Stable creeping and distant triggered slips by the 1999 Izmit Earthquake along the Ismetpasa section, North Anatolian Fault Zone, Turkey

The Ismetpasa section of the central North Anatolian Fault Zone, which has ruptured during the 1944 Bolu-Gerede earthquake (Ms 7.3) and the 1951 Kursunlu earthquake (Ms 6.9) is known as creeping. We present new findings on the rate of stable creeping and triggered slip associated with the distant 1999 Izmit Earthquake. Across the eastern wall of a highway station at Ismetpasa (N 40§52'15'', E 32§37'30''), we measured 41cm of displacement using total station on 31st August 2002. In 1969, Ambrasys (1970) reported 24 cm displacement of the wall and Aytun(1995) measured 18cm. Between 1969 and 1972, Aytun(1995) also measured 0.6cm/yr average creeping rate using geodetic methods at the same site. Altay et al. (1991) observed 0.77cm/yr creeping rate using creep-meter between 1982 and 1990. These data provides us that cumulative displacement is 23cm and average creeping rate is approximately 0.7cm/yr between 1969 and 2002. In the early summer of 2002, we found the triggered surface slips of 3-6cm of right lateral probably associated with the 1999 Izmit earthquake of Ms7.4, at three sites along 3km-long strand of the Ismetpasa. The epicenter of the earthquake is located 225km, and the eastern tip of the surface rupture is 155km west of Ismetpasa. Those sites are 1) 2km west of the highway station, we observed 3cm displacement on the concrete garden wall of s gas station. The owner of the gas station explained that significant damage of the wall was realized right after the Izmit earthquake. 2) 200m west of the station we measured 6cm displacement on the railway road. 3) At Hamamli village, 1km east of the station, a few cm offset was founded on the brick-wall of house for livestock and on the paved road near the house a few days after the Izmit earthquake. We measured 6cm horizontal and 2cm vertical offset there. There is no information on a stable creeping at sites 1) and 2) since the 1999 earthquake. It is not clear whether creeping on the section has been constant or consisted of episodic small slips like the 1999 event since 1990. In addition such a high creeping rate can't be neglected when we consider the recurrence of large earthquake events on NAFZ. From these points of view, we started the periodic geodetic measurements of the fault creep at Ismetpasa.