An tsunamigenic earthquake occurred on 26 August 2012 at 22:37 CST with an epcenter off the coast of Usulután, El Salvador. It measured 7.3 on the moment magnitude scale (Mw) and had a focal depth of 16.0 kilometres (10 mi).[1] It was felt along the country's coast and in San Salvador although there was no damage. Along the San Juan del Gozo Peninsula, a tsunami triggered by the shock left 40 people injured. Waves were measured with a maximum run-up of 6.3 m (21 ft). The earthquake and tsunami was caused by a rupture on a subduction zone associated with the Middle America Trench.[2]
  | |
| UTC time | 2012-08-27 04:37:19 |
|---|---|
| ISC event | 601626911 |
| USGS-ANSS | ComCat |
| Local date | 26 August 2012 |
| Local time | 22:37 CST |
| Magnitude | Mw 7.3 |
| Depth | 16.0 km (10 mi) |
| Epicenter | 12°08′20″N 88°35′24″W / 12.139°N 88.590°W |
| Type | Thrust |
| Areas affected | El Salvador and Nicaragua |
| Max. intensity | MMI II (Weak) |
| Tsunami | 6.32 m (21 ft) |
| Foreshocks | Yes |
| Aftershocks | Yes |
| Casualties | 40 injured |
Tectonic setting
editA convergent plate margin extends along the west coast of Central America where two tectonic plates collide. Oceanic lithosphere of the Cocos plate subducts beneath the continental crust of Central America. This continental crust is part of the Caribbean plate. Sunduction occurs along the Middle America Trench, and the Cocos plate moves towards Central America at an estimated 8.23 ± 0.22 cm (3.240 ± 0.087 in) per year.[3] The subduction zone is seismically active and has been responsible for large and tsunamigenic earthquakes when it ruptures. One of these large earthquakes affected Nicaragua in 1992, measuring Mw 7.6 and caused a destructive tsunami.[4]
Earthquake
edit
Applying seismic inversion on 83 broadband P-wave records, a west–northwest striking, northeast dipping fault plane was ascertained, corresponding to the shallow portion of the megathrust closest to the seafloor. The rupture exended from 23 km (14 mi) depth along the megathrust towards the trench and propagated through the fault at 2 km (1.2 mi) per second. The model determined that an approximately 50 km (31 mi) length of the megathrust produced slip of up to 1.2 m (3 ft 11 in). This event released energy slower and with a longer duration relative to the megathrust events of Guatemala and Costa Rica several months later which exhibited a typical faster energy release. The El Salvador event displayed tsunami earthquake characteristic similar to the shock that affected Nicaragua in 1992.[5]
Multiple eyewitnesses on the peninsula described the shaking as light. One compared it to a swaying boat lasting 30 to 40 seconds, another said suspended light fixtures swayed and corrugated metal roofing vibrated. A sea turtle hatchery worker at Corral de Mulas said the shaking persisted for two to three minutes.[6] According to residents living in San Salvador, the earthquake was not perceived at all or it was weak.[7] Servicio Nacional de Estudios Territoriales evaluated the shaking to be II (Weak) on the Modified Mercalli intensity scale.[8] Similarly, witnesses of the 1992 shock described weak shaking that is a characteristic of tsunami earthquakes.[9]
Tsunami
editEight minutes after the earthquake, at 22:45, the Pacific Tsunami Warning Center (PTWC) issued an advisory along the Central American coasts. They evaluated that the event as a slow earthquake at 22:47. Eleven minutes later, the PTWC raised their advisory to a tsunami warning after receiving strong evidence of its rupture characteristic. The warning was cancelled at 00:27 after there was no indication of significant damage. There was only two tide gauges at Acajutla and La Union; an amplitude of 14 cm (5.5 in) was recorded at the former location while no tsunami was detected on the latter gauge. No tide gauges were installed at the coast nearest to the epicenter. A 40 cm (16 in) tsunami was recorded at the Galapagos Islands three hours later.[6] The tsunami impacted a sparsely unpopulated length of the Salvadorian coast. In Nicaragua, it flooded three coastal settlements with an estimated flow height of 0.5 m (1 ft 8 in).[9]
Along the coast of the San Juan del Gozo Peninsula, Usulután, close to the epicenter, the tsunami had greater coastal effects. Several dozen conservationists were collecting sea turtle eggs along the beach when the tsunami struck.[10] The Ministry of Natural Resources investigated 11 sites on the peninsula. These sites shared similar geomorphology; these beaches were steep-sloped and had black sand, atop the berm was a dune crest, and the terrain was relatively flat or slightly sloping beyond the berm. A section of beach near La Maroma village experienced the greatest impact of the tsunami. The area also has large sea turtle hatchery, where the walls of a ramada were destroyed and its wooden supports tilted due to the force of the tsunami. A hatchery worker in the ramada was carried by the tsunami for 90 m (300 ft) towards a tree branch some 2.1 m (6 ft 11 in) above the ground. The tsunami flooded as far as 340 m (1,120 ft) inland. Another survivor who stood outside the ramada was swept beyond the tree branch. A Civil Protection coordinator said 40 people at the beach were injured including three who required medical treatment.[6]
A resident of El Retiro claimed that two people and horse were pulled down the beach by the tsunami. Another eyewitness in Corral de Mulas reported two waves with the second being the largest. The waves topped a fence post located 1 m (3 ft 3 in) above the dune crest and several meters inland. Tsunami overwash and inundation was evident in the area. Similarly, debris accumulated by the inundation was observed near the beaches of Ceiba Doblada. In other parts of Ceiba Doblada, the tsunami deposited sand onto the terrain. At Isla de Mendez, the tsunami had an estimated height of 6.32 m (20.7 ft) and penetrated 350 m (1,150 ft) inland. A 15 km (9.3 mi) stretch east and west of the area experienced 3–6 m (9.8–19.7 ft) tsunami waves. Some 25 km (16 mi) west, such as in the resort town of Costa del Sol, there was no wave damage.[6]
See also
editReferences
edit- ^ ISC-OB Event 601626911 [IRIS].
- ^ Álvarez-Gómez, José A.; Vázquez, Alejandra Staller; Martínez-Díaz, José J.; Canora, Carolina; Alonso-Henar, Jorge; Insua-Arévalo, Juan M.; Béjar-Pizarro, Marta (2019). "Push-pull driving of the Central America Forearc in the context of the Cocos-Caribbean-North America triple junction". Scientific Reports. 9 (11164): 11164. Bibcode:2019NatSR...911164A. doi:10.1038/s41598-019-47617-3. PMC 6671955. PMID 31371752.
- ^ Zamora, N.; Babeyko, A.Y. (2016). "Tsunami potential from local seismic sources along the southern Middle America Trench" (PDF). Natural Hazards. 80 (2): 901–934. Bibcode:2016NatHa..80..901Z. doi:10.1007/s11069-015-2004-3. S2CID 130969961. Retrieved 21 April 2021.
- ^ Satake, Kenji (15 November 1994). "Mechanism of the 1992 Nicaragua Tsunami Earthquake". Geophysical Research Letters. 21 (23): 2519–2522. Bibcode:1994GeoRL..21.2519S. doi:10.1029/94GL02338. Retrieved 21 April 2021.
- ^ Ye, Lingling; Lay, Thorne; Kanamori, Hiroo (2013). "Large earthquake rupture process variations on the Middle America megathrust" (PDF). Earth and Planetary Science Letters. 381: 147–155. Bibcode:2013E&PSL.381..147Y. doi:10.1016/j.epsl.2013.08.042.
- ^ a b c d Francisco Gavidia-Medina (2015). "Field survey report of tsunami effects caused by the August 2012 offshore El Salvador earthquake" (PDF). Science of Tsunami Hazards. 34 (4): 231–255. Retrieved 22 April 2021.
- ^ Muñoz, Juan Andrés (27 August 2012). "Un sismo de magnitud 7,4 sacude El Salvador; se cancela la alerta de tsunami" [A 7.4 magnitude earthquake shakes El Salvador; tsunami warning is canceled] (in Spanish). CNN Español. Retrieved 21 April 2021.
- ^ Pineapple, R; Cavajal, A.; Melgar, G. (27 August 2012). "Un fuerte terremoto de magnitud 7,4 sacude la costa de El Salvador" [A strong 7.4 magnitude earthquake shakes the coast of El Salvador] (in Spanish). El Mundo. Retrieved 21 April 2021.
- ^ a b Borrero, J.C.; Kalligeris, N.; Lynett, P.J. (2014). "Observations and Modeling of the August 27, 2012 Earthquake and Tsunami affecting El Salvador and Nicaragua". Pure and Applied Geophysics. 171 (12): 3421–3435. Bibcode:2014PApGe.171.3421B. doi:10.1007/s00024-014-0782-2. S2CID 1554690.
- ^ DPA (11 September 2012). "Experts confirm that there was a tsunami in El Salvador after the August earthquake" [Expertos confirman que hubo tsunami en El Salvador tras sismo de agosto] (in Spanish). El Mercurio On-Line. Retrieved 21 April 2021.
External links
edit- El Salvador Tsunami, August 27, 2012 Main Event Page (NOAA)
- El Salvador Tsunami, August 27, 2012 Local Impacts (NOAA)
- The International Seismological Centre has a bibliography and/or authoritative data for this event.