Eerie Rock Towers Act As Earthquake Sensors

Eerie rock formations in California’s desert acted as earthquake sensors, according to a new study.

There are tall, rusty spires of rock called hoodoos about 120 miles north of Los Angeles in Red Rock Canyon. The tall, thin structures are made from sedimentary rock.

Harder layers work to protect the softer layers below. Over time, erosion has worn away the less-resistant rock, reports Live Science. The spires are all that is left.

One of California’s largest fault lines, the Garlock Fault, is just three miles north of the canyon’s fragile rock formations. Roughly 500 years ago, an estimated 7.5 magnitude earthquake struck the fault line closest to the canyon.

The study suggests that the hoodoos are proof that the earthquake did not shake the canyon much, despite being an estimated 7.5 magnitude. Abdolrasol Anooshehpoor, a geophysicist with the US Nuclear Regulatory Commission, stated:

“The fact that they didn’t break indicates the ground motion was lower than you might expect.”

Yahoo! News notes that the only caveat is that the researchers assumed in the study that the hoodoos looked the same 500 years ago as they do today. Anooshehpoor stated:

“This is a big uncertainty. Basically, we assume in the past 500 years, in time since this earthquake happened, the shape has not changed much.”

During the study, Anooshehpoor and his team studied two of the most fragile-looking hoodoos. They scanned their shapes and brought a sample back to the lab. Through computer modeling, the scientists were able to discover what amount of shaking was needed to break the fragile rock formations.

The upper limit on the shaking needed to crush the rocks matches the 2008 US Geological Survey’s seismic hazard maps for the region. Geologist David Haddad, who wasn’t involved in the study, stated, “I think they did a good study. They’re basically validating the 2008 seismic hazard map for California.”

[Image via I, Jonathan Zander [GFDL, CC-BY-SA-3.0 or CC-BY-SA-2.5], via Wikimedia Commons]