FOCAL PARAMETERS of CRIMEAN-BLACK SEA REGION EARTHQUAKES in 2016–2017

Abstract

Focal parameters of twenty-one 2016–2017 earthquakes of the Crimean-Black sea region with KП=6.5–13.1 have been recovered. Solutions of focal mechanisms have been obtained for the four strongest earthquakes. The dynamic source parameters – scalar seismic moment M0, the radius of circular dislocation r0, released stress , shear deformation , apparent stress ησ, radiation friction r, average slip along fault ū, energy of dislocation formation in the source ЕU, moment magnitude Mw – have been restored for twenty-one earthquakes by 149 amplitude spectra using Brune theoretical dislocation model. The type of slip in the source of May 13, 2016, felt an earthquake, which happened near the southern coast of Crimea, is a strike-slip. The June 28, July 22 and October 15, 2016 earthquakes occurred in the Black sea basin under the action of horizontal compressive stress, the type of slip in the source is a reverse fault. In the source of the June 16, 2017 earthquake, a thrust of active rupture wing occurred under the action of horizontal compression stress of the meridional direction. This type of movement is typical for earthquakes in the eastern part of the Crimean-Black Sea region. The mechanism parameters of these earthquakes were used to determine the direction of the source radiation to the recording station to account for relevant amendments in the calculation of the seismic moment M0. In general, average values of M0 and r0 for 2016–2017 earthquakes were within the confidence intervals of long-term dependencies M0(KП), r0(KП). The best correspondence of seismic moment values to the long-term dependencies was obtained for the earthquakes of the June 28, July 22, October 15, 2016 and June 16, 2017, with known focal mechanisms because the corrections for real radiation direction Rφ were introduced in the formula for M0 calculation. For reliable estimates of the spectral and dynamic source parameters of the 2016–2017 Crimean earthquakes, only very clear records of body waves at seismic stations with reliable characteristics of recording equipment were used. The averaging of the source dynamic parameters was done by 2–10 station definitions, which provided a small value of standard deviations. In this regard, quantitative estimates of focal parameters can be classified as reliable for further use for scientific and scientific-applied problems, in particular, for the development of geodynamic models.