Arie Verdel¹, Johno van IJsseldijk², Elmer Ruigrok^3,4 and Cornelis Weemstra^2,4, (1)Netherlands Organization for Applied Scientific Research, Applied Geosciences, Utrecht, Netherlands, (2)Delft University of Technology, Geoscience and Engineering, Delft, Netherlands, (3)Utrecht University, Utrecht, Netherlands, (4)Royal Netherlands Meteorological Institute, Seismology and Acoustics, De Bilt, Netherlands