ATTENUATION RELATIONSHIP FOR THE HORIZONTAL COMPONENT OF PEAK GROUND ACCELERATION (PGAH) USING GENE EXPRESSION PROGRAMMING (GEP)

Although, earthquake had been considered as an unknown phenomena several centuries ago, today, given the scientific advances made in the field of seismic geotechnical engineering and more knowledge of internal structure of the earth, it is possible to understand the various phases of earthquake and its effects on the earth movement. However, despite the achieved progress, it is impossible to prevent earthquakes or to predict the precise time of its occurrence anywhere in the world, but it is possible to prepare for it by building earthquake resistant structures. In fact, the purpose of designing earthquake resistant structures is to construct structures that can withstand seismic loads that does not undergo a lot of damage and rescue the inhabitants. In order to achieve this goal, it is necessary to predict and estimate the severity of possible earthquakes in each area in accordance with its various features which is impossible but through risk analysis. The prerequisite of risk analysis studies is to identify the parameters of powerful earth movement for different areas. The amount of earth movement is attributed to the magnitude, distance from the site to the source, the sourcemechanics, geology of the region, surface topography and dynamic properties of the material propagation (Kramer). Also, other parameters including soil nonlinear behavior, orientation, propagation failure, field effects and the impact of stress loss on earth’s movement can be even more effective than some of the above mentioned independent parameters (Somerville & Graves, 2003). To predict and estimate the parameters of the powerful earth movement, due to using above effective parameters, relations named attenuation relationships are applied. Attenuation relationships indicate the decrease of parameters of powerful earth movement by distance from the earthquake center and usually, their outputs are peak horizontal and vertical accelerations (PGA), peak ground velocity, and elastic and inelastic response spectra. Of course, in most researches and studies, attenuation relationships are used to obtain the peak ground acceleration.

Keywords:

Attenuation relationships , Genetic algorithm , Maximum horizontal acceleration , moment magnitude , hypo central distance , shear wave velocity