Damage caused by the earthquake of 7 December 1986 (M = 5.7) and its aftershocks in low-storey residential buildings in the town of Strazhitza, Bulgaria, situated in the epicentral zone are systematized. A scale of damages is compiled for two types of buildings which is coordinated with the MSK-64 scale. The territorial distribution of the seismic intensity is compared with the results of the detailed engineering-geological study. A correlation between the Quarternary deposit thickness and the observed seismic intensity is obtained
Routine determination of network magnitudes by means of the Eurasian homogeneous magnitude system (HMS) is described and tested on a selection of recent shallow earthquakes. The HMS earthquake magnitudes appear to be more accurate and more reliable than the conventional earthquake magnitudes used in the present seismological practice. A preliminary investigation of correlations between magnitudes determined from different wave types shows a possible dependence of the correlation on the type of focal mechanism of earthquakes
Earthquakes manifested in a small volume of the earth's crust are analysed, presuming that the orientation of the rupture disturbances is conditioned by the local neotectonic conditions. A relation is sought between the seismic manifestations and the modern crushing structures in the earthquake region. In this very case, the earthquakes in the Velingrad district (Bulgaria) are analysed, which began with an earthquake of the 5,3 magnitude and a maximum intensity of the VII-VIII degree by the Medvedev-Schponheuer- Karnik scale and the followed 504 earthquakes for a period of 179 days. From the data obtained, a presence of a complex ridge-like structure can be presumed, which develops in a valley depression on the background of a vault block rising in the limits of the granite layer of the earth crust, to a 15 km depth. The frequency of the earthquakes is obtained as a function of the difference (tsg - tpg) and the greatest earthquake frequency is shown to be in the interval of 0,8-1,4 sec and the greatest difference of times corresponds to a 20 km hypocentral distance
In geophysical inverse problems, the distribution of physical properties in an Earth model is inferred from a set of measured data. A necessary step is to select data that are best suited to the problem at hand. This step is performed ahead of solving the inverse problem, generally on the basis of expert knowledge. However, expert-opinion can introduce bias based on pre-conceptions. Here we apply a trans-dimensional algorithm to automatically weigh data on the basis of how consistent they are with the fundamental assumptions made to solve the inverse problem. We demonstrate this approach by inverting arrival times for the location of a seismic source in an elastic half space, under the assumptions of a point source and constant velocities. The key advantage is that the data do no longer need to be selected by an expert, but they are assigned varying weights during the inversion procedure.