Structural corrections for slowness and azimuth of seismic signals arriving at Gauribidanur array

Abstract Slowness and azimuth anomalies directly measured from the data recorded at seismic arrays have been used for observing deviations from spherical symmetric earth. Interpretation of such observations for reliable refinement of earth models requires correction for the effect of irregularities in the crust and upper mantle structure beneath the recording sites because it introduces large systematic errors in slowness and ray direction. Observations of large systematic errors in slowness and azimuth for teleseismic events approaching Gauribidanur (GBA) seismic array from the east were compensated by introducing a number of dipping Moho beneath recording sites. It was found that a dipping interface having a dip of 6° and a strike of N13°E explains observations of ray direction anomalies in a satisfactory manner. This can deviate seismic rays up to 11.5 per cent in slowness and 6.5° in azimuth. The quantum of errors seems quite significant as far as refinement of earth models is concerned. A correction table has been prepared which would be useful in the analysis of slowness and azimuth of earthquakes recorded at GBA from the eastern direction. We have applied these structural corrections successfully to the observed slowness and azimuth of earthquakes from this direction. This is illustrated in the form of array diagrams.