عنوان مقاله [English]
The current paper deals with a new use of fuzzy logic in the domain of seismic zonation methodologies with a case study in Meybod, Iran. Determining the risk function of an earthquake is an important issue and for the complete solution, the seismic specialist shall necessarily find the soil response and present an appropriate zonation output to the civil engineer. For tackling this problem, a fuzzy clustering method has been useful in acquiring microtremor data more specifically in the city of Meybod. We use microtremors resulting from weak ground motions as the available and valuable output. Dataset is divided into a few subsets based on its intrinsic complexity by GK fuzzy clustering. Features in this classification practice are including the coordinates, the output dominant frequency of H/V method and the respected amplitudes. Euclidian distance matrix norm is constructed to detect hyper ellipsoidal clusters with different orientations (shape and size) in the dataset. The cluster means are then refreshed in an iterative manner so as to identify the uniform seismic answer into the isolated gatherings. An examination between the output of this methodology and those got from boreholes shows the relatively high relationship and it could be applied effectively for further near-surface geophysical applications.
The analysis of regional seismic hazard through the finding of zones with seismically similar behavior is named seismic microzonation. It categorizes and symbolizes stable zones that are prone to local amplification of seismic motion as well as zones prone to seismic hazards. Seismic microzonation represents an extremely valuable tool for seismic prevention and risk assessment in the land management studies, for the design of buildings or constructions and for emergency preparation and seismic strengthening plans. It provides a knowledge-based on local seismic hazards in different zones and permits the establishment of hazard hierarchies that may be used to plan seismic risk mitigation measures at various scales.
Central Asia is an area with a high probability of great earthquakes, mostly due to the Asia-India crash where the northward-moving Indian plate collides the Eurasian plate (see e.g., Molnar and Tapponnier, 1975). High seismic activity in this packed and fixed area was carried out for quantifying the level of seismic hazard. In 1969, Seed and Idriss carried out a study of the ground motion records of 1957, the San-Francisco earthquake. Their results obviously confirmed in the same urban area and only at a distance of a few hundred meters apart, different types of ground motions were recorded. This may mostly depend on the thickness and features of shallower and softer soil layers (Bramerini et al., 2015). Since now, many earthquakes (e.g. Mexico City, 1986; Kobe, 1992; Izmit, 1999) have verified that local ground specifications may meaningfully control the seismic response on the surface.