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

Abstract

A 7 year time series of satellite radar images over Unimak Island, Alaska-site of Westdahl Volcano, Fisher Caldera, and Shishaldin Volcano-was 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 3.6 km north of Westdahl peak and at depth of about 6.9 km 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 7.9 km in length, 0.54 km in width, and located at about 5.5 km below sea level underneath the center of Fisher Caldera with strike angle of N52°E. Very little deformation was detected near Shishaldin peak; however, a region approximately 15 km east of Shishaldin, as well as an area at the Tugamak range at about 30 km 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.

Pyroclastic Flow Deposits and InSAR: Analysis of Long-Term Subsidence at Augustine Volcano, Alaska

“…We subsequently model and subtract stratified atmospheric phase signals (φ i,j,atm−s ) from Equation (2) using the Weather Research and Forecasting (WRF) model and following the approach described in Gong et al, [46,47]. This separate step is required as stratified atmospheric signals are significant at Augustine and can often not be removed using spatial or temporal filters.…”

Modeling 3‐D crustal velocities in the United States and Canada

“…[]. The horizontal velocity field found near Alaska's Pacific coast and to the west of longitude 155°W is complex due to volcanic and seismic activities [ Cross and Freymueller , ; Gong et al ., ]. The horizontal velocity field occurring in northeastern Alaska remains uncertain due to a lack of geodetic data and to ongoing postseismic motion associated with the M 7.9 Denali Fault earthquake of 2002.…”

A 25‐Year History of Volcano Magma Supply in the East Central Aleutian Arc, Alaska

“…Previous studies have shown that a spherical “Mogi” source is sufficient to model the volcanic deformation at Westdahl and Makushin volcanoes (Gong et al, 2015; Lu et al, 2002, 2003; Mann & Freymueller, 2003). Akutan has a more complex magma plumbing system (DeGrandpre et al, 2017), but we found a Mogi source is still sufficient enough for studying the volume change history of Akutan volcano because the largest inflation events were well described by a Mogi source (Text S4).…”

“…Lu et al (2003) and Gong et al (2015) processed the InSAR images/time series using ERS1/2 and ENVISAT data for Westdahl volcano throughout the period of the 1990s and 2000s. For Makushin volcano, Lu et al (2002) and Lu and Dzurisin (2014) processed the InSAR images using ERS1/2 and ENVISAT data.…”

“…Lu et al (2003) used interferometric synthetic aperture radar (InSAR) to study the period 1992-2000, finding that the rate of inflation seemed to decay exponentially with time. Similarly, Gong et al (2015) processed SAR data for 2006-2015 and also found that the time series of volume change showed an exponential decay. For Makushin volcano, Lu et al (2002) processed several InSAR images from 1992 to 2000 and found preeruptive inflation before the 1995 eruption.…”