There are seismographs which, explicitly defined, are instruments that measure and record details of earthquakes, such as force and duration. The results are manifested on computers in the wavy signs often associated with heart monitors. Seismographs help determine the magnitude of earthquakes, on the Mercalli, Richter, or Moment Magnitude scales.
mercalli scale- Intensity
Shaking
Description/Damage
I
Not felt
Not felt except by a very few under especially favorable conditions.
II
Weak
Felt only by a few persons at rest,especially on upper floors of buildings.
III
Weak
Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.
IV
Light
Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
V
Moderate
Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.
VI
Strong
Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
VII
Very strong
Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
VIII
Severe
Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.
IX
Violent
Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.
X
Extreme
Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.
2. Richter Scale- strength increases by tens. weak, one, is barely felt by anyone, catastrophic, twelve, is absolutely devastating.
3. moment Magnitude- this is good for any earthquake,big or small, far or near. this takes the magnitude waves at a moment and converts them to the scale to see how big they were.