Earthquakes and Tsunamis in Cayman

Grand Cayman lies close to the boundary zone of the Caribbean and North American tectonic plates. This transform boundary, where the plates slide past each other, is known to generate earthquakes.

Tsunamis are most often triggered by underwater earthquakes, with waves spreading outwards very rapidly from the site of the earthquake. Out at sea these waves typically measure around one foot in height and may travel at speeds of 400 mph. When the tsunami reaches the shallow waters of a continental shelf, the wave slows and its height increases.

Although tsunamis triggered by earthquakes can occur in Cayman, the probability is believed to be very low: Cayman’s underwater landscape, with steep drop-offs close to shore and very little continental shelf, may well reduce the risk of dangerous tsunamis.

Earthquake of January 28th 2020

The strongest recorded earthquake in the Cayman Islands occurred on January 28th 2020 and measured 7.7 magnitude. Its epicentre was 67 miles from Cayman Brac and 154 miles from Grand Cayman. Although there were multiple reports of sinkholes and some reports of one-to-two-foot-high waves, no major structural damage occurred. Over 10 aftershocks were felt, with the strongest tremor measuring 6.1 magnitude with the epicentre just 35 miles east of Grand Cayman. In addition to the Cayman Islands, affected countries include the Bahamas, Jamaica, Haiti, Honduras and Cuba. Before this, the strongest recorded earthquake in the Cayman Islands, which occurred on 14 December 2004, measured 6.8 and very minimal damage occurred.

A tsunami threat warning was briefly issued and residents were advised to stay away from the coast. However within an hour, Hazard Management Cayman Islands announced the Tsunami All Clear.

Advance Preparation for Earthquakes and Tsunamis

Earthquakes strike without warning, and tsunamis with very little warning, so there is not a great deal one can do to prepare, but it is important to be familiar with the recommended course of action in case of such an event.

Cayman’s building code regulations ensure that modern buildings are strong enough to withstand a certain degree of quaking so the main hazards are unsecured appliances, objects and structures that could fall and cause injury, downed power lines and damaged water and sewerage systems.

As a preventative measure Hazard Management Cayman Islands recommends bolting down appliances and bookshelves, placing heavy objects on lower shelves and making sure one has emergency supplies – non-perishable food items, water, first aid kit, flashlight and a battery operated radio – at hand.

In the event of a tsunami, small buildings close to the coast are the ones at greatest risk as they are not designed to withstand the impact of a tsunami. For those living close to the sea, it is important to have a family emergency plan in place and to familiarise yourself with the nearest safe place to evacuate to.

What To Do During an Earthquake

If indoors: duck, cover and hold. Get under a solid piece of furniture (e.g. a table or desk) or under a reinforced doorway, cover your head and eyes to protect yourself from flying objects, and hold on to the furniture with one hand. Do not move until the shaking has stopped.

If outdoors: remain outdoors until the shaking has stopped. Move to an open space away from buildings, glass, electrical cables or other objects that could fall and cause injury.

If driving: slow down and pull over to the side of the road in an open area. After the shaking stops proceed carefully being aware of the potential for splits in the road and sinkholes.

After an Earthquake

• Evacuate the building
• Do a head count and report any missing persons to emergency services
• Beware of broken glass and debris
• Be prepared for aftershocks which could cause further damage
• Check for fire, gas leaks, spilled chemicals, etc.
• If at the coast, move inland in case of a tsunami

What To Do During a Tsunami

The Cayman Islands does not currently have a siren system (this is considered too costly to install and maintain). However, in 2021, a National Emergency Notification System was implemented which allows Government to interrupt radio broadcasts with emergency notifications.

There is usually very little warning time if a tsunami threatens so residents should NOT wait for an official warning but take action immediately. Below are some important tips for what to do in the event of a tsunami.

• If you are at the coast and see the water receding, move away immediately - this typically occurs just before the tsunami strikes.
• Be aware that subsequent waves may strike at intervals of anywhere between 15 minutes and one hour.
• If you are close to the coast and a tsunami warning is issued, move inland to higher ground or to a higher floor in a tall building.
• If you are out at sea, stay out at sea.

NOAA Tsunami Risk Model in Cayman

In September 2023 scientists from the US National Oceanographic and Atmospheric Administration (NOAA) arrived in Grand Cayman to run a Cayman Islands Tsunami Hazard Assessment to scientifically measure exactly where a tsunami could be produced in Cayman, at what height and how strong the earthquake would need to be. The project was part of a wider Caribbean Tsunami Ready project funded by the US Agency for International Development (USAID) through ITIC-CAR.

The NOAA tsunami model used 39 potential earthquake scenarios which are regarded as having the greatest likelihood of producing a significant tsunami impact on the Cayman Islands. It was found that of all the scenarios, the most significant threat for the Cayman Islands related to an earthquake occurring directly south of the Cayman Islands along the transform plate boundary line, as opposed to other larger but more distant events such as in the subduction zones in the Eastern Northeastern Caribbean or near the coast of Colombia.

Dr Arcas ran the model using the January 2020 7.7 magnitude earthquake rupture parameters, but shifted the earthquake location along the transform plate boundary line, so that in each case, the epicentre occurred directly south of each of the three inhabited Cayman Islands (Grand Cayman, Little Cayman and Cayman Brac). This is a minor change from what actually occurred in January 2020 and therefore considered a realistic possibility. The model showed that tsunami impacts would indeed occur, especially for the southern coasts of the Islands. In some areas, the arrival of the tsunami would be in as little as 5 minutes after the earthquake, and wave heights could be up to 18ft in isolated areas. However, even along the south coast, the inundation was no more than 0.5km. Interestingly, the coastal areas abutting the North Sound were found to be at lower risk from a tsunami. Currents of up to 3m/second, which could cause damage, were also modelled by Dr Arcas.

These worst-case tsunami risk scenarios will inform Hazard Management Cayman Islands' (HMCI) efforts to increase awareness, preparedness and response planning, including the production of evacuation maps for vulnerable communities along parts of the coastline. The joint effort of the US and the Cayman Islands contribute to the UN Ocean Decade goal that 100% of communities at risk are prepared for and resilient to tsunamis by 2030. [Information provided by Simon Boxall at HMCI]