Re: Why are there no earthquakes in Florida?

Dear John:

There are both faults and earthquakes in Florida. For information about the 
geologic structure and hazards of Florida, and specifically faults and 
earthquakes in Florida, you can contact the U.S. Geological Survey 
(http://www.usgs.gov) or the Florida Geological Survey (located in  
Tallahassee). Geology departments at Florida universities should each have 
at least one faculty member knowledgable about these matters. So, if the 
information I give you here is insufficient, those are very good sources 
for more details.

There is a former plate boundary in Florida, because most of the Florida 
peninsula was once part of Africa. The suture is buried quite deep, and is 
not a zone of active plate movement now, but there are many ancient faults 
associated with it. Other (newer) faults in Florida are associated with the 
thick sedimentary succession deposited on the western Florida continental 
shelf. These faults form when thick masses of sediment start to slide 
slowly downward because of their great and unevenly distributed weight. 
Earthquakes are commonly associated with movement on growth faults, as 
these are called. 

Other earthquakes may be caused by ground settling resulting from water or 
hydrocarbon extraction.

Major earthquakes are unknown in Florida, and minor earthquakes are not 
common, but they do occur. The two largest earthquakes recorded in Florida, 
according to the US Geological Survey database, occurred in 1780 and 1879. 
Both measured VI on the modified Mercalli scale (used before the invention 
of the Richter scale). The Mercalli scale is based on human reactions and 
property damage; VI corresponds to "felt by all, many frightened and run 
out of doors." So you see, these are not major earthquakes. 

Most major earthquakes are associated with tectonic plate boundaries, giant 
bolide impacts, and volcanoes. Of these three causes, only giant bolide 
impacts are possible in Florida, and these are exceedingly rare (the last 
one was in Tunguska, Siberia, in 1908). This is why there are few 
earthquakes in Florida.

David C. Kopaska-Merkel
Geological Survey of Alabama
PO Box O, 420 Hackberry Ln
Tuscaloosa AL 35486
(205) 349-2852
(205) 349-2861 FAX
Email: davidkm@ogb.gsa.tuscaloosa.al.us