Deep Moonquakes
on the Far Hemisphere of the Moon

Principal Investigator: Yosio Nakamura

Funding Agency: NASA Planetary Geology and Geophysics Program

Status Report, 22 April 2002 (PDF file)

Abstract
Of more than 12,500 natural seismic events recorded by the long-period seismometers on the moon during the Apollo project between 1969 and 1977, only about 40% of them have ever been identified and classified. We here propose to analyze the remaining 60% of the events in the Apollo Passive Seismic Experiment database to search for deep moonquakes on the far hemisphere of the Moon. The purpose of the search is to differentiate two competing hypotheses: 1) the Moon is truly asymmetrical and no deep moonquakes exist on the far side and 2) the interior of the Moon is basically symmetrical and deep moonquakes do occur on the far-side of the moon but had escaped earlier identification. Such a search, which was impossible earlier because of limited compute capacity and capability, is now well within our capability. Confirming either one of these hypotheses will have great impact on our understanding of the dynamics of the lunar interior. If hypothesis 1 is true, then the consequence will be very significant, calling for more detailed examination of numerous now unclassified events, which may lead to eventual identification of a new class of events. However, if hypothesis 2 is true, then a further analysis of the identified events will focus on a better delineation of the deep interior of the moon including the possible metallic core. Thus we propose to do further examination and interpretation of the result regardless of which hypothesis turns out to be true. The results of this renewed effort will also be of significant help in designing a lunar seismic network in the future.