Tomographic P-wave velocity inversion has been performed for the Pannonian region using first arrival times of local and regional events from the bulletins of the International Seismological Center and the Hungarian Earthquake Bulletins. The input data consist of 4071 arrival times of 570 events. A three-dimensional velocity model has been gained by joint hypocenter-velocity inversion on a coarse and a fine non-uniform cartesian grid of nodes. The initial one-dimensional model was determined by genetic algorithm. A bending ray tracer has been used to calculate the theoretical travel times and ray paths. The reliability of the inverted velocity parameters were checked by the checkerboard method and by the analysis of the model resolution matrix. The results are generally in agreement with the known structural characteristics of the Pannonian Basin. An interesting high-velocity anomaly has been found in the uppermost mantle beneath the southern part of the Great Hungarian Plain.
In this study we introduce new rock physical models which describe the pressure dependence of seismic velocity and quality factor. The models are based on the idea (accepted in the literature) that microcracks in rocks are opened and closed under the change of pressure. The models were applied to acoustic P wave velocity data measured on core samples originated from oil-drilling wells (27 samples) and also seismic velocity and quality factor data sets published in international literature. During the measurements the pulse transmission and the spectral ratio techniques were used. Measurements were carried out at various incremental pressures and parameters of the models were determined by linearized inversion methods. The calculated data matched accurately with measured data proving that the new rock physical models apply well in practice.
More than 5000 high precision seismic phases of 560 selected aftershocks (
≥ 2.0) of the January 26, 2001 Bhuj earthquake (
7.7) in western India are used for joint determination of the hypocentral parameters and for 3D inversion of P-wave velocity and
structures in the source area. The aftershocks are located with an average rms of 0.19 s, and average error estimates of latitude, longitude and depth are 1.2, 1.1 and 2.3 km respectively. Most of the aftershocks occurred in an area 70 × 35 sq km; the intense activity was observed at a depth range 12–37 km. A bimodal distribution of aftershocks indicates that the main shock rupture propagated in upward and downward directions. Further, the best located aftershocks show two trends, one in northeast, parallel to Anjar Rapar Lineament, and the other in northwest parallel to the Bhachau Lineament. Fault-plane solutions of the northeast trending aftershocks indicate reverse faulting with left-lateral strike-slip component. These solutions are comparable with the main shock solution. The northwest trending aftershocks, on the other hand, show reverse faulting with right-lateral strike-slip motion. The estimated velocity structure indicates that the source zone of the Bhuj earthquake has a number of blocks showing lateral heterogeneities in P-and S-wave velocities. A block having higher P-and S-wave velocities appears to have uplift relative to its surroundings. The mainshock occurred at the boundary between the high
uplifted block and the adjacent low
block. Gravity observations support our 3D inversion results. This high velocity block is surrounded by rocks of higher
or lower rigidity, which possibly acted as a barrier zone.
, Humphreys E. D.
Upper mantle Pwavevelocity structure of the eastern Snake River Plain and its relationship to geodynamic models of the region , Journal of Geophysical Research , Vol. 102 , No