Liquefaction Potential Evaluation Along Active Faults at the Head of the Gulf of Aqaba, Jordan

Abstract

The city of Aqaba, Jordan lies within a major seismic region along the active plate boundary of the Dead Sea Transform. A NE-trending, strike-slip fault that originates in the Gulf of Aqaba apparently terminates under the city along four NW-trending normal- to oblique-slip faults. These normal faults accommodate active tectonic subsidence at the head of the Gulf of Aqaba. Paleoearthquake data from five trench excavations across these faults were collected to characterize the closest seismic source to the city. Ground rupture from an earthquake produced a fault scarp sometime before A.D. 1045-1278. A minimum estimate for the magnitude of the earthquake is M 6, the minimum threshold for surface ground rupture. Several multiple event scarps suggests that a minimum of seven earthquakes have occurred since 5 to 6 ka. This yields a minimum recurrence of earthquakes on the Aqaba fault seismic source of approximately 700-850 years. Subsurface exploration of boreholes and trench exposures indicates that the stratigraphic sequence is composed of liquefaction susceptible sediments. Shallow subsurface deposits consist of aeolian and beach sand interbedded with alluvial silt, sand, and gravel in the upper parts of the Quaternary fan deposits. We evaluated the liquefaction potential using Seed’s cyclic stress ratio approach. This method is based on the corrected field blow count of the Standard Penetration Test to an energy of 60% and effective overburden pressure of 100 kPa with corresponding attenuated peak ground acceleration of 0.1,0.2g, and 0.3g. Preliminary results of the liquefaction mapping indicate that the coastal areas have a high potential to liquefy and could experience severe damage as a result of earthquake shaking. Our analyses suggest that the eastern parts of the city lie predominantly within a nonliquefaction susceptibility zone

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