Wednesday, January 13, 2010

Sismo no Haiti

Major Tectonic Boundaries: Subduction Zones (zonas de subducção, convergência de placas tectónicas) -purple, Ridges (termo geológico para crista ou elevação ao longo de vários km, geralmente devido ao afastamento de placas, geração de novas crosta oceânica) -red and Transform Faults (falhas tectónicas ou placas tectónicas conservativas, que se formam geralmente nos bordos de falhas mais importantes, como falhas divergentes) -green
Tectonic Summary The January 12, 2010, Haiti earthquake occurred in the boundary region separating the Caribbean plate and the North America plate. This plate boundary is dominated by left-lateral strike slip motion and compression, and accommodates about 20 mm/y slip, with the Caribbean plate moving eastward with respect to the North America plate. Haiti occupies the western part of the island of Hispaniola, one of the Greater Antilles islands, situated between Puerto Rico and Cuba. At the longitude of the January 12 earthquake, motion between the Caribbean and North American plates is partitioned between two major east-west trending, strike-slip fault systems -- the Septentrional fault system in northern Haiti and the Enriquillo-Plaintain Garden fault system in southern Haiti. The location and focal mechanism of the earthquake are consistent with the event having occurred as left-lateral strike slip faulting on the Enriquillo-Plaintain Garden fault system. This fault system accommodates about 7 mm/y, nearly half the overall motion between the Caribbean plate and North America plate. The Enriquillo-Plaintain Garden fault system has not produced a major earthquake in recent decades. The EPGFZ is the likely source of historical large earthquakes in 1860, 1770, 1761, 1751, 1684, 1673, and 1618, though none of these has been confirmed in the field as associated with this fault.

Exemplo de falhas transformantes.

Exemplo de ridge/ crista oceânica.

Exemplo de zonas de subducção (convergência de 2 placas continentais e convergências entre crosta oceânica e crosta continental).

Strike-slip faults:

The fault surface is usually near vertical and the footwall moves either left or right or laterally with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults. Those with right-lateral motion are also known as dextral faults. A special class of strike-slip faults is the transform fault, which is a plate tectonics feature related to spreading centers such as mid-ocean ridges. Transform faults are often referred to as transform plate boundaries. Strike slip faults typically have near vertical fault planes, and since the displacement is parallel to the strike of the fault plane, there generally is no hanging wall or foot wall. Strike slip faults are defined by the relative motion of the block on the opposite side of the fault from the point of observation. For example, if the relative motion on the opposite side of the fault is to the left, it is called a “left-lateral strike slip fault”. If the relative motion on the opposite side of the fault is to the right, it is called a “right-lateral strike slip fault”.

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