MEDFORD, Okla., Oct. 10 (UPI) -- Residents of northern Oklahoma and southern Kansas woke to rumbles early Saturday morning, the reverberations of a slipping fault.
The earthquake, which struck at 4:20 a.m. local time, registered 4.4 on the Richter Scale. Its epicenter was located 11 miles from Medford, Okla., a small town not far from the Kansas border.
The quake could be felt as far south as Stillwater, Okla., and as far north as Wichita, Kan. Vibrations emanated from faulting in bedrock four miles beneath the surface.
No cause has been officially determined, but it is possible the quake was encouraged by human activity. Research suggests the frequency of small to medium quakes throughout the Midwest and Plains States has risen along with the growing presence of hydraulic fracturing, or fracking, operations.
Oklahoma has experience nearly 3,000 small earthquakes since 2008.
"There is evidence that some central and eastern North America earthquakes have been triggered or caused by human activities that have altered the stress conditions in earth's crust sufficiently to induce faulting," officials at the U.S. Geological Survey wrote.
In addition to fracking, dam construction, mining and quarrying operations can also induce faulting deep in the Earth.
SANTA CLARA, Calif., Oct. 10 (UPI) -- A northbound Caltrain was stopped in Santa Clara, Calif., Saturday morning when it struck and killed a woman who authorities say intentionally walked onto the tracks.
Caltrain officials tweeted "Caltrain #NB423 is stopped due to an emergency incident at the Santa Clara Station" at 8:19 a.m. The station is located at 1001 Railroad Ave.
In response to Twitter users asking for more details, Caltrain officials said an adult woman intentionally placed herself in the path of the train. Officials noted it takes a train one-half to one mile to stop and. Caltrain said the incident is tragic for the relatives of the woman as well as for the toll it is taking on Caltrain employees and customers.
First responders confirmed the emergency situation and helped move 125 passengers from the train onto northbound train 425.
Caltrain officials later tweeted "There are three tracks through the Santa Clara Station. Two have been cleared for operations at restricted speeds. #NB423." The agency also said the affected train was taken out of service but that all others are "operating on time."
No additional details regarding the incident have been released. The agency said that it has worked closely with suicide prevention groups in its community over the past two years, even discussing solutions to restrict patrons' access to the tracks. It has also cooperated with the local Transit Police to minimize the number of cars that turn onto rail tracks illegally through grade separations and additional fencing.
The agency recently added more trains to its fleet in anticipation of higher patronage during the Fleet Week boat show in San Francisco this weekend.