Oaxaca Region Research Articles

Long term (2005–2016) study of formaldehyde (HCHO) columns from satellite data in two regions in the south of Mexico. Evidence of the impact of agricultural activity

In order to determine the driver factors and the principal months of enhancement of HCHO over the Oaxaca and the Chiapas regions, important agricultural areas located in the south of Mexico, HCHO columns from the Ozone Monitoring Instrument (OMI) were monthly averaged (HCHOOMI) and used in conjunction with monthly averaged isoprene emissions (isoprene), monthly NOx emissions from biomass burning (NOx_bb), and monthly averaged NOx emissions from soils with their different sources (biomes: NOx_bio, fertilization and manure: NOx_fer, deposition of N: NOx_dep, pulses: NOx_pul, and total: NOx_tot) from January 2005 to December 2016. Based on scatterplots grouped by month due to the seasonality of the variables, Spearman rank correlations, and multiple linear regression models, we determined that isoprene was an important driver of HCHOOMI in the Oaxaca region, contributing both to its seasonality and peak presence during April and May; whereas NOx_bb was a relevant source in the enhancement of HCHOOMI during April and May, months in which the fire season occurs in the south of Mexico. In the Chiapas region, we determined that both isoprene and NOx_fer were important drivers of the seasonality of HCHOOMI and its peak months during April and May. NOx_bb was predominantly involved in the HCHOOMI enhancement during April and May. The overall multiple linear regression model for each study region was significant (F-statistic = 21.35, p<0.0001 for the Oaxaca region; F-statistic = 101.59, p<0.0001 for the Chiapas region) and explained 72% of the variation of HCHOOMI in the Oaxaca region, 85% in the Chiapas region. Based on the multiple linear regression model for each study region, monthly averaged modeled HCHO columns (HCHOMOD) were obtained. With the estimated regression coefficients, the contribution (in %) of the relevant emission fluxes for each region were calculated in order to know which source was the predominant one in the exacerbation of HCHOMOD. During the peak months of HCHOMOD (April and May) in the Oaxaca region, isoprene predominates over NOx_bb. In the Chiapas region both NOx_bb and NOx_fer caused the exacerbation of HCHOMOD during April and May, whereas NOx_fer was the major variable that caused the increase of HCHOMOD during June, July, and August, especially from 2014 to 2016. Overall, in this region the emissions of NOx were more important in the increase of HCHOMOD than isoprene. NOx_bb and NOx_fer were enhanced principally due to the agricultural activity taking place in the Oaxaca and Chiapas regions. Thus, this work demonstrates the impact of agricultural activity on HCHO columns observed by the OMI instrument. In addition, this work shows that HCHO columns can be modeled using HCHO columns obtained from satellite data and emission inventories. The analysis performed here can be applied to other similar regions not only in Mexico but elsewhere around the world.

Autonomía y radio ciudadana como formas de lucha emergentes de los pueblos originarios

This article reflects on and analyzes the struggle undertaken by the communities of the Cajono Zapotec ethnic group against the cacique groups of the Sierra Juárez Oaxaca region. The focus of analysis is centered on the proposal for autonomy and communality, carried out by the community of Santa María Yaviche in a context of tension and violence. The role of the radio station Radio Bëë Xhidza Aire Zapotec in this process makes it an emergent in the sense of the struggle of the communities and demonstrates the potential of imagination of these in the midst of the possibilities of enunciation and listening by others.

Analysis and incursion into the home delivery service in local companies

The home delivery service as a business model has increased significantly in recent years due to the pandemic. However, despite this, various businesses have decreased their sales or failed because they have not been able to adapt to this new way of distributing their products or have ventured without having any knowledge. In this context, this project is presented whose objective is to establish the main characteristics that allow the incursion of local restaurants to home deliveries, and that can be applicable to different places. The research method used is descriptive, based on the collection of field information and its analysis. The benefits offered by this research are applicable to local businesses in the Mixteca, Oaxaca region, but which in turn allow a broader picture of the contextualization of the problem that exists at the national and international level.

Rupture Characteristics Analysis of the 2020 Mw 7.4 Oaxaca, Mexico Earthquake Using Teleseismic, High-Rate GPS, and InSAR Data

The June 23 2020 Oaxaca Mw 7.4 interplate thrust earthquake struck the state of Oaxaca in Mexico, generating strong shaking and a long-lived tsunami. This earthquake is well recorded by the teleseismic, high-rate Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data, which provides an opportunity to understand the rupture characteristics of the Mexican subduction zone. Here, an integrated inversion strategy involving centroid moment tensor inversion and kinematic finite-fault inversion is used to study the rupture history of the 2020 Oaxaca earthquake. The fault geometry and source duration time derived from the centroid moment tensor solution are used as prior information in linear kinematic finite-fault joint inversion. The rupture initial point and relative weight of each dataset are determined to estimate a well-constrained rupture model. The finite-fault model shows the rupture expanded bilaterally around the hypocenter, the peak slip is 3.5 m, the main slip was located at a depth of 15–30 km, the whole rupture lasted about 20 s, and a 95% moment rate was released at 15 s. The half-duration of the finite-fault inversion is consistent with the centroid moment tensor inversion results (half-duration 9 s), which shows the good resolution of the temporal information. The total scalar moment was 1.5 × 1020 Nm, equivalent to a moment magnitude of Mw 7.4. The integrated inversion strategy used in this study is useful since the prior information can be derived and used to constrain the rupture process. Both the centroid moment tensor and finite-fault inversion mainly rely on identical temporal information provided by teleseismic P waveforms. The 2020 Oaxaca earthquake was mainly the interaction between Cocos and the North American plate, and the slow slip events may be the key factor affecting the seismogenic zone width in the Oaxaca region.

Interplate Slip Rate Variation Between Closely Spaced Earthquakes in Southern Mexico: The 2012 Ometepec and 2018 Pinotepa Nacional Thrust Events

AbstractOn 20 March 2012, a Mw 7.5 thrust earthquake started a series of seven large events (7.0 ≤ Mw ≤ 8.2) that struck central Mexico during a period of 9 years (2012–2021). Before this event, the Mexican subduction zone did not experience significant subduction earthquakes (Mw &gt; 7.0) for at least 12 years. Five of the events occurred in the plate interface, resulting in a significantly larger interplate slip rate in the states of Oaxaca and Guerrero. In this study, we explore how an aseismic slip transient caused by the 2012 Mw 7.5 earthquake affected the Oaxaca region and whether this earthquake had a causal relationship with the Mw 7.2 Pinotepa Nacional event that took place six years later in a nerby zone. To this end, we identified and analyzed characteristic repeating earthquakes along the Mexican subduction zone for assessing the plate interface slip history and found a remarkable increase in the aseismic slip rate following the 2012 mainshock, which suggests a long‐standing slip perturbation near the trench in Oaxaca that continued until the Pinotepa Nacional earthquake of 2018.

Integrated Analysis of the 2020 Mw 7.4 La Crucecita, Oaxaca, Mexico, Earthquake from Joint Inversion of Geodetic and Seismic Observations

ABSTRACT On 23 June 2020, a major thrust faulting earthquake ruptured the megathrust near a sharp transition of the plate boundary beneath the Mexico subduction zone, overlapping the rupture area of the 1965 Mw 7.5 (Ms 7.6) event. A joint inversion of geodetic and seismic observations and prediction of coastal uplifts indicate a compact rupture with a peak slip of ∼3.6 m. The cumulative seismic moment is 1.41×1020 N·m within 20 s of coseismic rupture, giving a moment magnitude of Mw 7.4. The rupture propagated with a relatively high rupture speed (∼3.5 km/s) downdip at depths from 20 to 30 km, terminating at the edge of a slow slip region. The energy-related static stress drop is ∼8.1 MPa. The aftershock distribution and the region where slow slip events occurred show a clear complementary relationship with the coseismic rupture zone of the 2020 Oaxaca event. The high-stress drop and associated deep compact rupture pattern suggest a homogeneous asperity with high strength beneath the Oaxaca region. Comparisons of rupture areas, mechanisms, and seismic waveforms show that the 2020 Mw 7.4 Oaxaca earthquake is a quasi-repeat of the 1965 earthquake. The inferred recurrence interval is ∼55 yr. Static stress transfer from mainshock may trigger near trench aftershocks but has small loading on the megathrust interface in the Tehuantepec seismic gap.

Bennettitales from the Middle Jurassic of northwestern Oaxaca, Mexico: Diversity, sedimentary environments, and phytogeography

The Jurassic flora of Mexico represents a key element for the knowledge of the paleoflora on the western margin of equatorial Pangea because of its abundance and diversity. Bennettitales were the dominant group and are represented by leaves and reproductive organs in Jurassic outcrops from southern Mexico. This group has been historically recorded in seven lithostratigraphic units in southern Mexico in a range from the Toarcian to the Callovian. These reports have focused on morphological and taxonomical aspects for the obtention of paleofloristic listings by locality but do not provide environmental data or have any impact on biostratigraphic or phytogeographic analyses. The highest number of localities in Mexico has been reported in the state of Oaxaca, where plant fossils are more abundant and better preserved in comparison with localities of Guerrero, Puebla, Veracruz, and Hidalgo states. Therefore, in order to reinforce the paleofloristic knowledge of southern Mexico, the present study documents the diversity of Bennettitales in northwestern Oaxaca region, which is composed of 11 fossil-genera and 41 fossil-taxa, included 30 valid species and 11 species that need taxonomic revision. We provide the description of a new species, Williamsonia sanjuanensis sp. nov., new findings of Williamsonia nathorstii, and the first record of Bennetticarpus for southern Mexico. We also describe fossiliferous outcrops of the Zorrillo and Zorrillo/Taberna undifferentiated formations and propose their sedimentary environments. In addition, we provide a proposal of one biozone based on Bennettitales. Finally, we recognize six spatio-temporal distribution patterns for this plant group in northwestern Oaxaca. These new data add to a growing set of information on the Jurassic flora of Mexico and allow to substantiate the paleobotanic importance of southern Mexico within the region of North America.

Rupture Models of Recent Mw&amp;gt;7 Thrust Earthquakes in the Guerrero–Oaxaca Region of the Mexico Subduction Zone Using Teleseismic Body Waves

Abstract We invert the teleseismic broadband (1–60 s period) ground-displacement body waveforms recorded for the 1995 Mw 7.3 Copala, the 1996 Mw 7.1 Oaxaca, the 2012 Mw 7.5 Ometepec, and the 2018 Mw 7.2 Pinotepa Nacional thrust earthquakes in the Guerrero–Oaxaca portion of the Mexico subduction zone to derive the best-fit rupture models using a sampling procedure in which input fault parameters are selected from a prescribed range of values. More than 400 independent inversions are performed for each event using random combinations of strike, rake, dip, and hypocenter depth. Waveform fits are observed to be relatively insensitive to variations in strike, rake, and focal depth but show a distinct dependence on fault dip. The lowest residuals are limited to a dip interval of about ±3°, indicating that a relatively precise estimate of the fault dip is necessary for the optimal derivation of slip models using teleseismic body waves. The best-fit teleseismic source models obtained for the four events show varying degrees of spatial detail, with the 2012 and 2018 earthquakes exhibiting more separated slip along the fault than has been observed in rupture models derived using frequency bands covering longer periods. Areas of high-interplate slip for the four events do not overlap, suggesting an adjoining pattern of asperity zones that is consistent with prior observations in northwest Mexico and in the New Britain region of the South Pacific. Additional investigation of this type of asperity interaction for recurrent events would be beneficial, given the implications for estimating the size and location of future large subduction earthquakes.

Source Characteristics of the 2020 Mw 7.4 Oaxaca, Mexico, Earthquake Estimated from GPS, InSAR, and Teleseismic Waveforms

AbstractOn 23 June 2020, an Mw 7.4 earthquake struck offshore Oaxaca, Mexico, providing a unique opportunity to understand the seismogenic tectonics of the Mexican subduction zone. In this study, near-field coseismic deformation caused by the event was retrieved from Global Positioning System (GPS) observations and Interferometric Synthetic Aperture Radar (InSAR) measurements. Given static geodetic measurements, high-rate GPS waveforms, and teleseismic waveforms, the fault geometry and rupture process for the 2020 Oaxaca earthquake were robustly determined by nonlinear joint inversions. The main slip was located at a depth of 20–30 km with a peak slip of 3.4 m near the epicenter. The total released moment was 1.70×1020 N·m, corresponding to Mw 7.4. The whole rupture process lasted 14 s, with the dominant rupture slip occurring 5–8 s after initial rupture. The mainshock rupture mostly occurred along the fault strike, covering a size of ∼55 km(along strike)×∼35 km(along dip) and totally overlapping with the 1965 Mw 7.5 rupture zone. We speculate that this 2020 earthquake is a repeat event following that in 1965. Fluid percolation under the slab may be one of the key factors affecting the seismogenic depth in the Oaxaca region.

Synthetic seismicity distribution in Guerrero–Oaxaca subduction zone, Mexico, and its implications on the role of asperities in Gutenberg–Richter law

Abstract. Seismicity and magnitude distributions are fundamental for seismic hazard analysis. The Mexican subduction margin along the Pacific Coast is one of the most active seismic zones in the world, which makes it an optimal region for observation and experimentation analyses. Some remarkable seismicity features have been observed on a subvolume of this subduction region, suggesting that the observed simplicity of earthquake sources arises from the rupturing of single asperities. This subregion has been named SUB3 in a recent seismotectonic regionalization of Mexico. In this work, we numerically test this hypothesis using the TREMOL (sThochastic Rupture Earthquake MOdeL) v0.1.0 code. As test cases, we choose four of the most significant recent events (6.5 &lt; Mw &lt; 7.8) that occurred in the Guerrero–Oaxaca region (SUB3) during the period 1988–2018, and whose associated seismic histories are well recorded in the regional catalogs. Synthetic seismicity results show a reasonable fit to the real data, which improves when the available data from the real events increase. These results give support to the hypothesis that single-asperity ruptures are a distinctive feature that controls seismicity in SUB3. Moreover, a fault aspect ratio sensitivity analysis is carried out to study how the synthetic seismicity varies. Our results indicate that asperity shape is an important modeling parameter controlling the frequency–magnitude distribution of synthetic data. Therefore, TREMOL provides appropriate means to model complex seismicity curves, such as those observed in the SUB3 region, and highlights its usefulness as a tool to shed additional light on the earthquake process.

The real Oaxaca decomposition: convergence within Mexico’s Oaxaca region in the twenty-first century—Do types of crime and religious belief matter?

The paper empirically examines municipality convergence within Mexico’s southern Oaxaca region. We find municipalities are converging more rapidly than the “iron law” of 2% with up to 8% β convergence. Though homicides from the Drug War have negatively impacted growth, overall crime perhaps through strengthening local institutions has a positive but weak impact. Higher income inequality and Catholic belief are associated with higher per capita GDP growth in Oaxaca overall and within two microregions. The positive impact of a higher share indigenous population on growth in the relatively urban Valles Centrales microregion suggests a cultural element to policy making with the dependency ratio drag on growth suggesting a need for policies that give more attention to how retirees can continue to participate in the economy as well.

Zea maize reference materials for genetically modified organism detection in Mexico.

Zea maize reference materials for genetically modified organism detection in Mexico.

Alpha diversity of marine mammals of the Mexican South Pacific

Knowledge of the alpha diversity contributes to the determination of conservation priorities by identifying regions with high species richness and/or a large number of endemic, rare, or endangered species. The present study focused on the evaluation of species richness and composition of the marine mammal community off the coast of Oaxaca. A total of 293 surveys were carried out between December 2011 and April 2015. Additionaly, observation and stranding records found in the literature and zoological collections (corresponding to the period 2008-2014) were revised to estimate alpha diversity. The results allowed us to conclude that the current richness of marine mammals for the state, comprises 21 species distributed in 2 orders, 3 suborders, 5 families, and 17 genera. This represents a 75% increase in the known richness prior to this study. All species of marine mammals are found in some risk category according to the NOM-059-Semarnat-2010 (Mexico), IUCN, and CITES. Our results highlight the importance of the Oaxaca region in the Mexican South Pacific as a priority area for conservation, because of its high degree of richness, considerable diversity in species composition, and the concentration of vulnerable or endangered marine mammals.

¿Desarrollo regional para quién? El caso del Proyecto Aprovechamiento Hidráulico de Usos Múltiples Paso de la Reina, Oaxaca, México

Con el objetivo de conocer los efectos culturales y ambientales de proyectos de desarrollo en territorios indígenas, este estudio de caso describe el conflicto que ha involucrado a las comunidades de la región Costa de Oaxaca, a partir de la construcción de la presa Paso de la Reina. En la investigación se utilizó la observación y entrevistas a informantes clave, así como la recuperación de documentos producidos por los actores de este conflicto. Entre 2007 y 2014 ocurrió la intervención en dicho territorio indígena, y comenzó la respuesta de resistencia organizada de las comunidades, ante un proyecto regional que no pidieron y que tampoco han aprobado.

Seismicity rate increases associated with slow slip episodes prior to the 2012 Mw 7.4 Ometepec earthquake

The March 20, 2012 Mw 7.4 Ometepec earthquake in the Oaxaca region of Southern Mexico provides a unique opportunity to examine whether subtle changes in seismicity, tectonic tremor, or slow slip can be observed prior to a large earthquake that may illuminate changes in stress or background slip rate. Continuous Global Positioning System (cGPS) data reveal a 5-month-long slow slip event (SSE) between ∼20 and 35 km depth that migrated toward and reached the vicinity of the mainshock a few weeks prior to the earthquake. Seismicity in Oaxaca is examined using single station tectonic tremor detection and multi-station waveform template matching of earthquake families. An increase in seismic activity, detected with template matching using aftershock waveforms, is only observed in the weeks prior to the mainshock in the region between the SSE and mainshock. In contrast, a SSE ∼15 months earlier occurred at ∼25–40 km depth and was primarily associated with an increase in tectonic tremor. Together, these observations indicate that in the Oaxaca region of Mexico shallower slow slip promotes elevated seismicity rates, and deeper slow slip promotes tectonic tremor. Results from this study add to a growing number of published accounts that indicate slow slip may be a common pre-earthquake signature.

Conversations with the dead and the living in Oaxacan bioarchaeology

This commentary offers the perspective of someone who works outside the Oaxaca Region and beyond bioarchaeology.

Low Angle Contact Between the Oaxaca and Juárez Terranes Deduced From Magnetotelluric Data

We present the electrical resistivity model along a profile perpendicular to the Middle America trench in southern Mexico that reveals previously unrecognized tectonic features at upper to mid-crustal depths. Our results support the hypotheses that the upper crust of the Oaxaca terrane is a residual ~20 km thick crust composed by an ~10 km thick faulted crustal upper layer and an ~10 km thick hydrated and/or mineralized layer. Oaxaca basement overthrust the younger Juarez (or Cuicateco) terrane. The electrical resistivity model supports the interpretation of a slab subducting at a low angle below Oaxaca. Uplift in the Oaxaca region appears to be related to fault reactivation induced by low angle subduction. In the Juarez terrane, isostatic forces may contribute to uplift because it is largely uncompensated. In the Sierra Madre del Sur, closer to the coast, uplift is facilitated by slab-dehydration driven buoyancy. Both gravity and resistivity models are consistent with a thinned upper crust in the northeast end of the profile.

Productivity and energy efficiency of three tillage systems for maize (Zea mayz L.) production

The amount of inputs and dry matter yields of grain, stover and weeds were quantified in six sites located in the districts of Zaachila and Etla, in the Central Valleys of Oaxaca Region, Mexico. The tillage systems evaluated, which are the most widely used for corn production in this region, were full animal traction (FAT), mixed traction (MXT) and mechanical traction (MT). The higher productivity was achieved in the MT system, followed by the MxT system . According to the energy balance, the largest energy efficiency (EE) was achieved in the FAT system with a value of 34.4 and the least one with the MT system. The lowest EE of the MT system was associated to a higher use of machinery operations and the use of petrol derivate products . N o significant differences in EE were found between the FAT and MxT systems; when weed`s dry matter production was considered, EE in this last system was increased 14 %, while in the FAT system an 8 % increase was observed. Therefore, besides the FAT system MxT is also recommended because in the region it is common to have plots smaller than 1 ha and mechanical plowing is more efficient for primary tillage operations while animal power can be used as a renewable source of energy for tasks such as weeding and transport.

Provenance and Manufacture of Mixtec Style Objects Found on the Surrounding Structures of the Precinct of the Great Temple of Tenochtitlan

ABSTRACTSeventy six speckled greenstone items have been recovered on the surrounding structures of the Aztec precinct of the Great Temple of Tenochtitlan. Several researchers have identified the material as marble. Also, these objects have been labeled as Mixtec style due to the raw materials involved in their manufacture as well as their apparent similarity with other known Mixtec objects. The main objective of this essay is to determine the raw materials and the technology employed on its manufacture. Based on earlier composition analysis using Infrared spectroscopy (FTIR) and X-ray Fluorescence (XRF), it became clear that all items are made of the same calcite-serpentine mineral alloy, which probably comes from the Oaxaca region. It is interesting the homogeneity and standardization among these pieces by analyzing them with experimental archaeology and the characterization of their manufacturing traces. Comparing their raw material, morphology and techniques with those of Mixtec sites, the analysis revealed that they are not in fact related at all; however they do coincide with the manufacturing process of Tenochca (Aztec) style objects. This fact might point towards the actual origin of the raw materials, their obtainment and the technology behind the elaboration of luxury goods at Tenochtitlan.

‘Es honor de su nación’: Legal Rhetoric, Ethnic Alliances and the Opening of an Indigenous Convent in Colonial Oaxaca

This article examines the manner in which the caciques (noble Indians) and principales (Indian notables) from the Oaxaca region in New Spain adopted a ‘legal rhetoric’ in their quest to open a convent for noble Indian women during the eighteenth century. Through a close reading of the legal documentation produced in the petition for the convent for indigenous women in Antequera, I find that the caciques strategically used the same laws that had placed them in a subordinated place in the social hierarchy of the colony in order to negotiate certain rights and privileges. Aware of their belonging to the legally determined category of ‘Indians,’ indigenous peoples from the Valley of Oaxaca appealed specifically to the laws that had granted them a special judicial place in the colonial scheme. By referencing the Recopilación de las leyes de las Indias and several royal decrees (cédulas), the caciques appealed to colonial officials at a key historical moment, when Bourbon reforms sought to modernize all institutions, including the Catholic Church.