Lunar Seismology: a data and instrumentation review - Electronic Supplement

Strong Heterogeneity in Shallow Lunar Subsurface Detected by Apollo Seismic Data

“…Deep moonquakes are the most frequently observed events during the Apollo seismic experiment, whose source depth are between 750 and 1,200 km (Khan & Mosegaard, 2002;Lognonné et al, 2003;Nakamura, 2003). The detected 28 shallow moonquakes are located at depths of 0-220 km in the crust and upper mantle (see Nunn et al, 2020aNunn et al, , 2020b for a review). The focal mechanisms of most moonquakes are still unexplained.…”

“…We compared the spectrum of the synthetic traces with that of the Apollo long-period (LP) traces. LP seismograms are recorded primarily in peak mode with a peak sensitivity of 0.45 Hz (Nunn et al, 2020a(Nunn et al, , 2020b. Therefore, given the peaked nature of this response, even the dominant frequency of some events is much larger than that of the peaked response (Nunn et al, 2020a(Nunn et al, , 2020b, thus we can only observe the highest energy around the peak.…”

“…Apollo deep moonquake data are available via the Zenodo archive (Nunn et al, 2020a(Nunn et al, , 2020b. Apollo shallow moonquake data were downloaded from Data ARchives and Transmission System (DARTS) (https:// www.darts.isas.jaxa.jp/planet/seismology/apollo/PSE.html).…”

“…LP seismograms are recorded primarily in peak mode with a peak sensitivity of 0.45 Hz (Nunn et al, 2020a(Nunn et al, , 2020b. Therefore, given the peaked nature of this response, even the dominant frequency of some events is much larger than that of the peaked response (Nunn et al, 2020a(Nunn et al, , 2020b, thus we can only observe the highest energy around the peak. Among our numerical simulations, the frequency spectrum of 0.5 Hz dominant frequency (corresponding to 2 s dominant period) has an energy peak around 0.5 Hz and the maximum frequency reaches about 1 Hz.…”

“…Traditional methods are developed specifically for consolidated crusts (e.g., well-bedded layered sedimentary rocks), rather than for random models. Seismic data recorded on the Moon during the Apollo missions and on Mars with InSight have observed strong near-surface scattering (Karakostas et al, 2021;Latham et al, 1970;Lognonné et al, 2020;Nunn et al, 2020aNunn et al, , 2020b. Further research on the mechanism of wave propagation and energy trapping in strongly heterogeneous media is thus fundamental to planetary seismology and is critical for uncovering more structural details of extraterrestrial bodies.…”