Until some of the lunacy about hydraulic fracturing is laid to rest, it isn't going anywhere unless there is a reservoir associated with it that can be tapped.
We have had well over 10,000 horizontal wells fracced here in ND, and our biggest earthquake (1968, 4.4 magnitude, epicenter at Huff, ND) came long before horizontal drilling started here.
That said, it depends on the geology of the area, formation depth, and any nearby faults, although the problems with the latter usually are a result of fluid injection by disposal wells, not fracs on a producer.
In some areas (OH, and OK, to name a couple), disposal wells (not always oilfield related) have been believed to lubricate existing faults (known and unknown) and stimulate seismic activity.
We have a slew of disposal wells here, too, for disposal of the salt water that almost always accompanies the production of oil and gas, but have had no seismic events associated with or attributed to the disposal wells.