Fault location and rupture kinematics of the magnitude 6.8, 1992 Erzincan earthquake, Turkey, from strong ground motion and regional records

Abstract

Abstract The hypocenter location of the 13 March 1992, M = 6.9 Erzincan earthquake (Turkey) and its rupture kinematics have been studied using local and regional seismic records to understand its relationship with the tectonic activity of the Erzincan basin and of the North Anatolian fault (NAF). Regional records of the mainshock and the largest aftershocks were used to locate the respective epicenters. The mainshock S-P travel time delay and the P-wave polarization of the near-source accelerogram record in Erzincan (ERZ), calibrated by the aftershock records, constrain the mainshock hypocenter to be located about 10 km to the east-southeast of Erzincan, 39°42.3 N, 39°35.2 E, and at a best-fit depth of about 9 km. The activated fault is a major branch of the NAF along the eastern edge of the basin. Hypocentral depths greater than about 16 km are not supported by the data. The ground velocity record at ERZ has been synthesized for constraining the northwestward rupture, assuming a kinematic model with constant slip and rupture velocity, and a strike 125°, for a large number of models. The latter were constructed by varying the rupture parameters in a discrete domain. The best-fit fault models are located within 1 km of the epicenter above and have all their northwestern end within 5 km of ERZ. The up-dip limit of the rupture in the vicinity of ERZ ranges from 5 to 2 km in depth, in agreement with the absence of surface breakage. The estimated rupture velocity is 3 km/sec; the rise time is 0.35 sec; and the mean slip of about 1 m is poorly resolved, with a standard uncertainty of 0.5 m, being strongly sensitive to the rupture velocity and to the fault location. Combining these results with the seismic moment and the source duration provided by other studies leads to a total rupture length ranging between 20 and 35 km. The rupture thus propagated bilaterally on the NAF and was confined within the limits of the basin, stopping to the southeast near the intersection of the NAF with the Ovaçik fault.