Term for rapid economic growth when starting over or in a new place
With a bit of humor, you could use the Schumpeterian term "creative destruction" -the humor relates to the fact that Schumpeter used the term to describe an inherent structural feature of capitalism, not historical/natural accidents/disasters.

Apart from that tongue-in-cheek proposal, I am not aware of a compact term to express what you describe. A common way could be a "vintage theory of capital" approach, where it is recognized that "old and new" capital coexists with different levels of technology embodied in it, and so in a sense "averaging" the actual technological/efficiency level used in the economy. Then what you describe amounts to an abrupt loss of "old" capital which may lower the output level but creates a positive discontinuity in the actual average technology level used in the economy, creating abrupt and higer growth rates. 

You can broaden the concept of capital to also include "human capital" and maybe also "institutional capital" (and so "technology" will then refer also to "knowhow/experience" and "transactional technology" as well).