Deep seismicity revealing magma dynamics of the Askja volcano, north Iceland

Abstract

The Askja region is located on the mid-Atlantic spreading boundary in central Iceland. The study area includes the Askja caldera and the mountains Herðubreið and Herðubreiðartögl which are part of the larger Askja volcanic system. During a two month deployment in summer 2006 over 1800 earthquakes were detected in the region including 100 previously unwitnessed lower-crustal earthquakes. A new deployment of 22 Güralp 6TDs was conducted during July and August 2007 specifically designed to target these deeper events. Over 250 lower-crustal Askja events were recorded, more than double the number seen in 2006. Shallow earthquakes in the 2 – 5 km depth range within the caldera appear to delineate the upper edge of a magma chamber. In February 2007 a new region of lower-crustal seismic activity began below Upptyppingar mountain in the Kverkfjöll volcanic system, just 20 km E of Askja. One of our stations was directly above much of this activity and detailed relocations have been performed combining data from our network and the permanent Icelandic network; revealing short term clusters of ~10-100 events that are grouped very tightly horizontally and migrate vertically.