Viharas were for the purpose of living, Chaityas were assemblies for the purpose of discussions. Further, Chaityas were with Stupas, Viharas did not have stupas.
According to B. B. Lal, former DG of ASI, Kalibangan site shows that an earthquake occured around 2600 BC, which brought to an end the Early Indus settlement at the site. It is perhaps the earliest archaeologically recorded earthquake.
EXAMIANS