Richter magnitude scale

The Richter scale is one of the commonly used magnitude scales that are used in seismology to compare the strength ( energy release ) of earthquakes up to a value of 6.5. It is based on amplitude measurements of Seismogrammaufzeichnungen which were obtained in a relatively short distance of a few hundred kilometers from the epicenter. It is therefore also known under the term local - magnitude quake.

Nowadays records of measuring instruments used to determine the magnitude of earthquakes, which are distributed over the entire surface. The resulting determined intensity is usually given in moment magnitude values. Mistakenly is frequently spoken in the press of values ​​the Richter scale.

Formation

The scale was developed by Charles Francis Richter and Beno Gutenberg at the California Institute of Technology in 1935, initially as ML- scale (magnitude Local ) refers. In its basic publication on instrumental Earthquake Magnitude Scale in the Bulletin of the Seismological Society of America Charles Francis Richter turned on for the first time by K. Wadati 1931 published basic idea of ​​an instrumental earthquake scale on Californian earthquakes.

Basics

Because of their definition Richter scale has no upper limit, but the physical properties of the Earth's crust make an occurrence of earthquakes of magnitude 9.5 or higher nearly impossible as the rock can not save enough energy and discharges before reaching this level. The term commonly used in the media " open upwards " shall delimit the instrumental Richter scale of the intensity scale, which often strength and destructive power of an earthquake are characterized.

Most magnitude scales reach the upper range of values ​​a saturation: Grows the energy released in the quake continues to rise, the magnitude varies only with small and the scale loses its linearity. The Richter scale is subject to this phenomenon, it is for information above magnitude 6.5 are therefore not suitable. Any additional values ​​are usually to other magnitude scales.

Derivation

The value specified, the magnitude or size class, derived from the logarithm of the maximum amplitude ( deflection) in the seismogram. The determination of the magnitude given by the following relationship:

Where Amax represents the maximum deflection in micrometers ( microns ), with a short periodic Standardseismometer (Wood -Anderson seismometer ) would record an earthquake at a distance of 100 km to the epicenter. The cover may have to be adapted to the conditions for earthquakes in different distances for the purpose of correction. To the damping of the amplitude is taken into account, which in turn depends on the local speed and damping structure, the age of the earth's crust and the composition of the focal depth, as well as the heat flow conditions. Strictly speaking, this calibration functions are valid only for Southern California by judges and must be determined separately for different regions of the world.

Because of the common logarithm of the increase in magnitude to a point on the scale of an approximately ten-fold higher deflection ( amplitude) in the seismogram and approximately 32 times the energy release means ( exponential growth ) in the earthquake source. A magnitude of two or less is referred to as micro- earthquakes, as it can often not be perceived by human beings, and is detected only by local seismographs. Quake with a magnitude of about 4.5 and higher are strong enough to be detected by seismographs all over the world. However, the strength must be above 5 to be regarded as excessive earthquake.

Classification of the scale values

The magnitude values ​​can be assigned to typical effects in the area of the epicenter. It should be noted that the intensity and thereby the ground effects depend not only on the magnitude, but also on the distance to the epicenter, the depth of the epicenter under the epicenter, and the local geological conditions.

* The Richter scale is measured technically capped at magnitude 6.5. Higher magnitudes stronger quakes are determined by the moment magnitude scale ( MW).

Relation to other scales

Despite the fundamentally different approach to the Richter scale is often tried this with the intensity scales such as the modified and repeatedly refined Mercalliskala the Italian Giuseppe Mercalli (1850-1914), relate it. On another intensity scale, called MSK scale ( Medvedev - Sponheuer - Karnik scale), the magnitude of an earthquake is given for example in twelve degrees of strength. The grading is based on both subjective and objective criteria to.

For some time, the moment magnitude scale (abbreviated as MW ) is indicated in many cases, their determinants based on the physical parameters of the earthquake source.

The logarithmic relationship between energy and magnitude can be approximated with summarized

Where M is the magnitude and W is the equivalent ( explosive ) energy in tons of TNT.