There is no widespread tsunami threat in Puerto Rico, different from first reported by some media. However a local threat could be possible. A strong 6.5-magnitude earthquake struck at sea off the Puerto Rican coast at a shallow depth of less than 30 km early on Monday, the US Geological Survey reports.
The quake hit some 56 km off the northern coast of the island. The capital, San Juan, where 400,000 people live is located on the same side of the island.
No immediate injuries or damage has been reported. The tourism industry is extensive on this part of the island. The Pacific Tsunami Warning Center said the quake could trigger a local tsunami, but there is no threat for a widespread tsunami is in place.
The Puerto Rico quake on Monday comes almost exactly 4 years after a powerful 7.0-magnitude quake devastated another Caribbean island – Haiti.
The 2010 disaster took more than 100,000 lives and caused a humanitarian catastrophe in the nation, which remains one of the poorest in the world.
Seismotectonics of the Caribbean Region and Vicinity
Ekstenzivna raznolikost i složenost tektonskih režima karakteriše perimetar Karipske ploče, uključujući ne manje od četiri glavne ploče (Sjeverna Amerika, Južna Amerika, Naska i Kokos). Nagnute zone dubokih potresa (zona Wadati-Benioffa), okeanski rovovi i lukovi vulkana jasno ukazuju na subdukciju okeanske litosfere duž rubova karipske ploče Centralne Amerike i Atlantskog oceana, dok seizmičnost kore u Gvatemali, sjevernoj Venecueli i Kajmanu Greben i Kajmanski rov ukazuju na transformaciju rasjeda i tektoniku bazena koji se razdvaja.
Duž sjevernog ruba Karipske ploče, ploča Sjeverne Amerike pomiče se prema zapadu u odnosu na Karipsku ploču brzinom od približno 20 mm/god. Kretanje je prilagođeno duž nekoliko velikih transformacijskih rasjeda koji se protežu na istok od Isla de Roatan do Haitija, uključujući rasjed Swan Island i Oriente Fault. Ovi rasjedi predstavljaju južne i sjeverne granice Kajmanskog rova. Dalje na istok, od Dominikanske Republike do ostrva Barbuda, relativno kretanje između ploče Sjeverne Amerike i Karipske ploče postaje sve složenije i djelomično je prilagođeno skoro lučno paralelnom subdukcijom Sjevernoameričke ploče ispod Karipske ploče. To rezultira formiranjem dubokog rova Portorika i zone potresa srednjeg žarišta (70-300 km dubine) unutar potopljene ploče. Iako se smatra da zona subdukcije Portorika može izazvati megapotres, takvih događaja nije bilo u prošlom stoljeću. Posljednji vjerovatni događaj međuploče (potisak) dogodio se 2. maja 1787. godine i osjetio se na cijelom ostrvu uz dokumentovana razaranja na cijeloj sjevernoj obali, uključujući Arecibo i San Huan. Od 1900. godine, dva najveća zemljotresa koja su se dogodila u ovoj regiji bili su zemljotres M4 Samana 1946. avgusta 8.0. u sjeveroistočnoj Hispanioli i potres M29 Mona Passage 1943. jula 7.6. godine, oba su bila potresa plitkog naboja. Značajan dio kretanja između ploče Sjeverne Amerike i Karipske ploče u ovoj regiji je prilagođen nizu lijevo-lateralnih skliznih rasjeda koji dijele ostrvo Hispaniola, posebno Septentrionalni rasjed na sjeveru i Enriquillo-Plantain Garden Fault na jugu. Aktivnost u blizini sistema Enriquillo-Plantain Garden Fault najbolje je dokumentovana razornim zemljotresom M12 na Haitiju 2010. januara 7.0., povezanim naknadnim potresima i sličnim zemljotresom 1770. godine.
Krećući se na istok i jug, granična krivulja ploče oko Portorika i sjevernih Malih Antila gdje je vektor kretanja ploče Karipske ploče u odnosu na ploče Sjeverne i Južne Amerike manje kos, što rezultira aktivnom tektonikom otočnog luka. Ovdje se ploče Sjeverne i Južne Amerike povlače prema zapadu ispod Karipske ploče duž rova Malih Antila brzinom od približno 20 mm/god. Kao rezultat ove subdukcije, postoje i potresi srednjeg žarišta unutar potopljenih ploča i lanac aktivnih vulkana duž otočnog luka. Iako se Mali Antili smatraju jednom od seizmički najaktivnijih regija na Karibima, nekoliko od ovih događaja je bilo veće od M7.0 tokom prošlog stoljeća. Ostrvo Gvadalupe bilo je mjesto jednog od najvećih megapotresa koji se dogodio u ovoj regiji 8. februara 1843. godine, sa sugeriranom magnitudom većom od 8.0. Najveći nedavni potres srednje dubine koji se dogodio duž luka Malih Antila bio je potres M29 na Martiniqueu sjeverozapadno od Fort-De-Francea 2007. novembra 7.4. godine.
The southern Caribbean plate boundary with the South America plate strikes east-west across Trinidad and western Venezuela at a relative rate of approximately 20 mm/yr. This boundary is characterized by major transform faults, including the Central Range Fault and the Boconó-San Sebastian-El Pilar Faults, and shallow seismicity. Since 1900, the largest earthquakes to occur in this region were the October 29, 1900 M7.7 Caracas earthquake, and the July 29, 1967 M6.5 earthquake near this same region. Further to the west, a broad zone of compressive deformation trends southwestward across western Venezuela and central Columbia. The plate boundary is not well defined across northwestern South America, but deformation transitions from being dominated by Caribbean/South America convergence in the east to Nazca/South America convergence in the west. The transition zone between subduction on the eastern and western margins of the Caribbean plate is characterized by diffuse seismicity involving low- to intermediate-magnitude (M<6.0) earthquakes of shallow to intermediate depth. The plate boundary offshore of Colombia is also characterized by convergence, where the Nazca plate subducts beneath South America towards the east at a rate of approximately 65 mm/yr. The January 31, 1906 M8.5 earthquake occurred on the shallowly dipping megathrust interface of this plate boundary segment. Along the western coast of Central America, the Cocos plate subducts towards the east beneath the Caribbean plate at the Middle America Trench. Convergence rates vary between 72-81 mm/yr, decreasing towards the north. This subduction results in relatively high rates of seismicity and a chain of numerous active volcanoes; intermediate-focus earthquakes occur within the subducted Cocos plate to depths of nearly 300 km. Since 1900, there have been many moderately sized intermediate-depth earthquakes in this region, including the September 7, 1915 M7.4 El Salvador and the October 5, 1950 M7.8 Costa Rica events. The boundary between the Cocos and Nazca plates is characterized by a series of north-south trending transform faults and east-west trending spreading centers. The largest and most seismically active of these transform boundaries is the Panama Fracture Zone. The Panama Fracture Zone terminates in the south at the Galapagos rift zone and in the north at the Middle America trench, where it forms part of the Cocos-Nazca-Caribbean triple junction. Earthquakes along the Panama Fracture Zone are generally shallow, low- to intermediate in magnitude (M<7.2) and are characteristically right-lateral strike-slip faulting earthquakes. Since 1900, the largest earthquake to occur along the Panama Fracture Zone was the July 26, 1962 M7.2 earthquake.
