Planetary analogue study using microseismic analysis for near-surface lava tube detection and exploration

The paper presents new results from microseismic data analysis for the detection and delineation of near-surface lava tubes. Single-station, free-field seismic noise data were collected at the Corona Volcano area (Lanzarote, Canary Islands) as part of the PANGAEA-X 2017 European Space Agency (ESA) astronaut training campaign. The site was selected as it represents a suitable analogue for lunar maria and provided the opportunity to cross-validate and ground truth seismic and other geophysical studies. In this paper, we present our observations on the distribution of frequencies and amplitudes of standing waves generated by microtremors in the space between the ground surface and underground cavities by averaging amplitude spectra of microseismic records. This study shows that the frequency of the vertical component peaks is a relatively good indicator of presence, lateral extent and approximate dip of the cavities. However, only the vertical component peaks with a frequency either equal to or close to central to high amplitude (3.1–8.5) horizontal-to-vertical (H/V) peaks are related to lava tubes. If the P-wave velocities in the rocks overlying the lava tubes are known, then these frequencies can also be used to estimate the depth of such cavities. This study also identified some important pitfalls that may limit the use and accuracy of our approach. These include layering of rocks overlying the lava tubes, lateral changes in thickness, lateral variations of the P-wave velocity, and the presence of shallow void-rich zones. Overall, the results of this study confirmed that microseismic data are suitable for cavity detection. It is also, to our knowledge, one of the first studies dealing with microseismic data from near-surface lava tubes. With the recent increase in planetary exploration, this method can be easily adapted to support the geophysical exploration of volcanic terrains on the Moon and Mars.