Mohammad SASANI - PhD Student, International Institute of Earthquake Engineering and Seismology, Tehran, Iran
Mohammad Reza GHAYAMGHAMIAN - Associate Professor, International Institute of Earthquake Engineering and Seismology, Tehran, Iran
Anooshiravan ANSARI - Assistant Professor, International Institute of Earthquake Engineering and Seismology, Tehran, Iran

Tehran city, the capital of Iran, is located in the southern part of Alborz mountains in north of Iran, which is a very prone area to earthquake. The recent developments in early warning systems encourage its application for seismic hazard mitigation, especially in mega -cities like Tehran. Here, an effort was made to develop a new relation for magnitude estimation using the initial few seconds of the earthquake rupture. Among several methods applied for such purposes, the estimation of average ground motion period in a 3 sec time window from the beginning of an earthquake record (tc ) is the most applicable and reliable one.In this study, the earthquake data in Alborz region recorded by Road, Housing and Urban Development Research Center are collected from 1995 to 2013. The 218 data with magnitude larger than 4.7 are selected for tc estimation. Then, the P-wave arrival is picked visually for each record. The  c was computed for three different time windows of 2, 3 and 4 seconds after the P-wave arrival. Next, the new scaling relation between tc and magnitude (Mw) is developed. The results show that at least a 3 second time window after the P-wave arrival is needed for reliable estimation of magnitude by using tc . Furthermore, the developed relation is compared by those introduced by Wu and Kanamori (2005b), Kanamori (2005) and Heidari et al. (2013), which show a good agreement by the Wu and Kanamori’s relations. Meanwhile, it shows a clear difference with Heidari et al. relation. This could be attributed to their used data, which were limited to the low magnitude data with Mw lower than 4.6.

Earthquake Early Warning, Magnitude Estimation, Alborz Region, Dominant Ground Motion Period