SOURCE SPECTRAL PROPERTIES OF SMALL EARTHQUAKES IN THE NORTHERN NORTH-SEA

Source parameters of 40 small shallow earthquakes (M = 2.5-3.5) in the northern North Sea Region were calculated using P-wave spectra of dig ital records from the Western Norway Network station HYA. The results show a difference in the source spectral properties of earthquakes gen erated in the North Sea rift zone and the uplift zone of the Norwegian coastal margins. Corner frequencies f(0) of P-wave spectra are consta nt for the margin zone events for the seismic moment interval E12-E14 Nm. There is a tendency of decreasing f(0) with the seismic moment for rift zone events. Rift zone events have larger stress drops than marg in zone events with the same magnitude. Increase of stress drop with m oment was observed for both zones.