12. Fault Friction and the Upper Transition from Seismic to Aseismic Faulting

Abstract

This paper discusses the processes and mechanical factors that define the seismogenic zone and the updip transition from seismic to aseismic faulting. We review friction laws for granular and clay-rich fault zones and discuss them in the context of the mechanics of stick-slip and the requirements for instability. Seismogenic faulting is driven by the unstable release of stored elastic energy, and thus explanations of the upper stability transition must be couched in terms of fault-zone rheology. We summarize several observations that define the seismogenic zone and its upper boundary, including microseismicity, earthquake afterslip, and the spatial distribution of seismic moment release during large earthquakes. We focus on two hypotheses for the updip limit of seismic faulting. The clay mineral hypothesis posits that a thermally driven transition from a smectite to an illite structure produces a transition from aseismic to seismic behavior. The fault gouge lithification hypothesis posits that the stability transition reflects a threshold consolidation, or lithification, state and a switch from pervasive to localized shear. Existing laboratory data, which cover a limited range of conditions, indicate that the smectite-illite transformation results in an increase in friction but not a transition from stable to unstable behavior. It appears that other depth-and temperature-dependent processes may play an important role in altering the frictional properties of subduction faults and establishing the updip seismic limit.

Seismic variability of subduction thrust faults: Insights from laboratory models

“…Its relation with stress drop has been experimentally simulated with granular flow models [e.g., Higashi and Sumita, 2009]. Similar factors can play a role in subduction thrusts, favored by dehydration reactions in the subducting lithosphere [e.g., Pytte and Reynolds, 1988], changes in lithification state [Marone and Scholz, 1988;Marone and Saffer, 2007] and diagenetic processes [Moore and Saffer, 2001]. Thus, the initially rough profile of the lithosphere at the trench will be gradually smoothed as subduction evolves, minimizing roughness fluctuations with depth [Wang, 2010a].…”

“…It is generally accepted that the temperature range at which interplate seismogenic zones develop is from 100-150°C to 350-450°C [i.e., Hyndman and Wang, 1993;Wang, 1995;Hyndman et al, 1997;Currie et al, 2002]. On this basis, the updip limit of seismogenic thrust faulting is alternatively explained by the transition illite-smectite [Pytte and Reynolds, 1988] or by fault gouge lithification processes [Saffer and Marone, 2003;Marone and Saffer, 2007], while the downdip limit is possibly controlled by the brittle-ductile transition of the crustal material [i.e., Brace and Kohlstedt, 1980] or by the intersection of the slab with the forearc mantle wedge [Peacock and Hyndman, 1999].…”

Expedition 344 summary

“…The frictional state of the incoming sediment changes progressively with increasing temperature and pressure as it travels downdip. Important lithologic factors influencing friction are composition, fabric, texture, and cementation of rocks, as well as fluid pore pressure (Bernabé et al, 1992;Moore and Saffer, 2001;Beeler, 2007;Marone and Saffer, 2007;Collettini et al, 2009). For example, fault rocks with high phyllosilicate content are generally weaker than rocks with low phyllosilicate content (Ikari et al, 2011).…”

“…Sediment properties including porosity, permeability, consolidation state, and alteration history also exert a strong influence on fault zone behavior. At erosive margins, where the plate boundary cuts into the overriding plate, the composition and strength of the upper plate is also important (McCaffrey, 1993).Field observations and laboratory experiments suggest that a prerequisite for unstable sliding is that the incoming sediment is consolidated and lithified (Davis et al, 1983;Byrne et al, 1988;Marone and Scholz, 1988;Marone and Saffer, 2007;Fagereng and Sibson, 2010). This hypothesis posits that the updip limit of the seismogenic zone occurs near a threshold of consolidation and/or lithification in which fault zone behavior changes from distributed shear (stable sliding), where shear is accommodated by granular processes, to localized shear (unstable sliding) along discrete surfaces.…”

Faulting processes in active faults – Evidences from TCDP and SAFOD drill core samples

“…For example, many authors assume that the transition from aseismic creep at shallow depth to seismic slip occurs at depth between 5 and 15 km and has been attributed to the dehydration of smectiteeillite (e.g. Hyndman et al, 1997;Saffer and Marone, 2003;Marone and Saffer, 2007). The lack of earthquakes at shallow depth can be related to the velocity-strengthening behavior of phyllosilicate-rich gouges (Imber et al, 2008;Ikari et al, 2011).…”