Fassett, C.

Molaro, J.

Phillips, D.

Schmerr, N. C.

Weber, R. C.

NASA Technical Reports Server

Seismic expression of thermal degradation on the Moon
R. C. Weber1, D. Phillips2, J. Molaro3, C. Fassett1, N. C. Schmerr4
1.  NASA MSFC     2.  University of Alabama, Huntsville     3.  Planetary Science Institute     4.  U. Maryland, College Park
Geophone 4
Geophone Rock ALSEP 
central stationAGU2018 P53B-05
https://ntrs.nasa.gov/search.jsp?R=20190000526 2019-08-30T10:04:52+00:00Z
Thermal degradation of rocks
Degraded rocks have been 
observed on the Moon & linked 
to impact processes, although 
“the role of thermal cycling is 
unknown and possibly 
contributes to the destruction of 
lunar surface rocks, especially of 
relatively large size” (Basilevsky
et al., 2013)
Questions:
1) Are rocks thermally degrading 
in the present day?
2) If so, is this signal present in 
the Apollo seismic data?
20m boulder in the central peak complex of the lunar crater Schiller 
Thermal modeling
surface and interior stresses in an infinite halfspace and a finite boulder. The white 
arrows denote the orientation of the maximum principal stress, and the blue arrows 
denote the resulting direction of crack propagation. 
Thermal modeling of macroscopic thermomechanical behavior of lunar boulders in response to diurnal thermal 
forcing shows it can potentially contribute to breakdown (Molaro et al., 2017) (in lunar rocks down to 30cm) 
authors
Apollo seismic data
Lunar Seismic Profiling Experiment (LSPE)
was part of the
Apollo Lunar Surface Experiment Package (ALSEP)
Primary modes of operation:
1. Active experiment
2. “Listening” mode 
Heffels et al., 2017 (PSS)
Sollberger et al., 2016 (GRL)
Thermal Moonquakes
Continuous “listening mode” data contains many small “noise” events
Thermal Moonquakes
HMM event detection algorithm identified >50k detections showing strong diurnal occurrence patterns consistent with 
previous observations. Dimech et al., 2017 (Results in Physics). Approximately 1/3 of these represent distinct events.
insolation
Thermal Moonquakes
Early work located thermal moonquakes detected by LSPE & conclude signals possibly represented thermal movement of 
the regolith
• Used signal amplitudes
• Locations accurate to ~50m
Duennebier 1976, Proc. Lunar Sci. Conf. 
Apollo PanCam image
Thermal Moonquakes
LROC image
Event location
Event location
Method by Schmerr:
1. Fit location and origin time to model + observations
2. Input arrival times at 4 geophones
3. Minimize misfit between observed and calculated arrivals on 
1-km grid centered on array
New velocity model produced from re-analysis of Apollo 17 active 
experiment data using seismic wavefield gradient approach: 
Sollberger et al., 2016 (GRL)
Event location
Location results: testing with known locations of the active experiment explosive packages (EPs)
Sollberger et al., 2016 (GRL)
Event location
Analysis 1:
What do we see 
inside those contours?
rocks mapped by 
Haase et al. 2012 
(JGR)
Event location
Analysis 2: 
Are there any obvious 
patterns based on 
waveform type?
rocks mapped by 
Haase et al. 2012 
(JGR)
Thermal modeling
Do waveform rise/decay times 
indicate type of cracking? 
(sunrise)
(sunset)
Analysis 2: 
Are there any obvious 
patterns based on 
waveform type?
Future work
Acoustic emission (AE) sensors 
have recorded diurnal micro-
cracking associated with elastic 
wave generation within boulders 
in the field (Warren et al., 2013)
At the macro scale, thermally-
triggered rock dome exfoliation 
has also been observed on Earth 
(Collins et al., 2018)
Can thermal moonquakes 
be correlated with surface 
features?
Can we assess the extent 
to which thermally-
induced rock breakdown 
contributes to regolith 
production?
Can such processes 
contribute to regional 
microseismic noise?
(test with terrestrial 
analog data)


Seismic Expression of Thermal Degradation on the Moon

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