The properties of faults involved in earthquakes have important implications on the induced ground motions and the crustal stress state variations. The authors obtained samples of gouges and striated planes of rocks from various fault sites in Türkiye and Japan. Many experiments were carried out using direct shear, stick–slip and double shear and slip tests on the fault gouges and striated fault planes and mechanical tests on the host rocks. The experimental results are used to determine the parameters of three criteria. Furthermore, triaxial yield criteria were compared for fault gouge, striated surfaces and host rock for some fault zones in Türkiye. Some possible constitutive models for fault gouges and striated surfaces as well host rock under shearing conditions is presented. On the basis of experimental results, stress variations at earthquake fault zones are evaluated. This study presents some of the outcomes of these experimental results and discuss their implications on the strong ground motions and crustal stresses.