.. and not much doing

On Saturday, March 3, there was an earthquake in Jamaica. It wasn’t much of an earthquake, with an intensity of just 4.0 on the Richter scale. The centre was located about 18 km below the earth’s surface, just south of St. Margaret’s Bay in a sparsely settled area of Portland where a lot of Jamaica’s earthquakes happen.

The quake struck at about 2 o’clock in the afternoon, a time when most people were busy finishing lunch, shopping, doing weekend chores or watching Saturday sports. However, a lot of them felt a shake and couldn’t wait to tell the world about it. As soon as the U.S. Geological Survey (principal recorder of earthquakes around the world) confirmed the event, Facebook, Instagram and Twitter lit up with “I felt it” reports.

More than two dozen Jamaicans sent reports to USGS, most of them from the Kingston-St. Andrew- Portmore area. The majority of these reports mentioned brief, mild shaking. A few experienced longer periods (20-30 seconds) of stronger shaking, enough to rattle grills and move chairs.

Earthquakes happen because the floating chunks of the earth’s crust – “tectonic plates” – are constantly moving. Sometimes the edges of two plates get stuck as they move past each other, usually deep underground or underwater. Pressure builds until the stuck spot lets go, and the released energy is felt at the surface as an earthquake.

The Caribbean Plate is carrying us eastward past (and over) the North American Plate at an average speed of a little less than an inch a year, except when it gets stuck. Jamaica sits on a chip of the Caribbean Plate bounded on the south by the Enriquillo/Plantain Garden Fault. This big crack in the earth’s crust can be seen from space as a sharp cut through the mountains of Haiti before it disappears under water and runs into the east end of Jamaica. There it joins the local fault system, a web of cracks that allow the shock from any earthquake with its centre on or near land to be felt over a wide area.

Though the March 3 quake happened in northern Portland, most of the “felt it” reports came from Kingston. It appears that most of the shock from the quake passed southward down the Blue Mountain and Wagwater fault lines, major cracks that outline a belt of limestone thrown up during the lower-middle Eocene period of the earth’s development, about 35-40 million years ago.

By the same process, a 3.9-intensity quake on February 5 with its centre at Maggotty in St. Elizabeth was felt in Hanover, Westmoreland and St. James. The shock traveled north up the faults that outline the Montpelier-Newmarket limestone belt, most of which dates from the middle to late Miocene period (5-10 million years ago).

The March 3 quake probably caused more drama than it deserved, but even a moderate earthquake can be dangerous. There are a couple of very good reasons to be prepared.
First, if you’re a town planner or considering a major property investment, earthquake risk isn’t something you can ignore. In the last hundred years there have been four “serious” quakes in Jamaica, the last of them in June of 2005. UWI’s researchers are suggesting that we may be due for another one in the near future. Even something as mild as the 2014 Mother’s Day quake can still set off a deadly landslide on a slope eroded by deforestation or undermined by careless quarrying or construction.

Second, earthquakes aren’t the only disasters that happen in Jamaica. (It’s only a couple of months to the start of another tropical storm season.) Hurricanes, floods, landslides, fires and explosions come along much more regularly and often with little warning. A good disaster management plan has most of the same elements whether it’s for an earthquake or a bad rainstorm.

The next major earthquake may happen next week, or 100 years from now. Earthquakes can’t be prevented, and they give almost no advance warning. If we can learn to make good emergency plans and lose a few bad habits, it will save a lot of lives and property even if the ground holds still.