Abstract
Abu Dabbab seismogenic zone is located close to the Egyptian Red Sea coast. It is characterized by cannon earthquakes, long continued seismic activity, and frequent earthquake swarms. Earthquakes in this zone have occurred with high frequency over a long period of time in a confined linear zone that extends offshore in the Red Sea. A unique property is that earthquake signals can be heard by humans. Most previous studies suggested a magmatic origin for this activity. We perform a detailed earthquake tomography to image the crustal structure beneath Abu Dabbab and to explore the origin of its seismic activity and the cannon earthquakes. Based on the local and regional data, we construct a large-scale seismic tomography model for the entire region and then enhance it for the local area of Abu Dabbab. We find the seismicity forms an arc-shaped cluster that surrounds an aseismic block of high velocities and a low V (sub P) /V (sub S) ratio. According to the tomography results, we developed a new schematic geodynamic model proposing that the confined linear seismic zone in Abu Dabbab is due to the location of an active fault below a large, rigid, nondeformed block of Precambrian igneous rock, which reaches a depth of approximately 10 km. The surface between this block and the moving parts of the fault are lubricated by fluids penetrating into the crust from the Red Sea as a result of combined strike-slip and thrust displacements along the faults. These results reveal strong arguments for the tectonic origin of the seismicity associated with an important role of the fluid contents in Abu Dabbab area.