Source parameters of the Izmit-Bolu 1999 (Turkey) earthquake sequences from teleseismic data

Abstract

Body waveform modelling and far-field displacement spectral analyses were used to study the source parameters of five of the largest earthquakes of the (Izmit-Bolu) Turkey 1999 sequence. The derived source parameters for the August 17, 1999 M W 7.4 event are: strike = 267°, dip = 85°, rake = – 175°, h = 10 km, M 0 = 1.31×10 20 Nm. The length of the fault was found equal to 76 km, the average displacement 6.4 m and the static stress drop 90 bars. The Bolu November 12, 1999 M W 7.1 event has a focal mechanism with strike = 262°, dip = 53°, rake = –177°, h = 12 km, M 0 = 4.71×10 19 Nm, fault length of 56 km, average displacement 2.1 m and average static stress drop 29 bars. The focal mechanisms of three other aftershocks of the Izmit sequence indicate right lateral strike slip motion, as well. The slip vectors of the events studied are in accordance with the GPS velocity vectors, have a mean azimuth of 269° and reveal the extrusion of the Anatolian plate towards the Aegean.