Seismometers help understand and predict natural hazards

Scientists study the Earth and natural disasters through the science of seismology – how seismic waves move through the Earth – and seismometers are their most important tool. Geophysicist Mark Zumberge at the Scripps Institution of Oceanography is developing a new breed of seismometer to get a better look inside Earth and therefore help scientists understand and predict natural hazards.

Mark Zumberge: Basically a seismometer is a box with a spring inside with a mass hanging inside, and as the ground shakes the mass goes up and down.

Zumberge said a conventional seismometer records how its mass is displaced by waves of seismic energy with electric circuit boards. The electronics make the instrument bulky and hard to use in hot environments, like the interior of the Earth.

Mark Zumberge: We’ve come up with a way, using optical fibers, to bring laser light to and from the seismometer, to make very precise measurements of the vibrations of the mass of the seismometer.

The optical technology allows the device to be deployed in boreholes, narrow shafts drilled into the Earth. The advantage, Zumberge said, is that there’s not as much background activity that must be separated from the seismic activity.

Mark Zumberge: So we can study very large earthquakes nearby, but distant quiet earthquakes as well.

Zumberge said his new seismometer will provide a better perspective on what happens inside the Earth during an earthquake.

Mark Zumberge: Understanding how these processes evolve and how they affect us is important, in the long run, to predict and understand these natural hazards. A huge amount of what we know about the earth comes from seismology.

Zumberge said that the information that scientists get from seismometers helps them create pictures of what’s inside the Earth.

Mark Zumberge: Seismic waves penetrate the Earth, and depending on how waves travel through the Earth and how they’re reflected, what they bounce off of, how fast they go – all those aspects of wave propagation in the earth help us make pictures of what’s inside the Earth.

He said the problem with conventional seismometers is that they are run on electronic circuit boards, which cannot withstand the hot temperatures inside the Earth, and are tethered by cables. The optical seismometer – which uses a beam of laser light – can be deployed into boreholes drilled deep inside the Earth, which is a better environment for taking precise measurements. He said an improved seismometer might help scientists discover new signals of what goes on in the earthquake process. But he added that scientists are still a ways from predicting earthquakes in advance.

Mark Zumberge: Maybe someday we’ll learn enough to forecast better when earthquakes might occur, but that’s a long road.

May 17, 2010

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