Uncovering inner structures of planetary bodies using Geodesy and Seismology

Abstract Since the deployment of seismometer was placed on the Moon by Apollo astronauts, seismology is no longer limited to the Earth. Intensive study of Apollo seismic records enabled us to uncover the internal structure of the Moon and have been contributing to the lunar science for more than 40 years. At the same time, observation on the Moon was far from ideal from today of Earth standards and scientists suffered from the problem. In the seminar, I will discuss on my attempts to constrain source parameters and thermal and Q structure of the Moon through spectral analyses of the Apollo data. Apollo seismometer has a limited frequency band and previous spectral analyses suffered from the narrow frequency band. In my study, I improved the spectral analyses by combining numerically the data from long and short period seismometer of Apollo. With the expanded frequency band, I re-evaluated corner frequencies and seismic moments for more than 100 deep moonquakes, while the previous study only studies one single event. I also evaluated the stress drop and showed that this is comparable to tidal stress which implies that deep moonquakes are caused by tidal stress. I took this as an additional constraint and re-evaluated the brittle-ductile transition temperature with tidal strain rate and obtained a temperature profile that is compatible with deep moonquake occurrence and other geophysical observations. Finally, I will present my recent results for shallow moonquakes that differ significantly from those of deep moonquakes and preliminary Q structure I obtained with deep and shallow moonquakes and impact events.