The isthmus also hosts a number of lagoons along its western, Pacific coast, and these have enormous potential for commercially lucrative fishing. Oil and petroleum reserves and some other mineral reserves have also been located in the isthmus, though they have yet to be exploited to an extensive degree. The Isthmus of Tehuantepec experiences a hot and humid tropical climate. Average annual rainfall on the Atlantic Gulf of Mexico side of the isthmus in the east is around 3, millimeters, while the Pacific shores of Tehuantepec have a drier climate.
The isthmus hosts the Selva Zoque, one of the most ecologically significant areas in Mexico, an a region hosting the greatest diversity of terrestrial species in the country. Around 3, species of vascular plants, including orchid species and other valuable plant species like palmita, big-leaf mahogany, and tropical red cedar, are found in these forests.
A great diversity of animals, including spider monkeys, jaguars, White-lipped peccaries, and over species of birds, including the Harpy eagle, Grat curassow, and Ornate hawk-eagles, also inhabit the forests of the isthmus. Since the Isthmus of Tehuantepec was one of the least explored and exploited parts of Mexico up until now, preserving its native habitat was not a big issue.
The Trans-Isthmus Project plans to build large scale petroleum facilities, shrimp farms, industrial parks, and mono-cropped tree plantations throughout the region. Known as "Tehuanas", these women are known throughout Mexico for their colorful dresses, assertive personalities, and relatively equal relations with men, leading some to characterize them as "matriarchal".
The cuisine of the region is based upon traditional foods and ingredients. Dishes may range from simple to elaborate; most dishes incorporate maize and moles. Common items include tamales made with iguana , chicken, beef or armadillo ; guetabingui fried balls of rice and shrimp ; Garnachas topped with dried queso Oaxaca ; and pozol , a maize-based soup.
Map of the Straits of Florida and Gulf of Mexico. Andrews, per the resolution of the Senate of March 8, Isthmus of Tehuantepec facts for kids Kids Encyclopedia Facts. Other measurements whose fast axes are oriented in various directions, however, are interspersed throughout the same region. For anisotropy measurements in the southern part of the VEOX array, where the slab is shallower, the contribution of the continental crust to the delay time will be proportionally greater than for stations farther north.
On the other hand, the segment through the mantle wedge is longer for stations at the northern side of the deployment, while the segments through the Cocos slab and the North American crust stay relatively constant. The very few splitting measurements of crustal anisotropy that were possible have an average delay time of 0. These are in general agreement with earlier work by other colleagues. Shear-wave splitting measurements for the crust around the world have yielded delay times ranging between 0.
One additional consideration is that in order to add up the contributions from the slab, the mantle wedge, and the continental crust to the delay time, the fast polarization directions have to be oriented in the same direction within the three layers, otherwise these contributions will tend to cancel each other out. In summary, under the southern end of the VEOX array it is difficult to unravel the anisotropy contributions from the slab, the mantle wedge, and the North American crust.
The southern part of the array is located over the mantle wedge tip. For 2-D corner flow we thus would expect to see trench-parallel fast directions, but as we described, the anisotropic pattern is not well organized at the southern end of the array.
The anisotropy observed at the southern end of the VEOX line does not reflect processes in the mantle wedge alone because any anisotropy within the North American continental crust should also have a strong effect on the delay times. We do not believe that the use of different models leads to a significant error. Comparison with fig. If the delay time were produced solely by flow in the mantle wedge, ignoring any crustal contribution, this region would be interpreted to have an incoherent LPO.
This trend is in broad agreement with the model proposed by Kneller et al. Probably the best example of such a transition in the anisotropy pattern Kneller et al. Several studies have been conducted to determine the anisotropy in other segments of the MAT using local S waves from hypocentres within the slab. In Mexico, in a region located west of the present study Fig.
Soto et al. Given the limited depth extent of local earthquakes, they could not constrain the anisotropy in the mantle wedge. Abt et al. They further proposed that the mechanism driving along-arc transport is toroidal flow around the edge of the slab in southern Costa Rica, generated by greater slab rollback in Nicaragua.
This is indeed the case in the Isthmus of Tehuantepec region. These fast polarization directions are trench-perpendicular.
At this location, however, the teleseismic SKS and local S phases imply mantle flow parallel to the trench, both beneath the subducted Cocos slab and in the mantle wedge Abt et al. Based on current data it is not possible to tell where and how the transition from 2-D corner and entrained flow under Oaxaca to 3-D return flow under Nicaragua and Costa Rica takes place.
This is an interesting topic for future research. Measurements of anisotropy using local S waves from earthquakes within the subducting Cocos Plate were made with data from an array deployed across the Isthmus of Tehuantepec.
The region to the northeast of the contour would normally be considered the backarc, except that no volcanic arc exists right over this segment of the Cocos slab. In any case, the fast polarization directions are trench-perpendicular, and the lag times are on the order of 0. Based on other studies throughout this region, it is inferred that the core of the mantle wedge should have conditions such as high temperature, low stress and low water content which are conducive to A-type olivine fabric.
The splitting observations are thus inferred to indicate the existence of 2-D corner flow in this region, consistent with downdip motion of the subducted Cocos Plate. This region is located over the mantle wedge tip, where conditions such as low temperature, high water content and high stress exist. Therefore, the development of B-type olivine fabric would be expected. If 2-D corner flow operates in the wedge tip, then trench-parallel faxt axes should be observed, but are not.
Given the shallow depth of the slab at the southern end of the experiment, contributions to the observed anisotropy pattern from the slab, the mantle wedge, and the overlying continental crust are all expected to be significant, which may explain the poor coherence of the anisotropic pattern.
Comparison of local shear-wave splitting observations in the mantle wedge from VEOX data with teleseismic SKS splitting in a few permanent stations shows an agreement in the orientation of the trench-perpendicular fast axes. Furthermore, it suggests the existence of 2-D, entrained mantle flow beneath the Cocos slab. In another segment of the MAT, located in Nicaragua and Costa Rica and east of the region in the present study, local and teleseismic fast directions also agree.
In this case, however, the observations are trench-parallel and indicative of mantle flow parallel to the trench both above and below the subducted Cocos Plate. It is unknown how and where the transition from trench-perpendicular fast axes under Oaxaca to trench-parallel ones under Nicaragua and Costa Rica takes place.
We thank the editor Xiaofei Chen, Satoshi Kaneshima, and an anonymous reviewer for their suggestions to improve the manuscript. Google Scholar. Google Preview. Additional Supporting Information may be found in the online version of this article:. Figure S1. Compilation of SKS measurements in central Mexico. RP stands for Rivera Plate.
These measurements are taken from the work by van Benthem et al. Figure S2. Backazimuthal coverage of local S waves at each station, including the VEOX stations and the epicentres. Figure S3. Map of individual measurements in each square of the grid. In order to display the results in a straightforward, yet robust manner, the study area was divided into a grid made up of squares, each 0.
All individual measurements whose midpoint fell within the same square of the grid were plotted at the centre of the square. The energy plots for all measurements within each square were subsequently stacked.
The resulting average is shown in Fig. Table S1. Source parametres of local S earthquakes. Table S2. Individual, local S -wave splitting parametres. Table S3. Average, local S -wave splitting parametres by grid square. Table S4. Individual S -wave splitting parametres in the continental crust Supplementary Data. Please note: Oxford University Press is not responsible for the content or functionality of any supporting materials supplied by the authors.
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Volume Article Contents Abstract. Corner flow in the Isthmus of Tehuantepec, Mexico inferred from anisotropy measurements using local intraslab earthquakes. Oxford Academic. Mexico City, D. E-mail: raul ollin. Revision received:. Select Format Select format. Permissions Icon Permissions. Abstract Shear-wave splitting measurements were made using S waves from local earthquakes recorded by stations of the Veracruz-Oaxaca array, which was deployed across the Isthmus of Tehuantepec. Mantle processes , Body waves , Seismic anisotropy , Subduction zone processes , Dynamics of lithosphere and mantle , North America.
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