Effect of fault roughness on aftershock distribution and post co-seismic
strain accumulation
Abstract
We perform physics-based simulations of earthquake rupture propagation
on geometrically complex strike-slip faults. We consider many different
realization of the fault roughness and obtain heterogeneous stress
fields by performing dynamic rupture simulation of large earthquakes. We
calculate the Coulomb failure function (CFF) for all these realizations
so that we can quantify zones of stress increase/shadows surrounding the
main fault and compare our results to seismic catalogs. To do this
comparison, we use relocated earthquake catalogs from Northern and
Southern California. We specify the range of fault roughness parameters
based on past observational studies. The Hurst exponent (H) varies in
range from 0.5 to 1 and RMS height to wavelength ratio ( RMS deviation
of a fault profile from planarity) has values between 10-2 to 10-3. For
any realization of fault roughness, the Probability density function
(PDF) values relative to the mean CFF change show a wider spread near
the fault and this spread squeezes into a narrow band as we move away
from fault. For lower value of RMS ratio ( 10-3), we see bigger zones of
stress change near the hypocenter and for higher value of RMS ratio (
10-2), we see alternate zones of stress increase/decrease surrounding
the fault to have comparable lengths. We also couple short-term dynamic
rupture simulation with long-term tectonic modelling. We do this by
giving the stress output from one of the dynamic rupture simulation (of
a single realization of fault roughness) to long term tectonic model
(LTM) as initial condition and then run LTM over duration of seismic
cycle. This short term and long term coupling enables us to understand
how heterogeneous stresses due to fault geometry influence the dynamics
of strain accumulation in the post-seismic and inter-seismic phase of
seismic cycle.