CLEVELAND — Shock waves from an earthquake on the East Coast made the press box sway slightly and sent some fans toward the exits during the first game of a doubleheader between the Indians and Seattle Mariners.

As the Mariners were batting in the fourth inning Tuesday, the press box high above home plate and the third-base line moved left and right and continued for nearly 30 seconds. Fans sitting in the upper deck at Progressive Field noticed the unusual movement, and weren’t sure what was happening.

“It went on for at least a minute,” said Betsy Hammond, who was attending the game with her husband, Tim, and their three children. “We were looking around and someone stood up and yelled, ‘Is that an earthquake?’ Then someone who works here came over and said they heard it on the radio.”

Play was not interrupted on the field. The Indians reported no structural damage to the 43,000-seat ballpark.

The Hammonds were celebrating their son Liam’s 10-year-old birthday with his first game — one he’ll never forget.

“My first thought was, ‘That’s weird, I can’t move this seat,'” Tim Hammond said. “I thought it was the wind. I know the stadium is made to move, but I didn’t know what was moving it. I was thinking maybe they blew something up on that movie set. A lot of people got up and were like ‘We’re out of here.'”

Filming for “The Avengers” is taking place on East 9th Street near the ballpark.

The 5.8 magnitude earthquake centered northwest of Richmond, Va., shook much of Washington and was felt as far north as Rhode Island and New York City.

“The odd thing was that it went on for a long time,” Betsy Hammond said. “Then, the longer it went on, the more I wondered what was happening.”