The global diversity of intermediate-depth and deep earthquakes

Abstract:

We analyzed more than 800 deep and intermediate depth earthquakes (depth>50km and M>5.5), by stacking broadband P-wave pulses recorded globally. By a carefully applied processing we finally obtained more than 600 source time functions, and the associated rupture durations, robustly measured by comparing alternative versions of the same waveform. The obtained durations are used to study the depth dependence and the moment scaling properties for deep seismicity. Given the large number of estimated durations, magnitude scaling, depth-dependence and along-strike variations are analyzed globally and within subduction zones.

The global analysis of the dataset shows how, beyond the scatter in the scaled durations, the observed reduction in duration with depth can be explained by increasing wave speed with depth. Furthermore, the self-similar scaling of duration to seismic moment to the 1/3 power is not valid for deep seismicity, suggesting a different behavior from shallow earthquakes.

When comparing different subduction zones, coherent variation of the scaled durations is observed, suggesting a large diversity of intermediate-depth and deep earthquakes exists. The variations are correlated with geometry of the subduction and not to thermal state of the subducting plates.

We are in the process of estimating the radiated energy for our dataset as well in order to better constrain the mechanism of deep earthquakes, using the static and dynamic measures of earthquake behavior. Comparison of these and other measures with independent geophysical properties of slabs such as plate age, thermal parameter and convergence rate will be shown, in order to unravel any possible relation between the subduction zone style and earthquake rupture behavior.