Rutger Wahlström

The European-Mediterranean Earthquake Catalogue (EMEC) for the last millennium

The catalogue by Grünthal et al. (J Seismol 13:517–541, 2009a) of earthquakes in central, northern, and north-western Europe with Mw ≥ 3.5 (CENEC) has been expanded to cover also southern Europe and the Mediterranean area. It has also been extended in time (1000–2006). Due to the strongly increased seismicity in the new area, the threshold for events south of the latitude 44°N has here been set at Mw ≥ 4.0, keeping the lower threshold in the northern catalogue part. This part has been updated with data from new and revised national and regional catalogues. The new Euro-Mediterranean Earthquake Catalogue (EMEC) is based on data from some 80 domestic catalogues and data files and over 100 special studies. Available original Mw and M0 data have been introduced. The analysis largely followed the lines of the Grünthal et al. (J Seismol 13:517–541, 2009a) study, i.e., fake and duplicate events were identified and removed, polygons were specified within each of which one or more of the catalogues or data files have validity, and existing magnitudes and intensities were converted to Mw. Algorithms to compute Mw are based on relations provided locally, or more commonly on those derived by Grünthal et al. (J Seismol 13:517–541, 2009a) or in the present study. The homogeneity of EMEC with respect to Mw for the different constituents was investigated and improved where feasible. EMEC contains entries of some 45,000 earthquakes. For each event, the date, time, location (including focal depth if available), intensity I0 (if given in the original catalogue), magnitude Mw (with uncertainty when given), and source (catalogue or special study) are presented. Besides the main EMEC catalogue, large events before year 1000 in the SE part of the investigated area and fake events, respectively, are given in separate lists.

An Mw based earthquake catalogue for central, northern and northwestern Europe using a hierarchy of magnitude conversions

Data from 25 local catalogues and 30special studies of earthquakes in central,northern and northwestern Europe have beenincorporated into a Databank. The dataprocessing includes discriminating eventtypes, eliminating fake events and dupletsand converting different magnitudes andintensities to Mw if this is not givenby the original source. The magnitudeconversion is a key task of the study andimplies establishment of regressionequations where no local relations exist.The Catalogue contains tectonic events fromthe Databank within the area44°N–72°N,25°W–32°E and the time period1300–1993. The lower magnitude level forthe Catalogue entries is setat Mw == 3.50. The area covered by thedifferent catalogues are associated withpolygons. Within each polygon only datafrom one or a small number of the localcatalogues, supplemented by data fromspecial studies, enter the Catalogue. Ifthere are two or more such catalogues orstudies providing a solution for an event,a priority algorithm selects one entry forthe Catalogue. Then Mw is calculatedfrom one of the magnitude types, or frommacroseismic data, given by the selectedentry according to another priority scheme.The origin time, location, Mw magnitude and reference are specified for eachentry of the Catalogue. So is theepicentral intensity, I0, if providedby the original source. Following thesecriteria, a total of about 5,000earthquakes constitute the Catalogue.Although originally derived for the purposeof seismic hazard calculation within GSHAP,the Catalogue provides a data base for manytypes of seismicity and seismic hazardstudies.

Chi-square regression for seismic strength parameter relations, and their uncertainties, with applications to an Mw based earthquake catalogue for central, northern and northwestern Europe

A generalized chi-square regression approach to establishempirical relations between different types of seismic strengthparameters with uncertainties in all input data is presented anddiscussed in comparison with standard least-squares techniques.The chi-square technique can consider errors of individual entriesbut can also be applied when errors are not exactly known and onlyweaker quantitative constraints can be made. It can preserve thesymmetry of the derived relations and is preferred for complexregression models. Results for three types of regression modelsare presented for (1) a linear relation between MSand mbfor events in the North Atlantic Ocean; (2) a quadratic relationbetween Mw and ML forevents in central Europe; (3) linearrelations between ML and I0,with logarithmic dependency ofthe focal depth, for several regions in central and northernEurope.

The SHARE European Earthquake Catalogue (SHEEC) for the time period 1900–2006 and its comparison to the European-Mediterranean Earthquake Catalogue (EMEC)

This short communication describes the differences of the seismicity data file of the SHARE European Earthquake Catalogue from 1900 to 2006 in comparison to the European-Mediterranean Earthquake Catalogue by Grünthal and Wahlström (J Seismol 16:535–570, 2012). SHARE is the EC project Seismic Hazard Harmonization in Europe. Differences occur in the very north of the study area, in Greece and adjacent areas, and with respect to local volcanic earthquakes at Etna, Italy.

Regional spectral scaling relations of source parameters for earthquakes in the Baltic Shield

Abstract Spectral analysis of regionally recorded Lg waves is performed to determine source parameters such as seismic moment, source radius and stress drop of earthquakes in the Baltic Shield, and to derive regional spectral scaling relations. The data consist of about 350 Lg phases on short-period, vertical-component analog seismograms from earthquakes with magnitude ( M L ) ranging from 2 to 5.2. Source radii estimated from the corner frequency show only a slight increase with increasing seismic moment in the range 3 × 10 18 to 5 × 10 20 dyn cm, while the increase is more rapid for larger events. Baltic Shield earthquakes show increasing stress drops, ranging from about 0.1 to 10 bars, for increasing seismic moment. The relatively low stress drops could, in part, be explained by bias due to band-limited analog data. The slope of the curve relating seismic moment to corner frequency is steeper than −3, which suggests a departure from a constant stress drop scaling relation proposed for large earthquakes. The derived relationship between the seismic moment ( M o ) and magnitude ( M L ) is: log M o = 16.93 + 1.01 M L (for 2 ⩽ M L ⩽ 5.2 ).

Distribution of the energy release, b-values and seismic hazard in Egypt

A review of the seismicity and seismic history of Egypt indicates areas of high activity concentrated along Oligocene-Miocene faults. This supports the idea of recent activation of the Oligocene-Miocene stress cycle. There are similarities in the spatial distribution of recent and historical epicenters. Destructive earthquakes in Egypt are mostly concentrated in the highly populated areas of the Nile Valley and Nile Delta. Some big earthquakes located near the plate boundary as far away as Turkey and Crete were strongly felt in Egypt. The distribution of the energy release shows a possible tectonic connection between active zones in Egypt and the complicated tectonic zones in Turkey and Crete through geologically verified fault systems. The distribution of intensity shows a strong directivity along the Nile Valley. This is due to the presence of a thick layer of loose sediments on top of the hard rock in the Nile Valley graben. The distribution of b-values indicates two different zones, comparable with stable and unstable shelf areas. Stress loads in the northern Red Sea and northern Egypt are similar. Geologically, northern Egypt is a part of the Unstable Shelf area. The probability to have an earthquake with intensity V or larger within 94 years is more than 80% in the Nile Valley and Nile Delta areas, Egypt-Mediterranean coastal area, Aswan High Dam area, Gulf of Aqaba-Levant Fault zone and in the oil fields of the Gulf of Suez. The maximum expected intensity in these areas and within the same period is V–VI for a 80% probability and VII–VIII+ for a 10% probability. Intensity VIII–IX has been reported for several earthquakes in both historical and recent time.

Recent Kattegat earthquakes — evidence of active intraplate tectonics in southern Scandinavia

Abstract On June 15, 1985, an earthquake with a local magnitude M L (UPP) value of 4.6 occurred in the Kattegat area close to the Swedish-Danish border. It was one of the largest earthquakes in Sweden and Denmark during this century. Two more events occurred in the same area: on April 1, 1986 ( M L (UPP) = 4.2), and May 24, 1990 ( M L (UPP) = 3.3). The derived focal mechanisms have north-south trending P -axes which deviate by 45° from the NW-trending compressive stress field postulated by the ridge-push theory. The mechanisms can, however, be explained by local neotectonism. Both the locations and focal mechanisms, strike-slip faulting on NW striking planes, correlate well with the dominant neotectonic feature of the region, the Skalderviken depression. Seismic moments of the 1985, 1986 and 1990 events were 3.6 × 10 14 Nm, 1.4 × 10 14 Nm and 6.0 × 10 12 Nm, respectively. The 1985 earthquake had an estimated maximum intensity of VII (modified Mercalli scale) and was felt over an area with a mean radius of 180 km. The 1986 earthquake had a maximum estimated intensity of VI and a radius of perceptibility of 100 km. Despite the recent low seismicity of the area, the earthquakes studied here indicate the potential for the occurrence of major events. This is supported by the historical seismicity.

Fennoscandian seismicity and its relation to the isostatic rebound

Abstract Beside plate tectonics, isostatic rebound may be a main contributor in the seismogenic process in Fennoscandia. Extensional horizontal strain, presumably related to land uplift, calculated from mathematical modeling, geodetic data and curvature of uplift, show higher values than compressional horizontal strain, related to ridge push, estimated from sedimentary deformation in the basins surrounding the shield. The location of the current seismicity of central and northern Fennoscandia and the sites of large boulder caves near the Bothnian coast of central Sweden, show high correlation with the maximum curvature of uplift at present and late-glacial time, respectively; the caves may have been created by large earthquakes at the last phase of deglaciation. Large faults in northern Fennoscandia probably also have seismogenic origin dating to the late-glacial period. Differential strain along the Swedish coast of the Gulf of Bothnia, caused by a larger rate of uplift under the Gulf than of the adjacent land, is another seismogenic factor related to rebound. Earthquake focal mechanism solutions show a variety of faulting styles and stress orientations. Clearly, not all of them can be accounted for by ridge push. The proportion of small compared to large earthquakes ( b value) is larger in northern than in southern Fennoscandia. The maximum b is in the northern Gulf of Bothnia close to where the maximum rate of uplift is. The implication may be that tectonics and uplift are counteracting forces in the north, preventing large stress accumulation, whereas tectonics act more undisturbed in the south, resulting in larger stress build-up and thus relatively more large earthquakes. The temporal correlation between the seismicities of the Fennoscandian and the eastern Canadian shields on one hand and segments of the North Atlantic Ridge on the other, gives support to the idea of stress propagation under the Atlantic.

Maximum Likelihood Estimation of Seismic Hazard for Sweden

The maximum magnitude, the activity rate, and the Gutenberg-Richterb parameter as earthquake hazard parameters, have been evaluated for Sweden. The maximum likelihood method permits the combination of historical and instrumental data. The catalog used consists of 1100 earthquakes in the time interval 1375–1989. The extreme part of the catalog contains only the strongest historical earthquakes, whereas the complete part is divided into several subcatalogs, each assumed complete above a specified threshold magnitude. The uncertainty in magnitude determination was taken into account. For southern Sweden, the calculations giveb-values of 1.04 (0.05) for the whole area south of 60° N and 0.98 (0.06) for a subregion of enhanced seismicity in the Lake Vänern area. For the whole area north of 60° N, theb-value is 1.35 (0.06) and for the seismicity zone along the Gulf of Bothnia 1.26 (0.06). The number of annually expected earthquakes with magnitude equal to or larger than 2.4 [ML(UPP) or MM(UPP)] is 1.8 for the whole southern Sweden, 1.3 for the Lake Vänern region, 3.7 for northern Sweden, and 2.4 for the region along the Gulf of Bothnia. The maximum expected regional magnitude is calculated to 4.9 (0.5) for a time span of 615 years for southern Sweden and the Lake Vänern subregion, and 4.3 (0.5) for a time span of 331 years for northern Sweden and the Gulf of Bothnia subregion. However, several historical earthquakes with magnitude above 5 in nearby areas of Norway indicate that the seismic potential may be higher.

A catalogue of earthquakes in Sweden in 1375-1890

Abstract The present catalogue of earthquakes in Sweden between the years 1375 and 1890 contains 338 entries with maximum intensity, MM Scale, ranging from III to VII, radius of area of perceptibility from 10 to 300 km, and local magnitude, MM(UPP), from 2.2 to 4.8. The quantification of earthquake parameters also includes time and place of occurrence, and is based on macroseismic data compiled from various sources. The distribution of epicentres is shown in a map and is similar to that obtained from more recent, instrumental data—with highest seismicity in the Lake Vanern area and along the Gulf of Bothnia—except that historical data from Lappland are almost lacking. Various spatial and temporal inconsistencies in the catalogue are discussed. There is an apparent seasonal peak in the seismic activity during the winter months, which has no correspondence in the instrumental-time record and probably is an artifact of erroneous interpretation of frost-related phenomena. The catalogue, which can probably be ...