Ongoing Deep-Seated Activity in the Northern Volcanic Zone, Iceland - Insights From InSAR
Andrew Hooper(1), Freysteinn Sigmundsson(2) and Benedikt Ofeigsson(2)
(1) Delft University of Technology, Kluyverweg 1, 2629 HS, Delft, Netherlands
(2) University of Iceland, Askja Building, 101 Reykjavik, Iceland
Since February 2007 there has been persistent earthquake activity in the Northern Volcanic Zone, Iceland, in an area that was previously seismically inactive. The activity is centered around Upptyppingar and Álftadalsdyngja. The earthquake hypocenters are deeper (12-17 km) than normally observed in Iceland and over 7500 earthquakes have been located in the area up to March 2008. Previous episodes of deep-seated earthquake activity in Iceland have usually been linked with magma unrest, for example at Eyjafjallajökull, Vestmannaeyjar, and Askja. Recent continuous and campaign GPS measurements suggest this is also the case for the current activity, with horizontal velocities of up to 30mm/yr towards SSE observed since early summer 2007 (Geirsson et al, IAVCEI 2008). The scarcity of the GPS network, however, makes it difficult to distinguish between potential geometries for the deformation source.
We have formed interferograms from SAR data acquired by ALOS/PALSAR and Envisat/ASAR, using time series analysis in the latter case. We expect partial snow cover to be present from October onwards, and the ASAR C-band data indicate this is the case. However, with the PALSAR L-band data we are able to form coherent interferograms even with images acquired in December. We observe surface fracturing, with 2-3 cm of displacement, running SSW from Upptyppingar beginning in July 2007. By December, a regional displacement field is perhaps observable in the interferogram, however severe atmospheric contamination present in the December image complicates any interpretation. We will form more interferograms once the snow cover has mostly cleared, from June 2008 onwards, which we expect will exhibit displacements of sufficient magnitude to allow modeling of the deformation source.