Joint Inversion of GPS, InSAR, Tilt, and Borehole Strain Data from the 2000 Eruption of Hekla Volcano, Iceland

Abstract:

Multiple geodetic methods are in use to investigate and monitor ground deformation at active volcanoes worldwide. These methods include episodic and continuous GPS, InSAR, tilt, and borehole strain observations. Hekla volcano in Iceland has been subject to crustal deformation measurements since 1967, including all of the abovementioned methods. Here we present the first complete estimation of the GPS-derived co-eruptive deformation field for the February 26 to March 8, 2000, eruption of Hekla, which is Hekla's most recent eruption. The co-eruptive deformation field was challenging to obtain because of a) a temporal gap at most of the GPS sites between 1996 and 2000; b) deformation from two magnitude 6.5 earthquakes, which occurred ~50 km from Hekla in the South Iceland Seismic Zone in June 2000; and c) regional changes in site velocities, interpreted to be caused by increased melting rates of Iceland's glaciers. We interpret the new GPS deformation field with previously published dry-tilt (i.e., short leveling lines), InSAR, and borehole strain measurements, in a formal joint inversion. We model the surface deformation using elastic half-space models of the deflating magma chamber (modeled here as a sphere, ellipsoid, or vertical pipe) and the co-eruptive dike (modeled as a rectangular dislocation).

Our preliminary results indicate that the magma chamber that deflated during the eruption was at approximately 20 km depth, when modeled as a spherical source, wheras, a pipe-shaped structure reaches more shallow depths. The co-eruptive dike that formed along Hekla was shallow, likely less than 1-2 km in depth, and connected to the magma chamber through a narrow conduit in general accordance with previously published results for Hekla. Each of the applied methods to measure crustal deformation has its advantages with respect to spatial and temporal resolution, long-term stability, and independence, arguing for continued multi-technique efforts for measuring crustal deformation at active volcanoes.