Imposed strain localization in the lower crust on seismic timescales

Abstract

We show using numerical model experiments that upper crustal faults can impose ductile localization in the mid and lower crust over the seismic cycle, with strain-rates and integrated creep strain enhanced by a factor of 10, or a factor of 100 if lower crust is also thermally weakened. Imposed ductile localization is caused by the transfer in stress from the lower tip of the frictional fault to the mid-crust. Within the weak ductile mid-lower crust, this stress transfer also promotes significantly enhanced creep rates in a lobe that extends down-dip from the lower end of the fault. Comparison of model results with the Alpine Fault of New Zealand, shows how the interaction of faulting with other localization mechanisms can account for key aspects of the geodetic strain accumulating across the Alpine Fault. Localization of ductile strain in the lower crust imposed by faulting in the upper crust could explain the extension of major faults into the lower crust observed in seismic imaging. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences.