An Empirical Model for Significant Duration of the Ground Motions Containing Velocity Pulses

• Published in: Izvestiya. Physics of the solid earth 2021-11, Vol.57 (6), p.950-964
• Main Authors: Daryoushi, Masoud, Saffari, Hamid, Mahdavian, Abbas
• Format: Article
• Language: English
• Subjects: Azimuth; Coefficients; Direction; Directivity; Distance; Distribution; Duration; Earth and Environmental Science; Earth Sciences; Earthquakes; Empirical models; Energy distribution; Geophysics/Geodesy; Ground motion; Physics; Regression coefficients; Seismic activity; Shear wave velocities; Wave energy; Wave power; Wave velocity
• ISSN: 1069-3513; 1555-6506
• DOI: 10.1134/S1069351321060148

ln this study, two relationships have been presented for predicting the significant duration values and of pulse-like ground motions induced by forward directivity. These relationships are based on such variables as moment magnitude, distance from the fault, shear wave velocity of top 30 m of soil and effect of faulting mechanism. Meanwhile the corresponding forward directivity parameters, which include the length ratio, width ratio, azimuth and zenith of angles between the ray direction and fault direction have been considered in the proposed relationships. The effective duration of these ground motions has not been under consideration, yet, and mostly the issue of pulse period has been studied. It is demonstrated that there is a linear relationship between the pulse period and the significant duration of pulse-like motions and the pulse due to the forward directivity could convey on average about 40% of the wave Arias intensity. As the result, the situation of 60% distribution of the wave energy over time remains unknown. 142 pulse-like motions from 31 recorded earthquakes that have occurred worldwide have been incorporated in this study. The regression coefficients have been determined using the mixed-effect regression method. The predicted values have been compared to the corresponding recorded values. The results indicated the appropriate performance of the proposed relationships. As is expected from the physics of the problem, by increase in the moment magnitude, reduction of the shear wave and increase of distance from the fault, the significant duration increases. The highest value of significant duration is observed in the oblique-reverse mechanism. There is no specific bias or trend in the distribution of residuals. Comparison between the significant duration of non pulse-like motions and pulse-like motions shows that the significant duration values for the pulse-like motions are much smaller than the non pulse-like motions. In addition, contrary to the non pulse-like motions, in pulse-like motions, increase of the distance has not considerable increasing effect on the significant duration.