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

Historically, there is one larger quick clay landslide in Norway every year. Since 80 percent of those happen in known quick clay risk areas, it is important to monitor these sites continuously. Alna, a busy, urban area in Oslo, is an example of such a location where a quick clay slide could lead to substantial human and economical losses.

In this study we use ambient noise methods to monitor changes in the subsurface at Alna using a small array of three-component seismic sensors. To retrieve small velocity changes, we apply coda wave interferometry using 12 months of urban seismic noise (above 1 Hz).

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.