It is perfectly possible that Iran has used “tricks” such as conjoining explosions of several bombs of various powers in a short interval to create a fake earthquake lookalike. Putting a test in a earthquake prone area (end of the fault zone of the Zagros) is a way.
Could the Iranians have used the war in Iraq and the extension of their presence to build a tunnel on the other side of the border, where no one would have monitored ? Solely 2 km deep, only one Sn wave, the rest is only P waves. This is highly caracteristical of a nuclear test.
Another quake a few days later shows many S and Sn, more likely a natural one.
See also article on the other earthquake in the East, near Kerman, an obvious case due to close concentration of the quakes.
Iran has had fissile material at its hands for very long (the Toofan antitank missile since 2000, see depleteduranium.org on fission in armor piercing). Its thorium-rich underground would lead to U233 production in a nuclear reactor.