Probability of Peak Ground Horizontal and Peak Ground Vertical Accelerations at Tehran and Surrounding Areas

The active faults near Tehran are capable of producing Mw magnitudes of 6.62–7.23; at epicentral distances of 25 km from the active faults, and Mw = 7.23, the peak ground horizontal acceleration, PGH, is between 386 and 730 cm/s2 and peak ground vertical acceleration, PGV, is between 192 and 261 cm/s2; the historic earthquake of the fourth century BC, Mw = 7.16 produced the highest estimated PGH acceleration in Tehran, between 254 and 479 cm/s2 and PGV acceleration between 127 and 173 cm/s2. Earthquakes from 1909 to 2008, within 300 km from Tehran, are used for calculation of magnitude frequency relation, and results are applied to estimate PGH and PGV accelerations as a function of magnitudes for a set of fixed epicentral distance and site conditions; also as a function of epicentral distances for a set of fixed magnitudes and site conditions. Poisson’s distribution is used for probability calculation of PGH and PGV accelerations for several exposure times, site conditions and epicentral distances; accelerations with very high probability, near 1, are presented. At an epicentral distance of 10 km and exposure time of 450 years, in the northern part of Tehran, close to Mosha and the Northern Tehran faults, PGH acceleration is 800–420 cm/s2 and PGV is 400–220 cm/s2 with high probability. At an epicentral distance of 25 km and 1,000 years exposure time, PGH is 610–320 cm/s2 and PGV is 310–160 cm/s2 with high probability, where larger values are for soft soil and smaller values are for hard rock.