Seismic Noise Environment and Implications for Future Gravitational Wave Detection on the Moon

The renewed global interest in lunar exploration, with multiple robotic and crewed landings planned in the coming decades, presents a unique opportunity to pursue scientific objectives that are difficult or infeasible on Earth. Among these objectives, the detection of gravitational waves (GWs) from a lunar platform stands out as a particularly promising frontier in fundamental physics. While Earth-based GW observatories have made groundbreaking discoveries, their sensitivity is fundamentally limited by environmental noise, including persistent seismic disturbances. In contrast, the Moon offers an exceptionally quiet seismic environment three orders of magnitude smaller than on Earth, which is largely free from atmospheric and anthropogenic noise sources, as originally demonstrated by data from the Apollo Passive Seismic Experiment.

In this study, we revisit the Apollo-era seismic data to conduct a comprehensive assessment of the lunar seismic noise environment. Particularly, we revisit the transfer function of the Apollo instruments by using the existing catalog of the calibration signals. Using the newly developed transfer function (Specifically,) we perform a statistical analysis of background noise levels recorded at multiple Apollo seismic stations, characterizing the amplitude distribution, spectral content, and long-term variability of ambient seismic noise. Regional differences among the landing sites are examined to identify geophysical or environmental factors contributing to noise variability. We further analyze temporal trends in noise characteristics in relation to local time, surface temperature cycles, and tidal stresses, aiming to determine optimal observational windows for future ultra-sensitive measurements.

In addition to persistent background noise, we assess the impact of transient seismic events, which may also pose challenges for GW detection. We compile and analyze the statistical properties, such as occurrence rates, amplitudes, and durations, of the three main classes of seismic events observed on the Moon: deep moonquakes, shallow moonquakes, and meteoroid impacts. Their respective contributions to the lunar seismic signal environment are evaluated, with particular attention to their potential to mask or mimic GW signals in the relevant frequency ranges. Here, careful consideration is given to the deep moonquakes, as their frequent seismic activity defines the seismic floor level for potential future GW detectors. We synthesize deep moonquake seismograms to construct a representative template of this signal class. These synthetic waveforms are then used to simulate the response of a prospective lunar strainmeter, allowing us to explore the signature of deep moonquake noise in a gravitational wave measurement context. We discuss the data analysis strategies developed to distinguish this seismic noise from a true GW signal in order to remove it, emphasizing the importance of signal discrimination methods in future lunar GW observatories.

The results of our analysis provide updated and quantified constraints on the lunar seismic noise floor, as well as on the likelihood and characteristics of transient disturbances. These findings are essential for informing the design, site selection, and operational strategies of future lunar gravitational wave observatories. We conclude by discussing the implications of the current seismic environment for the detectability of various classes of GW sources, including low-frequency signals that may be inaccessible to Earth-based detectors.