A long period of worldwide colder temperatures

the answer is crop rotation

true. earthquakes are felt whenever there is a slip around a fault in the rocks below the earth. this reorientation of faults create sesmic waves and is known as earthquake, the severity of which is measured in richter scale. these are more prominent in hilly regions as the rocks usually form faults to balance the pressures on it.

i think the answer to your question is: settlement of the interior and economic growth. ( ^_^)／