LINEAR ELASTIC FRACTURE MECHANICS (LEFM) ANALYSIS OF CRUSTAL DEFORMATION ON EUROPA WITH COMPARISONS TO TERRESTRIAL ANALOGS

LEFM theory is an effective tool for the analysis of rock deformation on Earth. Application of LEFM has enabled quantitative analysis of elastic deformation around fractures at scales ranging from single cracks to crustal-scale features. The theory has been used to explain the geometries of and deformation around structures such as joints, faults, and igneous intrusions. The LEFM approach is useful because deformation of an elastic body around a fracture of a particular length and 3-D geometry is uniquely defined for any specific loading conditions, produced in nature by tectonic stresses or fluid pressure inside a crack. This places elastic constraints on the amount of opening across, and spacing between, dilating cracks of a particular size. It also constrains the magnitude and distribution of elastic displacement that can occur along a fault of a particular length. Additionally, linear elasticity can be used to describe the deformation of an elastic plate of a particular thickness, such as a tectonic plate undergoing bending in response to the loads and forces induced by mountain chains, subduction, or glacial loading.

The utility of these techniques has been demonstrated in several previous studies of structural features on Mars, Venus, and Europa. Applications to Europa are particularly relevant because of the potential to use linear elasticity and LEFM to quantify the magnitude of, and variability in, the elastic thickness of Europa’s ice crust, which is generally thought to overlie an inviscid water ocean. We show how LEFM theory can be used on Europa to explain: (1) the depth of brittle fracturing based on fault and fracture spacing at the surface; (2) the genetic association and angular relationships between fractures of different ages; (3) the distribution of displacement along strike-slip faults; and (4) bending of the ice crust in response to line loading induced by Europan ridges. In each case, we compare our analysis of Europan structural features with terrestrial analogs that have been shown to agree well with the predictions of LEFM. Each of these applications demonstrates the viability of LEFM when considering ice deformation on Europa, and places constraints on the elastic thickness of the Europan crust, which we estimate to be no more than 3 km, and somewhat variable geographically.