Markus Båth

Lateral inhomogeneities of the upper mantle

Abstract Detailed investigations of lateral inhomogeneities of the upper mantle properties are of major significance in the Upper Mantle Project. The paper gives a review of the present status of such research as far as seismological methods are concerned. These include studies both of stress systems and strain release (earthquakes) and of all kinds of seismic waves (body waves, guided waves, surface waves). There are certain methodical difficulties both in general (especially concerning the scale of any inhomogeneities which can be discovered) and in relation to special methods. Although seismology provides the most unambiguous data, there is great need for close coordination of results from other geophysical disciplines. Several ideas and suggestions in the paper have not yet left the level of hypotheses, but if they could serve as stimulus for further research, the purpose of the paper has been more than fulfilled.

An earthquake catalogue for Turkey for the interval 1913–1970

Abstract An earthquake catalogue has been prepared for the whole area of Turkey (within latitudes 35.5° N to 42.5°N and longitudes 25.5°E to 45.0°E) for the years 1913 to 1970. By computer recalculation of all source parameters and by using a consistent system for magnitude determinations, we have aimed at the highest possible homogeneity and completeness within the limits given.

Short-period Rayleigh waves from near-surface events

Abstract Short-period fundamental-mode Rayleigh waves (Rg) are generally well recorded by short-period seismographs within about 600 km of seismic events, such as explosions, rockbursts and earthquakes, which occur in the upper 3 km of the crust. Studies of these waves from records at the Swedish seismograph network revealed their usefulness to elucidate both path and source properties. They exhibit normal dispersion which requires a superficial low-velocity layer of about 1 km thickness, in part probably weathered and fractured granite. This layer has considerably higher attenuation than underlying more competent rock. The existence of Rg in regional short-period records is a reliable indication of shallow focal depth, and, provided adequate calibration is available, quite accurate depth estimation would be possible from the amplitude ratio of Rg to Sg1.

The seismology of Greece

Abstract A review and a bibliography are given of the seismological literature for the area of Greece in the period from 1950 up to the present time. The aim is to incorporate all aspects of seismology, starting with instrumental installations, passing on to earthquake catalogues, statistics and effects, and ending up with structural properties and seismotectonics. The purpose is to provide a service to every geophysicist who has an interest in this tectonically complex area and particularly to the numerous researchers engaged in geophysical expeditions to Greece.

Earthquake recurrence of a particular type

The recurrence relation for Turkish earthquakes, expressed as the single-frequency versus magnitude dependence, exhibits significant maxima and minima, reflecting true physical conditions. Various mathematical formulations are developed to fit the observed data for the single or the cumulative frequency and are compared with each other as regards their accuracy and simplicity. The results may be applicable to regions with high seismicity.

Seismicity of the Tanzania region

Abstract The seismicity of the East African Rift system within the region bounded by latitudes 2°N and 12°S and longitudes 28°E and 40°E has been studied as far as all available instrumentally based material permits. An earthquake catalogue is presented and the data contained therein are used for tectonophysical investigations, including frequency—magnitude relations and time and space distribution of the seismicity within the region. In addition, earthquake engineering aspects are discussed.

Earthquake frequency and energy in Greece

Abstract On the basis of a newly published, revised earthquake catalogue for the Greek area, a study is made of its seismicity in terms of earthquake frequency and energy as functions of space, time and magnitude. In addition, attempts are made to estimate the maximum possible magnitudes as functions of space. The study is essentially a methodological experiment, with tectonophysical and engineering results.

Propagation ofSn andPn to teleseismic distances

SummarySn andPn waves propagated to teleseismic distances are investigated by means of short-period seismograph records of the Swedish network.Sn is found in the distance range of 2400 to 4600 km andPn in the range 3500 to 3900 km, but only provided the path is exceptionally homogeneous. Almost all paths are restricted to the Russian platform. There are probably very few areas in the world offering similar propagation paths. The velocities just under the Mohorovičić discontinuity are found to be 4.72 km/sec and 8.26 km/sec for transverse and longitudinal waves respectively. In addition, other properties of the teleseismicSn andPn are investigated, such as periods, dispersion, amplitudes, particle motions, propagation mechanisms, and comparisons are made withPa, Sa, withLi, Lg1, Lg2 and withP. The fact that teleseismicPn occurs much more seldom than teleseismicSn could be explained by different velocity profiles just under the crust.

Seismic risk in Fennoscandia

Abstract Seismic risk is calculated by means of recurrence periods, obtained from least squares relations between number of earthquakes and magnitude. This method is described and applied to Fennoscandia. The results, summarized in tabular form, give the seismic risk for 54 regions, each comprising 2° in latitude and 2° in longitude, and for the magnitude range from 2.0 to 5.0 on the regional scale.

Average crustal structure of Sweden

SummaryRecords obtained at the permanent stations of the Swedish seismograph network from explosions carried out in Scandinavian waters in June 1969 are evaluated. The study includes determination of velocities for all crustal phases observed, furthermore of layer thicknesses, Poisson ratios and amplitude ratios. The purpose of the study is partly to provide a first approximation to the crustal structure in Sweden, partly to provide regional data for location of earthquakes and explosions in the area in the future. Average velocities (km/sec) are forPn 7.88±0.05,Pg1 6.25±0.08,Pg2 5.70,Sn 4.58±0.04,S* 3.70±0.04,Sg1 (Lg1) 3.58±0.03,Sg2 (Sg) 3.40±0.03,Rg 3.02±0.07. The average thickness is 12 km for the granitic layer, and 23 km for the basaltic layer, thus making the average crustal thickness equal to 35 km. Relative amplitudes plotted versus distance complete the dynamical side of the study and they are useful for identification of waves. A regional travel-time table is presented for the distance range 0°–10° with entries for each 0.1° and including all crustal phases read.