Tobago

Geography

Tobago is the second most southerly island of the Lesser Antilles. Tobago is 30 km (19 mi) northeast of Trinidad and is 41 km (25.5 mi) in length and 12 km (7.5 mi) at its greatest width. It is mountainous and dominated by the Main Ridge, which is 29 km (18 mi) long with elevations up to 640 m. There are deep valleys to the north and south of the Ridge and the southwestern tip of the island has a coral platform. Tobago has a maritime tropical climate influenced by the northeast trade winds. Temperatures range between 20 °C- 34°C and there are two seasons: Dry (January-May) and Wet (June-December).

Country Facts

Tobago is part of the twin-island republic of Trinidad and Tobago. Residents are often referred to as ‘Tobagonians’. Approximately 60,874 people reside in Tobago mainly in and around the capital, Scarborough. English is the country’s official language. It is governed by the Tobago House of Assembly. The island is considered the quieter of the twin-island nation and is steeped in rich culture and traditions. Currency used: Trinidad and Tobago Dollar (TTD).

Disaster Management

In the event of an earthquake or tsunami the Tobago Emergency Management Agency is the official authority in Tobago.

Tobago Emergency Management Agency
Fairfield Complex
Bacolet Street
Scarborough, Trinidad & Tobago

Tel: +1 868-660-7489
Email: temaeoc@gmail.com
Website: http://www.tema365.com/

Seismicity Overview

The Trinidad and Tobago area, as shown in the epicentral plot, is one of the more seismically active zones in the Eastern Caribbean, with an annual average output of about 260 earthquakes of magnitude greater than 2.0.  However, the activity rate is not uniform across the area.  The rate in the Tobago area has picked up since 1990 and whereas in the past the rate was on par with that seen on land Trinidad, it is now closer to that seen north of Trinidad.  Following are details of the significant magnitude events observed in the zones making up the area:

1. West of Tobago – The largest in the instrumental period occurred on 1997/04/02 Mt=5.6 and 2016/12/06 Mt=6.1.  There was some damage in south-west Tobago for the 1997 event.
2. South of Tobago – The largest known occurred on 1997/04/22 Mt=6.1.  There was significant damage in south-west Tobago, with flooding in some areas from large-scale groundwater discharge.

The island of Tobago consists of metamorphic, igneous and sedimentary rocks. These are organized into five lithological units: North Coast Schist, Tobago Volcanic Group, Ultramafic-Tonalitic Plutonic Suite and Mafic Dyke Complex, which are all overlain by Neogene and Quaternary sedimentary rocks. Several major faults transect these units trending mainly E-W and NNW-SSE.

Geology Map of Tobago

North Coast Schist Group (NCSG)

This low-grade metamorphic province outcrops in the northern third of the island. These are the island’s oldest rocks thought to be Lower Cretaceous in age. It is comprised of strongly deformed metavolcanic and metasedimentary rocks that experienced penetrative plastic deformation during greenschist facies metamorphism (Jackson and Donovan 1994).

Tobago Volcanic Group (TVG)

TVG is predominantly a volcaniclastic succession but also contains clinopyroxene-plagioclase phyric basalts and andesitic lavas. Some units of volcanigenic argillites contain Lower-Middle Albian radiolarians and Middle Albian ammonites indicating an Albian age for this unit (Jackson and Donovan 1994).

Ultra-Tonalitic Plutonic Suite

This unit intrudes both the NCSG and the TVG, and forms a zone of contact metamorphism in those areas that have been unaffected by faulting. It consists of four distinct and mappable units: deformed and metamorphosed mafic rocks, ultramafic rocks, diorite-gabbro, and biotite tonalite (Jackson and Donovan 1994).

Mafic Dyke Complex

The NCSG, TVG and Plutonic Suite are all intruded by a swarm of fine-grained dykes which contain hornblende ± clinopyroxene and plagioclase (Jackson and Donovan 1994).

Neogene and Quaternary Sediments

The Mesozoic basement rocks of Tobago are unconformably overlain by Neogene and Quaternary sedimentary rocks. This unit outcrops in the southwestern end of the island and comprises terrigenous and carbonate rocks (Jackson and Donovan 1994).

Jackson, T A, and S K Donovan. 1994. “Tobago.” In Caribbean Geology: An Introduction, edited by S K Donovan and T A Jackson, 193-208. Kingston: The University of the West Indies Publishers’ Association (UWIPA).

Latchman J.L. 1998. Seismic potential of the S.W. Tobago fault system. M.Phil thesis. St. Augustine. The University of the West Indies. Morgan, F.D., G. Wadge, J. Latchman, W.P. Aspinall, D. Hudson and F. Samstag. 1988.

The earthquake hazard alert of September 1982 in southern Tobago. Bulletin of the Seismological Society America. 78:(48): 1550-1562.

Robson, G.R. 1964. An earthquake catalogue for the Eastern Caribbean. Bulletin of the Seismological Society of America. 54:(2): 785-832.