Probabilistic seismic hazard assessment for Iraq using complete earthquake catalogue files

Probabilistic seismic hazard analysis (PSHA) has been carried out for Iraq. The earthquake catalogue used in the present study covers an area between latitude 29 degrees - 38.5 degrees N and longitude 39 degrees - 50 degrees E containing more than a thousand events for the period 1905 - 2000. The entire Iraq region has been divided into thirteen seismogenic sources based on their seismic characteristics, geological setting and tectonic framework. The completeness of the seismicity catalogue has been checked using the method proposed by STEPP ( 1972). The analysis of completeness shows that the earthquake catalogue is not complete below M-s = 4.8 for all of Iraq and seismic source zones S1, S4, S5, and S8, while it varies for the other seismic zones. A statistical treatment of completeness of the data. le was carried out in each of the magnitude classes. The Frequency Magnitude Distributions (FMD) for the study area including all seismic source zones were established and the minimum magnitude of complete reporting (M-c) were then estimated. For the entire Iraq the M-c was estimated to be about M-s = 4.0 while S11 shows the lowest M-c to be about M-s = 3.5 and the highest M-c of about M-s = 4.2 was observed for S4. The earthquake activity parameters ( activity rate lambda, b value, maximum regional magnitude m(max)) as well as the mean return period ( R) with a certain lower magnitude m(min) >= m along with their probability of occurrence have been determined for all thirteen seismic source zones of Iraq. The maximum regional magnitude m(max) was estimated as 7.87 +/- 0.86 for entire Iraq. The return period for magnitude 6.0 is largest for source zone S3 which is estimated to be 705 years while the smallest value is estimated as 9.9 years for all of Iraq. The large variation of the b parameter and the hazard level from zone to zone reflects crustal heterogeneity and the high seismotectonic complexity. The seismic hazard near the source boundaries is directly and strongly affected by the change in the delineation of these boundaries. The forces, through which the geological structure along the plate boundary in Eastern and Northeastern Iraq are evolved, are still active causing stress-strain accumulation, deformation and in turn producing higher probabilities of earthquake activity. Thus, relatively large destructive earthquakes are expected in this region. The study is intended to serve as a reference for more advanced approaches and to pave the path for the probabilistic assessment of seismic hazard in this region.