Macroseismic effects related to strong ground motion: a study of the South Iceland earthquakes in June 2000

The impact of the June 2000 South Iceland earthquakes has been assessed applying data collected in field surveys and strong-motion recordings from the Icelandic Strong-Motion Network. The areas within approximately 20 km of the causative faults suffered considerable damage, including transportation and utility systems as well as buildings, both with regard to structure and inventories. Ground subsidence and dislocations were significant in the near-fault zone. Aftershocks and permanent displacements of building foundations resulted in progressive structural damage. By introducing holistic measures derived from the acceleration data, a fair correlation was achieved between the obtained earthquake intensities and the recorded accelerations. The measures adopted were square root of the sum of the squares (SRSS) values of peak ground acceleration (PGA) and the trace of the Arias intensity tensor. It was found that the overall attenuation tended to be more rapid than reflected by common strong-motion models reported in the literature. There is no simple explanation for this behaviour but it is reasonable to suggest that it can be partly attributed to the heterogeneous and fractured crust that is characteristic of Icelandic geology.