Traces of Strong Earthquakes at Ahsiket, the Ancient Capital of the Ferghana Valley

Studies in archeoseismology were conducted in the Ferghana Valley revealing traces of strong earthquakes that occurred in ancient times. We pointed out in our previous publications that the ancient city of Eilatan perished in the 1st century BC when devastated by a strong earthquake. It was during that time that the capital Farghana (Akhsiket) was damaged. We also detected there a seismic rupture at the surface and other evident deformations in the previous structural elements. We determined the magnitude of the seismic disaster (М = 7.6) based on the greatest displacement on the seismogenic rupture emerging at the surface right in the middle of the ancient city. The associated seismic motion completely destroyed or considerably deformed all structures and seriously damaged and destroyed the city walls. It was probably for that reason that the new kings of the Ferghana Valley built a new residence for themselves on Mugtepe after the 90s BC. The site is referred to in a Chinese source Hanshu as Guishuan. We have succeeded to determine from data to be found in archeological sources that the abovementioned fortifications in the capital were built in the time span 104–90 BC, while the intensity X earthquake itself seems to have occurred approximately in 91–90 BC. The earthquake involved all of the Ferghana Valley, hitting the towns and villages in the northern Ferghana especially heavily. A conspicuous example is furnished by the falling-apart of massive fortress walls in the citadel and the Shahristan of the town of Farghana (Ahsiket). It is possible that the seismogenic rupturing that emerged at the surface in the ancient Ahsiket and Eilatan occurred at the same time. A similar strong earthquake occurred later on, during the 11th to the earlier half of the 12th century. We identified traces of this seismic event at several objects of the Karahanid age in the shakhristan and rabad. These materials must be incorporated for a new assessment of earthquake hazard for the Ferghana Basin.

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