Recent earthquakes raise concern over lesser-known - but dangerous - Puente Hills fault

This week's 4.4-magnitude earthquake in the Los Angeles area raised concerns over the lesser-known Puente Hills fault system, which seismologists say has the potential to unleash a devastating quake.

Monday's earthquake happened along the Puente Hills thrust fault system, stretching from the southern San Gabriel Valley through downtown L.A. and out to Hollywood.

It's a complex web of buried faults that seismologists say is far more dangerous than the famous San Andreas Fault.

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"We get about an order of magnitude more damage from a Puente Hills earthquake then from a San Andreas earthquake because so many people, so close, and it's not just that we're in L.A., we're in the older part of L.A. The part where the buildings aren't built to withstand earthquakes," seismologist Lucy Jones said.

At Pasadena City Hall - built in 1927 - the quake broke a pipe, sending water flowing outside the building. Inside the building, a person became trapped in an elevator.

Monday's quake happened along the same fault system responsible for the deadly 1987 Whittier Narrows quake, which claimed more than half a dozen lives and caused more than $350 million in damage.

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Since then, the system has been relatively quiet. The last four decades in Southern California have been relatively quiet for quakes until this year, which has seen a lot of shaking especially magnitude 4.

"We're thinking about the Puente Hills (fault system) because we had the earthquake right now, but everybody in Southern California lives within five miles of an active fault," Jones said. "We are riddled with them, and you can't live here worrying about any one particular fault. We don't know which one is going next."