Co-eruptive and post-eruptive source models at Okmok volcano from GPS and InSAR measurements

Okmok volcano is one of the most active volcanoes located in Aleutian Arc, Alaska. The most recent eruption that occurred in 2008 was much larger than the events during the 20th century. To gain a better understanding on the changes in the magma system caused by the 2008 eruption, we analyze the co-eruptive and post-eruptive deformation based on GPS and InSAR measurements. We first invert a time-dependent model for post-eruptive deformation from GPS and InSAR data independently. The InSAR model shows a Mogi source at the depth of 5.3 km bsl, while the GPS model prefers a vertical oblate spheroid model at the depth of 2.8 km bsl with the ratio between semi-major and semi-minor axis being 0.4. The distinct models for the GPS and InSAR suggest complexity of the magma system at Okmok volcano after the 2008 eruption, which we did not see before. We then invert the GPS and InSAR timeseries jointly. We find that the best fit joint model is the combination of a deep Mogi source with the cumulative volume change of 0.035 km³ and a shallow distributed sill with the averaged opening of 1.2 m. Of the joint model, the Mogi source location is determined by the InSAR model. The sill is located beneath the caldera at a depth of 0.5 km bsl. Finally, we calculate the co-eruptive displacement at more campaign GPS sites, which were surveyed before and after the 2008 eruption, by comparing the estimated pre-eruptive and post-eruptive time-dependent models. There are 31 total GPS sites that have co-eruptive deformation, although most of these also include 2 years of post-eruptive inflation, so for this data set the coverage is comparable to InSAR. We will determine the best fit co-eruptive source model based on the GPS and InSAR displacement and compare it to the post-eruptive source.