Report about felt earthquake!

Report about seismic event!


Earthquake magnitude and intensity

Earthquake size can be defined using two parameters – magnitude M and intensity I. The earthquake magnitude defines energy released in the seismic source. The value of magnitude is determined analyzing amplitudes of vibrations registered by seismometers. Intensity of an earthquake defines the size of surface shaking in some area. In different places the intensity value is different, usually it reaches maximum in epicenter and decreases with distance. Although the relation between magnitude and intensity is quite ambiguous and complicated. Intensity in a particular site depends on earthquake magnitude, focal mechanism, hipocenter depth, epicenter distance and soil type in the area. Earthquake is defined by only one value of magnitude and several values of intensity depending on the geological conditions of the site.
There are used various earthquake magnitude and intensity scales. The magnitude scale is logarithmic one without lower or upper boundaries. The most known in the society is Richter‘s scale. The method to assess the size of an earthquake was suggested by Japanese scientist K. Wadati in 1931, and later the method was developed by Ch. Richter. According to Richter‘s method, the earthquake magnitude is determined from seismograms recorded by Wood-Anderson seismometr placed 100 km away from the epicenter. In case of different epicenter distance the corrections into the calculations are included. Also, other corrections due to different geological conditions are included.
The Richter‘s scale is not popular to use for scientific purposes, because it is quite complicated to use. The most common scales used for scientific studies are local, body-wave, surface-wave, moment, energy magnitude scales, etc. The magnitude scales are logarithmic, thus, an earthquake smaller of magnitude one is ~30 times weaker in energy (Table 1), for example, earthquake of M 6.0 is about 30 times as powerful as an earthquake of M 5.0; and earthquake of M 7.0 is 900 times as powerful as an earthquake of M 5.0.
The values in magnitude scales can be both negative or positive, and the scales are open (Table 1). The negative magnitude values determine small and negligible seismic events, like cracking in the rocks. Stronger events are evaluated with positive magnitude values. The magnitude sales are open but there is a physical limit for its highest value depending on the size and composition of the Earth. The magnitude of the largest known earthquake was 9.5, it took place in Chile in 1960; during the earthquake the fault of 1500 km length has formed. Supposedly the earthquake of M 10.0 would result in a fault of San-Andreas type around the globe.

Table 1. Relation between earthquake magnitude and released amount of energy. Notations: TNT – explosive material trinitrotoluene, EQ – earthquake, g – gramme, J – joule, t – tonne, k – kilo (103), M – mega (106), G – giga (109), T – tera (1012), P – peta (1015), E – eksa (1018), Z – zeta (1021), Y – yota (1024).



Energy equivalent

of TNT mass





3 g

25 kJ

Micro cracks in rocks due to hydrofracturing


15 g

130 kJ

EQ in Spicbergen island, in the Arctic Ocean in 2004


85 g

360 kJ

Weak tectonic tremors


480 g

2 MJ

Exploding in constructions


2,7 kg

11 MJ

Exploding in seismic profiles


15 kg

63 MJ

Quarry and mine blasting


85 kg

360 MJ

Induced EQ in Poland due to mining activities


480 kg

2 GJ


2,7 t

11 GJ

EQ in Dallas, USA in 2012


15 t

63 GJ

EQ in South Finland in 2004


85 t

360 GJ

EQ in Australia in 2013


480 t

2 TJ

EQ in the Kaliningrad District of Russia in 2004


2,7 kt

11 TJ

Chino Hills EQ in South California, USA in 2008


15 kt

63 TJ

Explosion of nuclear bomb "Little Boy" in Hiroshima in 1945


85 kt

360 TJ

Zumpango del Rio EQ in Mexico in 2011


480 kt

2 PJ

Haiti EQ in Haiti in 2010


2,7 Mt

11 PJ

Cashmere EQ in Pakistan in 2005


15 Mt

63 PJ

San Francisco EQ in California, USA in 1906


85 Mt

360 PJ

Sumatra EQ in Indonesia in 2007


480 Mt

2 EJ

Tohoku EQ in Japan in 2011


2,7 Gt

11 EJ

The strongest ever recorded Valdivia (The Big Chilean) EQ in Chile in 1960


15 Gt

63 EJ

The magnitude would be equal generation of a fault of San-Andreas type which would circle the globe


100 Tt

420 ZJ

Formation of Chicxulub crater in Jukatan peninsulart after meteorite impact 65 Ga ago


310 Yt

1,3*1039 J

Starquake recorded in neutron star SGR1806-20 in 2004

The intensity of the resultant ground shaking is evaluated in a scale of 12 levels, from negligible I to devastating XII. There are a lot of intensity scales nowadays. From the middle of XX century in Europe the most popular was Medvedev-Sponheuer-Karnik scale (MSK-64), which was later updated and called European Macroseismic Scale (EMS-98) (Table 2) and used since 1998. In the USA there is usually used Modified Merkalli scale, in Japan there is used ten levels intensity scale compiled by Japan Meteorological Agency (JMA).

Table 2. European Macroseismic Scale EMS-98.








Not felt

Not felt by anyone.


Scarcely felt

Vibration is felt only by individual people at rest in houses, especially on upper floors of buildings.



The vibration is weak and is felt indoors by a few people. People at rest feel swaying or light trembling.

Noticeable shaking of many objects.


Largely observed

The earthquake is felt indoors by many people, outdoorsby few. A few people are awakened. The level of vibration is possibly frightening. Windows, doors and dishes rattle. Hanging objects swing. No damage to buildings.



The earthquake is felt indoors by most, outdoors by many. Many sleeping people awake. A few run outdoors. Entire sections of all buildings tremble. Most objects swing considerably. China and glasses clatter together. The vibration is strong. Topheavy objects topple over. Doors and windows swing open or shut.


Slightly damaging

Felt by everyone indoors and by many to most outdoors. Many people in buildings are frightened and run outdoors. Objects on walls fall. Slight damage to buildings; for example, fine cracks in plaster and small pieces of plaster fall.



Most people are frightened and run outdoors. Furniture is shifted and many objects fall from shelves. Many buildings suffer slight to moderate damage. Cracks in walls; partial collapse of chimneys.


Heavily damaging

Furniture may be overturned. Many to most buildings suffer damage: chimneys fall; large cracks appear in walls and a few buildings may partially collapse. Can be noticed by people driving cars.



Monuments and columns fall or are twisted. Many ordinary buildings partially collapse and a few collapse completely. Windows shatter.


Very destructive

Many buildings collapse. Cracks and landslides can be seen.



Most buildings collapse.


Completely devastating

All structures are destroyed. The ground changes



Information prepared by Vilma Stankevičienė
Tel.: +370 5 233 0142
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