The isoseismal maps for 22 earthquakes in different regions of Iran were analyzed to study the ATTENUATION of seismic intensity with the distance from the epicentre under a certain surface wave magnitude (Ms). The ATTENUATION RELATIONSHIPS were derived by using an iterative least squares fit procedure. These equations were derived from more basic concepts assuming that the intensity is proportional to the logarithm of seismic energy density at any location empirically. The isoseismal maps are elongated in the direction of local structural trend of causative faults. Therefore, ATTENUATION RELATIONSHIPS for the main direction of fault, transverse to it and average ATTENUATION were derived. Ia = 11. 564 + 0. 943 M − 2. 508 Ln(Ra + 33) ,  ,  ,  ,  ,σ = 0. 79 ,  ,  ,  ,  ,  ,Ra <, 200 km along the main direction of fault Ib = 9. 469 + 0. 717 M − 2. 121 Ln(Rb +13) ,  ,  ,  ,  ,  ,σ = 0. 49 ,  ,  ,  ,  ,Rb<, 140 km transverse to the main direction of fault I =11. 926 + 0. 831 M − 2. 7 Ln(R + 22)  ,  ,  ,  ,  ,  ,  ,  ,σ = 0. 49 ,  ,  ,  ,  ,  ,  ,  ,R<, 167 km average ATTENUATION Where M is the surface wave magnitude and I is the intensity at a distance R (km) from the epicenter. The ATTENUATION of seismic intensity in Iran is faster than the East and West of China and Sicily and Calabria in Italy, apart from different tectonic characteristics of these regions.

Structural dynamic analyses need different earthquake parameters such as design base acceleration, design spectra and earthquake records. In order to obtain base acceleration and design spectra of a site, prevailing method is based on seismic hazard analyses. In this method, base acceleration and design spectra are obtained from seismicity of the region, site condition based on probable statistical methods. One of the obligations in this method is having ATTENUATION relations for different parameter such as PGA. In this research we update and make improvements of the PGA ATTENUATION relationship, presented by Ghodrati et al. (2007) for site rock and soil bed conditions of the seismo-active states of Zagroz and, Alborz and central Iran. A total of 858 strong-motion accelerograms recorded for Alborz and central Iran and Zagros are used to obtain ATTENUATION relation, which 477 records due to Alborz and central Iran. Regression analysis has been done for maximum of horizontal components and PGA ATTENUATION relation coefficients are obtained.

The main objective of this study is to present new method on the basis of genetic algorithms for ATTENUATION relationship determination of horizontal peak ground acceleration and spectral acceleration. The proposed method employs the optimization capabilities of genetic algorithm to determine the coefficients of ATTENUATION RELATIONSHIPS of peak ground and spectral accelerations. This method has been applied to 361 Iranian earthquake records with magnitudes between 4.5 and 7.4 obtained from two seismic zones, namely Zagros and Alborz-Central Iran. The obtained results indicated that the proposed method can be characterized as a powerful tool for prediction horizontal peak ground and spectral accelerations.

The earthquake is one of the natural hazards that have caused many casualties and financial losses throughout the world over the years. This has been the reason why the earthquake hazard analysis studies should be studied more seriously. Iran is also located in one of the seismically active regions of the world, the Himalayan-Alpine belt, which experiences many earthquakes every year. The Arias intensity function, as one of the important earthquake strong motion parameters, contributes greatly to the analysis of seismic hazard, which can be used to estimate the stability of slopes during the earthquake. The purpose of this research is to develop a new ATTENUATION relationship for Arias intensity function in the Iranian plateau using intelligent methods. In this research, 1012 strong motion data were used. Initially, the data required to be filtered were corrected and then all data was analyzed. In this study, parameters such as magnitude of earthquake, focal depth, shear wave velocity and geographic position of the region were used as a variable for the ATTENUATION relationship. Moment magnitude (Mw) was used as earthquake magnitude and earthquakes with magnitudes of above 4 were used in this research. The geographic location of Iran was divided into two regions of Central Alborz and the Zagros region. Gene Expression Programming (GEP), a kind of intelligent algorithm, was used as a method for regression and calculation of the objective function. The advantage of this method is that at first the model for the objective function is not specified and the model is presented optimally by the intelligent method. The fitness function is also defined based on the root least squared error (RMSE). Finally, the ATTENUATION relation based on this fitness function was calculated and the observed results have a high fitness.

According to the IAEA and USNRC (United State Nuclear Regulatory Commision) regulations, calculating a strong ground motion during an earthquake is of great importance for the design of nuclear facilities, especially nuclear power plants. In the absence of precise seismic studies and in case of severe earthquakes, many radioactive contaminants are released into the environment, with irreparable physical and financial losses, hazarding the nuclear facilities, people and the environment. In this research, in order to develop the earthquake ATTENUATION RELATIONSHIPS for Boushehr, an important region, simulation of the ground motion was used along with the stochastic finite fault method. The results obtained from the simulation have been compared with the results obtained from the valid world relations for the Zagros region. Evidently, they show good consistency. The proposed model is a theory-empirical relationship of the Bushehr susceptible region, which can be used to assess the safety of the existing nuclear power plant in Boushehr and to design new nuclear power plants in the future.

Extended AbstractIntroductionUnfortunately, seismic data recorded globally during the last fifty years does not include every type of wave propagation conditions in the environment, types of construction, the rupture process on the fault, and the geometrical relationship between the construction and the fault. This is especially seen in near-field regions. Before the 1999 Chi-chi earthquake in Taiwan and the 1999 Izmit earthquake in Turkey, there were only about 20 records of earthquakes with a magnitude greater than 7 at a distance of less than 20 kilometers from the fault.The Turkish earthquake added 5 records and the Thai earthquake added 65 records to this collection, but only two fault rupture scenarios were added to our knowledge, while thousands of other possible scenarios may occur. Thus, seismologists and earthquake engineers have tried to estimate parameters related to strong near-field motions of the earth with an acceptable confidence using various experimental and theoretical simulation methods.           MethodsIn earthquake engineering and seismology, earthquake phenomenon and the resulting movements are generally investigated and analyzed using dynamic and kinematic methods. Seismological models and problems are thus divided into two categories: Kinematic models which are based on slip distribution and do not take the state of stress on the fault into account. Dynamic models deal with the physics of fault rupture and its causes. Simulation methods are also divided into three main categories: deterministic (low frequencies), stochastic (high frequencies) and hybrid (broad band) methods.Generally speaking, simulating strong ground motion plays an important role in the estimation of related parameters especially in regions lacking such data. Accelerographs are used to simulate strong ground motions. The present study has introduced, investigated and validated two methods: decisive simulation models (Discrete-Wave Number and Finite Fault) and Finite Fault models. It also explains how the simulated recording are produced for near-field (less than 20 km to a seismogenic fault) and far-field events, presents ATTENUATION RELATIONSHIPS for the Zagros seismotectonics region, and predicts parameters of strong ground motions.Results & DiscussionDue to the special geological conditions and the existence of many active faults in Iran, our country is considered to be located in an earthquake-prone region. Zagros region is considered to be the most earthquake-prone region of Iran. Finite fault modeling combines various aspects of plate source with the ground motion model based on point source. Since previously mentioned limitations are not naturally present in finite fault modelling, the method takes geometry of the fault and the directivity effect into account. Time delay method and the sum of accelerations recorded in maps of a two-dimensional network are used for simulation in finite fault model. The fault plate is divided into various elements and a minor event is simulated for each one. The overall seismic acceleration equals the sum of the effects of these minor events. The strong ground motions in each micro-fault are calculated using the random point source method and then summed up at the desired point with an appropriate time delay to obtain the ground motion of the entire fault.Previous geological and seismic studies of each seismic region are used to determine the key parameters of the simulation input. To produce a comprehensive database, a significant number of stations are taken into account around the fault based on different hypotheses and artificial accelerograms are produced in accordance with the seismological parameters of the region. A suitable function is then selected and an ATTENUATION relationship is fitted. The simulation results and the resulting ATTENUATION relationship are then compared with valid global ATTENUATION RELATIONSHIPS and their consistency (compliance percentage) is investigated. ConclusionThe present study has produced a wide range of simulated records (about 20 thousand records) for Zagros seismotectonics region. Thus, the resulting RELATIONSHIPS will hopefully have sufficient accuracy and efficiency to be used in structure designing and urban development. It worth noting that the regression correlation coefficient (R-Square) was above 0.95 in all fits.These ATTENUATION RELATIONSHIPS can provide a new perspective on site selection, and help us in understanding the dynamic behavior of structures, and the development of various infrastructure. They also help urban managers to predict and reduce earthquake damages.

Introduction  A significance of seismic studies is that the correct seismic analysis of any type (seismic hazard analysis, seismic risk analysis, ground seismic response analysis, seismic site effects, and structural dynamic analysis) can offer useful economic parameters and avoid conservative design and implementation, which lead to an irrational increase in project costs and poor implementation, which in turn causes increased risk and possibility of destruction. According to the seismotectonic map of Iran (Berberian, 1976), earthquakes in Alborz are shallow. There are also some intermediate earthquakes, and overall, the eastern Alborz is more earthquake prone than the western Alborz [1].Materials and MethodsThe maximum magnitude (Mmax) is usually estimated based on the general characteristics of seismic activity and geological similarities. In applied studies, Mmax is often estimated based on correlation of seismic magnitude and different fault parameters such as rupture, fracture surface area, maximum surface displacement, and seismic moment release rate. Multiple correlations have been proposed to relate these parameters and the earthquakes magnitude. (Table 1) shows some correlations by different scholars. Correlations in (Table 1) were used to calculate the maximum empirical magnitude [3].Table 1. Correlations between the earthquake magnitude and different fault parametersCorrelationProposed byNo.Ms=5.4+LogLRMohajer and Nowroozi (1978)1Mw=3.66+0.91LnLRZare (1995)2Ms: Surface wave magnitude                                                          Lf: Fault length (km)Mw: Moment magnitude                                                                  LR: Rupture length (km) Seismicity Parameter EstimationThe K-S method was used to achieve seismicity parameters within the scope of this study [2].Discussion and ResultsThe results of probabilistic seismic hazard analysis were calculated using ATTENUATION RELATIONSHIPS Zare 1999 [4], Ambraseys 1995, Boore, Joyner and Fumal 1981in studying region. These results are presented in (Table 2) and (Table 3).Table 2. strong vertical ground motionReturn periodH.PGA(g)4750.2524750.44Table 3. strong Horizontal ground motionReturn periodH.PGA(g)4750.4224750.70 ConclusionThe recent Malard Earthquake with a magnitude of 5.2 on the Richter scale and multiple earthquakes with magnitudes above 4 have increased the importance of seismic studies in the region. Seismic hazard studies are among the key preliminary urban development studies for preventing seismic vulnerability. The identification of seismic source zones is closely related to development infrastructure in any region. The results of these studies are widely used in vital projects such as water, gas, oil transmission lines, dam and airport construction, and residential development, and overlooking them may cause great damages. The earthquake hazard analysis based on the accurate location of seismic zones will provide more reliable results. The investigation of the region under study, its history of seismicity, and the recent earthquakes indicate the existence of seismic activity in the region. Considering the shallow depth of earthquakes, the intensity of earthquakes occurred in the region is high. Moreover, the calculation of β and λ parameters (ranging from 6.2 to 7.6) shows the seismicity of the region, indicating the need for observing safety measures in the constructions in the region. As mentioned earlier, the recent seismic activities and earthquakes in the region have doubled the importance of seismic studies and measures for strengthening seismic stations in the region. Moreover, the review of seismic catalogs show that the study area has been inactive over the past few decades and hence its sudden activity is quite significant. Also according to the calculations, Alborz Province is located in highly active seismic zone.