One of the aids used in locating the position of the right lateral transform fault (RLTF) was provided by the world map “Surface of the Earth” generated by Peter W. Sloss (see figure 4). This map has a weak topographic high crossing southern Louisiana and Texas. This high is the surface expression of the Cretaceous Shelf Edge as it extends across the south. However, in southwestern Texas this ridge makes a 125-degree southward turn (arrows).
When the RLTF was placed along this south trending high, the answer to several Mexican East Coast geological problems were satisfied (figure 2).
- In northeastern Mexico, Cretaceous and older are present west of the northern RLTF; east of this line, however, the Tertiary section expands tremendously and the older Mesozoic is missing.
- The San Carlos and Tamaulipas volcanic fields are aligned perfectly with this RLTF trend.
- The Lower Cretaceous Tuxpan Platform is located along the western edge of the RLTF. This location places it on the high side of the transform fault and in a perfect position for the growth of the Golden Lane reef trend.
- This right lateral transform fault easily answers the question of why the Tuxlas volcanic field is offset southward from the Trans-Mexican Volcanic Belt. Along this transform line separation of the Trans-Mexican Volcanic Belt and the Tuxlas volcanic field occurred. Tuxlas was moved south leaving a trail of three submarine volcanoes along the separation line.
- The southern movement of the GoM plate along the RLTF could be the cause of the northeast-southwest trend to the Mexican Ridges deformation belt.
Earthquake Activity
With active tectonic plate movement there will be accompanying earthquake activity. As the GoM plate moves in a southeasterly direction dozens of recently recorded earthquakes have been detected by this action (figure 1).
For this study only the quakes that were recorded in the water portion of the GoM are presented. (Earthquakes located in the southern part of the Bay of Campeche were not included in this count.)
Thirty-six quakes were generated within the Gulf’s open waters and all are confined to the area of the GoM plate. Most of these earthquakes are located on or near the trailing edge of the moving plate. Several outline the transform faults; the rest are scattered over the surface of the GoM plate.
Most of these earthquakes are small in strength (MS=3 to 4).
In 2006, however, there were two that struck along the eastern edge of the trailing edge of the GoM plate, registering MS=5.2 and MS=6.0 (red circles). The MS=6.0 caused slight damage along Florida’s west coast.
On May 23, 2007, a third strong quake hit (MS=5.2) 80 miles off the coast of Tampico (red circle).
There is definitely tectonic activity acting along this moving GoM plate. This study simply points to the fact that there will be more earthquakes occurring along this plate and some will be quite large – they could be in the MS=5 range to a possible MS=6.5.
Rotating GoM Plate
Every aspect of the GoM plate has the appearance of a freely rotating block moving in a counterclockwise direction.
With this plate located in the middle of opposing moving blocks, tectonic forces would be a major cause of this rotational movement as follows:
- On the northern boundary of the GoM plate the North American mass is moving west.
- The GoM plate itself is moving southeast.
- Jamming in from the west in a northeasterly direction is the Cocas plate.
- The Caribbean plate is moving east with contact across the southern edge of the GoM plate.
Yucatan’s Eastward Motion
Bertha Márquez-Azúa and Charles DeMets, in their 2003 article “Crustal Velocity Field of Mexico,” state that all sites in the Yucatan Peninsula move toward the east at three-four mm/year, possibly defining an independent Yucatan block (figure 2).
Physiographic features of the mountain ranges support their statement. The RLTF joins the Chiapas fault near the Tuxlas volcanic field. From there this complex trends southeast to east and follows the prevailing mountain ranges of southern Mexico, Guatemala and Honduras. This would argue that the Yucatan portion of the plate is moving in an easterly direction.
Tectonic Forces
Figure 3 describes the forces exerted by even small tectonic plates. The Scotia Plate could be called the “armor piercing plate” the way it has crashed through what appears to have been a connection between the tip of South America and the Antarctic Peninsula.
On the northern tip of South America a similar situation exists, with the Caribbean Plate appearing to “crash” through Central America.
There would be more than enough force and energy generated by these movements to rotate the GoM Plate.