Today a few hours ago we have an earthquake ın İstanbul of magnitude 5,9 in richter scale. I searched information about the tunnel safety in the area and found some article.

Marmaray tunnel (Marmaray tüneli) connecting the continents of Europe and Asia under İstanbul's Boğaziçi (Bosphorus) strait. How safe is it in an eartquake?

The Marmaray tunnel of İstanbul is 20 kilometers away from the North Anatolian Fault Line extending from the east to the southwest of the Islands in the Marmara Sea. Therefore, the tunnel ıs very much in an earthquake zone.

In theory the Marmaray tunnel can withstand an earthquake of 9 in richter scale. But let us hope it does not come. Marmaray is part bored, part sunken tunnel build a few years ago (8-10?).

Here is an article

https://raillynews.com/2019/09/is-marmaray-earthquake-resistant/