Evaluation of the effect of alluvial and ground classification in Mashhad City, according to spectra ratio of microtermor waves method

In this paper، the results of evaluation of earthquakes site effect using the microtremor measurement، which have been obtained from 200 points in Mashhad city، are presented. Also by combination of the iso-resonance period and soil texture map، the ground classifieation map has produced according to the Iranian code of practice for seismic resistant design of buildings (2800 standard). This map shows that the resonance period of ground increase from south and west toward the center and east of city. But it decreases toward the north near Mashhad north fault in Khajeh Rabi area. Based on the Iranian 2800 standard، the south and south western parts of Mashhad city are classified in IB and IIB، while the central classified in IIIB، north part classified in IIB and limited area in east and north- east have a IV classes.