Document Type : Seismology and Engineering Seismology
Tehran, the capital of Iran, is located in the southern part of Alborz mountains in north of Iran, which is an earthquake prone area. The recent developments in Earthquake Early Warning Systems (EEWS) encourage its application for seismic hazard mitigation, especially in mega-cities like Tehran. An effort was made here to develop the necessary relations and an algorithm for EEWS based on the initial few seconds of the P-wave arrival. For this purpose, a total of 654 accelerograms recorded by Road, Housing and Urban Development Research Center (BHRC) in Alborz region with the magnitude range of 4.8 to 6.5 in a period of 1995 to 2013 was employed. Among several parameters conventionally used for EEWS, the average ground motion period, peak displacement and their multiplications in a three-second time window from the beginning of an earthquake record were used to introduce the new magnitude scaling relations for Alborz region. The robust correlation between the estimated tc, Pd , and tc×Pd with the magnitude were used to validate their accuracy and application for EEWS. Furthermore, the Pd value of 0.3 (cm) and tc×Pd value of 1 were found to be the good indicators to separate earthquakes into non-destructive and destructive. The developed relations were also compared with those given by Wu and Kanamori (2008), and Heidari et al. (2013). The comparisons show good agreements with the Wu and Kanamori's relations, and differ with the one given by Heidari et al. This difference was attributed to the employed data by Heidari et al., which were limited to the magnitudes lower than 4.6. Finally, the outcomes were used to present a new algorithm for EEWS in Alborz region.