THE U.S. GEOLOGICAL SURVEY SAYS A 5.9 MAGNITUDE EARTHQUAKE CENTERED NORTHWEST OF RICHMOND, VA., SHOOK MUCH OF WASHINGTON, D.C.  THE SHAKING WAS FELT AS FAR NORTH AS THE MARTHA'S VINEYARD, MASS., GOLF COURSE WHERE PRESIDENT BARACK OBAMA WAS JUST STARTING A ROUND.  THE GEOLOGICAL AGENCY SAYS THE EARTHQUAKE, WHICH STRUCK AT 1:51 P.M. EDST, WAS HALF A MILE DEEP AND WAS CENTERED NEAR LOUISA, VA.  PARTS OF THE PENTAGON, WHITE HOUSE AND CAPITOL WERE EVACUATED.  THERE WERE NO IMMEDIATE REPORTS OF INJURIES.  THE EAST COAST GETS EARTHQUAKES, BUT USUALLY SMALLER ONES AND IS LESS PREPARED THAN CALIFORNIA OR ALASKA FOR SHAKING.  AT REAGAN NATIONAL AIRPORT OUTSIDE WASHINGTON, CEILING TILES FELL DURING A FEW SECONDS OF SHAKING.  AUTHORITIES ANNOUNCED IT WAS AN EARTHQUAKE AND ALL FLIGHTS into and out of reAgan AND BALTIMORE BWI AIRPORT WERE PUT ON HOLD