Analysis of Accelerations from the 1 October 1995 Dinar, Turkey, Earthquake

Abstract

The Dinar earthquake, 1 October 1995, occurred in southwestern Turkey and had a moment magnitude of 6.4 and a normal faulting mechanism. The earthquake caused 90 deaths, over 200 injuries, and a large amount of damage. It was recorded by seven strong-motion accelerographs. The strong-motion accelerograph at Dinar is on the edge of the surface projection of the fault. The record from Dinar is possibly unique in its proximity to the causative fault for this type of mechanism. The Dinar strong-motion station is in a small, stiff building on soft sediments with a shallow water table. The peak acceleration was 0.32 g on the horizontal component perpendicular to the fault trace. The earthquake was caused by rupture on the Dinar fault, which is a normal fault trending generally toward the south-southeast, with the hanging wall on the west. There was surface rupture along about a 12-km segment of this fault. The Dinar strong-motion station is at the south end of the fault, under 1 km from the nearest surface trace. The hypocenter was at the south end, beneath Dinar, with rupture propagating toward the north and away from the strong-motion site. A specific composite source model was found that reproduces the statistical characteristics of the ground motions and also approximately reproduces the low-frequency waveform in the strong motion. In this model the fault length, L, is 12.5 km, the width, W, is 17.3 km, and the moment M 0 is 4.72 × 10 25 dyne cm. The fault strikes 130° and dips 45° toward the southwest, from the surface to 12 km. For the composite parameters, the largest subevent ( R max ) is 4.0 km, the rupture velocity is 1.5 km/sec, and the subevent stress drop is 60 bars. After Anderson (1997) the composite source model parameters imply that the static stress drop was 36 bars, the radiated seismic energy in this event was 4.3 × 10 21 ergs, the apparent stress was 18 bars, and the Savage-Wood ratio was 1.0. Most of the seismic energy is released at depths greater than 2 km. The major asperity is beneath the location where synthetic aperture radar interferometry found the maximum surface deformation.