Earthquake induced metamorphism
- Date: Friday 2 November 2018, 15:00 – 16:00
- Location: Earth and Environment - Seminar rooms 1 and 2, 8.119
- Type: Institute of Geophysics and Tectonics, Seminars, Earth and Environment
- Cost: Free
Institute of Geophysics and Tectonics seminar. Speaker Bjorn Jamtveit, University of Oslo.
Prior to orogeny, the lower continental crust is dry, strong, and often under considerable tectonic stress. Transformation to rheologically weaker rocks that subsequently undergoes more or less localized ductile deformation occurs through fluid-induced metamorphism. Earthquakes may play a key role during the incipient stages of this transformation process both in continental and oceanic settings, by connecting initially dry rock volumes to external fluid reservoirs. Deep crustal earthquakes often evolve through an initial stage of dynamic rupture, that creates asymmetric damage of the wall rocks at very high stress levels. Heating during the subsequent seismic slip, may cause melting and melt injection into fragmented wall-rocks. When fluids follow in the wake of the rupture, fluid-rock interactions within the permeable wall-rocks lead to mechanical weakening by the production of fine grained and hydrated products. This may induce shear deformation of the wall-rocks subsequent to the initial fragmentation. Reduced ability to hold differential stress, causes significant pressure perturbations within volumes of mechanically weaker product rocks and may cause local high-pressure metamorphism in the absence of tectonic burial. Earthquakes occurring below the normal seismogenic regime may be triggered by local fluid production in systems experiencing a rise in temperature, otherwise stress pulses related to shallower earthquakes is a generic mechanism that will provide transient loading of the lower crust and associated aftershocks in any orogenic setting.