Steadily propagating slip pulses driven by thermal decomposition

• Published in: Journal of geophysical research. Solid earth 2015-09, Vol.120 (9), p.6558-6591
• Main Authors: Platt, John D., Viesca, Robert C., Garagash, Dmitry I.
• Format: Article
• Language: English
• Subjects: Buffers; Computational fluid dynamics; coseismic friction; Decomposition; Decomposition reactions; dynamic rupture; dynamic weakening; Earthquakes; Faults; Fluid flow; Geological faults; Geophysics; Healing; Plate tectonics; Pore pressure; Porosity; Pressurization; Pressurizing; Propagation; Properties; Properties (attributes); Pulse propagation; Releasing; Rupture; Rupturing; Seismic activity; Seismology; Slip; Solutions; Steady state; Stresses; Temperature; Temperature effects; Temperature rise; Thermal decomposition; Thermal degradation; Thermal expansion; Velocity
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1002/2015JB012200

Geophysical observations suggest that mature faults weaken significantly at seismic slip rates. Thermal pressurization and thermal decomposition are two mechanisms commonly used to explain this dynamic weakening. Both rely on pore fluid pressurization with thermal pressurization achieving this through thermal expansion of native solids and pore fluid and thermal decomposition by releasing additional pore fluid during a reaction. Several recent papers have looked at the role thermal pressurization plays during a dynamically propagating earthquake, but no previous models have studied the role of thermal decomposition. In this paper we present the first solutions accounting for thermal decomposition during dynamic rupture, solving for steady state self‐healing slip pulses propagating at a constant rupture velocity. First, we show that thermal decomposition leads to longer slip durations, larger total slips, and a distinctive along–fault slip rate profile. Next, we show that accounting for more than one weakening mechanism allows multiple steady slip pulses to exist at a given background stress, with some solutions corresponding to different balances between thermal pressurization and thermal decomposition, and others corresponding to activating a single reaction multiple times. Finally, we study how the rupture properties depend on the fault properties and show that the impact of thermal decomposition is largely controlled by the ratio of the hydraulic and thermal diffusivities χ = αhy/αth and the ratio of pore pressure generated to temperature rise buffered by the reaction Pr/Er. Key Points Thermal decomposition can contribute substantial dynamic weakening Thermal decomposition leads to longer rupture durations and larger slips Thermal pressurization and decomposition can combine in multiple ways to propagate a slip pulse