Slip-length scaling in large earthquakes: The role of deep penetrating slip below the seismogenic layer

Bruce E. Shaw

Published 2008, SCEC Contribution #1386

Coseismic slip is observed to increase with earthquake rupture length
for lengths far beyond the lengthscale set by the seismogenic layer.
The observation, when interpreted within the realm of static dislocation theory
and the imposed limit that slip be confined to the seismogenic layer,
implies that earthquake stress drop increases as a function of rupture length
for large earthquakes and, hence, that large earthquakes differ from small.
Here a three dimensional elastodynamic model is applied to show that the
observed increase in coseismic slip with rupture length may be satisfied while
maintaining constant stress drop across the entire spectrum of earthquake sizes
when slip is allowed to penetrate below the seismogenic layer into an underlying
zone characterized by velocity-strengthening behavior.
Is this deep coseismic slip happening during large earthquakes?
We point to a number of additional associated features of the model
behavior which are potentially observable in the Earth.
These include the predictions that a substantial fraction, of
order a third of total coseismic moment,
is due to slip below the seismogenic layer, and that slip below the seismogenic
layer should be characterized by
long risetimes and a dearth of high frequency motion.

Citation
Shaw, B. E. (2008). Slip-length scaling in large earthquakes: The role of deep penetrating slip below the seismogenic layer. Bulletin of the Seismological Society of America, 98, 1633. doi: 10.1785/0120070191.