Earth Science: EarthQuakes – Measurement and Consequences
It may not be possible to predict earthquakes, but by studying them scientists hope to find ways of lessening their damage.
Early in the 20th century, volcanologist Giuseppe Mercalli created a scale categorizing earthquakes based on damage incurred. This Mercalli intensity scale ranges from Level 1, which is registered only by seismographs, to Level 12, which results in severe changes on the Earth’s surface and the destruction of almost all buildings. The more popular and more scientific Richter scale, developed by Charles Francis Richter, calculates the intensity of an earthquake as “magnitude” (M) on a logarithmic scale.
The M-value is determined from the distance between the hypocenter of the earthquake and the seismological recording station, as well as the amplitudes recorded on seismographs. Earthquakes with magnitudes less than 2.0 are not perceivable by people. Numbers on the Richter scale represent an earthquake ten times more powerful than the number below it. Thus an earthquake of 5.0 M is ten times more powerful than one with an intensity of 4.0 M.
Today, scientists use the more precise moment-magnitude scale. To calculate the M-value, this scale multiplies the area of the fault’s rupture by the distance moved along the fault. The study and measuring of earthquakes is crucial In aiding scientists and engineers with planning for future occurances, especially because there could be deadly consequences. Currently, most scientists focus primarily on mitigating the hazards of earthquakes by improving structural stability of buildings.
Consequences of an earthquake
No earthquake has cost so many lives as that in the Chinese province of Shaanxi in 1556. An earthquake was recorded with a magnitude of 8.0. Approximately 830,000 people were killed-many of whom died in their beds as their houses collapsed. Unexpected by-products of earthquakes, such as fires, floods, and lack of shelter or food, can be as destructive as the tremors themselves.
After earthquakes in San Fran- cisco in 1906 and Kobe, Japan, in 1995, survivors had to cope with extensive fires that raged for days. The capital of Portugal, Lisbon, was hit by a tsunami following a significant earthquake in 1755, submerging the city under water. After a devastating earthquake in Kashmir in 2005, difficulty in providing timely assistance to such a remote, inaccessible region as this meant that survivors faced winter without shelter or sufficient food.
SEISMOGRAPHS
Seismographs, used to measure vibrations of an earthquake, come in a wide variety. Early seismographs used a weighted, hanging pendulum to etch or draw vibrations onto glass or paper. The stronger the earthquake, the greater the amplitude.
Modern seismographs employ more sophisticated recording instruments with electronic sensors and amplifiers.