Seismic activity caused by melt injection in Herdubreid-Askja area, North Iceland?

Abstract

Herðubreið area is located within the mid-Atlantic divergent plate boundary in north Iceland. The study area includes the subglacially formed mountains Herðubreið and Herðubreiðartögl and the volcanic system of Askja comprising a nested caldera volcano and a fissure swarm transecting it. A 10-km broad belt of persistent shallow seismicity occurs beneath Herðubreið and Herðubreiðartögl. As the stations of the permanent Icelandic seismic network are mainly tens of kilometres away from these mountains, a 20-station network of broadband Güralp 6TD seismometers was deployed and operated in the area during July–August 2006 in order to gather more detailed data on this activity. Also, an abundant dataset was gathered on a cluster of shallow seismicity in the SE part of the Askja volcano. A remarkable and unexpected discovery was the detection of lower-crustal seismicity, probably related to magma movements, within the Askja volcanic system and to the east of it. The recorded 47.3 GB dataset is excellent, with 97% recovery. Approximately 1800 local earthquakes were located, some 100 of which occurred in the lower crust at hitherto unknown depths of 15-25 km.