Abstract

Aftershock sequence of 19th May, 2009 Lunayyir earthquake (Mw 5.7) has been recorded by deploying seismic stations immediately after the occurrence of the main shock. Analysis of this sequence clarified that; the major part of cumulative seismic moment released during the first hours after the occurrence of the main shock; their orientation is north west (NW) parallel to the Red Sea axial trend along Najd faulting system; it is clustered at two depths; from 5-10 and 15-25 km beneath Lunayyir area; illustrated successive periods of maxima and minima; decayed rapidly following the relation of n(t)=37.28 t-0.6. Fault plane solutions for five large events indicate normal faulting is the major mechanism. These findings are in agreement with the north east (NE) (transform fault) trend runs crossing the Red Sea into Shield area where the activity has been initiated and travelled through the Lunayyir area. While the NW Najd faulting system runs parallel to the Red Sea axial trend and intersected with NE fault trend underlying Lunayyir area. Accordingly, it can be concluded that, the recent earthquake activities at Lunayyir lava flow area are related to the present-day Red Sea tectonics. Monitoring earthquake activities through installing permanent seismic network around the area is highly recommended.

Key words: aftershock sequence, fault plane solution, stress, and Lunayyir.