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La toba Amealco y su correlación con la formación Las Américas a través del graben de Acambay, estados de México, Michoacán y Querétaro, Mexico
... La zona del graben de Acambay está principalmente formada por rocas volcánicas miocenas a cuaternarias sobre un basamento plutónico y metamórfico (Sánchez-Rubio, 1984;Aguirre-Díaz, 1993;1995;. Los materiales más jóvenes corresponden a una sedimentación fluvio-lacustre que rellenó pequeñas cuencas formadas por relieves volcánicos y barreras tectónicas a lo largo del rio Lerma. ...
... El terremoto de 1912 fue generado en la falla Acambay-Tixmadejé pero produjo fracturas superficiales en los tres sistemas de fallas (Urbina y Camacho, 1913;Langridge et al., 2000;Rodríguez-Pascua et al., 2012). La falla Acambay-Tixmadejé, con una longitud de 42 km y un buzamiento hacia el sur, llega a formar escarpes de hasta 500 m en rocas volcánicas Neógenas (Figura 1;Sánchez-Rubio, 1984;Suter et al., 1992;1995;Aguirre-Díaz 1993;1995). Esta falla normal fue la principal fuente sismogenética del terremoto de Acambay en 1912 (Langridge et al., 2000). ...
... El terremoto de 1912 fue generado en la falla Acambay-Tixmadejé pero produjo fracturas superficiales en los tres sistemas de fallas (Urbina y Camacho, 1913;Langridge et al., 2000;Rodríguez-Pascua et al., 2012). La falla Acambay-Tixmadejé, con una longitud de 42 km y un buzamiento hacia el sur, llega a formar escarpes de hasta 500 m en rocas volcánicas Neógenas (Figura 1;Sánchez-Rubio, 1984;Suter et al., 1992;1995;Aguirre-Díaz 1993;1995). Esta falla normal fue la principal fuente sismogenética del terremoto de Acambay en 1912 (Langridge et al., 2000). ...
This study focuses on the identification and seismic characterization of the San Mateo fault, herein described for the first time. This fault is located in the central part of the Acambay graben, central Mexico. It is a 13 km long active normal fault with E-W direction and dip to the south. Two trenches were excavated in the locality of La Lechuguilla to determine the recent chronology of paleoearthquakes along this fault and to estimate its seismic parameters. At least three paleo-breaks have been found in one of these trenches and new radiocarbon ages indicate that they occurred from Late Pleistocene to the Holocene times. The oldest event (Event 1) occurred in 31.0-29.3 ky cal BP. Event 2 occurred in 19.1-6.5 ky cal BP and the younger faulting (Event 3) in 6.0 to 4.2 cal ky BP. These results suggest a recurrence interval of surface ruptures of about 11.57 ± 5.32 ky. A slip rate of 0.085 ± 0.025 mm / year and a magnitude (Mw) of 6.43 to 6.76 is estimated from the maximum coseismic displacement of 0.85 ± 0.163 m and a rupture length of 13 km. If we consider a maximum rupture length of 25 km, including the possible continuity of the fault under the present day sediments filling the graben, a Mw magnitude of 6.7 ± 0.3 could be expected. The paleoseismic data and fault scaling relationships suggest that the San Mateo fault is a significant seismic source in terms of hazard. This study also highlights the recency of the volcanic activity in the Acambay graben.
... In Table 2) was the most polluted site, with both low depth and current velocity; due to the 6 constant flux of mainly non treated industrial sewages into the river. The waters had wide 7 intervals of pH, anoxic conditions, high temperatures and moderate to high conductivities. 8 Twenty one species of Navicula s. str. ...
... Up to now only few floristic 3 or taxonomic studies of Mexican river diatom communities have been published however the 4 high morphological variability exhibited by Navicula spp was not reported and, frequently, 5 only one or two valves were illustrated. The morphological and morphometric variations 6 found in the Lerma River could be interpreted as adaptations to a highly polluted system, thus 7 pointing out to the importance of having the widest possible survey of the variability of these 8 taxa as part of biomonitoring programs. 9 Unlike classic freshwater hydrosystems, which show upstream to downstream gradients 10 of eutrophication; the Lerma River has high levels of pollutants from its upper section, 11 immediately downstream from the springs. ...
... erifuga Lange-Bertalot; N. germainii; N. riediana Lange-Bertalot & Rumrich; 16 N. rostellata Kützing; N. simulata Manguin). 17Navicula antonii (sampling sites 1, 2, 3, 5, 6); N. capitatoradiata (2, 3, 4); N. cryptocephala18 (2, 7); N. erifuga(1, 2, 3, 4,5,7, 8,9); N. germainii(1, 2,6); and N. veneta (highest percentages and all of them are good indicators of heavily eutrophic waters,20 with a broad spectrum of conductivity tolerances. Among them, N. antonii is considered as a good21 indicator of anthropogenically affected waters (eutrophic to hypereutrophic) and N. veneta is very 22 tolerant to polysaprobic conditions dominant in industrially polluted water (Lange-Bertalot 2001).23 ...
Background. Lake Patzcuaro has been exposed in the recent past to environmental deterioration with increasing eutrophication as a result of deforestation, indiscriminate use of agrochemicals, overfishing, unplanned urban growth, and sewage dumping. Goals. In order to contribute to the phycofloristic inventory of the Lake, we present the taxonomic description of the periphytic diatoms found, including morphometric information, meristic data, figures, as well as ecological and distributional notes. Methods. Sampling was carried out in four sites during two periods: after the rainy season (October 2004) and the dry season (May 2005); samples were gathered by scraping rooted and floating vegetation. Diatoms' thecae were cleared with hydrochloric acid and hydrogen peroxide; permanent slides were made with Naphrax (R) resin and analyzed through optic microscopy. Results. A total of 83 periphytic diatom species were recorded, including eight varieties and one form; 20 species (24%) represent the first records for Mexico and 57 (68.6%) are new to the study area. Sixty-two species (74.7%) have cosmopolitan distribution and six (7.2%) have tropical affinity. Species richness was slightly higher after the rainy season (October 2004) with a total of 69 taxa, compared to 65 species recorded during the dry season (May 2005). Among the sampling sites, the island of Janitzio had the highest diatom diversity (46 taxa during the dry season). Conclusions. Deterioration of Lake Patzcuaro in the previous decades has taken a toll on the health of its ecological system. Diatoms identified in this study indicate a clear tendency of eutrophication of the waterbody.
... La zona del graben de Acambay está principalmente formada por rocas volcánicas miocenas a cuaternarias sobre un basamento plutónico y metamórfico (Sánchez-Rubio, 1984;Aguirre-Díaz, 1993;1995;. Los materiales más jóvenes corresponden a una sedimentación fluvio-lacustre que rellenó pequeñas cuencas formadas por relieves volcánicos y barreras tectónicas a lo largo del rio Lerma. ...
... El terremoto de 1912 fue generado en la falla Acambay-Tixmadejé pero produjo fracturas superficiales en los tres sistemas de fallas (Urbina y Camacho, 1913;Langridge et al., 2000;Rodríguez-Pascua et al., 2012). La falla Acambay-Tixmadejé, con una longitud de 42 km y un buzamiento hacia el sur, llega a formar escarpes de hasta 500 m en rocas volcánicas Neógenas (Figura 1;Sánchez-Rubio, 1984;Suter et al., 1992;1995;Aguirre-Díaz 1993;1995). Esta falla normal fue la principal fuente sismogenética del terremoto de Acambay en 1912 (Langridge et al., 2000). ...
... El terremoto de 1912 fue generado en la falla Acambay-Tixmadejé pero produjo fracturas superficiales en los tres sistemas de fallas (Urbina y Camacho, 1913;Langridge et al., 2000;Rodríguez-Pascua et al., 2012). La falla Acambay-Tixmadejé, con una longitud de 42 km y un buzamiento hacia el sur, llega a formar escarpes de hasta 500 m en rocas volcánicas Neógenas (Figura 1;Sánchez-Rubio, 1984;Suter et al., 1992;1995;Aguirre-Díaz 1993;1995). Esta falla normal fue la principal fuente sismogenética del terremoto de Acambay en 1912 (Langridge et al., 2000). ...
This study focuses on the identification and seismic characterization of the San Mateo fault, herein described for the first time. This fault is located in the central part of the Acambay graben, central Mexico. It is a 13 km long active normal fault with E-W direction and dip to the south. Two trenches were excavated in the locality of La Lechuguilla to determine the recent chronology of paleoearthquakes along this fault and to estimate its seismic parameters. At least three paleo-breaks have been found in one of these trenches and new radiocarbon ages indicate that they occurred from Late Pleistocene to the Holocene times. The oldest event (Event 1) occurred in 31.0-29.3 ky cal BP. Event 2 occurred in 19.1-6.5 ky cal BP and the younger faulting (Event 3) in 6.0 to 4.2 cal ky BP. These results suggest a recurrence interval of surface ruptures of about 11.57 +/- 5.32 ky. A slip rate of 0.085 +/- 0.025 mm / year and a magnitude (M-w) of 6.43 to 6.76 is estimated from the maximum coseismic displacement of 0.85 +/- 0.163 m and a rupture length of 13 km. If we consider a maximum rupture length of 25 km, including the possible continuity of the fault under the present day sediments filling the graben, a M-w magnitude of 6.7 +/- 0.3 could be expected. The paleoseismic data and fault scaling relationships suggest that the San Mateo fault is a significant seismic source in terms of hazard. This study also highlights the recency of the volcanic activity in the Acambay graben.
... La zona del graben de Acambay está principalmente formada por rocas volcánicas miocenas a cuaternarias sobre un basamento plutónico y metamórfico (Sánchez-Rubio, 1984;Aguirre-Díaz, 1993;1995;. Los materiales más jóvenes corresponden a una sedimentación fluvio-lacustre que rellenó pequeñas cuencas formadas por relieves volcánicos y barreras tectónicas a lo largo del rio Lerma. ...
... El terremoto de 1912 fue generado en la falla Acambay-Tixmadejé pero produjo fracturas superficiales en los tres sistemas de fallas (Urbina y Camacho, 1913;Langridge et al., 2000;Rodríguez-Pascua et al., 2012). La falla Acambay-Tixmadejé, con una longitud de 42 km y un buzamiento hacia el sur, llega a formar escarpes de hasta 500 m en rocas volcánicas Neógenas (Figura 1;Sánchez-Rubio, 1984;Suter et al., 1992;1995;Aguirre-Díaz 1993;1995). Esta falla normal fue la principal fuente sismogenética del terremoto de Acambay en 1912 (Langridge et al., 2000). ...
... El terremoto de 1912 fue generado en la falla Acambay-Tixmadejé pero produjo fracturas superficiales en los tres sistemas de fallas (Urbina y Camacho, 1913;Langridge et al., 2000;Rodríguez-Pascua et al., 2012). La falla Acambay-Tixmadejé, con una longitud de 42 km y un buzamiento hacia el sur, llega a formar escarpes de hasta 500 m en rocas volcánicas Neógenas (Figura 1;Sánchez-Rubio, 1984;Suter et al., 1992;1995;Aguirre-Díaz 1993;1995). Esta falla normal fue la principal fuente sismogenética del terremoto de Acambay en 1912 (Langridge et al., 2000). ...
This study focuses on the identification and seismic characterization of the San Mateo fault, herein described for the first time. This fault is located in the central part of the Acambay graben, central Mexico. It is a 13 km long active normal fault with E-W direction and dip to the south. Two trenches were excavated in the locality of La Lechuguilla to determine the recent chronology of paleoearthquakes along this fault and to estimate its seismic parameters. At least three paleo-breaks have been found in one of these trenches and new radiocarbon ages indicate that they occurred from Late Pleistocene to the Holocene times. The oldest event (Event 1) occurred in 31.0-29.3 ky cal BP. Event 2 occurred in 19.1-6.5 ky cal BP and the younger faulting (Event 3) in 6.0 to 4.2 cal ky BP. These results suggest a recurrence interval of surface ruptures of about 11.57 ± 5.32 ky. A slip rate of 0.085 ± 0.025 mm / year and a magnitude (Mw) of 6.43 to 6.76 is estimated from the maximum coseismic displacement of 0.85 ± 0.163 m and a rupture length of 13 km. If we consider a maximum rupture length of 25 km, including the possible continuity of the fault under the present day sediments filling the graben, a Mw magnitude of 6.7 ± 0.3 could be expected. The paleoseismic data and fault scaling relationships suggest that the San Mateo fault is a significant seismic source in terms of hazard. This study also highlights the recency of the volcanic activity in the Acambay graben.
... 1c). These faults affect Neogene and Quaternary deposits of scoria cones and domes, lava bodies of basaltic, andesitic, and rhyolitic composition, as well as pyroclastic deposits (Suter et al., 1991;Aguirre-Díaz, 1995Aguirre-Diaz et al., 2000;Garduño-Monroy et al., 2009;Ortuño et al., 2015). Volcanic rocks of the TMVB that surround the Acambay graben are Miocene to Quaternary in age (Aguirre-Díaz, 1996;Aguirre-Diaz et al., 2000) ( Fig. 1c), and form the footwall blocks of the graben and the basement of the hanging wall (Sánchez-Rubio, 1984;Aguirre-Díaz, 1993Aguirre-Diaz et al., 2000). ...
The Temascalcingo volcano is a dacitic stratovolcano located at the eastern part of the Acambay graben, a tectonic basin in the central sector of the Trans-Mexican Volcanic Belt (TMVB), which is an active, mostly calc-alkaline volcanic arc that crosses Mexico from the Pacific Ocean to the Gulf of Mexico. This study characterises the explosive activity of the San Mateo Pumice eruption that is the most recent and largest paroxysmal episode of this volcano and the last unit of the Cerritos Member. Indeed, this eruption is associated with an undated debris avalanche event consisting of a major sector collapse developed on the western flank of the volcano. Stratigraphic data suggest a highly explosive eruption that generated a relatively thick (up to 10 m) and widespread pumice fallout deposit, trending to the NE, and an aerial distribution of at least 100 km². This subplinian type eruption of VEI 4 lasted about 9 h and produced a plume height up to 12 km above the vent (i.e., ~14 km above sea level). This type of explosive eruption is relatively common in the TMVB, so a comprehensive geological study, with the corresponding numerical simulations like the one that was carried out, contributes to the understanding of the explosive volcanism of modest size stratovolcanoes that are common in the TMVB.
... These rocks form the footwall blocks of the graben and the basement of the hangingwall (Sánchez-Rubio, 1984;Aguirre-Díaz, 1993. The history of faulting for some faults, e.g., the Epitacio Huerta fault (activity since at least 2.2-2.5 Ma), is known from its association with the Amealco caldera (Aguirre-Díaz, 1995. In addition, there is evidence for intra-graben volcanism continuing during the Quaternary, e.g., Temascalcingo (Figure 3). ...
Intraplate earthquakes represent a significant risk to the cities located within the central part of the Transmexican Volcanic Belt as illustrated by the 1912 6.9 Mw Acambay earthquake. The epicenter was located 80 km northeast from Mexico City. The Acambay Graben is a part of a tectonic active intra-arc graben and bounded to the north by the 42 km south-dipping Acambay-Tixmadejé fault and to the south by the 73 km north-dipping Pastores (PF) and Venta de Bravo fault (VBF) zone. This last fault system has been linked to a 5.3 mb earthquake in 1979. In this study four trenches were dug exposing volcanic deposits, fluvio-lacustrine sediments, colluvial deposits and paleosols in the eastern part of the Venta de Bravo fault. We present evidence for two paleoearthquakes in the last 30 ka. The correlation of the events identified in a previous work in the western tip of the PF and our results in the eastern tip of the VBF is still an open question. However, using empirical relationships the expected maximum magnitude for joint rupture of these two faults with a 73 km trace is Mw=7, this magnitude is above the average of magnitudes estimations done in the other seismogenic sources in the region studied before, suggesting that the south border of the graben could be one of the most dangerous seismogenic source in the surrounding area of Mexico City.
... These rocks form the footwall blocks of the graben and the basement of the hangingwall (Sánchez-Rubio, 1984;Aguirre-Díaz, 1993. The history of faulting for some faults, e.g., the Epitacio Huerta fault (activity since at least 2.2-2.5 Ma), is known from its association with the Amealco caldera (Aguirre-Díaz, 1995. In addition, there is evidence for intra-graben volcanism continuing during the Quaternary, e.g., Temascalcingo (Figure 3). ...
Shallow, crustal normal faulting earthquakes represent a significant seismic risk to the local towns and regional cities of central Mexico. Within the Acambay graben, the Pastores fault is a ca. 33 km long active, east-west striking, north-dipping normal fault. Two paleoseismic trenches were excavated at the Manto del Río site to estimate preliminary active fault and seismic hazard parameters. Both trenches showed evidence for at least two latest Pleistocene to Holocene paleo-earthquake ruptures, constrained by radiocarbon dates from the West trench and through correlation of pyroclastic units between the trenches. The oldest faulting event (Event III) is bracketed within the interval ca. 31.5-41.0 cal kyr BP. Units higher in the trench are less displaced and provide evidence for at least one younger event. Rupture event II is bracketed within the interval ca. 23.9-34.6 cal kyr BP. The youngest faulting event (Event I; 12.2-12.6 cal kyr BP) is inferred from the presence of organic infill within the main fault zone (fissure). These results yield a preliminary recurrence interval of surface faulting of ca. 10-15 kyr for the Pastores fault. Based on a maximum single-event displacement (SED) of ca. 50 cm, an average SED of ca. 30 cm, and fault rupture lengths of up to 33 km, a magnitude of M 6.6-6.8 is estimated for surface rupturing events. Both the SED and latest Pleistocene to Holocene slip rate (ca. 0.03 mm/yr) at the trench site are likely to be less than values measured toward the western end of the fault where the rangefront is larger. The Acambay graben has distinct eastern and western halves, being divided by a N- to NNW-striking structural zone corresponding to the Taxco-San Miguel de Allende fault system. Paleoseismic data and empirical relationships suggest that the Pastores fault constitutes both a distinct seismic source from other active faults of the Acambay graben and a significant seismic hazard.
... These rocks form the footwall blocks of the graben and the basement of the hangingwall (Sánchez-Rubio, 1984;Aguirre-Díaz, 1993. The history of faulting for some faults, e.g., the Epitacio Huerta fault (activity since at least 2.2-2.5 Ma), is known from its association with the Amealco caldera (Aguirre-Díaz, 1995. In addition, there is evidence for intra-graben volcanism continuing during the Quaternary, e.g., Temascalcingo (Figure 3). ...
... La secuencia estratigráfica del graben fue descrita y medida en la pared sur del mismo en la región de Venta de Bravo-Tlalpujahua que se localiza a 25 km al SW del volcán de Temascalcingo (Aguirre-Díaz et al., 2000). Aquí se midió una sección de aproximadamente 60 m, compuesta en la base por rocas metasedimentarias y diques, y cubierta por depósitos piroclásticos, a su vez cubiertos por la Toba Amealco (4.7 Ma), que está cubierta por depósitos lacustres y lavas andesíticas-basálticas (Aguirre-Díaz, 1995Aguirre-Díaz, , 1996). Es interesante observar que las ignimbritas de la Caldera de Amealco se han identificado en ambos lados del graben de Acambay por lo que sirven como horizontes índices (Aguirre-Díaz et al., 2000). ...
The Temascalcingo volcano is located 70 km to the NW of Toluca city, and next to the town of the same name, in the State of México. It is one of several volcanoes within the Acambay graben. The Temascalcingo is an andesitic-dacitic stratovolcano, apparently of Pliocene age, with a summit caldera and affected by several normal faults of the Acambay Graben system. At the end of its volcanic evolution there was a destructive phase in the form of a lateral collapse, which formed a debris avalanche deposit and a lithics-rich pyroclastic flow deposit. This collapse occurred on the western flank of the volcano, leaving a horseshoe shaped amphitheater opened to the west and with a size of 6.5 by 3.5 km. The debris avalanche deposit is distributed on the same W direction, reaching at least 6 km from the source; includes hummocks up to 100 m high, and covers an area of 23 km2, representing a rock volume of 0.8 km3, including the exposed rocks in the hummocks. The lateral collapse of the Temascalcingo volcano is of Bezymianny type. The event was probably similar to that of the December 1997 eruption of Soufrière Hills volcano at Montserrat, and was caused by a combination of factors, including: 1) magma injection and emplacement of a lava dome that caused overpressure in the magmatic system and instability of the volcano, 2) an earthquake associated to the Acambay fault system that triggered the sector collapse of the volcano; and 3) fast depressurization related to the quick opening of the system by the landslide and the dome collapse that resulted in an explosive eruption that formed a block and ash pyroclastic flow and an eruptive column that formed a lapilli fallout.
Water supply in semiarid areas in Mexico depends on water extraction from compartmentalized aquifers where large drawdown rates can be observed due to increasing demand from urban, industrial and agricultural users. Understanding the behavior of these aquifers is a necessity in order to improve the estimation of water balances. Accordingly, this study assembles both geochemical and isotopic data to identify the source of recharge to the San Juan del Río graben aquifer and to determine its dynamics. The geological model developed with the aforementioned data reveals a complex system composed of a heterogeneous multilayered compartmentalized aquifer. The San Juan del Rio basin is composed of (1) the Amealco perched aquifer, (2) a shallow granular aquifer, and (3) a fractured aquifer. Hydrogeochemical and isotopic data (δ2H, δ18O, δ13C and correct carbon activity (Δ14C)) allow for identification of three end-member sources: (1) local meteoric recharge, (2) old groundwater contained in the siliciclastic shallow aquifer, and (3) regional/local hydrothermal recharge. The contribution of both meteoric and regional hydrogeothermal flow to the different aquifer compartments is determined through a principal component analysis of the hydrogeochemical data. With the aforementioned analysis it was found that the dominant contribution source for all aquifer compartments is meteoric water (up to 60% with a median of 50%), while the regional hydrothermal groundwater contribution represents 15%, even for the shallow aquifer.
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