Abstract

This seminar will be held online. Details will be sent to the Earth Sciences and Bullard mailing lists. If you are not in Earth Sciences but would like to attend, please contact the talk organisers.

Evidence of episodic deformation below hypocentral depth during the seismic cycle, i.e. on seismic time scales, is provided from various geoscientific fields, including geodesy, seismology, numerical modelling as well as the deformation record of rocks. Along shear zones, which represent the deep continuations of seismically active fault zones, crustal blocks can be displaced against each other by several tens of kilometres on the time scale of million years. Yet, many aspects on the coupling between long-term creep of rocks in shear zones and episodic deformation related to the seismic cycle are unknown. In this talk, I will firstly review deformation experiments that simulate transient high-stress coseismic deformation and postseismic creep at relaxing stresses. Secondly, I will focus on the deformation record of high-pressure low-temperature metamorphic rocks from a shear zone on Crete to discuss the grain scale processes during the prolonged history of episodic deformation during exhumation from the subduction channel. This shear zone records long-term diffusional creep in metasediments with viscosities on the order of 10¹⁹ to10²⁰ Pa s and high-strain rates on the order of 10^-9 to 10^-10 s^-1 causing internal stress-build-up to a few tens of MPa with cyclic cracking and sealing within time intervals of hundreds to thousand years. Locally and transiently, external and fast stress build-up due to the proximity to the tip of a seismically active fault in overlying crustal levels, causes high-stress crystal plasticity in quartz-rich lithologies, probably again triggering accelerated creep in the metasediments. This record demonstrates the relevance of stress-loading rates on the deformation behaviour of rocks.