Towards quick clay monitoring in the city of Oslo, Norway with urban seismic noise

<p><span dir="ltr" role="presentation">Historically, there is one larger quick clay landslide in Norway every year. Since 80 percent of those </span><span dir="ltr" role="presentation">happen in known quick clay risk areas, it is important to monitor these sites continuously.</span> <span dir="ltr" role="presentation">Alna, a </span><span dir="ltr" role="presentation">busy, urban area in Oslo, is an example of such a location where a quick clay slide could lead to </span><span dir="ltr" role="presentation">substantial human and economical losses.</span></p> <p><span dir="ltr" role="presentation">In this study we use ambient noise methods to monitor changes in the subsurface at Alna using a </span><span dir="ltr" role="presentation">small array of three-component seismic sensors.</span> <span dir="ltr" role="presentation">To retrieve small velocity changes, we apply coda </span><span dir="ltr" role="presentation">wave interferometry using 12 months of urban seismic noise (above 1 Hz).</span></p> <p><span dir="ltr" role="presentation">We compare the observed day-to-day changes to air temperature, precipitation, and water levels in a nearby river, and observe environmental velocity fluctuations well correlated with air temperature and precipitation. In particular, freezing and thawing produces strong changes in seismic velocity (up to 4 percent). The surface wave-coda used here is sensitive to changes in shear wave velocity, which in turn can be used to detect changes of the sub-surface properties. Therefore, observed velocity variations at Alna could have potential for monitoring and early warning of quick clay instabilities.</span></p>