Downtown buildings were rocked yesterday by a special effects explosion touched off by the movie crew of Columbia Pictures’ “The Last Action Hero,” but the blast went off as planned and there were no injuries.“It was nothing out the ordinary,” said Greg Acevedo, spokesman for the Fire Department. “It was a special effects explosion, that’s it. There were no injuries. We didn’t send any equipment.” The blast was triggered by the crew for the film, which stars Arnold Schwarzenegger. The actor wasn’t on the location site at the time. The explosion at Temple Street and Beaudry Avenue, just west of the Civic Center, leveled a home built by the movie company and it was felt up to a mile away. “We definitely felt it and heard it — it shook the whole building,” said David Clark, whose money management office is eight blocks away. “It felt a little bit like an earthquake.” Several windows in neighboring homes were broken by the blast, and Columbia said it would repair them.