Gobekli Tepe: tectonic environment and consequent strategic position

Gobekli Tepe: tectonic environment and consequent strategic position

Eric R. Force

The ancient archaeological site of Gobekli Tepe in Turkey has attracted a great deal of attention since its discovery (or rediscovery) in 1994.  Its great age—thought to be about 11000 years—in conjunction with the complexity of its cultic/religious architecture (Schmidt 2001) poses new questions about the evolution of civilizations.

The purpose of this posting is not to ponder these questions, but merely to place the location of the site(s) in its tectonic context.  As it happens, I have studied the historic and instrumental seismicity of the sites’ region, for the purpose of interpreting excavation reports of much younger—but still prehistoric—tells there (Force, 2017).  That study has implications for Gobekli Tepe that are not apparent in the study itself, but may be of interest to students of the much older culture.

Gobekli Tepe is 12  km northeast of the modern town of Sanliurfa, Turkey, commonly called Urfa in older literature, and Edessa in even older literature, back to its founding in the Hellenistic era.  The site can be found in Google Earth  images at latitude 37 degrees 13’02.73”N and longitude 38 degrees 51’16.00”E.  Both town and site are at the head of a drainage basin emptying southward into the Euphrates River near Raqqa, Syria, as the Balikh River.   In Turkey this drainage is called the Colop.

The site of Gobekli Tepe is about 50 km north of the Syrian-Turkish border, but is nevertheless at the northern margin of the Mesopotamian plains geomorphically or physiographically.  That is, its location should not be considered as part of the Anatolian province in the sense of its plateaus and mountains.  Indeed, its plate boundary location places it not on the Hellenic/Turkish plate but on the impinging Arabian plate!  Gobekli Tepe is a most strategic site in its segment of the northern margin of the Mesopotamian plains, as was ancient Edessa much later—but before the Syrian-Turkish border divided the drainage basin in two. 

The Balikh/Colop basin at Sanliurfa is a graben, i.e. a tectonic basin, here outlined by north-south faults that extend southward at least to the Syrian border but immediately to the north become the Bozova dextral fault extending northwest (e.g. Selcuk and Gokten 2012, fig. 1).  The age of faulting to form these features is unclear—at least to me—but thought to be Holocene.

The basinal terraces and floodplain at Sanliurfa are bordered by Cenozoic sedimentary rocks, mostly limestones including the Gaziantep Formation of Eocene and Oligocene age.  The site of Gobekli Tepe is in such uplands marginal to the basin. The basin floor was probably important from some combination of its riparian characters for gathering, hunting, and/or agriculture, rather than directly to its tectonic context.   Since the discovery of Gobekli Tepe, related and somewhat similar sites of great antiquity have been discovered nearby, so far all in its Turkish segment (Guler et al. 2012).  The probable southern extension of the graben as Syria’s Balikh drainage is also the site of Neolithic tells, showing a continuity of cultural connection into Mesopotamia (Force 2017 reviews work of Akkermans and others).

The seismic character of the immediate area of Sanliurfa and Gobekli Tepe is shown on generalized seismic risk maps as moderately low, considerably lower than most of Turkey, and lower than the Taurus Mountains immediately north (Erdik et al. 1999; Tsapanos et al. 2005).  That is, the modest modern seismicity of the northern Mesopotamian plains on the Arabian tectonic plate extends into Turkey as an arc south of boundaries between it and the Eurasian and Hellenic/Turkish plates to the northeast and northwest respectively, which are more seismically active,

Thus there is no reason other than the location of Gobekli-related ancient sites around and near a tectonic basin to suppose that tectonic activity has influenced the course of the sites’ development.  And of course no excavation report suggests any such influence—but that is generally the case in this region regardless of the age of site, even where in retrospect some influence can be gleaned from excavation reports (Force, 2017).  In addition, the death of Klaus Schmidt in 2014 has slowed answers to the many questions his site presents. 

My own method of addressing questions about seismic history of ancient sites is to use the modern instrumental seismic record and the recorded seismicity in the historic period, to establish a rough pattern of intensities and recurrences that can be projected into prehistoric periods.  The pattern can be used to establish seismicity expectations for a given stratigraphic/archaeologic record.  Only time will tell what the reception of this method will be, but unless tectonic plate motions change between prehistoric and historic periods, it seems logical.  My existing data base of instrumental and historic seismicity for the region that includes Gobekli Tepe (Force, 2017) can continue this reasoning. 

That paper examines modern/historical seismicity along three transects, one of which is centered on the Balikh River drainage and extends north into Turkey up to a latitude of 38 degrees, i.e. past Gobekli Tepe.  The main source of historical data is the voluminous compilation by Ambraseys (2009), to which can be added Sbeinati et al. (2005) for nearby earthquakes in Syria.  Along the Balikh transect no modern earthquakes were recorded instrumentally, though several plot on nearby transects.

Quite a few damaging earthquakes are recorded at Sanliurfa (recorded both as Urfa or Edessa) in AD 499, 569-570, 679, 860, 1114, 1157, and 1162.  In addition there are records of earthquakes felt there in AD 1003, 1120, and 1822.  The epicenters of a considerable number of these earthquakes were to the west and northwest, along the Levantine margins of the Arabian plate.  The remarkable number of earthquakes occurring between AD 500 and 1200 is due in part to increased attention due to concurrent religious wars, in which some of these earthquakes played a part (Raphael 2010).

But ten earthquakes in 1500 years (to the present) is remarkable, and the apparent clustering in time even more so.  Indeed the clustering may suggest additional earthquakes in periods when observers were not paying attention.

The Syrian part of my Balikh transect shows damaging earthquake recurrences averaging about 500 years between 36 and 37 degrees latitude (Force, 2017, fig. 3) and this new information for Urfa/Edessa shows a dramatic northward increase in earthquake frequency-–one not apparent in modern seismic risk maps due to their reliance on instrumentally recorded seismic events.

What does this mean for students of Gobekli Tepe?  Perhaps an expectation of archaeologic evidence of seismic events, quite possibly about ten of them given the duration of the site’s activity and the historic record of regional seismicity.  The correspondence of tectonic basins (grabens) with ancient sites of Gebekli type may prove to be significant, but that is currently unclear. 

However, the continuity of this graben with Mesopotamian plains certainly conferred strategic advantage on the site of Gobekli Tepe.  This site could project power southward along its graben into northern Mesopotamia!  This view puts Gobekli Tepe into a more regional framework. 

References

Ambraseys, N.,  2009, Earthquakes in the Mediterranean and Middle East: a multidisciplinary study of seismicity up to 1900:  Cambridge

Erdik. M., Biro, Y. A., Onur, T., Sesetyan, L, and Birgoren, G., 1999, Assessment of earthquake hazard in Turkey and neighboring regions:   Annali di Geofisica v. 42, p. 1125-1138.

Force, E. R., 2017, Seismic environments of prehistoric settlements in northern Mesopotamia: a review of current knowledge:  Bulletin of the American Schools of Oriental Research v, 378, p. 55-69.

Guler, M., Celik, B, and Guler, G., 2012, New pre-pottery Neolithic settlements from the Veransehir district:  Anatolia v. 38, p. 164-180.

Raphael, K., 2010, The impact of the 1157 and 1170 earthquakes on Crusader-Muslim politics and military affairs, in Ancient Earthquakes:  Geological Society of America Special Paper 471, p. 59-66.

Sbeinati, M. R., Darawcheh, R., and Mouty, M., 2005, The historical earthquakes of Syria:  Annals of Geophysics v. 48, p. 347-435.

Schmidt, K., 2001, Gobeki Tepe, southeastern Turkey. a preliminary report on the 1995-1999 excavations:  Paleoorient v. 26, p. 45-54.

Selcuk, A. S., and Gokten, Y. E., 2012, Neotectonic characteristics of the Inonu-Eskisehir fault system in the Kaymaz (Eskisehir) region:  influence on the development of the Mahmudiye-Cifteler-Emirdag Basin:  Turkish Journal of Earth Sciences v. 21, p. 521-545.

Tsapanos, T. M., Leventakis, G.-A., Koravos, G. Ch., Tatsiopoulos, G. A., and Sertaridou, I. Ch., 2005, Seismic hazard and seismic risk analysis in Turkey deduced from mixed files: Journal of Balkan Geophysical Society, v. 8, p. 89-98.