Abstract:
The relatively simple tectonic environment of mid-ocean ridge transform fault (RTF) seismicity
provides a unique opportunity for investigation of earthquake and faulting processes.
We develop a scaling model that is complete in that all the seismic parameters are related
to the RTF tectonic parameters. Laboratory work on the frictional stability of olivine aggregates
shows that the depth extent of oceanic faulting is thermally controlled and limited
by the 600°C isotherm. Slip on RTFs is primarily aseismic, only 15% of the tectonic offset
is accommodated by earthquakes. Despite extensive fault areas, few large earthquakes occur
on RTFs, and few aftershocks follow the large events. Standard models of seismicity,
in which all earthquakes result from the same seismic triggering process, do not describe
RTF earthquakes. Instead, large earthquakes appear to be preceded by an extended fault
preparation process marked by abundant foreshocks within 1 hour and 15 km of the mainshocks.
In our experiments normal force vibrations, such as seismic radiation from nearby
earthquakes, can weaken and potentially destabilize steadily creeping faults. Integrating
the rheology, geology, and seismicity of RTFs, we develop a synoptic model to better understand
the spatial distribution of fault strength and stability and provide insight into slip
accommodation on RTFs.
