Time-frequency analysis of the 2017 Sarpol-e Zahab earthquake ground motions

A severe earthquake ground motion with moment magnitude Mw=7.3 took place in the western part of Iran on 12th November 2017. The aim of this proposed study is to assess the time evolution of the frequency-intensity content of Sarpol-e Zahab earthquake ground motions records by using of the Wavelet Transform (WT) methodology. For this purpose, the ground motions recorded at Sarpol-e-Zahab, Kerend and javanrod stations that has maximum PGA has been selected. Time–frequency analysis of ground-motions recorded at the Sarpol-e Zahab station shows that the most energy content of the T component is concentrated at time equal to 21 s but is distributed over a range of periods between (0.2 -0.5sec) with a lesser peak in energy at a period of about 0.6 sec, that there may be effect of moving resonance on building with periods between (0.2-0.5 sec). Also, it can be observed that most energy of the L component was highly concentrated at time equal to 21 s and a narrow period band (between 0.2 and 0.3 sec) that is considered as pulse like. This finding is consistent with damage observation in Sarpol-e-Zahab and it’s around villages where many dwellings and buildings which collapsed or suffered severe damage during this event had low fundamental period between (0.2-0.5sec).

Keywords:

Time evolution , wavelet transform , energy ground motion , low fundamental period