Petra,

I take it by "seismic waves travel in a circle" you mean snapshots of the P or S wavefront look like circles, which would be the case if there were no lateral variations in the speed of the seismic waves.

But it is sometimes the case, especially in faults that have broken recently and/or often, the zone within
tens of meters to a km from the fault is softer, which makes the waves travel more slowly. In fact, the slow waves can be trapped (critically refracted) so they stay trapped in the fault zone, and reverberate longer.

I'm not sure which feature the hot dogs refer to, but a soft fault zone may explain your description.

Doesn't sound like a good place for critical facilities if they are not built to very high standards.

John