The thin hot plume beneath Iceland

• Main Authors: Richard M. Allen, Guust Nolet, W. Jason Morgan, Krist| N Vogfjîrd, Bergur H. Bergsson, Pa Lmi Erlendsson, G. R. Foulger, Steinunn Jakobsdo Ttir, Bruce R. Julian, Matt Pritchard, Sturla Ragnarsson, Ragnar Stefa Nsson
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Iceland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.412.695; http://seismo.berkeley.edu/~rallen/pub/1997diffraction/GJI1999paper.pdf

We present the results of a seismological investigation of the frequency-dependent amplitude variations across Iceland using data from the HOTSPOT array currently deployed there. The array is composed of 30 broad-band PASSCAL instruments. We use the parameter t*, de¢ned in the usual manner from spectral ratios (Halderman & Davis 1991), to compare observed S-wave amplitude variations with those predicted due to both anelastic attenuation and di¡raction e¡ects. Four teleseismic events at a range of azimuths are used to measure t*. A 2-D vertical cylindrical plume model with a Gaussian-shaped velocity anomaly is used to model the variations. That part of t* caused by attenuation was estimated by tracing a ray through IASP91, then superimposing our plume model velocity anomaly and calculating the path integral of 1/oQ. That part of t * caused by di¡raction was estimated using a 2-D ¢nite di¡erence code to generate synthetic seismograms. The same spectral ratio technique used for the data was then used to extract a predicted t*. The t * variations caused by anelastic attenuation are unable to account for the variations we observe, but those caused by di¡raction do. We calculate the t * variations caused by di¡raction for di¡erent plume models and obtain