Strong Ground-Motion Characteristics Observed in the November 12, 2017, Mw7.3 Sarpol-e Zahab, Iran Earthquake

• Published in: Journal of earthquake engineering : JEE Vol. 26; no. 7; pp. 3488 - 3505
• Main Authors: Naserieh, Saeid, Ghofrani, Hadi, Shoja-Taheri, Jafar, Dezvareh, Mohsen, Mirzaei Alavijeh, Hossein
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 19.05.2022; Taylor & Francis Ltd
• Subjects: Arrivals; blind thrust-faulting; Building damage; Data analysis; Directivity; Earthquake accelerograms; Earthquake damage; Earthquakes; Empirical analysis; Forward rupture directivity; Ground motion; Ground stations; Modelling; Nonlinear dynamics; Rupture; Rupturing; Seismic activity; seismic quiescence; Seismology; Spatial distribution; Spectral analysis; Spectrum analysis; Stress propagation; sub-events; Thrust; Iran
• ISSN: 1363-2469; 1559-808X
• DOI: 10.1080/13632469.2020.1806950

The November 12, 2017, moment magnitude (M w ) 7.3 Sarpol-e Zahab earthquake, which occurred after a seismic quiescence, close to the Iran-Iraq border, is one of the largest events recorded in the Zagros fold and thrust belt. In this study, we analyzed strong-motion data of this event from 38 stations within an epicentral distance of 36 to 200 km. Spectral analysis of strong-motion data resulted in an M w estimate of 7.34, an average rupture velocity of 3.03 km/s, and a stress drop of 154 bars. We estimated that shear dislocation propagated over a rectangular fault area with a length of ~97 km and width of ~17 km. Comparison of the horizontal peak ground-motions from this earthquake with the ground-motion model for active crustal regions indicated overall good agreement; however, the model underestimates ground-motions at stations within distances of approximately 30 km or less. The model appears to underestimate the observed strong-motion recordings from the M w 7.4 September 16, 1978, Tabas and the M w 7.4 June 20, 1990, Manjil earthquakes as well. Investigation of the observed accelerograms showed that the Sarpol-e Zahab earthquake was nucleated by a sub-event with a local magnitude (M L ) of 4.9 which contributed about 0.02% to the total seismic moment. The empirical data indicated multiple arrivals due to the development of the rupture as two major sub-events. The spatial distribution of stations along with the time difference between the sub-events on the recorded time-series implies their occurrence from the hypocenter toward the S-SE direction which is coincident with the principal directions of the majority of damaged buildings. The estimated M w of these sub-events is 6.79 and 7.08, respectively. The distinctive characteristics of near-field recordings from Sarpol-e Zahab earthquake (e.g., multiple phase arrivals due to complex source process, forward directivity effect, and blind thrust faulting) make these data a valuable supplement to the recorded ground-motion database. The improved strong-motion database plays a fundamental role in calibrating seismological simulation models, developing ground-motion models that capture near-source effects, and performing nonlinear dynamic structural analyses.