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Report

Seismographs must be quite
steady themselves in order to
accurately record and measure
earthquake activity across the
planet. The machine itself is
mounted on a stable surface such
as concrete. The actual mea-
suring unit consists of a strong
weight, a hanging pen and a pa-
per drum. When an earthquake
occurs, this triggers the pen to
record the wave activity on the
paper wrapped around the drum.
Scientists can then study these
markings to measure the mag-
nitude, depth and location of the
earthquake. Faults

How are Earthquakes Ranked? What are Foreshocks and Af- estimated the annual number of
Scientists use a tool called the tershocks? earthquakes worldwide in the mil-
Richter Scale to measure the The Earth may give indica- lions.
strength of an earthquake and tions that a larger earthquake is However, since some of these
rank each earthquake in rela- about to occur by generating fore-
tion to others. The Richter Scale shocks. Foreshocks are basically earthquakes may be too minor to
be registered by a seismograph
was developed in 1935 and was smaller earthquakes.
named after its primary inventor, However, to date scientists or may be located in parts of the
Charles F. Richter. have not been able to come up world that are not currently moni-
tored by a seismograph, the exact
The Scale uses a logarithm to with any way to determine in ad- count can never be precisely de-
determine the overall size and vance when an earthquake will termined.
strength of an earthquake, which happen or whether an earthquake
is then expressed as a fraction. is a foreshock or an actual earth- Every year, new seismographs
For example, the size and strength quake. This can only be deter- are installed to help scientists
of a relatively minor earthquake mined after the fact. monitor more regions around the
might be expressed as a 2.3. A Aftershocks, as their name sug- globe.
major earthquake, however, might gests, are the movements of the What are some of the largest
be expressed as a 6.5. The scale tectonic plates settling back down Earthquakes in History?
runs from 1.0 to 9.0+. into a workable position post- These quakes were amongst
To date, it is estimated that earthquake. the largest quakes ever recorded:
the vast majority of recorded an- Some foreshocks and after-
nual earthquake activity falls shocks are so minor that they may • Chile: This South American
between the 2.0 to 3.9 range. not even register on a seismo- quake on May 22, 1960, regis-
Only a relatively small minority graph, while others may be quite tered a 9.0.
of earthquakes register as a 4.0 noticeable. • Alaska: This North American
and above. Over the last 47 years’ quake on March 27, 1964, reg-
worth of measurement data, only Annual Earthquake Count istered an 8.5.
a handful of earthquakes have The US Geological Survey
ranked above an 8.0 on the Rich- National Earthquake Information • Indonesia: This Asian quake on
ter Scale. Center, or USGS for short, has Dec. 26, 2004, registered a 9.0.
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