We determine the spatiotemporal characteristics of interearthquake
triggering in the International Seismological Centre catalogue on
regional and global scales. We pose a null hypothesis of spatially
clustered, temporally random seismicity, and determine a residual
pair correlation function for triggered events against this background.
We compare results from the eastern Mediterranean, 25 Flinn-Engdahl
seismic regions, and the global data set. The null hypothesis cannot
be rejected for distances greater than 150 km, providing an upper
limit to triggering distances that can be distinguished from temporally
uncorrelated seismicity in the stacked data at present. Correlation
lengths L and mean distances between triggered events hri are on
the order of 10 50 km, but can be as high as 100 km in subduction
zones. These values are not strongly affected by magnitude threshold,
but are comparable to seismogenic thicknesses, implying a strong
thermal control on correlation lengths. The temporal evolution of
L and hri is well fitted by a power law, with an exponent H 0.1 ?
0.05. This is much lower than the value H = 0.5 expected for Gaussian
diffusion in a homogenous medium. We observe clear regional variations
in L, hri and H that appear to depend on tectonic setting. A detectable
transition to a more rapid diffusion regime occurs in some cases
at times greater than 100 200 days, possibly due to viscoelastic
processes in the ductile lower crust.
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