We record and analyze small earthquakes around Tehran, Iran, using the permanent seismological network of the Institute of Geophysics of the University of Tehran and two temporary dense seismological networks installed for several weeks during 1999 and 2000. Regional seismicity is distributed throughout Central Alborz, extending from the Caspian Sea to the Iran Plain, with the highest level of activity east of Tehran related to the Mosha and to the Garmsar faults, which both dip northward and have had strong historical earthquakes. Our focal mechanisms, the first for these faults, confirm a left lateral strike slip motion.