Long‐term deformation driven by small ambient tectonic stresses and strong oscillating tidal within Enceladus with analogy to rock behavior near the San Andreas Fault

Abstract

Strong tidal stresses brought much of the icy shell of Enceladus into frictional failure at past times of high orbital eccentricity. The frictional behavior of shallow terrestrial rock exposed to repeated episodes of strong seismic waves provides analogy. Frictional failure produces cracks that lower the shear modulus. Seismic regolith develops where the shear modulus increases linearly with depth. Imposed peak strains barely cause frictional failure within self-organized regolith. With regard to Enceladus, eccentricity could continue to build up in the past since little anelastic strain, and hence tidal dissipation occurred within the self-organized regolith and within the underlying cold ice. A frictional instability analogous to the formation of weak major faults on the Earth likely occurred once the regolith was many kilometers thick. The effective coefficient of friction dropped to low levels along major faults within the deep cold ice. Tidal dissipation on these faults heated the ice starting thermal convention within the South Polar Terrain. Once thermal buoyancy produced stresses, the oscillating stresses from tides nonlinearly enhanced the rate of tectonic convection. Warm ice that dissipates tides now exists within Enceladus. The eccentricity will likely decrease and the object will then freeze.

Potential for a large earthquake near Los Angeles inferred from the 2014 La Habra earthquake

“…Paleoearthquake evidence suggests the Puente Hills blind thrust has produced earthquakes in the M w 7.2-7.5 range in the last 11,000 years [Dolan et al, 2003]. Using seismic data, Sleep [2015] and Roten et al [2014] reach similar conclusions that the upper compliant sediments relieve accumulated strain during moderate to large earthquakes: The uppermost few hundred meters of rock fails in oscillating dynamic friction beneath Whittier Narrows [Roten et al, 2014], and the ambient fault-normal stress relaxes during the process over time accommodating the shallow tectonic strain [Sleep, 2015]. Repeated strong shaking keeps the shallow ambient stress at low levels.…”