The Gulf of America was rocked by the second earthquake this week, just days after the strongest earthquake on record struck the body of water previously known as the Gulf of Mexico. This latest quake struck 4 miles west of the earlier, stronger one. According to USGS, the second quake hit at 9:04 pm Tuesday night from a depth of 16 km which is more shallow than the larger quake which struck at a depth of 26 km. This latest earthquake was rated a magnitude 4.1 event which remains strong by Gulf standards, but much weaker than the 6.1 which struck on Monday.
While the stronger quake earlier this week triggered tsunami bulletins, this latest earthquake didn’t.
USGS says that earthquakes with a magnitude of 2.0 or less are rarely felt or heard by people, but once they exceed 2.0 , more and more people can feel them. While damage is possible with magnitude 3.0 events or greater, significant damage and casualties usually don’t occur until the magnitude of a seismic event rises to a 5.5 or greater rated event.
The National Weather Service’s Pacific Tsunami Warning Center (PTWC), which is also responsible for issuing Tsunami Advisories and Warnings to the Gulf of America and U.S. East Coasts, issued a bulletin shortly after the Monday earthquake. “Based on all available data, there is no significant tsunami threat from this earthquake,” the PTWC said. They added, “However, there is a very small possibility of tsunami waves along coasts located nearest the epicenter.”
“There is no tsunami danger for the U.S. east coast, the Gulf of America states, or the eastern coast of Canada,” wrote PTWC in an additional bulletin to address other areas exposed to tsunami threats.
More than 3,600 people across much of Florida used the “Did you feel it?” online reporting tool at the USGS website to report feeling the earthquake on Monday. The same didn’t happen with this latest earthquake, which was much weaker and a bit more west than the first.
Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel towards land, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves.
A tsunami is a series of waves not simply a single event. The time between wave crests can vary from 5 minutes to an hour. The hazard may persist for many hours or longer after the initial wave. Impacts can vary significantly from one section of coast to the next due to local bathymetry and the shape and elevation of the shoreline. Impacts can also vary depending upon the state of the tide at the time of the maximum tsunami waves.
While the Pacific is better known for tsunamis, tsunami can and does occur in the Atlantic basin too. As with the Pacific basin, earthquakes can trigger a tsunami threat for the U.S. East and Gulf coasts. According to USGS, submarine landslides can be one result of an Atlantic-based quake. An offshore earthquake with a magnitude 4.5 or greater can destabilize the continental shelf, causing massive underwater avalanches. These landslides displace large volumes of water and can generate significant, localized tsunamis. This was the case during the 1929 Grand Banks earthquake near Canada, which caused a destructive localized tsunami. Distant tectonic earthquakes can also create problems; massive earthquakes along faults further away in the Atlantic, such as the Azores-Gibraltar Transform Fault near Portugal or the Puerto Rico Trench in the Caribbean, are capable of generating tsunami waves that travel across the ocean. While the infamous 1755 Lisbon earthquake created a trans-Atlantic tsunami that was recorded on the East Coast, the height of the waves reaching the US mainland was relatively small but different earthquake intensities and locations can trigger very different results.
It is very unusual for earthquakes to hit the Gulf of America. Monday’s earthquake was the strongest on record. The next strongest earthquake hit on September 10, 2006 when a magnitude 5.9 earthquake struck the central Gulf of Mexico. The next strongest earthquake on record hit on February 10, 2006 near Grand Isle, Louisiana; it was a magnitude 5.3 quake.
