PALEOSEISMOLOGY OF THE NORTH ANATOLIAN FAULT: A REVIEW AND NEW STEPS

Paleoseismology of the North Anatolian fault became a more urgent and important issue after the 1999 Kocaeli (Izmit) earthquake. A number of paleoseismological studies have been conducted since the earthquake, especially in the Marmara and adjacent regions. Though our understanding about the fault is being innovated with recent results, we do not have answers for the critical problems on the recurrence of large earthquakes along the fault. Firstly, geological data on the past events are not sufficient and accurate to be compared with historic catalogs. On the 1967 and farther east segments, 400 years or longer historic recurrence time contradicts with GPS slip-rate and observed slips in the last century. For example, one or two events between 11th century and 1668 on 1944 and 1939 segmentsare suggested by Okumura et al. (1994), but the timing is not well constrained. In the Marmara region, the historic information that indicates 200 to 300 year recurrence time after 1500 AD is concordant with geophysical data, but paleoseismological investigations have not presented firm geologic evidence of the surface faulting associated with those historic events yet. Radiocarbon dating in this area and age has difficulties to give reliable chronological constraints. Secondary, there are not enough data on longer-term (up to a few thousand years) geologic slip rate and slip-per-event earlier than the 20th century. Reliable data on past slips are indispensable to understand the nature of recurring earthquakes and hence to forecast coming events. This paper aims to demonstrate the tactics for the paleoseismology on the North Anatolian fault and to present a solution from the Gerede trench site on 1944 segment. The Gerede trench first studied in 1990 by the author is reopened in 2002 and will bring better constraints on timing and slips.