A surface explosion generates both ground shock and airblast pressure on nearby structures. Although ground shock usually arrives at a structure foundation earlier than airblast pressure because of the different wave propagation velocities in geomaterials and in the air, ground shock and airblast might act on the structure simultaneously, depending on the distance between the explosion center and the structure. Even though they do not act simultaneously, ground shock will excite the structure and the structure will not respond to airblast pressure with zero initial condition. Therefore, an accurate analysis of structure response and damage to a nearby surface explosion should take both ground shock and airblast pressure into consideration. But current practice usually considers only airblast pressure. Many empirical relations are available to predict airblast pressure. Most of them, however, only predict peak pressure values. The primary objective of this study is to define simultaneous ground shock and airblast forces that can be easily applied in structural response analysis. Parametric numerical simulations of surface explosions are conducted. Empirical expressions of airblast pressure time history as a function of surface explosion charge weight, distance to structure, structure height, as well as the ground shock time history spectral density function, envelope function and duration are derived. Time lag between airblast pressure and ground shock to structure is also determined. The empirical formulae are all given in analytical forms and they can be used in structural response analysis to surface explosions. (C) 2004 Elsevier Ltd. All rights reserved.