A 27-year-old man has been arrested on suspicion of setting a series of fires in the past four weeks along coastal North County that sheriff’s detectives estimate have caused more than $700,000 in damage. The suspect was arrested Friday afternoon after sheriff’s deputies responded to a report of a man starting a fire near North Coast Highway 101 and La Costa Avenue, officials said. He was booked into Vista jail on suspicion of arson, vandalism and trespassing. Detectives say the suspect set eight separate fires between Sept. 21 and Oct. 11 near two construction sites located between Highway 101 and the train tracks in Encinitas and Carlsbad. The sheriff’s bomb/arson unit said the Carlsbad Police Department, California State Parks, Encinitas Fire Department, Carlsbad Fire Department and the FBI Joint Terrorism Task Force assisted in the investigation of the fires.