In this study, one-dimensional (1-D) P- and S-wave velocity structures of upper crust in the Erzincan basin and precise hypocentre locations of aftershocks of 13 March 1992 Erzincan earthquake (Ms = 6.8) have been determined by using 1-D inversion algorithm VELEST and relocation algorithm HYP2000, interactively. 22,291 P- and 10,192 S-arrival times of 1561 aftershocks recorded at 58 temporary stations have been used. Six layers have been defined within upper 20 km of the crust. In the uppermost crust about 2 km thick sedimentary cover of the Erzincan basin has very low P-wave velocity as well as low V-p/V-s ratio. The P-wave velocity reaches 6.3 km/s at 7 km depth with an increasing gradient. A thick crustal layer with a P-wave velocity of 6.9 km/s has been defined in the 7-20 km depth range. Several tests have been applied to check the stability of the velocity structure and the accuracy of the aftershock locations. The general geometry of the aftershock distribution given by previous studies has not been drastically changed but more accurate aftershock locations have provided evidences for more reliable correlation to tectonic features and clues for new proposals on the recent deformation. Examination of well-constrained aftershock cluster between Pulumur and the southeast of the Erzincan basin as well as very recent local seismic activity after 27 January 2003 Pulumur earthquake (Ms = 6.0) imply that a new antithetic fault activity to the North Anatolian Fault (NAF) zone similar to the Ovacik Fault and the Avcidag Fault has developed. The Yedisu Fault segment (NAF-1) of the NAF displays relatively inactive character as defined in the previous studies. (c) 2004 Elsevier B.V. All rights reserved.