1909 Benavente earthquake
  | |
| UTC time | 1909-04-23 17:39:36 |
|---|---|
| ISC event | 610326344 |
| USGS-ANSS | ComCat |
| Local date | 23 April 1909 |
| Local time | 02:40:32 |
| Magnitude | Mw 6.0 |
| Depth | 10 km |
| Epicenter | 38°54′N 8°48′W / 38.9°N 8.8°W |
| Areas affected | Portugal |
| Max. intensity | MMI IX (Violent)[1] |
| Casualties | 60 dead, 75 injured |
The 1909 Benavente earthquake occurred on 23 April at 17:39:36 local in the Santarém District of the Central Region, Portugal. The estimated moment magnitude 6.0–6.3 earthquake had a maximum Mercalli intensity of IX (Violent). It nearly destroyed the town of Benavente, killing 60 and injuring 75 people as a result.[2]
Geology
[edit]The northeast-trending Lower Tagus Valley of mainland Portugal covers a 3,200 km2 (1,200 sq mi) area and extends to Lisbon at its southern end. Earthquakes around the valley are usually moderate or small in magnitude with the 1909 shock being the most recent large earthquake. In the last 30 years of the 20th centory, at least 39 earthquakes had been felt; 3 with magnitudes of at least 4.0 while 16 events were between 3.0 and 3.9. The first documented earthquake in the region was on 26 January 1531, estimated at Mw 6.9, which caused serious damage in Lisbon and killed two percent of the population. The study of potentially active faults beneath the valley is obstructed by a thick sedimentary layer especially along the Tagus River's eastern bank.[3]
Earthquake
[edit]Reassessment of the earthquake magnitude suggest a value of 6.0–6.3 on the moment magnitude scale.[4][5] The reassessed magnitude is significantly lower than the previous value of 6.6. The most consistent focal mechanism solution is reverse faulting along a northeast–southwest striking fault plane at an estimated depth of focus of 10 km.[4] The location suggest it occurred in a seismic zone in the Lower Tagus Valley. The earthquake was the largest recorded crustal earthquake in the Iberian peninsula during the 20th century. It was felt for 215,000 km2 (83,000 sq mi) which was relatively large for its magnitude; in comparison, the 1908 Messina earthquake which measured 7.2 had a felt area less than a third of that.[3]
There are no documented surface ruptures associated with the earthquake. This suggests the earthquake rupture along the seismogenic structure near the surface were distributed along branch faults or dipped at very shallow angles.[6] If surface ruptures were to occur, it was likely they were destroyed due to flooding in the valley. Surface fissures and sand volcanoes were observed in the ground.[6]
Impact
[edit]The earthquake was assiged a maximum Mercalli-Cancani intensity of X near the epicenter, over 450 km2 (170 sq mi). Liquefaction occurred in the Tagus and Sorraia river plains. At Lisbon, 30 km (19 mi) away, the shaking was felt VI (Strong).[7] Intensity VI was also felt in the cities of Setúbal and Évora, causing some damage. Shaking intensity V was felt in Spain.[8] A reassessment of the maximum intensity on the Modified Mercalli intensity scale in 1956 revised the maximum intensity to IX (Violent).[5]
The towns of Samora Correia and Muge sustained the heaviest damage occurred. Nearly 90 percent of these towns were destroyed.[9] In Benavente, the foundation of a building detached from its structure and tumbled into the Tagus river. Two churches were severely damaged and unsafe for use. A seminary sustained damage when plasters fell from the front facade.[10] Forty percent of buildings in Benavente were razed or had to be torn down. Another 40 perent needed extensive renovation. Only 46 of the 207 structures in Santo Estevao survived the shock.[5]
See also
[edit]References
[edit]- ^ National Geophysical Data Center / World Data Service (NGDC/WDS) (1972), Significant Earthquake Database (Data Set), National Geophysical Data Center, NOAA, doi:10.7289/V5TD9V7K
- ^ Jorge Talixa (12 April 2009). "Centenário do sismo de 1909 que arrasou Benavente e Samora Correia será assinalado com novo simulacro" [Centenary of the 1909 earthquake that devastated Benavente and Samora Correia will be marked with a new simulacrum] (in Portuguese). Público. Retrieved 28 October 2021.
- ^ a b Teves-Costa, P.; Batlló, J. (2011). "The 23 April 1909 Benavente earthquake (Portugal): macroseismic field revision". Journal of Seismology. 15 (1): 59–70. Bibcode:2011JSeis..15...59T. doi:10.1007/s10950-010-9207-6. S2CID 129731577.
- ^ a b Daniel Stich; Josep Batlló; Ramon Macià; Paula Teves-Costa; Jose Morales (1 September 2005). "Moment tensor inversion with single-component historical seismograms: The 1909 Benavente (Portugal) and Lambesc (France) earthquakes". Geophysical Journal International. 162 (3). Oxford University Press: 850–858. Bibcode:2005GeoJI.162..850S. doi:10.1111/j.1365-246X.2005.02680.x. ISSN 1365-246X. S2CID 130288266.
- ^ a b c J. F. B. D. Fonseca; S. P. Vilanova (2010). "The 23 April 23 1909 Benavente (Portugal) M 6.3 Earthquake". Seismological Research Letters. 81 (3): 534–536. Bibcode:2010SeiRL..81..534F. doi:10.1785/gssrl.81.3.534.
- ^ a b J. Cabral; C. Moniz; J. Batlló; P. Figueiredo; J. Carvalho; L. Matias; P. Teves-Costa; R. Dias; N. Simão (2013). "The 1909 Benavente (Portugal) earthquake: search for the source". Natural Hazards. 69 (2): 1211–1227. Bibcode:2013NatHa..69.1211C. doi:10.1007/s11069-011-0062-8. hdl:10400.9/2321. S2CID 129232872. Retrieved 29 October 2021.
- ^ "Sismo sentido em Lisboa na mesma zona dos grandes abalos de 1531 e 1909" [Earthquake felt in Lisbon in the same area as the great earthquakes of 1531 and 1909] (in Portuguese). Diário de Notícias. 18 March 2021. Retrieved 29 October 2021.
- ^ "110 ANOS DO SISMO DE BENAVENTE" [110 YEARS OF THE BENAVENTE EARTHQUAKE]. IPMA. 24 April 2019. Retrieved 29 October 2021.
- ^ Nuno Miguel Ropio (22 April 2009). "Magnitude de terramoto corrigida 100 anos depois" [Earthquake magnitude corrected 100 years later] (in Portuguese). Jornal de Notícias. Retrieved 29 October 2021.
- ^ Teresa Lopes Moreira (19 March 2019). "Memórias da Cidade: Quando a Terra tremeu em 1909 e 1969" [Memories of the City: When the Earth shook in 1909 and 1969]. Correio do Ribatejo. Retrieved 29 October 2021.
Further reading
[edit]- de Pro-Díaz, Y.; Vilanova, S.; Canora, C. (2022). "Ranking Earthquake Sources Using Spatial Residuals of Seismic Scenarios: Methodology Application to the 1909 Benavente Earthquake". Bulletin of the Seismological Society of America. 113 (2): 710–731. doi:10.1785/0120220067. ISSN 0037-1106. S2CID 254778078.