The province of Khorasan, extending from 30.0N to 39.0N and from 55.0E to 62.0E, is the region with the highest seismic activity in the Iranian plateau. For use in the seismic hazard mapping of the area, we computed probabilistic ground-motion values of peak horizontal accelerations and of acceleration response spectra for periods of 0.2 and 0.3 seconds with 5% critical damping. We employed a model that allows earthquakes to occur as finite-length ruptures along faults. We assumed that earthquake occurrences have Poisson distributions and that the occurrence rate remains constant during the time period considered. We employed the attenuation relations for the ground-motion values obtained for the Khorasan region. We defined fourteen fault zones as sources of seismic energy release in the area. The occurrence rate at each source zone was estimated as a function of magnitude by employing instrumental and historical data and also available seismotectonic information. For a grid of more than 7000 sites, we have calculated the level of acceleration and acceleration response spectra that have a specified probability of exceedance during a given time period. The results are illustrated by different contour maps for several probabilities and return periods of 10, 50, 100, and 250 years. We also provided the curves which illustrate the level of the strong-motion values in terms of different return periods and variety of probabilities for thirty cities in the state.

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