Reflection imaging of the Moon's interior using deep‐moonquake seismic interferometry

Abstract

The internal structure of the Moon has been investigated over many years using a variety of seismic methods, such as travel time analysis, receiver functions, and tomography. Here we propose to apply body-wave seismic interferometry to deep moonquakes in order to retrieve zero-offset reflection responses (and thus images) beneath the Apollo stations on the nearside of the Moon from virtual sources colocated with the stations. This method is called deep-moonquake seismic interferometry (DMSI). Our results show a laterally coherent acoustic boundary around 50 km depth beneath all four Apollo stations. We interpret this boundary as the lunar seismic Moho. This depth agrees with Japan Aerospace Exploration Agency's (JAXA) SELenological and Engineering Explorer (SELENE) result and previous travel time analysis at the Apollo 12/14 sites. The deeper part of the image we obtain from DMSI shows laterally incoherent structures. Such lateral inhomogeneity we interpret as representing a zone characterized by strong scattering and constant apparent seismic velocity at our resolution scale (0.2-2.0 Hz).In this study we analyze deep-moonquake seismograms. We apply body-wave SI [e.g., Claerbout, 1968;Wapenaar et al., 2008;Schuster, 2009] via autocorrelation of the first P wave phase to the P wave coda. This allows us to retrieve the zero-offset subsurface reflection response from virtual sources colocated with the Apollo stations. For the sake of shorthand notation, we term this technique deep-moonquake seismic interferometry (DMSI). Obtaining virtual reflection responses of the Moon beneath the Apollo stations obviates the need for active seismic sources, such as explosives and artificial impacts recorded by the Apollo instruments.Our goal is to identify the lunar seismic Moho using the DMSI technique. Knowledge of the crustal thickness is important to the understanding of the evolution of the Moon; it has implications for bulk composition, petrogenesis, and other aspects of lunar evolution. Previous studies using various seismic methods have reported widely NISHITSUJI ET AL.DEEP-MOONQUAKE SEISMIC INTERFEROMETRY 695 PUBLICATIONS

Lithospheric image of the Central Iberian Zone (Iberian Massif) using global-phase seismic interferometry

“…Since the early 1990s, a number of multidisciplinary geophysical studies have been undertaken to characterize the crust and lithosphere in the Iberian Massif: first to the NW, then to the SW, and up to and across the Toledo mountains. Detailed crustal and, sometimes, lithospheric structures have been delineated primarily from high-resolution controlledsource (normal-incidence and wide-angle) seismic reflection/refraction data (Pulgar et al, 1995;Ayarza et al, 1998;Simancas et al, 2003;Carbonell et al, 2004;Flecha et al, 2009;Palomeras et al, 2009Palomeras et al, , 2011Martínez-Poyatos et al, 2012;Ehsan et al, 2014Ehsan et al, , 2015. However, there is a gap in seismic information at the Central System and surrounding basins.…”

“…The results from normal incidence seismic profiles ESCIN-2, IBERSEIS-NI, and ALCUDIA-NI (Pulgar et al, 1995;Simancas et al, 2003;Martínez-Poyatos et al, 2012) as well as the velocity information provided by the wide-angle datasets acquired as part of those experiments (e.g. IBERSEIS-WA and ALCUDIA-WA; Palomeras et al, 2009;Ehsan et al, 2015) are evaluated in our interpretation.…”

Antarctic Ice Properties Revealed From Teleseismic P Wave Coda Autocorrelation

“…This principle is appealing because it utilizes seismic data of just one recording component (e.g., vertical or radial). Thus, the autocorrelation analysis can be used to reprocess old data archives of which only one, for example, only vertical, component is available (Kennett et al, ) or in planetary seismology where each recording component is invaluable due to the high cost of deploying a seismometer in space missions (e.g., Nishitsuji et al, ; Zhan et al, ). Three‐component data enable the extraction of reflection responses from each component independently, which provides additional constraints on elastic structures beneath a station.…”

Retrieval of the P wave reflectivity response from autocorrelation of seismic noise: Jakarta Basin, Indonesia

“…Tonegawa et al [] autocorrelated horizontal components of the seismic records and estimated the azimuthal anisotropy direction of low‐velocity marine sediments in the northwestern Pacific. The method has been recently extended to lunar imaging with moonquakes by Nishitsuji et al []. In addition to the use of the full seismic wavefield, the reverberated portion of earthquake signals can also be used for imaging in an autocorrelation framework.…”