Coseismic velocity variations caused by static stress changes associated with the 2001 Mw=4.3 Agios Ionis earthquake in the Gulf of Corinth, Greece

The analysis of temporal variations in the seismic velocity across faults can be used to
estimate in situ stress changes. Seismic velocity of propagation depends on the fault
stiffness, which is a function of stress. The coda wave interferometry technique is applied
to seven families of repeating earthquakes (multiplets) recorded on the southern shore of
the Gulf of Corinth, Greece, to estimate high precision velocity changes in the Earth
’
s
crust associated with the
M
w
= 4.3 Agios Ioanis earthquake. Results show that the Agios
Ioanis event causes a perturbation in elastic properties at seismogenic depth, resulting in a
reduction of 0.2% in the seismic velocity. The results are not consistent with either damage
induced by dynamic stresses nor a fluid transient origin. In contrast, both the spatial
distribution and magnitude of the velocity perturbation correlate well with modeled static
stress variations. This suggests that the measured changes in the mechanical properties of
the seismogenic crust can be attributed to a change in static stress field associated with the
M
w
= 4.3 Agios Ioanis earthquake. The velocity changes indicate an unclamping of the
Pyrgaki fault at depth, which has local hazard implications