zenith and azimuth angle dependence of extensive air shower thickness

The arrival time distribution of simulated extensive air shower particles, for 10^14-10^16 ev showers initiated by protons, for the observation level of the alborz-i array in tehran, has been investigated. we report the results of our analysis on the arrival time spread of simulated shower particles in several regions in the shower front, which are suitably chosen to demonstrate the variation of shower thickness with the core distance, and azimuth angle, for slanted showers of different zenith angles. using the standard deviation of the time distribution as an indicator of the shower thickness, and defining appropriate observation zones on the ground, we found an asymmetry in the shower thickness of slanted showers. it seems that the early parts in the shower front are thicker than the late parts. a misinterpretation of the thickness of slanted shower fronts in an other research has been corrected. implications for improvement of accuracy in the shower axis direction estimation has been discussed.