Deep moonquake properties: deciphering stresses and deformation patterns

Between 1969 and 1972, five seismometers were placed on the near side of the moon as part of the Apollo space missions. Four of these stations operated until 1977, forming the lunar seismic network. This lunar seismic data provides unique insights into the structure and dynamics of the lunar interior. A range of seismic signals were recorded during the 7-year operation of the seismic network, including meteoroid impacts, artificial impacts, shallow moonquakes and deep moonquakes.

This project will focus on deep moonquakes. There are notable similarities between deep moonquakes and intermediate earthquakes. Both are thought to occur at conditions that inhibit brittle failure. Likewise, both quakes repeatedly arise in the same small area, referred to as nests. Finally, the physical mechanism of both events remains unclear. Understanding the source properties of deep moonquakes may provide insight into the processes occurring on Earth.

Deep moonquakes also exhibit more enigmatic behaviours that are not observed in intermediate earthquakes, including a strong periodicity linked to the solid Moon tides. However, the relationship between tidal stress and moonquake occurrence is not simple, and moonquakes respond to a range of different orbital characteristics. It is still unclear if this periodicity indicates whether tidal or tectonic stresses drive moonquakes.

Despite deep moonquakes making up nearly half of the moonquake catalogue, their source mechanisms are still poorly explained, and few studies have focused on the properties of rupture. The focus of this project will be to investigate the relationship between coseismic stress drop and tidal phase. There has been a range of studies evaluating the tidal stress acting on deep earthquakes, but they do not adequately describe the stress drop of the seismic source. Further analysis of the source properties of deep moonquake nests could provide insight into the rupture processes in the moon's interior and the relationship between rupture and tidal stresses.

A range of seismic techniques commonly applied to terrestrial data will be modified appropriately and applied to the Apollo data. This will include spectral fitting, empirical Green's Functions and inter-station phase coherence analysis to determine the rupture extent, stress drop and radiated energy of previously unstudied deep moonquakes.

This project falls within the Lunar Science topic of the Astronomy and Space Science research area.