Determining the distribution of stress on the active faults using casagrande method; Gerede (Bolu) segment of the North Anatolia fault zone

In this study, using preconsolidation pressure method we studied the distribution of stress on the Gerede (Bolu) segment of the North Anatolian Fault Zone (NAFZ), which is one of the most important intracontinental active transform fault zones of the world. The same method, which was first used on the Meers fault in the USA, was used on the Gerede segment. In the historical earthquake records, there were 12 earthquakes having intensities V and over and there were 62 earthquakes with magnitudes 4 and over in the instrumental records between the years 1973-2006. In the study area the most destructive Gerede-Bolu earthquake of Ms=7,4 occurred on February 1, 1944. Undisturbed block samples were collected from the four trenches excavated at various locations on the Gerede (Bolu) segment. 84 consolidation tests were performed on these samples in various directions relative to the principal stress directions that caused the faulting. Using Casagrande method and the findings of the experiments, we found the preconsolidation pressure values of the samples. The relationships between preconsolidation pressures and the effective principal stresses that caused the faulting were determined. By means of these calculations, we determined the directions and magnitudes of effective principal stresses in the formation of faulting at near surface depths on the Gerede (Bolu) segment of the North Anatolian Fault Zone.