Journal of Seismology and Earthquake Engineering
Volume:11 Issue: 4, Winter 2010

Four earthquakes (Mw 6.0-6.4) which occurred at 3 major segments of Sumatran Fault Zone (SFZ) were analyzed to identify their fault planes. The events were relocated to assess physical insight into the hypocenter uncertainty. The earthquake source parameters were determined from three-component local waveforms recorded by IRIS-DMC and Geofon broadband IA networks. The epicentral distances of all stations were less than 10°. Moment tensor solutions of the events was performed, simultaneously with the determination of the centroid position. Joint analysis of the hypocenter position, centroid position and nodal planes of the vents indicated the Sumatra fault planes. The hypocenters of all four events clearly prefer that strikes parallel to Sumatra Island to be the fault plane in all cases. Regional moment tensor solutions of this paper along with the focal mechanisms, which represent the only double couple of moment tensor, is plotted. The MT solutions consist of all events have strike slip one fault type. The preferable seismotectonic interpretation is that the events activated Sumatra fault zone at a depth of about 14-18 km, corresponding to the interplate of Sumatra fault boundary.

The dynamic response of flexible five-story building supported on the variable frequency pendulum isolator (VFPI) under bi-directional near-fault ground motions is investigated. In order to verify the effectiveness of the VFPI, the seismic responses are compared with the friction pendulum system (FPS) and variable friction pendulum system (VFPS). The response of the system with bi-directional interaction is compared with those without interaction in order to investigate the effects of bi-directional interaction of frictional forces. Moreover, a parametric study is carried out to critically examine the influence of important parameters on bi-directional interaction of the frictional forces of the VFPI. From the above investigations, it is concluded that under bi-directional near-fault ground motions, the isolator displacement in the VFPI is more than that of the VFPS and the FPS whereas the top floor absolute acceleration and the base shear are less than that of the VFPS and the FPS. Furthermore, if the bi-directional interactions of frictional forces of the VFPI are ignored, the isolator displacements will be under predicted and superstructure acceleration and base shear will be over predicted.

Shear behavior and the failure modes of shear stressed masonry walls have been the subject of many investigations. In the present paper, the performance of an interface elasto-plastic constitutive model for the analysis of unreinforced masonry walls by means of micro-finite element modeling is evaluated. The micro-model is utilized to obtain the behavior of unreinforced masonry walls, based on assumption that the masonry bricks, mortar and their interface are three separate elements. In the present modeling, the behavior of bricks and mortar is assumed to comply with the plastic-damage model which is based on multiple damage variables. The behavior of the interface element is assumed to comply with the coulomb friction model having a limit on the critical shear stresses. A nonlinear analysis is performed by the application of explicit formulae in which displacements and rotations between bricks are taken into consideration. To validate the model, experimental results of masonry elements and walls is compared with the results obtained from the numerical analysis. It is concluded that the suggested model is suitable for assessing the behavior of masonry walls under vertical and horizontal loading.

Experimental and analytical investigations have been conducted on a new type of infilled frames with Frictional Sliding Fuses (FSF). The results show that these infilled frames have adjustable strength and high ductility similar to other structural elements. Furthermore, the ultimate strengths and deformation capacities of such infills are much more than regular similar fuse-less infilled frames. To study the behavior of such infilled frames in out of plane direction, a specimen was loaded transversally after being failed by in-plane loadings and having the experience of 6% drift in this direction. The results reveal that the infill has sufficient strength against out of plane components of regular earthquakes. The infill with the proposed configuration of this study is modeled by finite element method, in ABAQUS, to study the influence of the fuse sliding strength on its ultimate strength. It is shown that the ultimate strength is raised linearly by increasing the sliding strength of the fuse. In summary, the results confirms that such infilled frames can be regarded engineered for their high ductility as well as the capability of being adjusted for a desired strength.

The results of long-term seismic monitoring with use of natural sources conducted in the seismic dangerous area of the Caucasus mineral waters are presented. In order to study the subsurface geodynamics and its stress state in the study area, a technique has been developed based on studying energy of converted PS waves. The analysis of obtained data allowed middle-term criteria for predicting local tectonic earthquakes to be formulated proceeding from the model within the scope of the avalanche-unsteady crack formation (AUCF) theory. It has been shown that the catastrophic far earthquakes (distance up to 7000km) with M >7.0, after which intense surface waves had been recorded in the area of Caucasus Mineral Waters, changed anisotropic properties and stress state causing the increase of local seismic activity. This shows the induced seismicity. Induced process reduces the reliability of formulated criteria. This reveals the necessity to correct the model of earthquake origin in accordance with the AUCF theory.