# What is an earthquake used for measurement

## Measurement and strength of earthquakes

As early as the 18th century, scientists tried to quantify the strength of earthquakes. However, since no suitable measurement methods were available, one had to be content with describing the earthquake intensity subjectively. Only in the course of the 20th century were procedures and scales developed to describe the energy (the magnitude) of earthquakes independently of the observable effects and at varying distances from the earthquake focus.

### From observation to measurement

It is still in use today "Modified Mercallis Scale" (MM scale), the principles of which were developed in 1902. The MM scale names a total of twelve levels with Roman numerals: from I for “imperceptible” to XII for “major catastrophe”. The individual stages describe how an earthquake affects people and structures. In level VII (“very strong”), standing is difficult and “normal” buildings suffer from slight to moderate damage.

The one introduced in 1935 is particularly popular Richter scale. In contrast to the MM scale, it is based on a specific measurement of the vibration. From the oscillation amplitude, she calculates the Magnitude as a common measure of the magnitude of the earthquake. Theoretically, the Richter scale represents earthquakes up to a maximum value of 10. However, from a magnitude of 6.5 onwards, the scale loses its informative value.

For particularly strong earthquakes, seismologists today do not use the Richter scale, but often use the one developed in 1977 "Moment magnitude scale". It also uses the vibration amplitudes to determine the energy released by an earthquake. However, the calculation method is better suited for high magnitude values.

A high magnitude earthquake does not necessarily cause severe damage to human civilization. It is also crucial how close a town is to it Earthquake focus (Hypocenter) is located. A hypocenter a few kilometers below a city can cause greater destruction than a very high magnitude at great depth or hundreds of kilometers away.

### Localization of earthquakes

An important task of the measurement method is to determine the exact location of an earthquake. For this purpose, the researchers use a wide-ranging, worldwide network of measuring stations. If the same quake is recorded by several different stations, there are small time differences because the earthquake waves need different lengths of time to reach the stations. The epicenter and the hypocenter can be easily determined from these time differences.

The epicenter refers to a place on the earth's surface from which a quake appears to emanate. The Hypocenter is the "real" place where the earthquake originated, where two earth plates, for example, get caught and then loosen again. The hypocenter, also known as the earthquake focus, lies in the rock vertically below the epicenter.

Seismograph / © public domain (public domain)

### Measuring device

A device for the quantitative measurement of earthquake waves is called seismograph or seismometer. It translates the energy of an earthquake into a trembling curve - the stronger the deflections, the stronger the tremors. The course of the curve shows the chronological sequence of the quake. The curve is printed out on continuous paper and / or saved digitally.

A seismograph consists of an inertial mass and a movable device cover. In the event of an earthquake, the casing of the device vibrates while the inertial mass remains in place. The seismograph usually records this relative movement using an electromagnetic method.