The Apollo missions installed seismic stations on the Moon between 1969-1979. Thousands of small moonquakes were recorded, classified as deep or shallow. Deep moonquakes originated 600-1000km below the surface, indicating a molten lunar interior and core. Moonquakes have monthly periodicities correlated to lunar tides, and are thought to be induced by tidal stresses. While the Moon lacks evidence of tectonic activity, moonquake swarms may be signs of minor crustal adjustments or related to volcanism. Studying moonquake data provides insights about the Moon's internal composition.

1. History: The Apollo Missions
• Starting in 1969 during the
Apollo 12 mission, 6
seismic stations were
installed
• In the next 10
years, thousands of small
scale (2-3) earthquakes
were recorded
• These earthquakes have
since been classified into
deep and shallow
moonquakes

2. Moonquakes!
By Kassandra Del Greco

3. Moonquake or Meteoroid
• H-phase
• Time from
beginning of signal
to maximum signal
amplitude

4. Internal Structure of the Moon
• Using moonquakes to determine there is mantle and
core
• Lack of evidence of deep moonquakes originating on
the far-side may indicate a molten interior/core

5. Deep Moonquakes
• 10 focus’ identified by 1971 although most moonquakes
originated from the A1
• Depths of 600km-1000km (Moon’s radius 1737.4km)
• Periodicity of moonquakes indicates they are induced by
tides
• Polarity reversal cycles can be attributed to a
combination of tidal stress and a constant thermal stress

6. Tidal Stress
• Deep moonquakes occur
in monthly cycles
• 7-month periodicities
correlate to long-term
gravity variations
• Moonquakes occur at
depths of max tidal stress

7. Other Sources of Stress
• Slight expansion of the Moon by internal
radiogenic heating or slight contraction on
cooling
• Localized strains due to uncompensated
masses
• Localized thermal stress

8. Sources of Stress
• Cumulative amplitude curves with linear
slope could indicate 3 types of stress
• Thermal Stresses of possible volcanic origin
• Tectonic Stresses at low stress levels
• Dislocations along pre-existing fractures

9. Moonquake Swarms
• Distinctive sequence of moonquakes closely grouped in
space and time
• Characterized by an abrupt beginning and ending of activity
• Semi-monthly periodicity indicates lunar tide trigger
• They do not have matching waveforms as regular deep
moonquakes do
• Suggested relation to volcanism as they are found on earth

10. Moonquake Swarms

11. Evidence Against Tectonics
• Yearly seismic energy release in far below that of the
earth
• Internal convection leading to lunar tectonism is most
likely absent
• Much less heat is relased from the Moon than would be
expected with convection
• This would indicate that swarms are signs of continuing
minor adjustment to crustal stresses

12. Conclusion
• Moonquakes are cool (literally)
• Unlikely tectonic association
• Tidal stress
• Studying the way seismic waves travel can
give insight on the interior composition of
the moon
• More studies should be done

13. References
Latham, G. V., M. Ewing, J. Dorman, D. Lammlein, F.
Press, N. Toksöz, G. Sutton, F. Duennebier, Y. Nakamura
(1972), Moonquakes and lunar tectonism, Moon, 4, 373–382.
Nafi Toksoz, M., Groins, N.R., Cheng, C.H.
(1977), Moonquakes: Mechanisms and Relation to Tidal
Stresses, Science 27 May 1977: 196 (4293), 979-981.
[DOI:10.1126/science.196.4293.979].
Nakamura, Y. (2005), Farside deep moonquakes and
deep interior of the Moon, J. Geophys.
Res., 110, E01001, [DOI:10.1029/2004JE002332].