I wonder if the explanation of the deep ditches filled with sand radiating out from the Basilican might have been for drainage rather than protection from sea earthquakes.
Makes sense if you have a building built and find it’s on a site which has serious underground water problems.
That would make sense if there were any sign (such as a contemporary document, the Turks were literate, or rather had a literate class) showing awareness of the water. It doesn’t sound like the water is much of a problem for the basilica if it antedates the Moslem takeover. There’s always the possibility that the water was deliberately introduced in order to alleviate the strain of earthquakes — trouble is, well, think of the Leaning Tower of Pisa. :’)