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A comprehensive approach to the reliable estimation and modeling of spatially variable seismic motions for lifeline earthquake engineering applications

Final Activity Report Summary - ICEARRAY (A comprehensive approach to the reliable estimation and modeling of spatially variable seismic motions for lifeline earthquake engineering applications)

The ICEARRAY, made possible by a Marie Curie International Re-integration grant from the European Commission, is an array of earthquake accelerographs that has been deployed in the South Iceland Seismic Zone (SISZ). The array is the first of its kind in Iceland and is located in the town of Hveragerdi in the western part of the SISZ, which is a region with a history of destructive earthquakes, some exceeding magnitude 7. ICEARRAY's purpose is to record intense ground motions from future significant earthquakes in the SISZ, thereby providing measures of the differential ground motions over distances of 50-1900 metres caused by travelling seismic waves due to earthquakes. Such measures are important when designing lifelines of modern societies (pipelines, bridges, electric transmission lines, etc.) to withstand earthquakes. Additionally, the ICEARRAY recordings of seismic ground motions will provide additional insight into the nature of earthquake rupture on faults.

At 15:45 UTC on 29 May 2008, a magnitude 6.3 earthquake struck in the western part of the South Iceland Seismic Zone (SISZ) near the town of Hveragerdi. The ICEARRAY produced a large number of high-quality recordings of this earthquake - recordings that are believed to constitute a globally unique dataset. The recorded strong-motions appear to consist of the seismic waves from two earthquake faults. The first one is located approximately 6.5 km from Hveragerdi and appears to be a 10 km long north-south trending fault. The second one is an almost 20 km long north-south trending fault that passes less than 2 km from the town. All the recordings of ICEARRAY during this earthquake show high intensity strong-motions, manifested by the peak horizontal ground accelerations exceeding in some cases 80 % g (g is the the acceleration of gravity). In some areas, there is evidence of vertical accelerations exceeding 100 % g, which means that the earthquake motions were strong enough to throw objects up in the air. Also, the recordings show large amplitude and long-period velocity components, which are characteristic of intense ground shaking very close to the earthquake itself. The recordings also show that the town of Hveragerdi has moved approx. 14 cm to the north-west as a result of the earthquake. It is believed that these ICEARRAY recordings will have lasting implications in the fields of earthquake engineering and engineering seismology.

Prior to the earthquake of 29 May 2008, the ICEARRAY project had already established preliminary estimates of the differential ground motions during small earthquakes recorded on the ICEARRAY network. Additionally, sophisticated methodology of synthesising earthquake faulting and the corresponding strong-ground motions had been developed. Central to this method was the calibration of a versatile, yet simple earthquake source model (the Specific Barrier Model; SBM) using data from three SISZ earthquakes during the years of 1988 and 2000. In view of the remarkable dataset recorded during the 29 May 2008 earthquake, these estimates will now be more comprehensively determined, and the earthquake model and simulations calibrated to the earthquake scenario of 29 May. The comprehensive modelling of the earthquake faults based on the SBM, the simulation of the associated ground motions and the differential motions over the 1900 m long array, will be completed during the third year of the ICEARRAY project.