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Why So Many Earthquakes Lately?

Your browser does not support this object. View the original here: http://www.youtube.com/watch?v=JeKZzIo49qY

Video published July 9, 2010 | Download MP4 | View transcript

Above: Why has the San Diego region experienced so many earthquakes lately? We speak to a seismologist from the Scripps Institution of Oceanography about what's causing all the recent quakes.

Transcript

WHAT'S BEHIND ALL THE EARTHQUAKES WE'VE HAD LATELY? AND DOES THIS WEEK'S 5.4 MAGNITUDE QUAKE HAVE ANY CONNECTION TO THE 7.2 EARTHQUAKE THAT SHOOK OUR REGION ON EASTER DAY? WE'VE INVITED SCRIPPS INSTITUTION OF OCEANOGRAPHY DR. DEBBIE KILT TO TALK TO US ABOUT ALL THE SEISMIC ACTIVITY WE'VE EXPERIENCED OVER THE LAST FEW MONTHS. MY FIRST QUESTION IS, WHAT DO YOU KNOW ABOUT WEDNESDAY'S EARTHQUAKE? WHERE WAS THE EPICENTER? AND WHAT FAULT LINE DID IT OCCUR ON?

4:50, JUST BEFORE 5:00 P.M. ON THE COYOTE CREEK SECTION OF THE SAN YOSENTO FAULT. IN A REGION WE TYPICALLY HAVE EARTHQUAKES.

IT'S BEEN CHARACTERIZED AS AN EARTHQUAKE, NOT AN AFTERSHOCK. DO YOU AGREE WITH THAT ASSESSMENT.

ONLY AFTER LOOKING AT IT CLOSELY. YOU HAD TO REALLY LOOK AT IT AND SAY WHAT'S THE SPATIAL DIFFERENTIAL AND THE TEMPORAL DIFFERENTIAL.

AND YOU FOUND?

THE TIME DIFFERENCE IS THREE MONTHS, QUITE SUBSTANTIAL. THE SPACE DIFFERENCE IS 100 MILES. WE USUALLY LOOK TO SEE HOW MANY MAIN SHOCK FAULT LENGTHS AWAY IS THAT. TWO MAIN SHOCK FAULT LENGTHS. MAYBE AN AFTERSHOCK, SPATIALLY, BUT TEMPORALLY, THREE MONTHS, WAY TOO LONG. AN EARTHQUAKE.

YOU MENTIONED THE QUAKE OCCURRED ALONG THE SAN JOSENTO FAULT.

CONTINUALLY HAVING SHOCKS, EARTHQUAKES, WE HAVE AN EARTHQUAKE THERE ALMOST EVERY DAY. WE ALSO HAVE MAGNITUDE FIVE ON THAT FAULT. WE'VE HAD A MAGNITUDE FIVE IN 2001, A MAGNITUDE FIVE IN 2005. WE'RE CONTINUALLY HAVING MAGNITUDE FIVES. THIS ISN'T OUT OF THE ORDINARY.

BUT IT SEEMS LIKE IT'S OUT OF THE ORDINARY. I LIVED IN SOUTHERN CALIFORNIA FOR A HECK OF A LONG TIME, AND I DON'T REMEMBER THIS MANY EARTHQUAKES, OF THIS SIZE OCCURRING WITH THIS KIND OF FREQUENCY.

I THINK THAT'S BECAUSE WE'RE ALL THINKING EARTHQUAKES, HAITI, EARTHQUAKE, CHILE, EARTHQUAKE, EASTER, EARTHQUAKE, IT'S ALL AROUND US. HAITI WAS A MAGNITUDE SEVEN. WE HAVE 15 MAGNITUDE SEVENS EVERY YEAR. NOT OUT OF THE ORDINARY FROM A SEISMOLOGICAL POINT OF VIEW. 7.2, WE'D EXPECT A 6.2, 5. ET CETERA. NEAR EPICENTER WITHIN A MONTH OR TWO. EXACTLY AS WE'D EXPECT FROM A SEISMOLOGICAL POINT OF VIEW.

IS IT FAIR TO SAY THAT THE SAN HOSENTO FAULT LINE POSES MORE OF A RISK TO SAN DIEGO THAN THE SAN ANDREAS FAULT LINE WHICH WE'VE HEARD SO MUCH ABOUT OVER THE PAST 10, 15, 20 YEARS.

WE CAN LOOK SPATIALLY. SAN DIEGO ARE MUCH CLOSER TO THE SAN HOSENTO FAULT. THE CLOSER WE ARE TO THE MAJOR FAULT, THE STRONGER WE'LL FEEL THAT SHAKING. IF YOU WENT "I FELT THAT EASTER EARTHQUAKE IN SAN DIEGO." SOMEONE IN L.A. SAY "I FELT IT, BUT NOT AS STRONG AS YOU." YOU'RE MUCH FURTHER AWAY. THE SAME THING WITH THE SAN HOSENTO AND SAN ANDREAS.

YOU KNOW, WE'VE HEARD SO MUCH ABOUT THE BIG ONE. THE BIG ONE IS COMING. BUT WHAT CONSTITUTES THE BIG ONE? WE HAVE THE ONE THAT OCCURRED ON EASTER DAY AND YOU KNOW, 5.4, I UNDERSTAND IS NOT THE BIG ONE. BUT WHAT DO WE SEE AS THE BIG ONE THESE DAYS?

WHAT PEOPLE ARE WORRIED ABOUT IS THE SOUTHERN PART OF THE SAN ANDREAS FAULT. IT HASN'T RUPTURED IN OVER 300 YEARS. WE'RE OVERDUE FOR WHAT WE EXPECT FOR A BIG EARTHQUAKE. MAYBE IN THE ORDER OF 7.5, MAYBE AN 8 AT THE MOST. IT'S LIMITED BECAUSE THE SHALLOW DEPTHS OF THE SAN ANDREAS FAULT. WE DON'T GET THAT LONG, DIG, BIG EARTHQUAKE THAT WE MIGHT IN CHILE.

WHEN YOU HAVE THESE TINY TUMBLERS, DOES THAT RELIEVE THE STRESS AND MAYBE PUT OFF THE BIG ONE?

IT DOES, BUT IT'S SO SMALL. WE TAKE THOUSANDS OF MAGNITUDE SIXES TO RELIEF THE STRESS FROM THE MAGNITUDE EIGHT. WILL WE HAVE A THOUSAND MAGNITUDE SIXES WITHIN THE NEXT YEAR, I DON'T THINK SO.

THAT'S MY TIME QUESTION. WHAT CAN WE EXPECT NOW IN THE NEXT YEAR OR SO? BASED ON WHAT WE'VE SEEN IN THE PAST COUPLE MONTHS?

WE LIVE IN EARTHQUAKE COUNTRY, WE KNOW WE'RE ON A PLATE-TECTONIC BOUNDARY AND WE EXPECT EARTHQUAKES. I'D EXPECT TO HAVE AN EARTHQUAKE AND BE PREPARED. HAVE YOUR EARTHQUAKE PREPAREDNESS KIT. IF AN EARTHQUAKE OCCURRED RIGHT NOW, WHERE WOULD YOU GO, WHAT WOULD YOU DO? ASK YOURSELF THAT EVERY HOUR, JUST GOING THROUGH YOUR DAY. DO I WANT TO BE UNDER BIG LIGHTS? BIG CEILING FAN. JUST KEEP IT IN MIND.

OKAY, DR. KILT, THANK YOU SO MUCH FOR THAT INFORMATION.

THANK YOU.

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