عنوان مقاله [English]
As is well known, strong earthquake motions are affected by many factors such as source mechanism, wave propagation path, site location conditions and so on. The importance of maximum frequency and frequency content has been recognized. Various indices, for example, peak ground acceleration and peak ground velocity are strongly influenced by local site conditions.
In this study, the relationship between different definitions of duration with Peak Ground Acceleration (PGA), focal depth and soil conditions of the site using accelerometer records in Iran was calculated and presented. The number of 1054 three-component records of 197 seismic events recorded with a moment magnitude greater than or equal to 5.0 were used. The results show that with increasing PGA, bracketed and uniform durations increase, while for significant durations, records with high durability generally have had little PGA. Mathematical relationships have also been shown for variations of any durations with PGA and focal depth and soil type variations. The relationship between the durability and the maximum amplitude of strong earthquake motions is important for the seismic design of structures, especially reinforced concrete structures, which suffer from stiffness degradation and strength loss in successive earthquake cycles.
The results of the analysis are as follows:
With increasing peak acceleration (PGA), bracketed and uniform durations increase, while this relationship is not as effective. In terms of major effective durations, records of effective durability (5-95) had a high (above 20 sec) peak acceleration (PGA) of less than 0.1g.
Also, the softer the soil, the slope of the bracketed and uniform durability relationship with PGA increases.
As the focal depth increases, the durability of different definitions decreases. Especially after a focal depth of 20 km, the interval with a threshold of g0.05 is generally less than 10 seconds.
The relationship between shear wave velocity at 30 m depth and effective durability indicates that with increasing shear wave velocity, effective durability decreases.