HR: 0830h
AN: NG41C-0073    [PDF]
TI: Fractional Kinetics of Volcanic Earthquake Time Series
AU: Chastin, S
EM: schastin@glg.ed.ac.uk
AF: University of Edinburgh, School of GeoSciences West Mains Road, Edinburgh, EH9 3JW United Kingdom
AU: * Main, I
EM: ian.main@ed.ac.uk
AF: University of Edinburgh, School of GeoSciences West Mains Road, Edinburgh, EH9 3JW United Kingdom
AB: We analyse the USGS earthquake catalogue for the effusive volcanoes of Hawaii from 1959 to 2001. The distribution of inter-event times $\Delta t$ and inter-hypocentral distances $\Delta r$ between $>$10$^5$ subsequent events is contrasted with a surrogate catalogue where time correlation is deliberately destroyed as null hypothesis. Both series are non-stationary. The distribution of $\Delta r$ is normal, with a characteristic scale $\sim$ 20km and finite variance. The inter-event time distribution has three distict regimes. Two are power-laws, with a break of slope from a higher to a lower exponent around the mean value $<$ $\Delta t$ $>$ $\sim 10$ hours, and then an exponential decay with a characteristic time of $\sim 3$ years. The elevated probability of occurrence of the shortest inter-event times reflects the tightly time-clustered swarms commonly observed in volcano-tectonic (VT) sequences. The power-law exponent in the middle range is $\sim$ - 0.25. Its broad-bandwidth scaling suggests the system conserves the memory of an event for a very long period of time. This induces an anticorrelation between subsequent events in the $\Delta t$ series, with a Hurst exponent H $\sim$ 0.77, compared to 0.5 for a memoryless process. The mean distance $\Delta r$ evolves with $\Delta t$ in a way that is characteristic of a self-affine object produced by fractional kinetic processes with two distinct scaling regions. A region of statistically-significant, rapidly-accelerating, increase in $\Delta r \propto \Delta t^n$ with $n$ $\sim$ 1.6 is found for $\Delta t$ $<$ 10 hours and $\Delta r$ $<$ 20 km. Outside this region the curve cannot be differentiated from the temporally random null hypothesis, and $\Delta r$ increases only very slowly with time following a power law $\Delta r \propto \Delta t^{n'}$ with $n' \sim 0.1$. The cross-over in scaling relations at (20 km, 10h) implies that the layered rheology of the lithosphere may inhibit rapid triggered diffusion or migration of VT events beyond the seismogenic thickness.
DE: 3220 Nonlinear dynamics
DE: 7280 Volcano seismology (8419)
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting