Bulletin of Volcanology

, Volume 73, Issue 2, pp 143–153 | Cite as

Mechanism of the 1996–97 non-eruptive volcano-tectonic earthquake swarm at Iliamna Volcano, Alaska

Research Article

Abstract

A significant number of volcano-tectonic (VT) earthquake swarms, some of which are accompanied by ground deformation and/or volcanic gas emissions, do not culminate in an eruption. These swarms are often thought to represent stalled intrusions of magma into the mid- or shallow-level crust. Real-time assessment of the likelihood that a VT swarm will culminate in an eruption is one of the key challenges of volcano monitoring, and retrospective analysis of non-eruptive swarms provides an important framework for future assessments. Here we explore models for a non-eruptive VT earthquake swarm located beneath Iliamna Volcano, Alaska, in May 1996–June 1997 through calculation and inversion of fault-plane solutions for swarm and background periods, and through Coulomb stress modeling of faulting types and hypocenter locations observed during the swarm. Through a comparison of models of deep and shallow intrusions to swarm observations, we aim to test the hypothesis that the 1996–97 swarm represented a shallow intrusion, or “failed” eruption. Observations of the 1996–97 swarm are found to be consistent with several scenarios including both shallow and deep intrusion, most likely involving a relatively small volume of intruded magma and/or a low degree of magma pressurization corresponding to a relatively low likelihood of eruption.

Keywords

Iliamna Volcano VT earthquake Earthquake swarms Stress tensor inversion Fault-plane solutions 

Supplementary material

445_2010_439_Fig9_ESM.jpg (50 kb)
Online Resources 1

Lower-hemisphere projections of 13 FPS calculated for the background period. All FPS are shown with polarity data (+ compressional, o dilational) and P- and T-axes plotted on the focal sphere. The date (year, month, day, hour, minute) and location (latitude, longitude, and depth (BSL), where negative depths indicate earthquakes located above sea level) are also given above each FPS. (JPEG 50 kb)

445_2010_439_Fig10_ESM.jpg (197 kb)
Online Resources 2

Lower-hemisphere projections of 52 FPS calculated for the swarm period. All FPS are shown with polarity data (+ compressional, o dilational) and P- and T-axes plotted on the focal sphere. The date (year, month, day, hour, minute) and location (latitude, longitude, and depth (BSL), where negative depths indicate earthquakes located above sea level) are also given above each FPS. (JPEG 196 kb)

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.Department of GeologyUniversity of South FloridaTampaUSA
  2. 2.Alaska Volcano ObservatoryUnited States Geological SurveyAnchorageUSA

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