Mechanics of talc-rich faults
Whether faults creep by slow continuous and stable motion, generate slow slip or low-frequency seismicity, or rupture by an unstable spontaneous event (i.e., an earthquake) is related to the mechanical properties of the minerals in place. Talc is one of the weakest minerals and is expected to form in fault interfaces. There is a lack of experimental data on the mechanical properties of talc under the pressures and temperatures that exist along deep faults and subduction zones. This study presents results from
a set of deformation experiments on talc under pressure-temperature conditions that simulate deep faults and subducted slab interface. The results show a transition from pressure-dependent to pressure-independent strength at high temperatures (∼700°C). In addition, at increased temperature (≥600°C) talc shows an increased tendency for strain localization. These extremely low frictional strengths are about an order of magnitude lower than most rocks and are consistent with inferred weak interfaces along the San Andreas fault and various subducted slab interfaces at depths where creep and/or slow slip events occur.
In subduction zones, one tectonic plate plunges beneath another into the Earth's interior. Some of the earthquakes that occur at subduction zones are unusual due to their occurrence at depths of 70 to 300 km (intermediate depths), or their tremor-like long wave-length seismicity ('slow earthquakes). However, this might be explained through the unique mechanical properties of hydrous minerals and their stability field at depth. Laboratory experiments show that hydrous minerals, such as serpentine, can cause seismicity at depths of 70–300 km.
Seismicity is correlated with the faults that formed due to plate bending. This observation can be explained if the amount of faulting prior to subduction controls the amount of hydrous mineral formation, which subsequently determines the intensity and rate of subduction zone‐related intermediate‐depth earthquakes.
Effect of hydrous mineral at subduction zone seismicity