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The earthquakes study before the instrumental epoch is performed following the macroseismic data, from the descriptions of the effects produced by earthquakes in bibliographical sources.
Nowadays, from the begining of this century, when an earthquake is felt by the population, a macroseismic survey is carried out in order to analise the effects and to stablish the intensity value in the different municipalities (Table II).
The more significant earthquakes of XX century correspond to the 19th, november 1923, in the Vall d'Aran with a maximum epicentral intensity of VIII (MSK) and the 12th, march 1927, in the Sant Celoni area with a maximum intensity of VII (MSK).
Intensitats mà ximes percebudes a Catalunya al segle XX
TABLE I: Approximative correspondence between the magnitude (Richter) and the intensity (MSK) felt in the epicentral area
Magnitude | Maximum epicentral intensity |
|---|---|
3,5 - 4,0 | IV |
4,0 - 4,5 | V |
4,5 - 5,0 | VI |
5,0 - 5,5 | VII |
5,5 - 6,0 | VIII |
6,0 - 6,5 | IX |
TABLE II: Brief description of the degrees of the intensity scale (MSK).
Intensity | Description |
|---|---|
I | Non felt |
II | Shock felt by some people at rest |
III | Shock felt in closed buildings |
IV | Movement of the hanging objects |
V | Movement of the small objects |
VI | Slight and small damages |
VII | Moderate damages |
VIII | Big damages |
IX | Generalized big damages |
