(1), 21-28.
•Goins et al. (1981), Seismic energy release of the Moon, Journal of Geophysical Research: Solid Earth, 86(B1), 378-388.
•Latham et al. (1969), The Apollo passive seismic experiment, Science, 165(3890), 241-250.
•Nakamura et al. (1979), Shallow moonquakes: Depth, distribution and implications as to the present state of the lunar interior, Proc. Lunar Planet. Sci. Conf., 2299-2309.
•Nakamura et al. (1981), Passive seismic experiment long period event catalog (ver. 1008c), UTIG Technical Report, No. 118.
•Nunn et al. (2020), Lunar seismology: A data and instrumentation review, Space Science Reviews, 216(5), 89.
•Onodera (2023), New Views of Lunar Seismicity Brought by Analysis of Newly Discovered Moonquakes in Apollo Short-Period Seismic Data, ESS Open Archive, October 27, DOI: 10.22541/essoar.169841663.38914436/v1.
Recently, Onodera (2023) analyzed all the SP data and succeeded in discovering more than 22,000 new moonquakes. Most of the new events have similar characteristics to those cataloged, including thermal moonquakes, impact-induced events, and shallow moonquakes. Among them, I pay particular attention to shallow moonquakes because they are the most energy quakes on the Moon, the most similar events to terrestrial quakes, and are used to evaluate lunar seismicity in the context of comparative planetology (e.g., Nakamura et al., 1979; Goins et al., 1981; Banerdt et al., 2020). Although only 28 shallow moonquakes were identified before, the newly discovered 46 shallow moonquakes are expected to contribute to revealing the nature of the most mysterious moonquakes (e.g., spatiotemporal distribution, excitation mechanism) and improving the assessment of lunar seismicity. These topics are important not only for promoting lunar seismology but also for the hazard assessment on the Moon.
In the presentation, I will show the updated lunar seismicity parameters (such as magnitude of completeness, a-value, and b-value) using both cataloged and newly discovered shallow moonquakes. Moreover, referring to the relation between the b-value and the degree of heterogeneity within a medium, I will discuss the source environment of shallow moonquakes, which gives us implications for their excitation mechanism.
References:
•Banerdt et al. (2020), Initial results from the InSight mission on Mars, Nature Geoscience, 13(3), 183-189.
•Frohlich & Nakamura (2006), Possible extra-solar-system cause for certain lunar seismic events, Icarus, 185(1), 21-28.
•Goins et al. (1981), Seismic energy release of the Moon, Journal of Geophysical Research: Solid Earth, 86(B1), 378-388.
•Latham et al. (1969), The Apollo passive seismic experiment, Science, 165(3890), 241-250.
•Nakamura et al. (1979), Shallow moonquakes: Depth, distribution and implications as to the present state of the lunar interior, Proc. Lunar Planet. Sci. Conf., 2299-2309.
•Nakamura et al. (1981), Passive seismic experiment long period event catalog (ver. 1008c), UTIG Technical Report, No. 118.
•Nunn et al. (2020), Lunar seismology: A data and instrumentation review, Space Science Reviews, 216(5), 89.
•Onodera (2023), New Views of Lunar Seismicity Brought by Analysis of Newly Discovered Moonquakes in Apollo Short-Period Seismic Data, ESS Open Archive, October 27, DOI: 10.22541/essoar.169841663.38914436/v1.