How do scientists study earthquakes?

Answer 1

With a really big ruler! No, not quite. There are two ways in which scientists quantify the size of earthquakes: magnitude and intensity.

Magnitude is a measure of the amount of energy released during an earthquake, and you've probably heard news reports about earthquake magnitudes measured using the Richter scale. Something like, "A magnitude 7.3 earthquake struck Japan today. Details at ten." Did you ever wonder why, if it's that important, they just don't tell you right away?

The Richter scale was invented, logically enough, in the 1930s by Dr. Charles Richter, a seismologist at the California Institute of Technology. It is a measure of the largest seismic wave recorded on a particular kind of seismograph located 100 kilometers (about 62 miles) from the epicenter of the earthquake.

Think of a seismograph as a kind of sensitive pendulum that records the shaking of the Earth. The output of a seismograph is known as a seismogram. In the early days, seismograms were produced using ink pens on paper or beams of light on photographic paper, but now it's most often done digitally using computers. The seismograph that Dr. Richter used amplified movements by a factor of 3000, so the waves on the seismograms were much bigger than those that actually occurred in the Earth. The epicenter of an earthquake is the point on the Earth's surface directly above the source, or focus, of the movement that causes the quake.

Dr. Richter studied records from many earthquakes in southern California, and realized that some earthquakes made very small waves whereas others produced large waves. So, to make it easier to compare the sizes of the waves he recorded, Richter used the logarithms of the wave heights on seismograms measured in microns (1/1,000,000th of a meter, or 1/1000th of a millimeter). Remember, you have to be using a particular kind of seismograph located 100 km from the epicenter when you make the measurement; otherwise, all sorts of complicated calculations have to be made. That's why seismologists spend so many years in college!

A wave one millimeter (1000 microns) high on a seismogram would have a magnitude of 3 because 1000 is ten raised to the third power. In contrast, a wave ten millimeters high would have a magnitude of 4. For reasons that we won't go into, a factor of 10 change in the wave height corresponds to a factor of 32 change in the amount of energy released during the earthquake. In other words, a magnitude 7 earthquake would produce seismogram waves 10 x 10 = 100 times as high and release energy 32 x 32 = 1024 times as great as a magnitude 5 earthquake.

The Richter scale is open-ended, meaning there is no limit to how small or large an earthquake might be. Due to the nature of logarithms, it is even possible to have earthquakes with negative magnitudes, although they are so small that humans would never feel them. At the other end of the spectrum, there should never be an earthquake much above magnitude 9 on the Earth simply because it would require a fault larger than any on the planet. The largest earthquake ever recorded on Earth was a magnitude 9.5 that occurred in Chile in 1960, followed in size by the 1964 Good Friday earthquake in Alaska (magnitude 9.2), a magnitude 9.1 earthquake in Alaska during 1957, and a magnitude 9.0 earthquake in Russia during 1952. Two large earthquakes, one a magnitude 9.0 and one a magnitude 8.2, occurred on Dec. 26, 2004 and March 28, 2005, respectively, along the same fault zone off the coast of Sumatra, Indonesia.

The list of really large earthquakes in the previous paragraph brings up another interesting point. Five earthquakes of magnitude 9 or above have been recorded during the past 45 years, which averages out to one every decade. It turns out that earthquake occurrences seem to follow what is called a power-law distribution, meaning that if there is on average on magnitude 9 earthquake every ten years somewhere in the world, then on average there should be one magnitude 8 earthquake every year, 10 magnitude 7 earthquakes every year, and 100 magnitude 6 earthquakes every year. So, if someone "predicts" that a magnitude 6 earthquake will occur somewhere in the world during the next week, don't be too impressed if it happens because random probability tells us that there should be a magnitude 6 earthquake somewhere in the world every 365/100 = 3.65 days! In reality, things are a little more complicated. But, you get the picture.

What did people do before the Richter scale was invented? To some degree, one of the same things that we do today. They observed the intensity or effects of an earthquake at different locations. Whereas the magnitude of an earthquake is a single number regardless of where it's felt, intensity will vary from place to place. In general, the intensity will be much greater near the epicenter than at large distances from the epicenter. This decrease in intensity with distance is known as attenuation. Imagine it this way: If I drop a rock into a pool of water, the difference between magnitude and intensity is similar to the difference between the height of the splash exactly where I drop the rock and the height of the waves all over the pool. Earthquake intensity is most often measured using the modified Mercalli scale, which was invented by the Italian geologist Giuseppi Mercalli in 1902 and uses Roman numerals from I to XII. In the United States, we use the modified Mercalli scale, which was adjusted to account for differences in buildings between Italy and Southern California. An earthquake intensity of I is generally not felt, and an intensity of XII represents total destruction of buildings. Some kinds of geologic deposits, most notably water saturated muds, amplify seismic waves and may produce intensities much greater than those for nearby areas underlain by bedrock. Thus, after an earthquake seismologists can interview people and make maps showing the intensity of an earthquake in different areas to better understand the influence of rock or soil type on seismic waves.

Answer 2

They use seismographs. Scientist have many underground sensors so when there is an earthquake they look at all the sensors to see which way the waves are coming from to each sensor so that they can pin point the epicenter of the earthquake and see which waves came 1st and it's specific magnitude on the Richter Scale.

Answer 3

Scientists study and attempt to predict earthquakes in the following ways:

1. Reference to oral traditions, official papers, and eyewitness accounts regarding previous earthquake activity;

2. Physical evidence, such as:

Soil upheavals on the earth's surface;

Presence of volcanoes;

Location in the area of earthquake fault lines, such as the San Andreas fault line of southern California;

Increases in radon gas levels in wells and basements;

Ground water;

Animal behavior modification, such as suddenly homelessness of burrowing animals or suddenly agitated flight and communication patterns by birds;

3. Indications of underground activity, such as:

Disruption of light beam transmission from one side of a fault line to another;

Magnetic field modifications;

Movements of the earth's soil and crust;

Vibrations or shock waves.

Answer 4

Scientist who study earthquakes use an important tool called the seismograph.

Answer 5

by using instruments like creep meters or magnetometers or pore pressure meters

Answer 6

Scientists (more specifically seismologists) monitor earthquakes using a piece of equipment known as a seismometer.

Answer 7

Scientists try to predict earthquakes so they use several different instruments to pick up very slight movements under the earth. These movements also happen before volcanoes erupt.

Answer 8

At present scientists can not forecast an earthquake. All they can do is inform on the likelihood of an earthquake in a given location over a period of time.

Answer 9

with a seismograph

Answer 10

seismographs