Deformation at the northern end of the Icelandic rift mapped by InSAR (1992-2000), a decade after the Krafla Rifting Episode
Résumé
From 1975 to 1984 the northern Icelandic rift underwent a rifting crisis. Large widening, rapid and local subsiding and uplifting occurred on the Krafla fracture swarm with several fissure eruptions. Since 1992 the area has been regularly covered by the two ERS radar satellites, allowing us to form 110 INSAR interferograms with 22 SAR scenes for mapping crustal deformation. At the regional scale, the signal is characterised by a series of parallel fringes oriented N15°W. The polarity of these fringes is constant throughout the mapped area. The measurement represents an increase of 1.7 cm/y in ground to satellite distance for the Western bloc. This signal is estimated to correspond to the combination of a horizontal opening movement and a vertical movement. In addition, the local signal at Krafla is marked by a series of concentric circular fringes forming a circle centred on the volcano and two U shaped structures, respectively upright to the South and upside down to the North of the volcano. The signal geometry indicates that the main component of movement affecting Krafla is vertical. The measured signal corresponds to a 2.2 cm/y increase in the ground to satellite distance, representing a maximum 2.4 cm/y ground subsidence. The large number of interferograms on which the deformation signal affecting Krafla is visible allows us to ascertain that the deformation rate remains constant since 1992.