El Mezquital Research Articles

Spatio-temporal distribution of the b-value in the volcanic complex and geothermal field of Tres Vírgenes; Baja California Sur, Mexico

Analysis of 1275 seismic events recorded at least at 4 seismic stations during 2009–2013, enabled to conduct the analysis of the b-value from the Gutenberg-Richter relation in time and space in the Tres Vírgenes Volcanic and Geothermal Complex (TVVGC). A mean value of 1.64 (b = 1.64 ± 0.08) was calculated for all the TVVC, which is alike to estimations obtained at other geothermal zones and volcanic regions. The spatial distribution can be characterized by four zones with distinctive ranges of b-values. Zone A (b = 2.07 ± 0.2) corresponds to the central part of the TVVC. Zone B (b = 0.63 ± 0.04) comprises El Aguajito caldera, and El Cimarrón Fault. Zone C (b = 2.33 ± 0.3) is centered between the La Virgen Volcano, and La Virgen Fault. The zone west of La Virgen volcano, delimited by the Mezquital, and Bonfil Faults, constitutes zone D (b = 0.946 ± 0.1). A large regional and local tectonic heterogeneity is associated with zones A and C. Zone A comprises the geothermal production operation zone. Zones B and D can be correlated with regional tectonics. Larger seismicity levels are observed in zones A and C (a-values of 6.52 and 7.8 respectively) with respect to zones B (a = 2.81) and D (a = 3.05). The minimum magnitude of completeness (Mc) was 2.3 and 2.6 for zones A and C, and 1.2, and 1.5 for zones B and D. At depths of 3.5 and 7.0 km, values of b = 1.47 ± 0.1 and 2.24 ± 0.2 were obtained. For depths less than 2.5 km, and larger than to 7.1 km, we estimated b = 0.93 ± 0.1 and 0.789 ± 0.05. Similarly, the largest values of the a-parameter (i.e., 4.72 and 7.66), are associated with depths between 3.5 and 7.0 km. The lowest values, 3.23 and 3.25, correspond to shallow depths of less than 2.5 km, or larger than 7.1 km. The largest values observed between 3.5 and 7.0 km might indicate that permeability is low at the Mesozoic granitic basement, and intense seismic activity (seismic swarms) is associated with tectonic and geothermal processes. Cylindrical to vertical oblate volumes are associated with four high b-value anomalies which correlate with deep reaching NW-SE regional faults (i.e., El Mezquital, La Virgen-El Campamento, and El Azufre-Reforma). These anomalies stretch along several depth intervals. A recently reported distribution of Vp, and Vp/Vs beneath the volcanic complex further indicates that the combination of tectonic and geothermal process giving rise to two of such anomalies might be due to the presence at depth of partially melted magma. In particular, beneath the northwestern portion of the La Virgen volcano, and north of the geothermal field. This interpretation implies that magma emplacement was controlled, in particular by deep reaching NW-SE regional faults, which were emplaced at different times along the NE-to-SW directed magmatic evolution of this volcanic complex. Another issue is that there are several independent heat sources beneath the TVVC.

Teotihuacan neighborhoods’ expansion in Northwestern Mexico. Cultural implications and social processes from ceramic analysis of El Mezquital-Los Azules, Guanajuato

From the beginning of our era, the multi-ethnic capital of the central plateau, Teotihuacan, served as a great religious center and a hub for artisanal production and consumption. By AD 200, Teotihuacan entered a phase of expansion, which took different forms depending on the quality of resources and the political importance of the particular regions to which its influence spread. This paper examines the specific role of one site located along a key trade route in north central Mexico. Our study utilizes a multi-method approach, combining typological, archaeometric (NAA and petrography) and iconographic data from ceramics from the site of El Mezquital- Los Azules (Guanajuato) to improve our understanding of the mechanisms of the Teotihuacan expansion in Northwestern Mexico. The results of these ceramic analyses allow us to distinguish imports from imitations, and provide a better understanding of the possible messages conveyed by the iconography of the imitations. Based upon our findings, we argue that this commercial staging post was an emanation of the neighborhoods of Teotihuacan, and was integrated in its constantly evolving social fabric.

Arthropods in Natural Communities in Mescal Agave (<i>Agave durangensis</i> Gentry) in an Arid Zone

Problem statement: The arthropods have a very important role in the a rid zones due to their interactions with many organism and because t hey constituted an important element in the structure of the plant community. Nevertheless thei r importance there are few knowledge about the community of arthropods associated to vegetation in arid zones in the North of Mexico. The present study had the objective of determining the abundanc e, richness and diversity of arthropods in three localities where there are natural populations of m escal agave in the State of Durango, Mexico. Approach: In order to know the structure community of the a rthropods associated to the mescal agave, we perform a sampling schedule during March 2008 to November 2010 by direct collection, using transects in three different localities with the presence of mescal agave. The relative abundan ce, species richness, Shannon's diversity index, Pielou 's Index of evenness, Jaccard's similitude and Simpson's dominance indexes were determined. Results: A total of 4665 individual arthropods associated to mescal agave corresponding to 39 spec ies were found. El Mezquital had the highest abundance and relative abundance (44.1%) with 29 species. The mean species abundance was not significantly different between localities using Tu rkey's test. The highest density per unit of area w as found in El Mezquital (La Brena had the highest spe cies diversity (1.89), evenness (0.61) and dominance (0.78). At the taxon level, Hymenoptera had the highest number of species represented (14), followed by Coleoptera (9) and hemiptera (5), with the remaining taxons with four, two and one species each. Conclusion: The greatest similitude was observed between La Br ena and El Mezquital (46%) which shared seven taxons, while the least si militude was observed between El Venado and La Brena (29%). Dominance/diversity curves are presented for each locality. The species Caulotops sp., Acutaspis agavis , Chilorus sp., Scyphophorus acupunctatus and Peltophorus polymitus were the ones with highest relative abundance. Although the diver sity values are above the minimum, previously unreported arthropod species associated to mescal a gave were recorded. The results can be useful to know the dynamic in the community associated to agave, in order to development best conservation and exploit management of that important plant.

Morpho polyphemus (Lepidoptera: Papilionoidea: Morphinae): A New Record from Zacatecas, Mexico

Morpho polyphemus, a butterfly whose geographic and temporal distribution in Mexico is relatively well known, is reported for the first time from the state of Zacatecas. This species was observed at El Mezquital, on both sides of a river with riparian subtropical vegetation.

Developing Sustainable Peripheries

In March 1984 approximately 800 families squatted on previously unoccupied lands on the edge of Guatemala City in an area known as El Mezquital. In the following months, squatters continued to arrive, eventually forming a community of more than 25,000. This was the first major organized act of squatting that successfully established a community in the city since 1976. Dozens of other invasions-to employ the term most commonly used in Guatemala-had been broken up by the police in the early 1980s (CITGUA, 1991: 70). However, following the success of Mezquital, other squatters have established communities throughout the city.1 Although the Guatemalan state still forcefully breaks up land seizures, many of these settlements in the past 16 years have slowly been transformed into neighborhoods. The increase in urban squatting has come at a crucial point in Guatemalan history. Since 1984 Guatemala has experienced fundamental changes in its body politic. In the transition from dictatorship to democracy and from 35 years of civil war to peace, new spaces have opened up for marginalized actors to have a political voice.2 As the case of urban squatting makes clear, these new spaces are important. They are not, however, without their limits and silences. The squatters have benefited, particularly in the 1980s, from the spotlight provided by the presence of international organizations and the emergence of a relatively independent press, articulating a strong critique of the conditions under which they live. Nevertheless, they slowly lose the ability to voice their concerns. This silencing occurs, at least in part, because of modern development institutions providing crucial

Quality assessment of an aquifer recharged with wastewater for its potential use as drinking source: “El Mezquital Valley” case

Mexico City, with a population of 18 million, has been sending its wastewater for more than 100 years to the Tula Valley where it is used to irrigate 90,000 ha. Due to the large wastewater volume (60 m3/s) sent through unlined channels, combined with the use of very high irrigation rates, artificial recharge of the local aquifer has been occurring. This recharge is estimated in more than 25 m3/s. As a consequence, the water table has raised and several springs have appeared in the last decades with flows between 100 to 600 L/s. These springs and several wells are the water sources in the region. An evaluation of the Tula Valley aquifer quality was performed to analyze the use of such water as source of drinking water for Mexico City. The work is divided into 5 individual projects: (a) drinking water quality in the Tula Valley; (b) water availability in the Tula Valley; (c) wastewater treatment due to its use for irrigation, (d) use of membrane processes to treat groundwater; and (d) biota developed in the new surface water reservoirs. Results show that it is feasible to use this reclaimed water as drinking source.

A Shallow Crustal Earthquake Doublet from the Trans-Mexican Volcanic Belt (Central Mexico)

The Trans-Mexican volcanic belt is an active volcanic arc related to subduction along the Middle America trench and characterized by shallow seismicity and synvolcanic to postvolcanic extensional arc-parallel faulting. The Mezquital graben is a major intra-arc basin of the central Trans-Mexican volcanic belt. A doublet of moderate shallow shocks occurred in March and October 1976 in the region of this graben. These earthquakes were recorded by the Mexican National Seismological network, in particular, by the Bosch-Omori seismograph ( T = 18 sec) at the Tacubaya Observatory in Mexico City. We have carefully relocated the two main shocks and their major aftershocks by reading the original records and using a modified crustal velocity model for this region. A difference of ∼50 km is observed between the locations reported by the Mexican Seismological Service and those obtained in this study, which are additionally supported by the damage distribution of these earthquakes. A first-motion analysis, based on regional and teleseismic records, defines for the March and October shocks normal fault mechanisms, characterized by east–west-striking fault planes, which coincides with the orientation of the master faults of the Mezquital graben. After calculating the instrumental response, the source parameters were obtained from the Bosch-Omori seismograph records by body-wave modeling. For the March earthquake, we estimate a seismic moment of 4.5 × 1023 dyne cm (equivalent to M w 5.0) and a stress drop of 0.7 MPa, assuming a circular rupture model (radius, 3 km). Given the poor quality of the Bosch-Omori record for the October earthquake, we used comparison with the March event of long-period ( T = 20 sec) teleseismic records at two stations to obtain corresponding source parameters for the October event. By assuming a similar stress drop as for the March event, we obtain a M of 5.6 × 1023 dyne cm and M w 5.1 with a rupture length of 6.5 km. According to gravity data, the regional east–west faults are longer than reported. In particular, our detailed measurements indicate that the master fault of the Mezquital graben continue westward in the subsurface below the basin fill. In a more regional context, additional magnetic data suggest that the El Mezquital graben and Aljibes half-graben might be connected at their southern limits by part of the same fault system. This is the first earthquake doublet reported from central Mexico and the biggest seismic event in that zone during the past 50 years. From a physical point of view, it is possible that the seismic energy released by the March event was partially transferred toward the east, triggering the October shock further east on the same fault system. The presence of moderate seismicity in this zone should therefore be taken into account when assessing its seismic hazard.

The role of external agencies in the development of El Mezquital in Guatemala City

This paper describes and discusses the role of different international agencies (including UNICEF and the World Bank) and NGOs in supporting development in El Mezquital, a settlement formed from a land invasion in Guatemala City the mid-1980s. It draws on interviews with the inhabitants and with staff from supporting agencies. The support from these international agencies and NGOs allowed considerable improvements in infrastructure and service provision, and supported important processes of community empowerment and greater status and possibilities for women. However, the paper also describes the limitations of this support, including the limited scope for participation, the projects that were planned and never implemented and the problems that the international support failed to resolve. It also describes the resentment from groups within the community with regard to what was achieved.

The role of external agencies in the development of El Mezquital in Guatemala City

The role of external agencies in the development of El Mezquital in Guatemala City

El Mezquital: a community’s struggle for development

This paper describes the history of the community in El Mezquital, from the land invasion in the mid 1980s, through its consolidation and growth, until the present, drawing principally on interviews with the inhabitants and staff from supporting agencies. It analyzes the development of the different, and sometimes conflicting, community organizations and compares their different mandates and objectives. It shows important processes of community empowerment, the changing role of women and community self-help initiatives. It also describes how, in much of the settlement, basic infrastructure and services were in place and of good quality. However, it also highlights the lack of employment opportunities, how many people still live in overcrowded conditions, and the problems of violence, drug addiction and street children. It also highlights the inadequacies on the part of government agencies - including their incapacity to respond to the needs of the community, their under-estimation of community capacity and the attempts at political manipulation.

El Mezquital: a community's struggle for development

El Mezquital: a community's struggle for development