Bruce E. Shaw

Abstract:
Fault models can generate complex sequences of events from frictional
instabilities, even when the material properties are completely uniform
along the fault.
These complex sequences arise from the heterogeneous stress and
strain fields which are produced through the dynamics of repeated ruptures
on the fault.
Visual inspection of the patterns of events produced in these models shows
a striking and ubiquitous feature: future events tend to occur near the
edges of where large events died out.  In this paper, we explore this feature
more deeply.
First, using long catalogues generated by the model, we quantify the effect.
We show, interestingly, that it is an even larger effect for future
small events than it is for future large events.
Then, using our ability to directly measure all aspects of the model,
we find a physical explanation for our observations by looking at the
stress fields associated with large events.
Looking at the average stress field we see a large stress concentration
left at the edge of the large events, out of which the future events
emerge.  Further, we see the smearing out of the stress concentration as
small events occur.  This shows why the epicenters of future small events are
more correlated with the edges
of large events
than are the epicenters of future large events.
Finally, we discuss how results from our simple model
may be relevant to the more complicated case of the Earth.