Characteristics, parameters and properties of the earthquake

The main parameters, which determine the strength and character of earthquakes, are magnitude, depth of seismic focus and intensity of energy on the earth's surface.

Magnitude (M) is a measure of the energy in the Earth's crust induced by seismic activity. Magnitude is common logarithm of maximum ground oscillation amplitude measured by seismograph at microns on the distance of 100 km from epicenter.

(2.1)

Seismic energy (E) depends on a magnitude by following formula:

(2.2)

Earthquakes can be recorded by seismometers up to great distances, because seismic waves travel through the whole Earth's interior. The absolute magnitude of a quake is conventionally reported by numbers on the moment magnitude scale(formerly Richter scale, magnitude 7 causing serious damage over large areas), whereas the felt magnitude is reported using the modified Mercalli intensity scale (intensity II–XII).

The Richter magnitude scale (also Richter scale) assigns a magnitude number to quantify the energy released by an earthquake.

The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs (adjustments are included to compensate for the variation in the distance between the various seismographs and the epicenter of the earthquake). The original formula is:

(2.3)

where A is the maximum amplitude of the Wood-Anderson seismograph, the empirical function A ₀ depends only on the epicentral distance of the station, δ. In practice, readings from all observing stations are averaged after adjustment with station-specific corrections to obtain the M_l value.

Because of the logarithmic basis of the scale, each whole number increases in magnitude represents a tenfold increase in measured amplitude; in terms of energy, each whole number increase corresponds to an increase of about 31.6 times the amount of energy released, and each increase of 0.2 corresponds to a doubling of the energy released.

Magntude by Richter scale is measured from 0 up to 9 (last value corresponds to the most powerful earthquake), table 2.1.

In Ukraine the scale MSK-64 is used for detection of the magnitude in scores, Table 2.2.

The following data from U.S. Geological Survey documents (Table 2.3) have emphasized, that the earthquakes effects with various magnitudes are observed near the epicenter. Thus, intensity of earthquake ground shaking depends on following factors: the magnitude value at the epicenter, the distance to the epicenter, the depth of the seismic focus, the location of the epicenter and geological conditions (certain terrains can amplify seismic signals).

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