Muge K. Akin

Seismic hazard map of Turkey using the deterministic approach

Abstract Because the instrumental records of Turkey are far from being satisfactory for modeling the seismic hazard using the probabilistic approach, an attempt was made in this study to accomplish it through the deterministic way. In this regard, all active faults of Turkey, small and large, were evaluated together to obtain major fault systems. Then, the procedure suggested by Wells and Coppersmith [Bull. Seismol. Soc. Am. 4 (1994) 975] applied to those faults to obtain the maximum magnitude earthquake that they can generate. To do this, it was assumed that 1/3 of the total fault length would rupture to yield the maximum earthquake. Following that, seven different attenuation relationships of the strong ground motion were utilized to calculate the maximum horizontal ground accelerations for the whole Turkey at 0.2° intervals using the computer model TUMDES written in BASIC programming language. The computed peak ground acceleration (pga) values were contoured and the iso-acceleration map based on Sadigh et al. [Seismol. Res. Lett. 1 (1997) 180] relationship was selected as the new seismic hazard map of Turkey on which the seismic zonations were determined as following: pga>0.3 g Zone 1; 0.3 g

Rockfall hazard analysis for an historical Castle in Kastamonu (Turkey)

The Kastamonu Castle located on a sandstone hill with Eocene age is one of the most historical and touristic places in Kastamonu city center. The settlement of the city expanded towards the hill of the Kastamonu Castle and adversely affected by rockfalls in the past. The rockfall problems around the castle could be related to jointing, weathering, freezing-thawing and earthquake effects or a combination. In this study, the rockfall hazard at the castle is evaluated by two-dimensional rockfall analyses along 17 profiles selected in different orientations. Different size of rock blocks and various types of movements are taken into consideration in the analyses. Fall-out distance, bounce height, kinetic energy and velocity of the sandstone blocks are separately evaluated. The obtained data are used to define the possible rockfall hazard zones. Finally, the areas having potential rockfall risks are distinguished. Based on the evaluation of the data, rock bolting after removing of unstable blocks and supporting the area with the protective fences are suggested.

Evaluation of the Rockfall Potential of Kastamonu Castle Using 3-D Analysis

The Kastamonu Castle is one of the magnificent monuments of the Kastamonu province (Turkey) located on a steep sandstone hill with Eocene age. The surrounding settlement around the castle suffered from numerous rockfall events in the past. Rockfalls after an initial block toppling are controlled by a bedding plane and two joint sets existing in the sandstone. The rockfall potential along the entire castle perimeter was evaluated by means of three-dimensional (3-D) rockfall analyses using the ROTOMAP software. Rockfall initiation was modelled along a detachment line situated just below the castle walls. The results indicate that the maximum run-out distances around the castle exceed the settlement boundary on the western, southern, and eastern sides. The northern part of the castle is less critical due to lower slope gradient. In order to protect the settlement from falling blocks, vital remedial measures are suggested.

A newly developed seismic microzonation model of Erbaa (Tokat, Turkey) located on seismically active eastern segment of the North Anatolian Fault Zone (NAFZ)

A methodology to model seismic microzonation maps is required in the hazard mitigation decision plans of the earthquake prone areas. The stage of disaster preparedness for new residential places is of great importance for detailed seismic microzonation models. The effects of local geological and geotechnical site conditions were considered in order to establish site characterization as the initial stage of the models in this study. Dynamic soil properties based on the empirical correlations between shear wave velocity (Vs) and standard penetration test blow counts were taken into account in order to define representative soil profiles extending down to the engineering bedrock. One-dimensional site response analyses were performed to analyze earthquake characteristics on the ground surface. The layers for soil classification, geology, depth to groundwater level, amplification, distance to fault, slope and aspect, and liquefaction-induced ground deformation potential of the study area were prepared in seismic microzonation models. The study area, Erbaa, is placed along the seismically active North Anatolian Fault Zone. Final seismic microzonation map of the study area was evaluated applying different GIS-based Multi-Criteria Decision Analysis (MCDA) techniques. Two of the MCDA techniques, simple additive weighting and analytical hierarchical process (AHP), are considered during the evaluation step of the final seismic microzonation map. The comparison is made in order to distinguish two different maps based on these MCDA techniques. Eventually, AHP-based seismic microzonation map is more preferable for the seismic design purposes in this study.

The Rockfall Potential of the Southwestern Part of Kastamonu Castle (Turkey) Based on 2-D and 3-D Analyses

Urbanization around steep rock slopes with jointed rock masses is mostly under the threat of rockfalls. Numerous catastrophic rockfall hazards have been reported throughout the world due to the downslope movement of detached rocks. It is quite critical to determine the rockfall potential of a location considering rockfall trajectories, run-out distances, bounce heights and the kinetic energies of falling rocks. Therefore, the determination of rockfall paths requires the use of rockfall simulations. In practice, 2-D and 3-D models are most commonly employed during rockfall event modeling. The rockfall trajectories are simulated on a slope profile with X and Y axis in 2-D models, whereas 3-D models encompass a real space with X, Y and Z axis to calculate the rockfall paths. In this study, the rockfall potential of the southwestern part of the Kastamonu Castle, which is situated on a steep sandstone hill, was evaluated on the basis of 2-D and 3-D rockfall analyses using RocFall v.4.0 and ROTOMAP software, respectively. The close vicinity of the Kastamonu Castle, especially the southwestern region, is surrounded by residential houses and these settlements were adversely affected by disastrous rockfalls in the past. Based on 2-D and 3-D simulations, two different preliminary rockfall hazard maps were prepared and rockfall high-risk areas were defined. Both the 2-D and 3-D analyses pointed out that the southwestern part of the castle is under the great danger of rockfalls of which the weight of falling blocks may reach up to 10 tons. Finally, it is concluded that the maximum fall-out distances in 3-D analyses are more remote than those of 2-D analyses in the study area.

Landslide Investigation of a Residential Area in Göynüklü Village, Bursa (Turkey)

Landslide is a natural process of the earth’s surface, inevitably resulting from gravity with many triggering factors such as rainfalls, earthquakes, slope steepening, removal of vegetation, etc. The most frequent landslide-triggering mechanism is water from intense rainfall or human-based sources. The wide ranges of landslides and the complexity and variability of their interactions with the environment are the key points of a landslide investigation. The rate of the movement is the main factor of high property damages. On 16th of March in 2006, a rapid landslide occurred in Goynuklu village in Bursa, Turkey. The properties were inevitably damaged after the failure. The triggering factors of the failure mechanism and the properties of the landslide were investigated to specify proper remedial measures at the site. The geotechnical investigations including surface and subsurface studies were performed to determine the extent of the landslide and its sliding surface accurately. Within the framework of the geotechnical investigations, the inclinometer measurements were also recorded after drilling boreholes. Besides, a number of trial pits were excavated for evaluating the shallow sliding surfaces. Samples taken from the boreholes and trial pits were tested in the laboratory to obtain the soil class and the distribution of the grain size of the soil layers as well. The field tests including the hydraulic effect on the soil layers were also resolved by means of in situ permeability tests. Based on the data obtained, the characteristics and mechanism of the landslide were analyzed. The landslide occurred on a translational sliding surface in Neogene sediments including non-stratified sandstone-siltstone-claystone layers and a landfill site in a residential area. The shear strength characteristics of the sliding surface were calculated by back-analyses.

Dynamic soil characterization and site response estimation for Erbaa, Tokat (Turkey)

Site amplification is one of the most important factors controlling damage in urban areas through strong earthquakes. Local site effects play an important role in earthquake-resistant design and should be considered for site response analyses. In this study, ground response analyses in Erbaa, Turkey, a settlement in the North Anatolian Fault Zone, using one-dimensional equivalent linear analysis and empirical approaches based on shear wave velocity profiles are evaluated and compared. The ground response analyses were performed with consideration of shear wave velocity, and modulus reduction and damping behavior for different confining pressure and plasticity index-dependent models. The results of ground response analyses and amplification values from empirical equations using shear wave velocity are illustrated in terms of amplification and predominant period maps of the seismically active Erbaa settlement area. The comparison has been made in these produced maps of the study area in order to evaluate different site response analyses.