GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 3.3 729 is related to the period 15 July 2003 – 29 June 2004, with images acquired by the ENVISAT satellite (ESA) along the descending orbit (Track 115). After the processing steps, the descending interferogram is unwrapped to retrieve the LOS deformation measurements (Fig. 1a). In the considered period, the DInSAR measurements shown an uplift phenomenon, with a maximum deformation value of approximately 12 cm. Since the measurement surface is detailed (i.e., the Okmok volcano topography), the LOS deformation dataset is processed to obtain the ground deformation field evaluated at the constant reduction level, specifically at 1.5-km a.s.l. (Fig. 1b). At this stage, we applied our methodology to the DInSAR measurements to evaluate the geometric parameters of the active source; we applied both the Multiridge and ScalFun methods along the E-W (Fig. 2a) and N-S (Fig. 2b) profiles to retrieve the following results (Castaldo et al., 2018): • Multiridge method: a source was located at a -4.9±0.06 km depth (Fig. 2c and 2d) from the constant reduction level (1.5-km a.s.l.), which corresponded to a depth of -3.4±0.06 km b.s.l. with horizontal UTM coordinates equal to 690.9±0.08 km East (Fig. 2c) and 5924±0.07 km North (Fig. 2d); • ScalFun: a homogeneity degree of (Fig. 2e and 2f) was computed on the central cyan ridge for both the E-W and N-S profiles; this value corresponds to a Structural Index of , suggesting that the source geometry related to the measured ground deformation field can be well-approximated by a spherical reservoir. Discussion. The Okmok volcano deformation field has been studied by many authors (Lu et al., 2005; Masterlark et al., 2010; Biggs et al., 2010; Masterlark et al., 2012) which all interpreted that deformation was due to the inflation or deflation of a spherical magma chamber. For these authors, the source depth ranged from 3.1 to 3.5 km, while the source position ranged from 690.3 km to 690.72 km for the East UTM coordinate and 5923.6 km to 5923.98 km for the North UTM coordinate. Our results are in good agreement with those of the aforementioned works, indicating a depth source equal to 3.4±0.06 km and a horizontal position at 690.9±0.08 km E and 5924±0.07 km N. Moreover, we estimated a Structural Index of and, therefore, we can state that the geodetic source geometry is well represented by the spherical model. Fig. 1 - (a) Descending LOS deformation map between 15 July 2003 and 29 June 2004, which is superimposed onto the Okmok volcano topography; (b) Descending LOS deformation map reduced to a flat surface, which is located 1.5-km a.s.l. The black dashed lines indicate the positions of the E-W and N-S profiles, while the black continuous line represents the island coastline.