IDENTIFICATION AND ANALYSES OF SUBTERRANEAN TECTONIC CAVES

Subterranean void spaces on planetary bodies are a critical area of study for both astrobiology and in situ resource utilization (ISRU). Lava tubes identified on the Moon and Mars are being studied as subsurface areas of interest. However, lava tubes are relatively rare in the solar system, and where found, often limited in spatial extent (e.g., tubes are typically confined to a single lava flow). Alternatively, the ubiquitous nature of extensional fractures, normal faulting, and pit crater chain formations found on terrestrial planets, asteroids and icy moons suggests that dilational faulting may be the dominate formation mechanism for creating subsurface void space.

Dilational faulting can occur when extensional strain is applied across mechanically stratified layers, or where hybrid mode failure (Mode I opening combined with either Mode II sliding and/or Mode III tearing) occurs under low differential stress. Mechanical stratigraphy influences where faults nucleate, the type of failure mode, the strike/dip geometry, and the degree and distribution of displacement along the fault. In particular, the stratigraphic layering of mechanically strong rock (e.g., basalt) with relatively weak rock (e.g., regolith) found on planetary bodies lends itself to the formation of dilational faults. On Earth, these dilational faults have a significant influence on the flow and storage of fluids, volatiles and minerals. Dilational fault systems likely play a similar role on other solid bodies in our solar system in controlling where resources may be found, whether the target is groundwater/ice, methane, metals, minerals or other vital ISRU. Fortunately, dilational faults often reveal themselves in the form of collapsed pit crater chains, which can often be identified in visual imagery and topographic datasets. Quantifying pit crater chains and their underlying faults can, in turn, help constrain the degree of subsurface void space available and help define the permeability architecture. Geophysical investigations of dilational faults and pit crater chain formations at Earth analog sites should be performed to better quantify the degree of subterranean void space associated with these common planetary features, toward better targeting future ISRU and astrobiological investigations.