PALEOSEISMOLOGY OF THE 1912, 1944 AND 1999 RUPTURES ON THE NORTH ANATOLIAN FAULT: IMPLICATIONS FOR LONG-TERM PATTERNS OF STRAIN RELEASE

We excavated over fifty trenches at five sites along the 1912, 1944 and 1999 surface ruptures to study the past earthquake history along the North Anatolian fault east and west of the Marmara Sea. Along the 1912 rupture on the Galipoli peninsula, we excavated nearly 30 trenches near Kavakkoy to resolve cumulative slip of 9 m from the 1912 and 1766 earthquakes. We also found evidence for two additional surface ruptures after about AD 900, which probably correspond to the large regional earthquakes of 1063, and 1344. These observations suggest fairly periodic occurrence for the past millennium and a rate of about 15 mm/yr if all events experienced similar slip. Along the 1999 rupture, we excavated two sites near Kosekoy to resolve the occurrence of three events after AD 1650. In addition to 1999, one is almost certainly the large 1719 earthquake that had very similar damage distribution to 1999. The other event may be the poorly studied 1878 earthquake or one of several other large events (such as 1754 or 1894) that are poorly located in the region. Radar surveys show about 6 m of accumulated slip on the main rupture after AD 1650, where about 2 m of slip occurred in 1999. Thus, although the intermediate event may have been smaller in magnitude, it apparently had similar slip at Kosekoy, suggesting characteristic behavior. Finally, we excavated over a dozen trenches at Gerede along the 1944 rupture to resolve five earthquakes after about AD 550. The 1944 rupture expressed 5 m of slip at the trench site. The penultimate event also experienced a similar amount of slip, based on offset stream channels. Cumulative slip for all five events is about 18-25 m based on 3D trenching of a channel margin, suggesting a slip rate of 12-17 mm/yr for the past 1500 years. In addition to quasi-periodic behavior and sparse evidence of similar slip at a site, our observations suggest that the slip rate for the past 1000-1500 years has been on the order of 15 mm/yr, considerably slower than the 23 mm/yr indicated by GPS, suggesting that part of the current GPS rate is a transient feature.