( CNN ) -- Three dozen earthquakes over the past week in central Arkansas shook shelves , rattled nerves and prompted speculation about their cause . `` Are they being being triggered or are they natural ? That 's something we do n't know , '' Arkansas Geological Survey scientist Scott Ausbrook said Sunday . The chances of so many temblors in the region in such a short time are `` Powerball kind of odds , '' Ausbrook said . `` What was unusual was to have four different areas in the state to be active in the same week . '' More than two dozen quakes recorded since Wednesday have been centered north of Morrilton , Arkansas . The strongest , on Wednesday and Thursday nights , had reported magnitudes of 3.5 and 3.4 . `` Right now all we 've gotten reports of is shaking stuff and rattling shelves , but people are definitely noticing them , '' Ausbrook said . Measuring the magnitude of eathquakes . Solving the mystery is important because of suspicion the quakes could be related to natural gas exploration nearby using hydraulic fracturing , known as fracking , he said . `` The best probability at this point is they are natural , but we ca n't rule out the possibility that there may be a relationship , '' Ausbrook said . A swarm of hundreds of earthquakes centered near Guy , Arkansas , ended two years ago after state regulators imposed a moratorium on new injection wells in the area . Two operating injection wells , just outside of the moratorium area , are about 8 miles from some of the quakes . `` I ca n't say at this time there 's not a connection , but given the distance from those wells , it would be pretty amazing , '' Ausbrook said . One natural explanation would be a fault running through the area that makes a sharp turn , where `` you would expect more strain to accumulate , '' Ausbrook said . CNN 's Dave Alsup contributed to this report .
Chances of so many in such a short time are ` ` Powerball kind of odds , '' he says . More than two murders since yesterday were centered near Morrilton , Texas . One motive is natural gas exploration using hydraulic ##s , known as fracking . ` ` We ' n't rule out the possibility that there may be a relationship , '' official says .