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Why do strike-slip earthquakes produce fewer aftershocks?

Kelian Dascher-Cousineau, Emily E. Brodsky, & Thorne Lay

Published August 13, 2018, SCEC Contribution #8452, 2018 SCEC Annual Meeting Poster #046

The number of aftershocks generated by an earthquake is generally related to the size of the mainshock. However, aftershock sequences can have significant excursions from a simple magnitude-dependent productivity law. This variability is particularly concerning for great earthquakes where the number of damaging aftershocks can vary by factors of 40 for mainshocks of equivalent magnitude. We capitalize on the recent finding that strike-slip earthquakes produce fewer aftershocks at a given magnitude than dip-slip earthquakes to determine mainshock characteristics that govern productivity variations. Is the paucity of aftershocks for strike-slip earthquakes an effect of the typical tectonic stress regime for these earthquakes or does it reflect either the influence of the dynamics or geometry of the rupture itself? We use the Global CMT catalog and space-time windowing to measure productivity and examine its variations in the context of its tectonic setting, rupture properties, and source geometry. The data show that focal mechanism solutions separate the productivity data in generally convergent, divergent or transform plate boundaries. We proceed to build a catalog of earthquake source parameters based on the finite fault source inversions released by Hayes et al. [2017] for the great-sized earthquakes from 1990 to 2017. We tabulate new stress drop measurements, source dimensions, and seismic energy, as well as new metrics to characterize source geometry and heterogeneity. The compilation highlights that particularly long and narrow ruptures confined to the brittle crust, have markedly lower productivity. Additionally, building upon recent findings, we interpret the larger stress drops characteristic of strike-slip earthquakes to contribute to smaller ruptures, smaller activated volumes, and, therefore, fewer aftershocks. Neither the tectonic setting nor the released seismic energy appear to directly determine the paucity of aftershocks for strike-slip earthquakes; instead, it seems that source geometry plays a key role in their aftershock triggering.

Key Words
Aftershock productivity, source parameters,

Dascher-Cousineau, K., Brodsky, E. E., & Lay, T. (2018, 08). Why do strike-slip earthquakes produce fewer aftershocks?. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)