Effects of Low-Magnitude Earthquakes’ Focal Mechanisms on the Evolution of Aftershock Sequences

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

Most studies of earthquake interaction via incremental stress transfer have focused on the effects of the largest events only. In aftershock sequences, these events typically constitute the mainshock alone, or the mainshock and the largest aftershocks. Some of the gross spatial and temporal features of aftershock sequences can be accounted for with this approach, but the role played by interactions between lower-magnitude events remains unclear. To date, comparatively little attention has been paid to aftershocks’ focal mechanisms, which, in principle, enable incremental stress changes associated with lower-magnitude events to be computed and incorporated in stress transfer models. Here, we consider the interaction between one earthquake and the next in terms of the vector joining their hypocenters and represented in a coordinate system defined by the earlier event’s focal mechanism. This approach enables us to describe the sequence of focal mechanisms with reference to a common coordinate system and to take into consideration the perturbations produced by all earthquakes large enough for a focal mechanism to be calculated. We investigate whether the faulting geometry of each aftershock contributes to the sequence’s overall evolution, using complete and declustered examples.

Presenting Author: John Townend

Authors