A Summary of Instrumental Data on the Recent Strong Vrancea Earthquakes, and Implications for Seismic Hazard

Abstract

The paper is intended to summarize the most important instrumental data of direct relevance for engineering activities, obtained in connection with the strong Vrancea earthquakes of and to point out some significant consequences and conclusions derived on this basis. Two main objectives of this analysis may be emphasized: (a) in-depth analysis of the radiation pattern; and (b) analysis of the spectral contents of ground motion in connection with the features of local conditions, and with the intention of assessing the relative importance of two main factors: source mechanism and long-distance wave propagation, versus features of local geological conditions. Some specific methodological developments used in this context may be mentioned: (a) use of a new approach to the quantification of ground motion intensity on the basis of instrumental (accelerographic) information; (b) analysis of radiation pattern in spectral and directivity terms; (c) parametric analysis of site-specific transfer functions for the local sequences of geological layers; and (d) a critical view on the outcome of postearthquake survey techniques, keeping in view the implications of the spectral features of ground motion. The main results obtained are related to: (a) ground motion radiation features that have to be taken into account in connection with the data on the source mechanisms of the successive events dealt with; (b) expected spectral features of future strong ground motion at different sites; (c) methodological developments proposed for the assessment of local transfer functions; and (d) implications for microzonation activities.

Standardized Multiapartment Blocks Built in Romania Before 1990: Seismic Design Levels Vs. Earthquake Performance

“…The selection of period intervals was based on the 36 dB frequency band (0,25-16 Hz). 25,26 The band was divided into 12 subintervals of 3 dB each, of which six were selected for the present study (Table 3).…”

Variability of Ground Motion Amplitudes Recorded in Bucharest Area during Vrancea Intermediate‐Depth Earthquakes

“…Significant long-period spectral amplifications have been observed in Bucharest, the capital city of Romania, during large magnitude Vrancea intermediate-depth earthquakes occurring in the past 40 years [1,2]. A combination of source and site effects appears to be reason for the occurrence of such amplifications [3][4][5][6] during large magnitude earthquakes.…”