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Aftershock Productivity on Volcanoes: What can it tell us about interpreting aftershocks?

Ricardo Garza-Giron, Emily E. Brodsky, & Stephanie G. Prejean

Published August 15, 2016, SCEC Contribution #6988, 2016 SCEC Annual Meeting Poster #255 (PDF)

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Most earthquakes have aftershocks and in some systems, it is thought that the majority of the earthquake rate is comprised of aftershocks. However, volcanic earthquakes are intrinsically different from tectonic ones in that magmatic movement can stress rocks more quickly than plate tectonics and elastic strain can be more difficult to sustain over long periods of time. In this study, we measure the aftershock productivity of 27 volcanoes in the Alaska Peninsula and the Aleutian Islands. We utilize a standard model of aftershock production developed for tectonic systems where it is usually observed that the number of aftershocks of a mainshock magnitude M is equal to K10 a(M-­Mref) where K and a are constants that vary regionally and Mref is a reference magnitude. Of the volcanoes studied here, 22 showed a mainshock-­aftershock behavior such as the one observed in global or regional tectonic regimes. The remaining volcanoes did not have enough seismicity for us to make a clear assessment. Of those, 13 volcanoes are well­fit by the model with p­values below 0.01. Those that are well­fit have a level of aftershock productivity similar to an ordinary tectonic system like Southern California (K=0.02). Intriguingly, the ones that are not well­fit are open systems, while those that are well­fit are primarily closed. To some extent, this distinction is a result of the low seismicity in open systems, however, Shishaldin volcano has high seismicity, poor aftershock clustering and is an open system. It is a single case, but perhaps it suggests a more general behavior. It is possible that only closed systems are able to store enough elastic strain to make efficient aftershock production. The volcanic results hint that aftershock productivity may be a useful indicator of stress accumulation in the crust.

Key Words
Aftershocks, volcanoes, Alaska

Garza-Giron, R., Brodsky, E. E., & Prejean, S. G. (2016, 08). Aftershock Productivity on Volcanoes: What can it tell us about interpreting aftershocks?. Poster Presentation at 2016 SCEC Annual Meeting.

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