The earthquake activity of Norway and nearby offshore areas is low to intermediate, with few events above magnitude 5. Recent significant improvements in instrumental coverage in parallel with a better utilization of older (including historical) data have shown that the seismicity in the south is predominantly confined to the coastal areas and to the Viking Graben, while from the northern North Sea to Svalbard the earthquakes in a broad sense follow the continental margin. Fifty‐one focal mechanism solutions from these areas, about half of them new, reveal stress directions that clearly indicate a connection to the plate tectonic “ridge push” force, at least for the areas at a minimum distance from the continental margin. Along the margin, stress directions also indicate a possible connection to postglacial uplift as well as to lithospheric loading effects. A dominance of normal faulting on the landward side and reverse faulting on the oceanic side agrees with this interpretation. On a regional level, the seismicity in these areas correlate quite well with geologic features such as grabens, fault zones, fault complexes, fracture zones, and the margin itself, indicating that these structures act in a general sense as weakness zones in the presence of a regionally more stable stress field. In the northern North Sea, however, an area with quite anomalous stress orientations, with strike‐slip faulting, is found in a region transitional between normal and reverse faulting. Most of the earthquake foci are confined to the presumably brittle parts of the crust, but many events are also located quite close to, and on both sides of, the Moho discontinuity.

Three earthquakes of magnitude around 5 occurred offshore western Norway on 5th February, 1986, on 8th August, 1988, and on 23rd January, 1989. These earthquakes, representing the highest seismic activity level in this area for at least 30 years, were all felt by people over most of southern and central Norway. Focal-mechanism solutions for these earthquakes indicate thrust faulting along N-S to NNE-SSW striking fault planes, in response to NW-SE compressional stress, most probably of plate tectonic origin.A number of high-quality digital recordings of the ground motions at various distances from these and other recent earthquakes in Norway have shown that source spectral as well as wave attenuation characteristics in this area are reasonably consistent with what has been derived from other intraplate areas.

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A new local magnitude ML scale has been developed for Norway, based on a regression analysis of synthesized Wood-Anderson records. The scale is applicable for distances up to more than 1000 km, and the data used comprise 741 short-period recordings at 21 seismic stations from 195 earthquakes in the magnitude range 1 to 5 occurring in and around Norway over the last 20 years. Magnitude corrections for distance have been evaluated in terms of a geometrical spreading term a and an anelastic attenuation term b, and the significant regional crustal differences in the area under investigation made it desirable to develop these for several subsets of the data base. The results for a are generally found to be around the commonly found value of 1.0 (using the Lg phase), while the values of b are found to be around 0.0008, consistent with the weak, intraplate attenuation expected for Norway. Compared to interplate California, this difference in attenuation represents more than a factor of ten in amplitude at a distance of 1000 km. New ML scales are commonly tied to Richter's original definition at the standard reference hypocentral distance of 100 km. The significantly weaker Lg wave attenuation in Norway, however, requires a smaller reference distance. We have chosen a value of 60 km, based on an overall assessment of regional coverage, focal depths, and quality of the data. The resulting ML formula for Norway reads M L = log A w a + a log ( R / 60 ) + b ( R - 60 ) + 2.68 + S , where Awa is synthesized Wood-Anderson amplitude (in mm), R is hypocentral distance (in km), and S is a station correction term that for all 21 stations is found to lie within the range ± 0.22. When using the entire data base, the spreading term a equals 1.02 (± 0.09), and the anelastic attenuation term b equals 0.00080 (± 0.00009). When only strictly continental ray paths are selected, the a value decreases to 0.91 (± 0.11) while the value of b increases to 0.00087 (± 0.00011), a difference which on the average accounts for less than 0.1 magnitude units. While all values used in the regressions have been derived for vertical amplitudes, a separate analysis has shown that these are not significantly different from the horizontal ones, and the new scale is therefore applicable to both. In order to facilitate the practical use of this new ML scale, a relation has also been established between observed seismogram amplitudes in nanometers (corrected for instrument response) and the synthesized Wood-Anderson amplitudes. This relation reads log Awa = 0.925 log Aobs − 2.32. The new ML magnitudes for the events analyzed are in good agreement with those calculated from a previously used relation developed by Båth for Sweden. The ML values have also regressively been related to a data set of Ms magnitudes, yielding the relation Ms = 0.83 ML + 1.09.