Publié le
par
Bernard Duyck
Since July 19, 2011, small
earthquakes repeatedly (seismic swarms) are reported in the island of Hierro in the volcanic archipelago of the Canaries.
Based on the PEVOLCA - the special plan of volcanic hazards in the Canary Islands - the local government has decided to change the volcanic alert level on September 23, by passing to yellow (warning or pre-emergency).
Below are a few significant figures and graphs of the IGN / AVCAN, trying to understand the situation:
Synopsis of
the INVOLCAN 02.10.2011 / AVCAN
- It can be seen on the bottom right graph, a significant deformation, which reached 3.5 cm. October 8.
- The number of earthquakes:
Histogram of the number and magnitude of earthquakes from 18.07 07.10.2011 -
Despite a decrease in the relative number of daily earthquakes in late September or early October, one can notice an increase in the number of earthquakes with magnitude greater than 2.0 (red), 83 of which were felt by residents.
- Location of earthquakes:
Location and depth of the hypocentres 09/10/2011 - Doc. IGN / AVCAN
After starting out in the area north of El Golfo, a shift took place beneath the island, after August 20. Then the earthquakes are concentrated in the southwest of the island (dark blue and red) since late September.
Based on the PEVOLCA - the special plan of volcanic hazards in the Canary Islands - the local government has decided to change the volcanic alert level on September 23, by passing to yellow (warning or pre-emergency).
Below are a few significant figures and graphs of the IGN / AVCAN, trying to understand the situation:
Synopsis of
the INVOLCAN 02.10.2011 / AVCAN- It can be seen on the bottom right graph, a significant deformation, which reached 3.5 cm. October 8.
- The number of earthquakes:
Histogram of the number and magnitude of earthquakes from 18.07 07.10.2011 -Despite a decrease in the relative number of daily earthquakes in late September or early October, one can notice an increase in the number of earthquakes with magnitude greater than 2.0 (red), 83 of which were felt by residents.
- Location of earthquakes:
Location and depth of the hypocentres 09/10/2011 - Doc. IGN / AVCANAfter starting out in the area north of El Golfo, a shift took place beneath the island, after August 20. Then the earthquakes are concentrated in the southwest of the island (dark blue and red) since late September.
The presence of a fault and submarine volcanoes is to report to the south of El Hierro.
The five underwater volcanic structures south of island El Hierro are indicated by asterisks - according to a Google Earth map.
- The stored energy : as the graph of the number of earthquakes than in the stored energy (below), we can see four cycles.
histogram of the energy stored between 19.09 and 09.10.2011 - Doc. AVCAN
After two severe shocks of magnitudes 3.7 and 3.8 with hypocentres to 12 and 16 km. deep, the 07/10 UTC, 10:29 p.m. and 11:27 a.m. , the seismographs recorded the 8.10 at 8:34, the strongest earthquake since July: magnitude 4.3 - 12.5 km depth. at 600 m the coast.
These events are reflected in the histogram of energy accumulated in the upper right.
The five underwater volcanic structures south of island El Hierro are indicated by asterisks - according to a Google Earth map.
- The stored energy : as the graph of the number of earthquakes than in the stored energy (below), we can see four cycles.
histogram of the energy stored between 19.09 and 09.10.2011 - Doc. AVCAN
After two severe shocks of magnitudes 3.7 and 3.8 with hypocentres to 12 and 16 km. deep, the 07/10 UTC, 10:29 p.m. and 11:27 a.m. , the seismographs recorded the 8.10 at 8:34, the strongest earthquake since July: magnitude 4.3 - 12.5 km depth. at 600 m the coast.
These events are reflected in the histogram of energy accumulated in the upper right.
The alert level remains still
unchanged.
(For a good understanding, see the folder "Séismes et énergie" -
University of Provence).
- The average depth of earthquakes:
In September, the average depth of energy release was 10-12 km. before descending on 28.09, and stabilize between 12 and 14 km.
The October 9, a new area of surface activity was developed, with 13 earthquakes between 0 and 4 km. deep.
This October 9 to 21 hours, we add up to 9940 earthquakes since the beginning of this crisis !
Folder containing the informational meeting points to be observed in case of evacuation.
Sources:
- AVCAN - Volcanic Actualidad de Canarias
- IGN, Instituto Geografico Nacional
- Gobierno de Canarias - notas de prensa 09/10/2011
(For a good understanding, see the folder "Séismes et énergie" -
University of Provence).
- The average depth of earthquakes:
In September, the average depth of energy release was 10-12 km. before descending on 28.09, and stabilize between 12 and 14 km.
The October 9, a new area of surface activity was developed, with 13 earthquakes between 0 and 4 km. deep.
This October 9 to 21 hours, we add up to 9940 earthquakes since the beginning of this crisis !
Folder containing the informational meeting points to be observed in case of evacuation.
Sources:
- AVCAN - Volcanic Actualidad de Canarias
- IGN, Instituto Geografico Nacional
- Gobierno de Canarias - notas de prensa 09/10/2011
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