A Colorado State researcher is studying Earth’s ancient earthquakes, or fossil earthquakes, to get a better understanding of how and why earthquakes happen.
Geologist Jerry Magloughlin is studying the rocks that form where earthquakes actually happen. By studying these unique fossil earthquakes, scientists can learn about how and why faults slip and produce earthquakes.
These fossils are the only well-accepted evidence proving that an area was affected by ancient earthquakes. Magloughlin unearthed some of these rocks in Northern Colorado’s Poudre Canyon.
“The rocks I found in northern Colorado are relatively small, humble examples of fossil earthquakes, but it’s still remarkable that these delicate rocks can be preserved for hundreds of millions of years,” Magloughlin said. “Much more interesting examples of the rock are either extremely thin or extremely thick. I’ve found microscopic ones from Ontario, possibly associated with very tiny ‘nanoquakes,’ and a 5-meter-thick rock from Scotland that must have formed about a billion years ago in a giant earthquake, or ‘megaquake.'”
When faults, or rock fractures, cut through Earth’s crust, various types of damage occur within the rock. The severity of damage depends in part on how quickly the two sides of the fault slide past each other. In some cases, this can be a very slow process resulting in so-called silent earthquakes that often go unnoticed. In other cases, the fault can slip several feet or more in a matter of seconds, producing the kinds of earthquakes capable of causing serious destruction.
In addition to studying how quickly slip occurs, the depth of the rock where the slip occurs also is studied. If the fault slips near Earth’s surface, rock can be crushed and made into a mud-like substance called fault gouge. During an earthquake – under certain conditions – the walls of the fault slip fast enough to produce frictional heat that melts the rock. The melted rock, reaching temperatures of more than 1,800 degrees Fahrenheit, solidifies into a new, distinctive rock creating a kind of fossil earthquake.
Due to the unique nature of these rocks and their ability to preserve the moment in time when earthquakes happen, scientists can better understand the mechanics of how faults operate and earthquakes occur.