"A remarkable increase in the rate of [magnitude-3.0] and greater earthquakes is currently in progress," the scientists state in the abstract for their study. "A naturally-occurring rate change of this magnitude is unprecedented outside of volcanic settings or in the absence of a main shock."
The surge in temblors is "almost certainly man-made," they found, and all of the potential causes they explore in the paper relate to drilling, or more specifically, deep underground injection of drilling waste.
Casting the quakes as a trend could make it more difficult for oil and gas companies and state regulators to discount the earthquakes related to drilling as rare, isolated events. That, in turn, could provide new ammunition to critics who want stronger regulations, or even a ban on drilling.
The group of scientists, led by geophysicist William Ellsworth, is to present the paper next month at the annual meeting of the Seismological Society of America in San Diego. The abstract for their study has already been posted.