Moment tensor of the 1999 Dead Sea calibration shot: limitations in the isotropic source retrieval without a detailed earth model

摘要

Records of the November 11, 1999, M-L = 3.9 calibration shot observed at three broad-band (1313) stations at a distance range from 35 to 63 km from the epicenter were inverted with a simple I-D model. Complexity due to the water-solid bedrock interface near the hypocenter effectively masks the explosive mechanism in first-motion polarities. Reverberation in the water and scattering in the crust result in the long duration of the source process if estimated with a simple structure model. Only the part with a significant non-zero isotropic (ISO) component should be considered. We selected this part on the basis of the estimate of error due to inexact modeling of the crust constructed by perturbing the thickness and velocities in individual layers by 5% of their current values. Within this interval, the isotropic process of explosive characteristics is detected. However, if we do not check the significance of the isotropic part in the formally reconstructed source process, then we might miss the information about the explosion and arrive with a spurious nearly double-couple source. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 17]