M6.5 Tremor Strikes Puerto Rico, 13 January 2014

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Location and tectonic setting of the M6.5 Puerto Rico earthquake. Image credit: USGS

Location and tectonic setting of the M6.5 Puerto Rico earthquake. Image credit: USGS

An earthquake just rocked the Caribbean region – with magnitude 6.5 (M6.5). The quake struck off the north coast of Puerto Rico, around 100km from the island’s capital San Juan, in the early hours of 13 January 2014.

Although the United States Geological Survey warned of the possibility of a local tsunami (within around 100km) in the event no tsunami occurred and at the time of writing there were no reports of deaths or injuries.

Poignantly, the tremor came just a day after services were held in Haiti to remember the estimated 316,000 people killed in the M7.0 earthquake of 12 January 2010.

January 2014 Puerto Rico Earthquake:

Tectonic Setting

The Caribbean tectonic plate is a sliver of crust caught between the North and South American plates and, to the west, the Cocos plate. As the former move eastwards and the latter westwards, the smaller Caribbean plate is squeezed between them, with the result that it experiences multiple complex forces and, as a result, its boundaries are complex and diffuse.

The northern boundary, which was the location of the most recent tremor, is characterised by lateral, or strike-slip, faulting in the east, becoming a subduction zone in the west. The area around Puerto Rico includes both a subduction zone (to the north) and areas of local extension (to the west).

Initial information for the USGS suggests that the cause of the tremor was reverse faulting along the subduction zone itself a point at which the North American plate is converging with the Caribbean plate at a rate of around 20mm per year.

Puerto Rico Quake: Seismic History

The past 30 days has seen plenty of low-level seismic activity. Image credit: USGS

The past 30 days has seen plenty of low-level seismic activity. Image credit: USGS

Although in recent years Puerto Rico has not fallen victim to a major tremor, the USGS notes that the subduction zone “is capable of hosting M8+ earthquakes.” That said, the tectonic history of the region includes known earthquakes of M7.5 (in 1914) M7.3 (in 1787) and 1918) and M7.0 (1917).

These earthquakes caused considerable damage, with that of 1918 generating a local tsunami and costing 116 lives. The 1867 quake also generated a tsunami.

Although major seismic events are rare along the northern boundary of the Caribbean plate, seismic activity at a lower level is extremely common, with regular small earthquakes along the subduction zone. In the past 30 days, for example, the USGS recorded over 160 tremors of at least magnitude 2.5 in the region of the Puerto Rico Trench.

Haiti Earthquake of 2010

Damage after the Haiti earthquake of 2010. Image: US Coastguard

Damage after the Haiti earthquake of 2010. Image: US Coastguard

Four years and one day before the tremor of January 13 2014, the northern edge of the Caribbean plate was the focus of an M7.0 earthquake which killed an estimated 316,000 people, making it the second most deadly in recorded history.

The tremor occurred further to the east, along an area of the boundary largely dominated by strike-slip faulting. The high death toll is attributable not just to the magnitude of the earthquake but to the density of the population and the nature of the buildings.

Poor construction and high levels of poverty contribute to high death tolls. Haiti provides a sobering reminder go the geologists’ truism – earthquakes don’t kill people: buildings do.

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© Copyright 2014 Jennifer Young, All rights Reserved. Written For: Decoded Science
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