Building 3-D Crustal Model with Radial Anisotropy in Iceland from Ambient Seismic Noise Tomography

Iceland is a place of great geophysical interest due to its location at a hotspot and on the Mid-North Atlantic Ridge. Despite numerous studies conducted on Iceland, there remain fundamental disagreements on such questions as whether the Icelandic crust is thin or thick, cold or hot. In addition, crustal seismic anisotropy, which can be caused by strain-induced preferred orientation of cracks, melt pockets, or crustal minerals, has not been well studied in Iceland. To improve our understanding of crustal formation and evolution of Iceland, Love wave tomography was conducted using ambient noise data recorded at the HOTSPOT experiment, which consists of 30 broadband seismic stations and operated from June of 1996 to August of 1998. Love wave phase velocity maps from 6 to 40 s were obtained. Then the phase velocities were inverted for 1D and 3D isotropic SH wave velocity in Iceland. The low velocity anomaly in shallow crust can be found along ridge and major volcanic zones which would probably be associated with partial melt that feeds the volcanoes, while low velocities is near the hotspot at deep crust, indicating melt accumulation or high temperature from the Iceland plume. Finally, the isotropic VSH model from Love wave inversion was combined with existing VSV model from previous Rayleigh wave study to establish a 3-D radial anisotropic model. In upper crust, VSV>VSH is largely found in the rifting zones, reflecting vertical alignment of cracks and melt sills. This finding suggests that horizontal flow that feeds mid-ocean ridges from the plume source is not strong in the upper crust of Iceland. In the lower crust, VSV>VSH concentrates at the current hotspot location while VSH>VSV occurs everywhere else in Iceland. This observation can be interpreted as vertical flow beneath the mantle plume and horizontal flow that transports crustal materials from the plume center to other rift zones in Iceland, suggesting that melt produced from the mantle plume is the dominant source for forming the crust of Iceland.