Broken bottles are seen on the floor after falling off the shelves at a CVS pharmacy, following a magnitude 5.1 earthquake in Fullerton, California March 29, 2014. (Reuters / Gene Blevins)

Broken bottles are seen on the floor after falling off the shelves at a CVS pharmacy, following a magnitude 5.1 earthquake in Fullerton, California March 29, 2014. (Reuters / Gene Blevins)

Experts now fear that the 5.1 magnitude earthquake that rocked Southern California on Friday evening could be a mere sampling of what’s to come if more seismic activity occurs along the Puente Hills thrust fault.

That break in the Earth’s crust is far less renowned that the more famous San Andreas fault that has been a major cause of concern for residents of the Los Angeles area for ages. Activity along the Puente Hills thrust is now being blamed for last week’s quake, however, and in turn has rekindled discussion about the potential catastrophes that could occur if a larger tremor takes LA by surprise once again.

Although the Puente Hills thrust is far less famous than the San Andreas fault, experts say another serious tremor there could cause grave consequences for Southern California.

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Friday evening’s incident was reportedly centered near the city of La Habra, around 20 miles southeast of downtown LA, and spawned upwards of 100 aftershocks throughout the region. The Puente Hills fault extends through a critical part of Southern California, though, and could have caused exponentially more damage if it was stronger and its epicenter was elsewhere.

This fault actually produces a worse earthquake than the San Andreas can,” United States Geological Survey Seismologist Lucy Jones told the Los Angeles Times. “It won’t be quite as big magnitude, but because we have so many people on top of it…it will be worse.”

Seismologists say the Puente Hills thrust fault stretches across northern Orange County into downtown Los Angeles all the way into Hollywood, and has the potential to affect a number of older, more vulnerable buildings that aren’t expected to withstand a serious quake.

According to the USGS, a hypothetical magnitude-7.5 quake along that same fault could potentially kill 3,000 to 18,000 people and cause up to $250 billion in damage — roughly double the death toll that experts would expect from a similar sized tremor along the San Andreas fault.

Such a quake, Jones told the Times, would “hit all of downtown” and “everywhere from La Habra to Hollywood.”

Friday’s event, Jones said, occurred when the Puente Hills fault slipped for only half a second, causing around 10 full seconds of shaking on the surface. Had the quake been stronger — say, magnitude 7.5 — then Jones said the fault could have slipped for upwards of 20 full seconds.

Serious disturbances along the lesser-known fault are expected only once every 2,500 years, according to the Times’ report, but scientists aren’t too sure when the last major one occurred.

We can’t predict earthquakes,” Southern California Earthquake Center director Thomas Jordan told KCAL9, “but you know, I’d say we’re a little bit nervous.”

It would be very damaging to central Los Angeles,” Jones added to the local news network, “An earthquake engineer once told me this could be the earthquake from Hell.”

On Monday, the Times reported that about 19 residents from the town of Fullerton remained displaced after their homes were damaged by Friday’s quake. Around 13 water lines broke as a result of the tremor, the paper reported, but all were back in business by Saturday.

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