Multiple causes for non-eruptive seismic swarms at Mt. Martin, Katmai Volcanic Cluster, Alaska (2004-2008)

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• 作者：John F. O'Brien^a ; ^{jobrien@mail.usf.edu} ; Diana C. Roman^a ; James P. Dixon^b ; John A. Power^c ; Richard Arnold^d
• 关键词：VT earthquakes ; Mt. Martin ; Stress field ; Katmai ; Fault-plane solutions ; Dike intrusion ; Directional statistics
• 刊名：Journal of Volcanology and Geothermal Research
• 出版年：2012
• 期刊代码：53_03770273
• 类别：ear
• 出版时间：1 June, 2012
• 卷：229-230
• 期：Complete
• 页码：13-22
• 文件大小：1709 K

摘要

In January 2006, the Alaska Volcano Observatory recorded a non-eruptive swarm of over 778 volcano-tectonic (VT) earthquakes in the Katmai Volcanic Cluster (KVC), Alaska. The swarm earthquakes have estimated hypocentral depths of 0-3 km below sea level (BSL) immediately below the summit of Mt. Martin volcano. In an effort to determine the cause of this swarm, we calculated 134 double-couple fault plane solutions (FPS) for a pre-swarm period (Jan 2004-Dec 2005), the swarm period (January 2006), and a post-swarm period (Feb 2006-Dec 2008), and examined temporal changes in FPS orientations using directional statistical analysis. Statistical tests of uniformity indicate that FPS orientations were heterogeneous during the pre-swarm period, and homogeneous during the 2006 swarm. 3D tests on P- and T-axis orientation data also indicate that FPS homogeneity may have persisted during the post-swarm period. Best-fit axial Von Mises distributions indicate a strongly preferred NNE-SSW P-axis azimuth for swarm FPS, and a NW-SE mean P-axis azimuth for the pre- and post-swarm period FPS. The NW-SE background P-axis azimuth is approximately parallel to regional maximum compressive stress along the northern segment of the Aleutian arc. Thus, we find evidence for a temporary ~ 90掳 reorientation of FPS P-axes during the 2006 swarm, and suggest that the change in FPS orientation may be indicative of intrusion of a shallow, small-volume magma- or fluid-filled dike beneath Mt. Martin in early 2006. In contrast, FPS for VT earthquakes comprising minor swarms in 2007 and 2008 indicate only normal faulting, suggesting a fundamentally different causative process from the major 2006 swarm. Our results demonstrate that the VT earthquake swarms which are a common occurrence in the KVC may be caused by several processes, including magma intrusion, tectonic activity, and hydrothermal fluid circulation; and highlight the need for increased monitoring and analysis during future periods of geophysical unrest.