Modeling post-eruptive deformation at Okmok volcano from GPS and InSAR using unscented Kalman filter

Okmok, occupies most of northeastern Umnak Island in the Aleutian arc, started inflating soon after the 2008 eruption. Seven GPS sites have been operated after the eruption. Two of them are located within the caldera, three are around the rim of the caldera and two are out of the caldera. The InSAR timeseries have been generated using data from the C-band Envisat and X-band TerraSAR-X satellites (Qu et al., 2015). Both GPS and InSAR indicate more than 0.6 m uplift within the caldera and subtle subsidence outside the caldera. Based on single Mogi source, an unscented Kalman filter was successfully used to model the deformation at Okmok detected by GPS during 2000-2007. We have expanded it to be able to model multiple Mogi sources at different depths and integrate the InSAR observations. Before applying the Kalman filter, We remove a time-independent Mogi source and phase ramp from each InSAR image and obtain its variance-covariance information from the residual. We also determine the relative weight between GPS and InSAR data using variance component estimation. The GPS and InSAR timeseries can then be combined for the Kalman filter. Preliminary results show that two Mogi sources are more likely beneath Okmok volcano. The deep source is located at 8.5 km depth which deflated 0.016 km3 during the first 3 years after the eruption then reached a stable state. The deflating source explains the subsidence outside the caldera which can not be modeled with only one inflating source in any way. The shallow source, migrating 0.5 km from north to south, is located at 2 km depth within the caldera where is close to the source position before the eruption (Freymueller et al., 2010). The magma volume accumulation of the shallow source in the following 7 years from the 2008 eruption is 0.035 km3.