In this study, we used fifty-six synthetic aperture radar (SAR) images acquired from the Sentinel-1 C-band satellite with a regular period of 12 days (except for one image) to produce sequential phase correlation (sequential coherence) maps for the town of Sarpole-Zahab in western Iran, which experienced a magnitude 7.3 earthquake on 12 November 2017. The preseismic condition of the buildings in the town was assessed based on a long sequential SAR coherence (LSSC) method, in which we considered 55 of the 56 images to produce a coherence decay model with climatic and temporal parameters. The coseismic condition of the buildings was assessed with 3 later images and normalized RGB visualization using the short sequential SAR coherence (SSSC) method. Discriminant analysis between the completely collapsed and uncollapsed buildings was also performed for approximately 700 randomly selected buildings (for each category) by considering the heights of the buildings and the SSSC results. Finally, the area and volume of debris were calculated based on a fusion of a discriminant map and a 3D vector map of the town.
Seismic intensity in the epicentral area of the 2003 Bam, Iran earthquake is estimated using a questionnaire survey conducted two months after the earthquake. The estimated average seismic intensity on the Japan Meteorological Agency (JMA) scale is 6.1 (VIII to IX in the MMI scale). The peak frequency of the horizontal-to-vertical spectral ratio derived from microtremor measurements conducted during reconnaissance is also compared with the seismic intensity. Collapse rates for various structure types, such as adobe, unreinforced/reinforced masonry, steel-frame, and reinforced concrete, are obtained by counting the number of demolished buildings within an area of about 50-m radius around an observation point. Results show large differences in collapse rates between unreinforced and reinforced masonry, and suggest the upper limit of seismic intensity that unreinforced masonry can sustain. This fact can be utilized for an initial damage assessment within affected areas after large earthquakes.
The goal of this study is to estimate source and path attenuation parameters of recorded earthquakes in Tehran province, Iran so they can be used for strong motion prediction purposes. For this, we have used four well recorded earthquakes recorded on Iran Strong Motion Network (ISMN). Assuming a simple geometric spreading of 1/r we have estimated Q factor for S-wave attenuation by characterizing spectral amplitude decay with distance at discrete frequencies. We propose the form of Q(f)=73f 0.72 for attenuation of S-wave in Tehran province. We show that the proposed attenuation quality factor is in the range of Q factors that have been proposed by the other studies. We have also estimated source parameters, such as seismic moment (M 0), corner frequency (f c) and Brune stress drop (Δσ) for each earthquake. We have fitted Brune source model to the observed spectra of motion by a grid search for least squares. Stress drop for studied earthquakes ranges between 7.7 to 37.1 MPa (77 to 371 bars).
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