Tsunami concerns I guess. Kamakura was indeed hit by a major tsunami a few centuries ago (10+ meters).
There is a real concern in the population, including some friends living there. Since the authorities were once more a bit too passive citizen groups have started to plan themselves escape routes up the surrounding hills recently. In terms of location the magnitude 7.0 quake that hit on Jan 1st could have triggered a tsunami in the Kamakura/Izu area. Fortunately it was extremely deep (370 km) and only gave a good wake up shake to the whole Tokyo area.
This did not prevent tens of surfers from hitting the waves on Tuesday though. :-)