A minor earthquake swarm has afflicted a part of Eastern Turkey which has probably the highest risk of a major earthquake along the North Anatolian Fault other than the Marmara Sea.
At 9:58pm UTC last night a Ml 3.6 earthquake struck in Tunceli Province, about 35 kilometres (22 miles) due west of the town of Yedisu. In the next two hours four further earthquakes, the largest a Ml 4.1 event at 10:52pm UTC, struck in the same location. All of these events are located perilouslyclose to the as-yet unruptured 65-kilometres long Yedisu Fault.
In 1939 a massive earthquake (Mw 7.9) struck west of the city of Erzincan. Ever since, twelve large earthquake (>Mw 6.5) have unzipped the North Anatolian Fault from east of Erzincan to Izmit on the Marmara Sea. The last major earthquakes on the fault was the Mw 7.4 earthquake near Izmit in August 1999 & the Mw 7.2 near Duzce in November 1999.
Prior to the Izmit earthquakes, Stein et al. had published a paper in the Geophysics Journal (Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering, 1996) which had noted how each earthquake along the North Anatolian Fault had increased stress on the adjacent segments which subsequently ruptured. They therefore successfully predicted the Izmit earthquakes three years before they struck.
In their paper Stein et al. also noted that there was one major seismic gap still remaining - the 65-km long Yedisu Fault, bounded by previous events which occurred in 1949 (Mw 7.1) & 1992 (Mw 6.5). These events, alongside all the other major earthquakes since 1939, had increased stress on the Yedisu Fault by a massive 10.1 bars - this is the equivalent to 10.1 atmospheres. Other stress increase caused by the 1949 & 1992 events had led to the 1971 Bingol earthquake (M 6.3) & 2003 Bingol earthquake (Mw 6.4) to the south-east of the Yedisu Fault.
It is therefore possible that these earthquakes which occurred last night may well be precursors to the expected >M7 Yedisu earthquake. If this were to strike, much like the 1939 & 1992 Erzincan earthquakes they would be expected to cause serious damage to the city of Erzincan and likely kill hundreds if not thousands of people.
Post Scriptum: The Moment Tensor Solution provided by the Kandilli Observatory seems to indicate these earthquakes did not occur on the Yedisu Fault but likely on a nearby strike-slip fault with an alignment more akin to the faults which ruptured in 1971 with the M 6.3 Bingol earthquake.
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