ATHENS, Greece (AP) — Schools on four Greek islands will remain closed through next week as earthquakes continue to rattle the region, authorities said Saturday.

More than 800 tremors of magnitude 3 and over have been recorded on the tourist islands of Santorini, Amorgos, Anafi and Ios since Feb. 1, triggering an exodus of most of Santorini’s 16,000 residents as well as visitors.

Even though the earthquake activity has somewhat abated, 11 tremors of at least magnitude 4 hit on Saturday, according to the Athens Institute of Geodynamics. The strongest was 4.9 at 11 a.m. There were no reports of major damage or casualties since the quakes started.

Experts say they cannot exclude stronger quakes.

Authorities in Athens said that schools in the four islands will remain closed until Feb. 14.

Greece’s strongest earthquake of the 20th century, a magnitude 7.7., struck near Amorgos in July 1956, killing 53.

Experts said the latest tremors have nothing to do with Santorini’s volcano, which around 1600 B.C. produced one of the most violent eruptions in human history. A second volcano nearby erupted about 375 years ago.