Design and Installation of ICEARRAY, A New Small-Aperture Strong-Motion Array in South Iceland

Abstract eng:
The tectonically unique and populated South Iceland Seismic Zone (SISZ) has been the location of numerous destructive earthquakes in the past. Its capability to produce earthquakes that may exceed magnitude 7 is a constant threat to lifelines in the region, such as pipelines, electric transmission systems, dams and bridges. In terms of engineering design and earthquake safety the spatial variability of earthquake ground motion is of particular importance to such horizontally extended structures. Up to now reliable regional quantitative models of the spatial variability have not been available due to lack of strong-motion arrays. Furthermore, quantification of the complexity of earthquake source processes and their effects, of paramount importance to near-fault sites, has not been possible in the region for the same reason. Therefore ICEARRAY, the first small-aperture strong-motion array in Iceland, has been installed in the SISZ. The array's purpose is: 1) monitoring future significant events in the region; 2) quantifying spatial variability of strong-motion over short distances; and 3) shedding light on earthquake source processes. ICEARRAY is equipped with CUSP-3Clp three-component, Internet-based digital accelerograps with GPS timing system and a perpetual connection to the Internet via wireless GPRS. The CUSPs are low cost, but have a high-dynamic range and possess a very low noise floor (~70 micro-g), thus additionally rendering the array useful for studying the weak-to-strong motion transitions over a wide magnitude range. We optimize its recording efficiency via a novel real-time common-triggering scheme, which also intelligently minimizes the analyst’s need to review data discerning between earthquakes and noise. The number of array stations and their arrangement were based on an optimisation of the shape of the corresponding array transfer function (ATF). The optimal ICEARRAY configuration comprises 14 stations, has an aperture of ~1.9 km, and a minimum interelement distance of ~50 m, and possesses a near-azimuthally independent ATF with a sharp main lobe, negligible sidelobes and a wavenumber range of 1.5-24 rad/km. Accordingly, the ICEARRAY has the intended capabilities of capturing seismic waves in the frequency range of 1-20 Hz, which is of main interest to earthquake engineering and engineering seismology applications.

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