Seismic scales

An earthquake scale is used to compare the strength or impact of earthquakes.

For a description of earthquake seismology, two fundamentally different types are used by Scales: The liberated at the site of the earthquake energy is graded on a magnitude scale, while the effects of vibrations on a hit by the earthquake point of the earth's surface are described by means of an intensity scale.

Overview

The severity of an earthquake is described by both magnitude and by intensity. These two often jumbled terms refer to different, but related observations. Magnitude is normally abbreviated with Arabic numerals and characterizes the size of an earthquake by the indirect measurement of the energy released. In contrast, the intensity is usually indicated by Roman numerals and describes the local impact and the potential damage in terms of people, animals, buildings and natural objects such as water or mountains. An earthquake has a magnitude of, but many intensities, since the effects depending on the circumstances such as the distance from the epicenter, the structure of the soil and the construction of buildings vary. In practice, different magnitudes can be specified for a quake, as a number of different magnitude scales exist. These are based on different measurement methods are based, so that the magnitude values significantly may differ to some extent.

Charles Francis Richter, the creator of the Richter scale, different intensity and magnitude as follows:

" I like to use the analogy to radio broadcasts. It applies to seismology, because seismographs take on elastic waves radiated from the earthquake source, just like radio receiver radio waves take to be broadcast from a transmitter. Magnitude can be compared with the power in kilowatts that radiates a transmitter. Local intensity after Mercalliskala is then compared with the signal strength at the receiver at a particular location, or to the signal quality. The intensity will decrease just like the signal strength in general with the distance from the source, although as this is just as dependent on local factors such as the propagation path between the earthquake source and the specific location. "

Intensity scales

The first simple classification of earthquakes according to intensity was developed by Domenico Pignataro in the 80s of the 18th century. As a first intensity scale in the modern sense, however, only the PNG Egen designed in 1828 scale apply, however his time with her was ahead. General recognition was not until the Rossi - Forel scale, which was introduced in the late 19th century. Since then, numerous intensity scales have been developed. The scale used is different depending on the country: in the United States is the Modified Mercalliskala (MM) in use, while in the European Union, the European macroseismic scale ( EMS) is used in Japan, the JMA scale as well as in India, Israel and Russia, Medvedev Sponheuer - Kárník scale ( MSK -64). Almost all of these scales have 12 intensity levels that correspond in value in about, in relation to the formulation and level of detail are different.

Magnitude scales

The first attempt to describe earthquake by a single absolute value, used the term magnitude based on the magnitude scale, which is the brightness of the stars in use.

Local magnitude ( Richter scale )

The Lokalmagnitudenskala (ML ), commonly known as the Richter scale, is a quantitative- logarithmic scale. In the 1930s, the Californian seismologist Charles F. Richter devised a simple numerical scale to describe the relative size of earthquakes in Southern California. The term " Richter scale " was coined by journalists and is not used in the technical literature. ML is determined by the measurement of the maximum deflection of a seismogram, which was recorded on a Wood Anderson Torsionsseismometer (or calibrated for a Wood Anderson Torsionsseismometer seismometer other type ).

Other recent Magnitudenmessungen include the measurement of Raumwellenmagnitude (body - wave magnitude ) mB, the Oberflächenwellenmagnitude ( surface wave magnitude ) MS or the decay or Codamagnitude ( duration magnitude ) MD. Each of these alternative magnitude is scaled so that it gives similar values as the Lokalmagnitudenskala. However, because they are based on the measurement of each of different areas of the seismogram, they do not always reflect the overall strength of the earthquake. Especially with strong or very strong earthquakes may occur saturation, that is, that the strength of the quake is systematically underestimated. This problem occurs when the Lokalmagnitudenskala already a strength of about 6, while in the case of Oberflächenwellenmagnitude it only starts from about 8. Despite the limitations of the older magnitude scales, they are still widely used because they can be computed quickly because catalogs of such magnitude go back decades and therefore easily comparable because they are sufficient for the majority of the observed seismic events, and not least because the public familiar with is.

Moment magnitude

Due to the basic limitation of the magnitude scales in 1977 designed a uniformly applicable magnitude scale by Hiroo Kanamori, the moment magnitude scale (moment magnitude ) MW. Especially for strong and very strong earthquake, the moment magnitude scale provides the most reliable indication of the strength of an earthquake. This is due to that it uses the concept of seismic torque which is derived from the concept of the moment in physics. It allows conclusions about the size of an earthquake - in particular the size of the underlying fault rupture and the offset on the error surface - as well as the physical energy it releases. This concept allows to derive not only the seismic moment from the seismogram, but as it were backwards calculate it by detecting geological details such as the size of the fault rupture and the offset.

The values for previously registered earthquakes spanning more than 15 mag.

Earthquake scale

Hindu–Arabic numeral system Rossi–Forel scale Japan Meteorological Agency seismic intensity scale Calibration Mercalli intensity scale

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