Abstract
Focal mechanism solution of the 27th August 2009 earthquake (mb = 4.0) that occurred in the Badr area, northwest of Saudi Arabia, approximately 50 km from the Red Sea has been determined from the P-wave first motion polarities. Results show normal faulting mechanism with a negligible component of strike-slip motion with NE T-axis direction. This type of mechanism is common with other earthquakes of the northwestern Saudi Arabia and is considered to present the tectonic movement of the region. The dominantly extensional tectonic regime in this province demonstrates the influence of NE extension in the Red Sea. The strikes of the solution are consistent with those of the main faults near the epicenter. Hypocentral location of this earthquake was carried out using the data from the King Abdulaziz City of Science and Technology Seismic Network, Saudi Arabia, and the Egyptian National Seismological Network, Egypt. The horizontal and vertical confidence estimates are 0.5 km for both. The local magnitude, M (L), following the Richter's original definition was also derived from ten digital three-component broadband seismograms. The average local magnitude determined in this study is 3.8 +/- 0.17. The estimated seismic moment of this event is .