EVENT MECHANISM ANALYSIS FOR SEISMICITY INDUCED BY A CONTROLLED COLLAPSE IN FIELD II AT OCNELE MARI, ROMANIA

摘要

The monitoring of a controlled collapse with an array of 36 uniaxial geophones provides stable and reliable point source event mechanism solutions based on automatic moment tensor inversion using time domain estimates of low frequency amplitudes with first polarities attached. Uniaxial recordings with 10% random noise allow for only marginally lower quality solutions compared to inversions based on triaxial recordings. Detailed analysis of failure mechanism components is carried out on 912 solutions with conditional number CN ＜ 100 and a correlation coefficient r2 ＞ 0.5. The largest pure shear (DC) components characterize the events surrounding the cavern ceiling, which exhibit normal and strike-slip failures. The majority of mechanism solutions include up to 30% explosional failure components, which correspond to roof caving under gravitational collapsing. The largest vertical deformation rate relates closely to the cavern roof and floor, as well as the rest of the salt formation, whereas the horizontal deformation rate is most prominent in areas of detected collapses.