Deep structure of the lithosphere beneath the territory of Bulgaria

Summary Teleseismic P residuals calculated for waves arriving from various azimuths and angles of incidence, and a 3-D inversion of the residuals provided the basis for characterizing the uppermost mantle structure beneath Bulgaria. The Moesian Platform and the Rhodopean Massif are two different blocks characterized by a lithosphere thickness of about 130–140 km with a zone of lithosphere thinning along their contact. Both units have opposite patterns of the directional dependence of relatively high and low P velocities. This directional dependence is interpreted by dipping anisotropic structures in the subcrustal lithosphere, which probably represent remnants of paleosubductions of an old oceanic lithosphere.

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The stress field in Australia from composite fault plane solutions of the strongest earthquakes in the continent

The purpose of this study is to make an estimate of the stress field in the Australian continent from composite fault plane solutions of the strongest events in the area. 21 seismic events with magnitude greater than 5.0 have been chosen from a database of 400 Australian earthquakes since 1902 for performing composite fault plane solutions. The choice is based on the availability of data for first P-wave arrivals. Using data from ISC bulletins we have calculated composite fault plane solutions for six major earthquake zones in the country. An individual fault plane solution for at least one event in each zone has been computed, too. The space distribution of the focal mechanisms confirms a dominant east-west compression stress in the continent, with different tilt in different areas. The main compression axes in the Tennant Creek area (Northern Australia) are with clear north-south direction. The general direction of the plate motion is north-northeast.