Aftershocks and temporal clustering of deep earthquakes

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Abstract
This paper evaluates how the focal depth, the geographic location, and magnitude affect the incidence of aftershocks and the occurrence of temporal clustering of nearby events for selected deep earthquakes (h> 70 km) in the catalog of the International Seismological Centre. For comparison, we also evaluate shallow (h< 70 km) and deep earthquakes for which locations and moment tensors are reported by the Harvard group. The primary conclusions are as follows: 1) The incidence of aftershocks depends strongly on focal depth, with aftershocks being less common for events between 100‐ and 450‐km depth than for shallower or deeper events. Events with focal depth shallower than 40 km have a higher incidence of aftershocks and more pronounced temporal clustering than do deeper events. 2) For the data available at present, the incidence of aftershocks and amount of temporal clustering for deep events are independent of geographic region, except for dependence caused by regional differences in the focal depths of events. 3) Deep earthquakes with large magnitudes are more likely to have aftershocks than are smaller magnitude events, in accordance with models where the number of aftershocks is a Poisson random variable that is a function of magnitude. However, several large events are anomalous in that they have many more aftershocks, or many fewer aftershocks, in the catalog than predicted by the model.

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