There are two centers of deformation on Seguam island. The caldera on the western half of the island is characterised by a constant subsidence rate of 1.5 cm/yr. Deformation on the eastern half of the island is variable in time alternating between periods of uplift and subsidence. During 1993, coeruptive interferograms show uplift at a rate of ~5 cm/yr. Subsidence then occurred between late 1993 – late 2008 at a rate of ~1.6 cm/yr. Until September 2000, uplift resumed at an average rate of ~2 cm/yr. Between September 2000 and July 2005, the volcano again subsided at ~1.4 cm/yr and finally from July 2005 – 2007, the volcano uplifted at ~0.8 cm/yr.
Both the eastern and western sources are modelled as point sources. In the west, the source is located at at ~2 km depth and volume decrease occurs at a rate of 0.0001 km³/yr. This subsidence is attributed to thermoelastic contraction of young lava flows plus cooling and degassing of magma stored beneath the caldera. Deformation in the east is thought to involve a persistent subsidence source located at ~2 km depth (volume change 0.0001 – 0.0002 km³/yr) plus an episodic uplift source at ~5.5 km depth (volume change 0.001 – 0.003 km³/yr). This uplift component is interpreted to be an upper crustal magma reservoir that is episodically replenished. Cooling and degassing of magma in the shallow part of the reservoir then contributes to localised subsidence of the caldera between intrusions such that when intrusion rate is low, the net displacement is downward.