Measurement and interpretation of subtle deformation signals at Unimak Island from 2003 to 2010 using weather model-assisted time series InSAR

초록

A 7year time series of satellite radar images over Unimak Island, Alaskasite of Westdahl Volcano, Fisher Caldera, and Shishaldin Volcanowas processed using a model-free Persistent Scatterer Interferometry technique assisted by numerical weather prediction model. The deformation-only signals were optimally extracted from atmosphere-contaminated phase records. The reconstructed deformation time series maps are compared with campaign and continuous Global Positioning System (GPS) measurements as well as Small Baseline Subset interferometric synthetic aperture radar (InSAR) results for quality assessment and geophysical interpretation. We observed subtle surface inflation at Westdahl Volcano that can be fit by a Mogi source located at approximately 3.6km north of Westdahl peak and at depth of about 6.9km that is consistent with the GPS-estimated depth for the 1998 to 2001 time period. The magma chamber volume change decays during the period of 2003 to 2010. The deformation field over Fisher Caldera is steadily subsiding over time. Its best fit analytical model is a sill source that is about 7.9km in length, 0.54km in width, and located at about 5.5km below sea level underneath the center of Fisher Caldera with strike angle of N52 degrees E. Very little deformation was detected near Shishaldin peak; however, a region approximately 15km east of Shishaldin, as well as an area at the Tugamak range at about 30km northwest of Shishaldin, shows evidence for movement toward the satellite, with a temporal signature correlated with the 2004 Shishaldin eruption. The cause of these movements is unknown.

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