Preliminary Report on Investigations of Neotectonics and Paleoseismicity on the East Coast of The Gulf of Aqaba, Kingdom of Saudi Arabia

SGS-OF-2001-2 Van S. Williams, Mohammed H. Al-Rehaili, Ghassan Al-Sulaimani, Abdullah Showail, Sultan Bahloul, and Mohammed Zahrani
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ABSTRACT
The area east of the Gulf of Aqaba is the most seismically active part of Saudi Arabia (Roobol, Al-Rehaili, and others 1999).
Sinistral movement on the 1000-km-long Gulf of Aqaba – Dead Sea transform fault has produced hundreds of earthquakes during 4000 years of recorded history (Ben-Menahem, 1991), and two large earthquakes in the last 20 years (Smith and Bokhari, 1984; Roobol, Al-Rehaili, and others, 1999).
Since the inception of the transform fault during the Late Miocene, 105 km of lateral offset (Le Pichon and Francheteau, 1978) has occurred.
Geologic structure beneath the Gulf of Aqaba is complicated because wedging action of large structural blocks between spurs of the main transcurrent fault caused widening and deepening of the Gulf through dramatic vertical tectonics.
Topographic relief from the bottom of the Gulf to the flanking mountains exceeds 4300 meters and normal faults trending parallel to the Gulf are common.
The largest instrumentally recorded earthquake on the Gulf of Aqaba part of the fault system was magnitude 7.3 and occurred November 22, 1995.
The effects of that earthquake and a wealth of background information are recorded by Roobol, Al-Rehaili, and others (1999).
This study revisited the area affected by recorded earthquakes to survey ground effects from the 1995 earthquake and search for evidence of prehistoric earthquakes.
Determining the location, timing, and magnitude of prehistoric earthquakes extends the record of seismicity and allows much more accurate planning to decrease the hazard from future earthquakes.  The recurrence interval of earthquakes on large faults may be many hundreds of years, so an instrumental record of less than 50 years is inadequate to realistically predict the chance of future earthquakes.
In this study, we have concentrated our attention on the “earth fissures” produced by the 1995 earthquake described by Roobol and others (1999).
These are better termed small faults because they show displacements of up to 30 cm.  These fault scarps offset Quaternary alluvian, and are located on much older and higher preexisting fault scarps that record long-term cumulative offset exceeding 18 m (figs. 1, 5).
The 1995 earthquake is only the latest of many similar and perhaps larger earthquakes recorded by many fault scarps in alluvium along the coast about 50 km south of the town of Haql.
Reading the complete record of these scarps will require detailed mapping, trenching, and extensive radiometric dating, but the information to be obtained may extend the earthquake history back perhaps 20,000 years. 

 

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Wlliams, V.S., Al-Rehaili, M.H., Al-Sulaimani, G., Showail, A., Bahloul, S., and Zahrani, M., 2001, Preliminary report on investigations of neotectonics and paleoseismicity on the east coast of the Gulf of Aqaba, Kingdom of Saudi Arabia: Saudi Geological Survey Open-File Report SGS-OF-2001-2, 11 p., 7 figs.