Other
Scientific paper
Sep 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011geoji.186.1365k&link_type=abstract
Geophysical Journal International, Volume 186, Issue 3, pp. 1365-1379.
Other
Radar Interferometry, Earthquake Source Observations, Seismicity And Tectonics, Volcano Seismology, Volcanic Arc Processes, Dynamics And Mechanics Of Faulting
Scientific paper
Microearthquake swarms occur frequently in volcanic environments, but do not always culminate in an eruption. Such non-eruptive swarms may be caused by stresses induced by magma intrusion, hydrothermal fluid circulation or possibly other tectonic processes such as slow-slip earthquakes. The Strandline Lake region of southcentral Alaska, located 30 km northeast of Mt Spurr volcano, experienced an intense earthquake swarm between 1996 August and 1998 September. A total of 2507 earthquakes were recorded by the Alaska Volcano Observatory's permanent seismic network during the swarm period, with a maximum magnitude of ML 3.6. The cumulative seismic moment of the swarm was 1.2 × 1015 N m, equivalent to that of a single Mw 4.0 earthquake. Because of the swarm's distance from the nearest Holocene volcanic vent, seismic monitoring was minimal and gas emission and GPS data do not exist for the swarm period. However, combined waveforms from a dense seismic network on Mt Spurr and from several regional seismic stations allow reanalysis of a representative set of swarm and background earthquakes. Swarm hypocentres calculated using a newly formulated 1-D velocity model and station corrections indicate a roughly circular swarm volume with dimensions of approximately 5 km, centred below 10 km below sea level (BSL). Composite fault-plane solutions for swarm earthquakes indicate oblique strike-slip faulting with a northeast-trending P-axis orientation. In contrast, a composite fault-plane solution for background earthquakes indicates a fundamentally different, though poorly constrained, local stress field orientation. Interferometric Synthetic Aperture Radar images spanning the swarm period unambiguously show no evidence of surface deformation, but do not rule out subcentimetre-scale deformation during the swarm. While a shallow (<10 km BSL) magma intrusion appears to be an unlikely cause of the 1996-1998 Strandline Lake swarm based on the new earthquake depths and the absence of strong surface deformation, it is possible that the swarm was driven by deep (>10 km BSL) magma intrusion representing an intrusive or protovolcanic segment of the Aleutian arc.
Biggs Juliet
Hansen Roger
Kilgore Wayne W.
Roman Diana C.
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