I seriously recommend that all mobile homes be properly anchored down. Always check with your local planning zoning or regulatory authorities for your specific location to get the proper guidelines pertaining to your homes geographic location.
Here is a handy chart to give you some guidelines. The diagram is for double wide mobile homes, however single wide mobile homes are very similar.
Anchor and Tie Down Diagram Recommendations Chart
Having your mobile properly anchored and tied down can mean a difference of serious injury or death in the event of severe weather. It does not take as much wind to move or rollover manufactured mobile homes as you might think.
There are also earthquake vibration shock absorbers for mobile homes available for areas that experience such phenomenons. I believe that some municipalities now require them.