During 1996 Akutan experienced a seismic swarm, and interferograms spanning June 1995 and September 1996 indicate ~60 cm of uplift on the western side of Akutan Island. This uplift is attributed to magma intrusion. On the northwest flank of the volcano, localised subsidence is observed in a region of intense ground cracking and extension. On the eastern half of the island, interferograms show broad subsidence comparable in magnitude to the uplift observed in the western part. This subsidence is coincident with thermal features and is thought to reflect depressurisation of the hydrothermal system as a result of the earthquake swarm. Displacements of ~5 cm are also observed on two normal faults that bound a graben on the southeast side of the island. This displacement suggests the island was in extension during the time of the earthquake swarm.
This deformation episode is modelled using a four-source model including an expanding dike dipping at 75º with top depth 0.4 km, two contracting horizontal dislocation planes at depth 3.6 and 16.5 km, and a further steeply dipping contracting dislocation plane with top depth 6.7 km.
Prior to and following the seismic swarm (1992 – 1995 and 1996 – 2002), the northwestern flank of Akutan was uplifted relative to the southwestern flank at ~1 cm/yr, whilst the region of ground cracking subsided by ~2 cm/yr following seismicity. This subsidence is thought to be caused by cooling and degassing of magma that was intruded in 1996.
Uplift of the northwestern flank continued between 2004 and 2009 at ~1 cm/yr. This deformation is modelled at the same horizontal location as the dike source associated with the earthquake swarm but at a greater depth of 5 – 6.5 km and a shallower dip. This long term, steady uplift of the volcano is attributed to slow accumulation of magma.
Interferograms also show persistent, time-varying subsidence within Akutan caldera at rates of 2 – 5 cm/yr. The source of this deformation is shallow (<2 km depth) and is associated with the hydrothermal system.