Re-Evaluating the Seismicity of the Jordan-Dead
Sea Transform System
Najib Abou Karaki
Dept. of Geology - Univ. of Jordan. Amman-Jordan
The Jordan Dead Sea Transform System (JDT), is
the major source of seismic hazard in the northwestern zone of the Arabian
Plate and the entire Sinai-Palestine Plate. Many attempts to evaluate
seismic hazard in the zone were based on catalogues of historical and
instrumental seismicity of the region, which present important shortcomings.
A critical revision of the seismicity of the region is made. We illustrate
the methods employed by giving some examples, corresponding to the historical
and instrumental periods. The revision process applied to the JDT seismicity
data, minimizes error accumulation, helps in the identification of true
events and improves the homogeneity and accuracy of the catalogues.
Up to date most of the seismic hazard studies
made for the JDT, were based upon historical seismicity catalogues and
routine epicentral distributions. As has been shown by the samples examined,
the data contain serious uncertainties. Such seismic hazard analyses
are bound to lead to distorted evaluations of the level of seismicity
in the zone. This applies, in particular, to some of the frequency magnitude
relationships proposed for segments of the JDT. The quality of such
relationships and the seismic hazard evaluations is obviously dependent
upon the quality of the basic data used to obtain them. We propose a
simple formula to test the chronology assigned to historical earthquakes.
A careful examination of instrumentally determined epicenters should
be carried out by performing relative locations whenever it becomes
possible. Focal mechanisms are scarce in the region. Therefore there
is a need to estimates those of small events, which should be used in
conjuction with neotectonic information and satellite imagery.