Surface rupture and rupture mechanism of the October 1, 1995 (M-w=6.2) Dinar earthquake, SW Turkey

A moderate earthquake (M-w = 6.2) caused substantial damage in the town of Dinar at 17:57 UT, on October 1, 1995. Surface rupture has been observed to be discontinuous for 10 km along the NW-trending Dinar fault segments. The surface rupture has consisted of nearly vertical cracks up to several tens of meters long and a meter wide that display linear, sigmoidal and anastom osing geometries indicating the mechanism of displacement on the fault plan e. Most of these cracks display a dip-slip component of displacement (0.05- 0.6 m); those with anastomosing geometries indicate a large dip-slip (>0.25 m). Sigmoidal crack patterns show both right and left strike-slip (rotatio nal) component of displacement and a small dip-slip (<0.25 m). The geometry of the cracks and related modes of slip suggest a 325<degrees> oriented ho rizontal principal stress direction. This direction makes an acute angle wi th the NW-trending plane of the Dinar fault. This angular difference is the cause of the strike-slip (rotational) movement manifested in the surface r upture and indicated by the focal mechanism solution of the earthquake. Und er the influence of this horizontal principal stress direction of compressi on, firstly en echelon cracks were formed. Then these cracks were modified by a predominantly dip-slip displacement on the Dinar fault, the initial cr acks were connected to each other by anastomosing cracks of a second rotati onal phase. The rotation led the hanging-wall block of the Dinar fault to d epart from its dip-slip orientation to an oblique southwesterly direction t owards the Mediterranean Sea as suggested by strike and dip-slip indicating cracks. (C) 2000 Elsevier Science B.V. All rights reserved.