PENDING. >> WELL, THERE ARE MANY FAULTS IN SOUTHERN CALIFORNIA, AND NOW WE ARE LEARNING THAT THERE'S ONE MORE THAT COULD BE MORE DANGEROUS THAN THE SAN ANDREAS FAULT. >> THE PUENTE HILLS FAULT IS IN A DENSELY POPULATED AREA. IT INCLUDES LOS ANGELES, PASADENA, MONTEREY PARK, AND WHITTIER. EYEWITNESS NEWS REPORTER LEANNE SUTER JOINS US LIVE AFTER SPEAKING WITH SEISMOLOGIST LUCY JONES ABOUT THE DANGERS. LEANNE >> DAVID AND ALLEN SEISMOLOGISTS HAVE KNOWN ABOUT THAT FAULT LINE AND THAT FAULT SYSTEM, I SHOULD SAY, FOR MORE THAN TWO DECADES NOW, THEY'VE ALSO KNOWN JUST HOW MUCH DAMAGE IT COULD CAUSE IF IT WERE TO ACTIVATE ON A MASSIVE QUAKE, ALL BECAUSE OF WHERE IT'S LOCATED. MONDAY'S 4.4 EARTHQUAKE WAS RELATIVELY SMALL, BUT PACKED A SERIOUS PUNCH. IT HAPPENED ALONG THE PUENTE HILLS THRUST FAULT SYSTEM, STRETCHING FROM SOUTHERN SAN GABRIEL VALLEY THROUGH DOWNTOWN LA OUT TO HOLLYWOOD. A COMPLEX WEB OF BURIED FAULTS THAT SEISMOLOGISTS SAY IS FAR MORE DANGEROUS THAN THE FAMOUS SAN ANDREAS FAULT. >> WE GET ABOUT AN ORDER OF MAGNITUDE MORE DAMAGE FROM THE PUENTE HILLS EARTHQUAKE THAN FROM A SAN ANDREAS EARTHQUAKE, BECAUSE SO MANY PEOPLE SO CLOSE. AND IT'S NOT JUST THAT WE'RE IN LA, WE'RE IN THE OLDER PART OF LA, RIGHT? THE PART WHERE THE BUILDINGS AREN'T BUILT. SO TO WITHSTAND EARTHQUAKES. >> PASADENA CITY HALL, BUILT IN 1927. A PIPE BROKE, SENDING WATER CASCADING OUTSIDE THE BUILDING. INSIDE, SOMEONE GOT 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. SINCE THEN, THE SYSTEM HAS BEEN RELATIVELY QUIET. IN FACT, 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 FOUR. >> WE'RE THINKING ABOUT THE PUENTE HILLS BECAUSE WE'VE HAD THE EARTHQUAKE RIGHT NOW, BUT EVERYBODY IN SOUTHERN CALIFORNIA LIVES WITHIN FIVE MILES OF AN ACTIVE FAULT. WE ARE RIDDLED WITH THEM, AND YOU CAN'T LIVE HERE WORRYING ABOUT ANY ONE PARTICULAR FAULT. WE DON'T KNOW WHICH ONE'S GOING NEXT. >> YEAH. THAT'S RIGHT. NO PREDICTING WHEN OR WHERE THAT BIG QUAKE IS GOING TO HIT. ONLY PREPARATION TO MAKE SURE THAT YOU ARE READY. BECAUSE AS DOCTOR JONES SAYS, IT IS GOING TO