15. There are no major fault lines running the central plains State of Oklahoma. Yet, according to the United States Geologic Survey (USGS), there were more earthquakes between the years of 2009–2014...

15. There are no major fault lines running the central plains State of Oklahoma. Yet, according to the United States Geologic Survey (USGS), there were more earthquakes between the years of 2009–2014 than the previous 38 years.

What statement is the best speculation on the increase of earthquakes in previously not-prone Oklahoma? 5.5

1. 
   
   
   
   1. Hydraulic fracturing in a region is correlated with a rise in seismic activity.
   
   
   2. Hydraulic fracturing is not spatial or temporally correlated to seismic activity.
   
   
   3. Seismic activity fluctuates so much that it is difficult to make any inferences or correlations.
   
   
   4. Hydraulic fracturing is certain to lead to massive earthquakes in a heavily extracted region.