FAULT LOCATION AND RUPTURE KINEMATICS OF THE MAGNITUDE 6.8, 1992 ERZINCAN EARTHQUAKE, TURKEY, FROM STRONG GROUND MOTION AND REGIONAL RECORDS

The hypocenter location of the 13 March 1992, M = 6.9 Erzincan earthqu ake (Turkey) and its rupture kinematics have been studied using local and regional seismic records to understand its relationship with the t ectonic activity of the Erzincan basin and of the North Anatolian faul t (NAF). Regional records of the mainshock and the largest aftershocks were used to locate the respective epicenters. The mainshock S-P trav el time delay and the P-wave polarization of the near-source accelerog ram record in Erzincan (ERZ), calibrated by the aftershock records, co nstrain the mainshock hypocenter to be located about 10 km to the east -southeast of Erzincan, 39 degrees 42.3 N, 39 degrees 35.2 E, and at a best-fit depth of about 9 km. The activated fault is a major branch o f the NAF along the eastern edge of the basin. Hypocentral depths grea ter than about 16 km are not supported by the data. The ground velocit y record at ERZ has been synthesized for constraining the northwestwar d rupture, assuming a kinematic model with constant slip and rupture v elocity, and a strike 125 degrees, for a large number of models. The l atter were constructed by varying the rupture parameters in a discrete domain. The best-fit fault models are located within 1 km of the epic enter above and have all their northwestern end within 5 km of ERZ. Th e 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 uncert ainty of 0.5 m, being strongly sensitive to the rupture velocity and t o the fault location. Combining these results with the seismic moment and the source duration provided by other studies leads to a total rup ture 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 Ovacik fault.