Newly Identified Events and Signals of Astronaut Exploration Activities in the Apollo Seismic Data

Abstract

Seismometers deployed on the lunar surface during the historic Apollo missions have established that the Moon is a differentiated body and that it is a host to a variety of seismic events both similar to and distinct from terrestrial earthquakes. Many questions about lunar seismicity and interior structure remain, inspiring a push for future geophysical experiments to be sent to the Moon. Here, I reinvestigated short period seismic data from the Apollo missions to locate new seismic events and to highlight procedures that will optimize our science return on future geophysical missions. I focused specifically on the short period data from Apollo 11, which has been underrepresented in lunar seismic analyses.

In my first study, I focused on detecting events within the Short Period (SP) data of the Apollo 11 Passive Seismic Experiment, which have not been studied extensively due to the brevity of the dataset, and the station’s proximity to the Lunar Module and resulting seismic noise. I built a catalog of 2435 seismic events and categorized them based on frequency content and waveform characteristics and find that there is a subset of events that share characteristics with naturally occurring thermal moonquakes. I use a model of the thermal evolution of the regolith in the near field to isolate possible source regions of these moonquakes.

Next, I focus on anthropogenic seismic signals from the Apollo 11 SP data. Specifically, I look at the jettisons of the portable life support systems (PLSS) and other equipment as a possible proxy for close-range active source seismic study. I used pixel tracking on rare television footage of the Apollo 11 jettisons to characterize the nature of the jettison trajectories and estimate the resulting impact momenta. I then developed a model using Hertzian impact theory to predict seismic ground motion from the momenta and fit them to the equipment jettisons at other Apollo stations, constraining geotechnical properties of the shallow lunar regolith.

Lastly, I investigated the SP seismic signals resulting from the Apollo Lunar Module (LM) launches. I used literature values for the thrust forces of the Apollo Ascent Propulsion System (APS) and developed a method for correcting SP seismic data from instruments that malfunctioned. With the known thrust forces and measured ground motion from the seismic data, I built a model that predicts ground motion resulting from rocket ignitions of different magnitudes in preparation for future lunar missions.