Spatial distribution of the seismicity parameters in the Red Sea regions

The spatial distribution of the seismicity parameters of the magnitude-freq uency relation has provided preliminary quantitative basis for establishing different zones of seismic activities in the southern Red Sea regions. Fou r zones were constructed from application of proposed models that yielded a pproximate b value range for each zone, thus, providing relative bases for preliminary classification as follows: zone III has b value less than or eq ual to 0.6; zone IT has b value less than or equal to 0.8; zone I has b val ue less than or equal to 1.0; and zone 0 has b value > 1.0. The zones were characterized through correlation to seismotectonic and some geophysical co nfiguration in the study area. Narrow contour spacing among zones is observ ed to occur along intersections of areas of probably different seismic sour ce zones, while wider spacing occurs seemingly for a prominently dominating source of seismic activity. Corresponding spatial distribution of estimate d maximum magnitude and expected magnitude at 90% non-exceedance in 50 year s was prepared. Likely occurrence of a major earthquake is spread over a wi der area of coverage characterized by presence of rift zones, structural di scontinuities, and dislocations in the study area. Broad confidence limits for the parameter values are encountered, but correlation to primary tecton ic structures is seen to be possible. Comparison of the present results to previous relevant studies indicates general agreement with regards to tecto nics and related phenomena. The spatial distribution of the parameters seem ed to provide appropriate basis of analysis to thr observed complexities of seismic occurrences in the Red Sea and adjacent shield areas. (C) 1998 Els evier Science Ltd. All rights reserved.