RELIABILITY OF SOURCE PARAMETERS OF LOW MAGNITUDE CRUSTAL EARTHQUAKES OF VRANCEA RETRIEVED BY HIGH FREQUENCY WAVEFORM INVERSION

摘要

The source parameters of low magnitude shallow earthquakes occurred in the Vrancea region and surroundings were previously estimated using an inversion procedure for high frequency local waveforms. Anticipating a gross approximation of the complex structure from the study area by the 1-D crustal models used in the forward modeling, the paper aims to assess the reliability of the resolved focal mechanism and source time function by stability tests which investigate the effect of hypocenter mislocation, mismodeling of the crust, frequency content of the inverted waveforms, and internal damping of the inversion algorithm on the retrieved solution. The analysis reveals that the over-simplification of the medium structure generates large uncertainties of the inverted source parameters, consequently not all the parameters may be accepted as sufficiently accurate. The most vulnerable is the source time function. The individual moment tensor components exhibit also poor resolution. By contrast, the double couple part of the moment tensor is determined fairly well, so that it allows correlations of the tension and pressure axes with the stress field in the area.