Trying to better understand how earthquakes are born, scientists showed off the first rock samples taken from a borehole being drilled into the mighty San Andreas Fault in California.
The borehole is a step toward creating the world's first underground earthquake observatory designed to study temblors up close.
Researchers hope the rock core collection, weighing about a ton (1 metric ton) in total, will help answer questions about the fault's makeup and determine what happens during stress buildup at great depths.
"These are kind of like moon rocks for people studying earthquake mechanics," said Stephen Hickman of the U.S. Geological Survey.
But as excited as scientists worldwide are about the rock cores, the cores likely will not help in earthquake prediction. That goal is still out of reach, despite a century of research into earthquake physics.
The cores were pulled earlier this month from two miles (3 kilometers) beneath a seismically active section of the fault halfway between San Francisco and Los Angeles.
Since 2004, a team of geophysicists and seismologists has been drilling atop a creeping segment of the 800-mile (1,287-kilometer) San Andreas Fault. Creeping occurs when two sides of the fault gently slide past each other, triggering small temblors.
Last summer, scientists penetrated an active section of the fault for the first time and began the arduous process of extracting rock samples to the surface.
Scientists next year plan to rig the borehole with sensors to try to catch an earthquake in the making. When completed, it will be the world's first underground earthquake observatory designed to study temblors up close.
The $25 million (17.7 million EUR) project is funded by the National Science Foundation, U.S. Geological Survey and Stanford University.