Geodynamics Research International Bulletin (GRIB), Vol. (I) - No. 02- (Special Issue on Intra- Plate Earthquakes) Feb.2014 All rights reserved for GRIB 42 Geodynamics Research International Bulletin (GRIB), Vol. (I) - No. 02- (Special Issue on Intra- Plate Earthquakes) Feb.2014 All rights reserved for GRIB Determination of Strong Ground Motion Using Empirical Green's Function in Boroujerd- Silakhor Earthquake- March 31, 2006 Jamileh Vasheghani Farahani* 1 , Mehdi Zare 2 1 Institute of Geophysics, Tehran University, Tehran, Iran. 2 International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran. * Corresponding Author (j_farahani@ut.ac.ir) Article History: Received: Jan. 15, 2014 Reviewed: Feb. 01, 2014 Revised: Feb. 03, 2014 Accepted: Feb. 08, 2014 Published: Feb. 14, 2014 ABS TRACT Earthquakes have always been an important cause of mortalities and property damage in Iran. In regions where there are few strong motion records, the simulation of earthquake waveforms can be an important source for strong ground motions prediction. Strong motion records are vital for earthquake engineering purposes and developing spectra for earthquake resistant designs. The simulated motions might be applied in the design of spectral development. One of the major methods in the strong motion simulation is the application of empirical Green’s function. In this method, aftershocks are considered as Green`s functions and the target event or main-shock is calculated by dividing the fault into smaller parts as subfaults ( each of which is a point source) and by using the summation principle and time delay in the wave distribution of each subfault. Empirical Green`s function method was first used by Hartzel, 1978. The present research is concentrated on the simulation of strong motions for Silakhor earthquake- M arch, 31 2006, with M w = 6.0. The simulation of strong motions based on the aftershocks of Silakhor event, shows proper consistency between the simulated and the recorded main-shock which is due to the maximal motion and the spectral ordinates. Keywords: Strong Ground Motion; Empirical Green’s Function Method; Aftershocks, Silakhor. 1. INTRODUCTION Recognizing the power of the earthquakes and how they affect the structures have always been great questions to designers to whom the building codes offer some answers. The simplest way to estimate earthquake loads is to use equivalent static method; however, despite the popularity and common use of this method, it cannot precisely clarify the structures’ behavior during an earthquake. In order to understand the reaction of the structures in each time step during the earthquake, accelerograph (velocity or displacement) time history should be used as the input load. Since high qualified strong motion records are not still available for all regions, finding an effective solution to supply the request is necessary. Empirical Green’s function (E.G.F) is an effective method in simulating strong ground motions. The first successful attempt for theoretical calculation of strong motions was presented by Aki (1963) and Haskels (1969), using kinematics source model, given by propagating the dislocation over a fault plane in an infinite homogeneous medium. Another approach to synthesize strong motions was proposed by Hartzel (1978), utilizing observed seismograms from small events as Green’s functions. Later methods proposed by Hadley and Helmberer (1980) and Irikura and Muramato (1982) in Japan, attempted to synthesize the main-shock motions using small shocks (foreshocks and aftershocks). This paper will represent the application of Empirical Green's function method for simulating the strong motions recorded in Boroujerd- Silakhor earthquake in Iran- using the recorded aftershocks. It is then intended to generate the synthetic ground motions for Lorestan region based on E.G.F. method. The accelerometric data, used in this study, are recorded in Iranian National Strong Motion Network. This network has recorded Iran’s earthquakes since 1974which have been maintained by the Building and Housing Research Center. First, the methodology of E.G.F, used in this research is explained, and then the greatest strong motion or mainshock in Boroujerd- Silakhor Vol. (I) - No. 02- (Special Issue on Intra- Plate Earthquakes) Feb.2014 5 th Article- P. 42 to 49 Available online at: www.geo-dynamica.com GRIB Geodynamics Research International Bulletin ISSN 2345 - 4997