Mapping Iceland's Crustal Structure using Ambient seismic Noise

Date

2012-08

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Abstract

Iceland is a place of great geophysical interest due to its location over a mantle plume and on the Mid-Atlantic seafloor spreading ridge. Despite numerous geophysics studies, disagreements still exist in regards to crustal thickness and temperature beneath Iceland. This research aims to improve the crustal model of Iceland by conducting Rayleigh wave tomography using ambient seismic noise data recorded during the HOTSPOT experiment, which consisted of 30 broadband seismic stations and operated from June of 1996 to August of 1998. Seismic observations based on cross-correlations of long ambient noise sequences between pairs of stations were used to obtain phase velocities at short periods. Phase velocities were mapped at periods ranging from 5s to 35 s from the ambient noise tomography. These maps reveal low velocities at the active volcanic zones and mid-Atlantic ridge in Iceland. Short period phase velocities were combined with the longer period velocity maps from teleseismic data [Li & Detrick, 2006] to invert shear-wave velocities. 1-D and 3-D shear-wave structures were determined, and a crustal thickness map of Iceland was constructed from the inversions of the combined data set. These graphs presented higher resolution in the crust and shallow upper mantle. The shear-wave velocity in the shallow crust map suggests a broad distribution of low velocity anomalies along all active regions, which is probably associated with partial melts that feed the local volcanoes. The lower crust map presents a more concentrated low velocity anomaly mainly over the Iceland hotspot, suggesting melt accumulation and/or high temperature related to the Iceland plume. In the upper mantle maps, smaller iv low velocity anomalies correlate well with current and past spreading ridge locations. Crustal thickness varies from 27 km to 40 km across Iceland. The thickest crust is imaged in the central and southeastern Iceland near the hotspot. These results suggest that the crust is thick and also hot in Iceland.

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Keywords

Iceland, Ambient seismic noise, Crustal structures, Shear-wave

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