Rayleigh-wave group-velocity of the Icelandic crust from correlation of ambient seismic noise

By cross-correlating 2 years of ambient seismic noise from 31 broadband stations distributed across Iceland, we have been able to measure Rayleigh wave group velocity in three discrete frequency bands centered on 4, 7 and 17 s, sensitive to approximately the top 6, 10 and 25 km of the crust, for 289, 420 and 139 station-to-station paths, respectively. These are inverted to yield tomographic group velocity maps of the Icelandic crust. The results correlate with the major tectonic features on Iceland, and agree well with earlier seismic studies based on traditional methods (active source and earthquake). Specifically, we obtain low velocities in the central parts of Iceland, coinciding with the rift zones and young crust. In contrast, the parts of Iceland covered with older Tertiary volcanics reveal relatively higher velocities. At the shorter periods (4 and 7 s) this correlation reflects porosity, degree of fracturing and alteration. At the longest period (17 s), i.e. at greater depth, this correlation may reflect the thermal state of the crust, with warm and seismically slow material near the rifts and cooler and seismically faster material beneath the Tertiary formations to the east and west.