DOI: https://doi.org/10.1016/j.jsames.2020.103105

Resumen

The roughly 600 km long Central Cordillera of Colombia shows a varied tectonic, magmatic, and exhumation history, despite the reasonably homogenous appearance concerning topography, outcropping lithologies, and strike. Here we show with new geo-thermochronological data the thermal evolution of the southern Central Cordillera since the Early Jurassic. Extensive Jurassic magmatism is recorded by U–Pb crystallization ages of arc plutons intruded by dike swarms and collateral volcaniclastic flows. Inverse modeling of zircon and apatite fission-track ages from Central Cordillera reveals a long period of slow cooling since the Early Cretaceous at rates of 2–3 °C/Myr, based on best-fit t-T path solutions. The Early Cretaceous phase is recorded by the cooling of Jurassic granitoids, most likely driven by slow erosional exhumation along the western flank of the Central Cordillera related to the collision and accretion of the Quebradagrande arc against the continental margin. The Late Cretaceous rapid exhumation event caused by the ~80-70 Ma collision and accretion of the Caribbean Large Igneous Province at the western margin of South America observed in other parts of the Central Cordillera, is not detectable in our study area . During the Eocene-Oligocene (ca. 45-31 Ma), the obtained time-temperature paths are compatible with slow cooling rates between 1 and 2 °C/Myr and slow exhumation at long-term average rates of about 0.1 km/Myr. The combination of geo-thermochronological data and petrology of clastic basin sediments presented in this study indicates that the unroofing of the southern Central Cordillera crystalline basement also occurred during the Eocene-Oligocene phase of the Andean Orogeny, as widely recognized by a major unconformity. The exhumation was coeval with the reactivation of crustal structures, such as the Plata-Chusma fault, as evidenced by the syn-tectonic deposits of the Gualanday Group.

DOI: https://doi.org/10.1016/j.jsames.2020.103110

Resumen

Volcanic geological maps provide significant data for volcanic hazard assessment, exploration of mineral-energetic resources, physical volcanology and petrological studies, as well as geophysical models. However, the lack of consensus about the best graphic representation of volcanic geological maps and the most efficient organizational structure of spatial data contained in these maps, has resulted in a variability of representations and data storage. Here we propose some guidelines to unify the representation of composite volcanoes geological maps that may facilitate the communication within a particular country and across political boundaries by reaching a common language. In this paper, we share the advances obtained in Colombia by the Servicio Geológico Colombiano (Colombian Geological Survey), through searching for improved cartographic strategies and efficient representations of mapped volcanogenic units in the North-Andean setting. The main objective of this paper is to provide a guideline for the digital representation of Pliocene-Holocene composite volcanoes geological maps, applicable elsewhere, that displays a comprehensive presentation based on an accurate and qualified geodatabase package. This contribution offers: (i) a catalogue of symbols for the representation of geological and geomorphological elements; (ii) a catalogue of colors and patterns for the representation of the different lithostratigraphic units; (iii) a graphic distribution prototype for the information within the resulting map sheet, and (iv) a geodatabase structure with its corresponding catalogue of objects. With this initiative, we aim to begin an international collaborative effort on reaching a common understanding of best practices in the representation and systematic digital organization of thematic maps of composite volcanoes.

DOI: https://doi.org/10.1785/012019022
DOI: https://doi.org/10.11606/D.14.2021.tde-20092021-120029

Resumen

The accurate and efficient analysis of seismic data requires the implementation of automatic rocessing algorithms. Therefore, the reliability and quality of these automatic results have become critical requirements for seismological networks. Two methodologies, Grid-search and Bayesian optimization, were used to optimize the automatic detection and phase picking parameters in SeisComP. These methodologies were tested using a set of stations selected from two seismological networks the Brazilian Seismic Network (RSBR) and Colombian National Seismological Network (RSNC). A comparison of manual and previous automatic locations, revealed numerous missing events and others with low-quality locations in automatic databases. We selected 508 manual events from 2017/01/01 to 2020/07/31 in Brazil, and 532 manual events from 2019/02/01 to 2019/02/15 near the Bucaramanga Nest in Colombia, as training data sets for the optimization process. A code was implemented to use an iterative grid-search to optimize the picking parameters. In addition, the Optuna Python package was used to implement the Bayesian optimization. Selected events were used as a training set, and an iterative process according to the Bayesian method was used. The results of both methodologies were compared. Both methodologies improved the system performance by increasing the number of picks and detections. Grid-search allowed us to perform a complete analysis of the results examining the entire space of parameters. However, Grid-search lose efficiency while increasing the number of parameters being optimized. On the other hand, the Bayesian algorithm is computationally more efficient by not exploring the entire parameter space. After the optimization process, automatic picks associated with P phases increases by 78% (76 picks) and 56% (903 picks) for RSBR and RSNC, respectively. Although not all new picks belong to new events, the number of locations calculated using new automatic picks doubled the automatic locations determined by the systems before the optimization process for both networks. Seismological centers could implement methodologies such as Grid-search or Bayesian optimization to improve their automatic processing systems. Besides, the standardization of these methodologies would help to make their implementation easier.

DOI: https://doi.org/10.1016/j.jsames.2021.103397

Resumen

The Guajira Arch is located in the northernmost portion of South America and holds the record of several stages of magmatism and metamorphism. We performed LA-ICP-MS U–Pb zircon geochronology coupled with Lu–Hf isotope geochemistry on 11 samples from a high-grade gneissic basement hosting interleaved complexes of younger meta-granitoids and meta-sediments to unravel its tectono-metamorphic evolution. The oldest rocks correspond to a Rodinia-type basement at ca. 1100-880 Ma, affected by mafic magmatism during the Permian at ca. 272 Ma, anatexis during the Carnian at ca. 230 Ma, updoming and the formation of an extensional detachment fault during the Norian at ca. 224 Ma concluding with Jurassic magmatism since ca. 190 Ma. Trace element geochemistry shows that Triassic zircons are depleted in HREE and yield lower Th/U ratios than Jurassic zircons enriched both in HREE, Yb, and Y. Hf systematics indicates a Triassic to Jurassic evolution towards more radiogenic compositions. The lithological associations, structural setting, U–Pb ages, and Hf isotope geochemistry of the Triassic-Jurassic rocks at the Guajira Arch characterize an active margin setting of a hot orogenic belt in NW-Gondwana, comprising the Central Cordillera of Colombia, the Santa Marta Massif, the Merida Andes, the Perijá Range, the Santander Massif and the para-autochthonous terranes south of the Ouachita-Marathon Suture (Oaxaquia, Acatlán, and Maya), and thus vindicate the existence of a conjugate margin with Laurentia until the Late Triassic, preceding the breakup of western Pangaea. The Triassic anatectites and Jurassic granitoids from the Guajira Arch yield Proterozoic Hf TDMi ages which are indistinguishable from the autochthonous Proterozoic basement and thus render an allochthonous origin by terrane accretion highly improbable. Instead, these data point to melting of the continental crust by the incorporation of primitive material reflecting a two-stage process at the boundary of a large underlying mantle convection cell (i) Triassic slab steepening, subduction arrest, updoming anatexis at ca. 230-223 Ma and (ii) Early Jurassic arc-magmatism at ca. 190-165 Ma due renewed convergence. Furthermore, we propose that the structural setting, lithology, and isotope geochemistry of the Guajira Arch units, fit into the style of a cordilleran core-complex emplaced in a roll-back extensional setting preceding Pangaea break-up.

DOI: https://doi.org/10.1785/0120180154

Resumen

Empirical site amplification models for surface and body waves based on the average shear‐wave velocity in the upper 30 m (⁠VS30⁠) are developed for predicting horizontal response spectra in the Bogotá basin, Colombia. By analyzing the earthquake ground‐motion data recorded in Bogotá, it is found that long‐period ground motions with a period of 2 s from shallow earthquakes are strongly amplified within the basin, possibly as a result of the generation of surface waves at the basin edge, whereas shorter‐period body waves with predominant periods between 0.5 and 1 s typically characterize records within the basin from deep earthquakes. The present results indicate that the attenuation relationship developed by Uchiyama and Midorikawa (2006) accurately reproduces the response spectra at reference rock sites. In this study, the site amplifications, defined as the ratio between the observed response spectrum and the reference spectrum obtained from the aforementioned attenuation relationship, are evaluated. Models of the site amplifications for surface and body waves are developed using the observed response spectra in Bogotá and validated by comparing the model results to observation data from the 1999 Quindío, Colombia, and 2017 Chiapas, Mexico, earthquakes. The results confirm that the surface‐wave amplification model developed in this study is shown to accurately reproduce the observed response spectra in Bogotá.

DOI: https://doi.org/10.1029/2019JB017835

Resumen

The Eastern Cordillera of Colombia, in the northern Andes, is an example of an orogen in which Mesozoic basins were compressed during the Cenozoic, forming a ~2,500-m-high plateau in its northern portion. Significant shortening and crustal thickening have contributed to the construction of the present topography and elevation. In this contribution, we combine the use of teleseismic receiver functions, Hf isotopes, whole-rock geochemistry, and U-Pb dating to help elucidate the main mechanisms that played a role in the crustal thickening and uplift of the cordillera. Receiver functions calculated for three stations on top of the plateau are consistent with the presence of thrusts that converge into major crustal interfaces at upper-middle crustal depths; they also suggest the existence of two crustal anisotropic layers beneath the western flank of the cordillera, which we interpret to have formed as a result of shearing. In the northern portion of the plateau, in the area where two Mio-Pliocene volcanic domes and their related deposits outcrop, a lower crustal high seismic velocity layer is suggested by the receiver functions; we propose magmatic underplating for the origin of this layer. The geochemical characteristics of the volcanic rocks in the area are consistent with partial melt in a mantle influenced by slab-related fluids; this magma could have been added to the crust and portions of it ascended and reached the surface, experiencing assimilation and differentiation during the process. We hypothesize that this Mio-Pliocene volcanism was related to flattening of the Nazca subducting slab.

DOI: https://doi.org/10.1093/gji/ggaa326

Resumen

Seven years after the beginning of a massive wastewater injection project in eastern Colombia, local earthquake activity increased significantly. The field operator and the Colombian Geological Survey immediately reinforced the monitoring of the area. Our analysis of the temporal evolution of the seismic and injection data together with our knowledge of the geological parameters of the region indicate that the surge of seismicity is being induced by the re-injection of produced water into the same three producing reservoirs. Earthquake activity began on known faults once disposal rates had reached a threshold of ∼2 × 106 m3 of water per month. The average reservoir pressure had remained constant at 7.6 MPa after several years of production, sustained by a large, active aquifer. Surface injection pressures in the seismically active areas remain below 8.3 MPa, a value large enough to activate some of the faults. Since faults are mapped throughout the region and many do not have seismicity on them, we conclude that the existence of known faults is not the only control on whether earthquakes are generated. Stress conditions of these faults are open to future studies. Earthquakes are primarily found in four clusters, located near faults mapped by the operator. The hypocentres reveal vertical planes with orientations consistent with focal mechanisms of these events. Stress inversion of the focal mechanisms gives a maximum compression in the direction ENE-WSW, which is in agreement with borehole breakout measurements. Since the focal mechanisms of the earthquakes are consistent with the tectonic stress regime, we can conclude that the seismicity is resulting from the activation of critically stressed faults. Slip was progressive and seismic activity reached a peak before declining to few events per month. The decline in seismicity suggests that most of the stress has been relieved on the main faults. The magnitude of a large majority of the recorded earthquakes was lower than 4, as the pore pressure disturbance did not reach the mapped large faults whose activation might have resulted in larger magnitude earthquakes. Our study shows that a good knowledge of the local fault network and conditions of stress is of paramount importance when planning a massive water disposal program. These earthquakes indicate that while faults provide an opportunity to dispose produced water at an economically attractive volume–pressure ratio, the possibility of induced seismicity must also be considered.

DOI: https://doi.org/10.1002/2016GL071929

Resumen

A large earthquake (Mw7.7) occurred on 16 April 2016 within the source region of the 1906earthquake in the Ecuador-Colombia subduction zone. The 1906 event has been interpreted as amegathrust earthquake (Mw8.8) that ruptured the source regions of smaller earthquakes in 1942, 1958, and1979 in this subduction. Our seismic analysis indicated that the spatial distribution of the 2016 earthquakeand its aftershocks correlated with patches of high interplate coupling strength and was similar to those ofthe 1942 earthquake and its aftershocks, suggesting that the 2016 and 1942 earthquakes ruptured the sameasperity. Our analysis of tsunami waveforms of the 1906 event indicatedMwaround 8.4 and showed thatlarge slip occurred near the trench off the source regions of the above three historical and the 2016earthquakes, suggesting that a depth-dependent complex rupture mode exists along this subduction zone.

DOI: https://doi.org/10.1007/s00024-021-02718-x

Resumen

The analysis of seismic ambient noise has been recently proven a viable alternative to the analysis of seismic waves generated by earthquakes. Although seismic ambient noise had traditionally been discarded from earthquake records, it has now been shown that the cross-correlation of the seismic ambient noise allows for the recovery of the Green’s function between the receivers. Furthermore, seismic noise has the ability to propagate continuously and independently of the occurrence of earthquakes, allowing for high-resolution tomographic studies in regions of low seismicity. Over the last two decades, the cross-correlation of continuous seismic noise recordings between pairs of stations has been widely utilized in surface-wave tomography studies. For the Northeast Brazil region, tomographic studies have been exclusively performed with seismic data from broadband stations; however, in addition to those stations, there exists a large volume of short-period data that might potentially improve the resolution of existing ambient noise tomographies. Thus, the goal of this work is to utilize, in addition to broadband data, short-period data recorded by 22 short-period stations in the Borborema Province. Through cross-correlation and stacking of ambient seismic noise, the emergence of the fundamental mode of the Rayleigh waves and their dispersive character was observed. Once the empirical Green's functions were retrieved, the accuracy of (phase and group) dispersion curves for periods up to 10 s and its tomographic inversion were assessed. Our results demonstrate that short-period dispersion measurements can be successfully integrated in regional tomographic studies for improved resolution.

DOI: https://doi.org/10.1002/2013GL058109

Resumen

Intermediate-depth earthquakes occur at depths where temperatures and pressures exceed those at which brittle failure is expected. There are two leading candidates for the physical mechanism behind these earthquakes: dehydration embrittlement and self-localizing thermal shear runaway. A complete energy budget for a range of earthquake sizes can help constrain whether either of these mechanisms might play a role in intermediate-depth earthquake rupture. The combination of high stress drop and low radiation efficiency that we observe for Mw 4–5 earthquakes in the Bucaramanga Nest implies a temperature increase of 600–1000°C for a centimeter-scale layer during earthquake failure. This suggests that substantial shear heating, and possibly partial melting, occurs during intermediate-depth earthquake failure. Our observations support thermal shear runaway as the mechanism for intermediate-depth earthquakes, which would help explain differences in their behavior compared to shallow earthquakes.

DOI: https://doi.org/10.20965/jdr.2020.p0645

Resumen

Colombia is tectonically active, and several large earthquakes have ruptured the Colombia-Ecuador subduction zone (CESZ) during the last century. Among them, the Colombia-Ecuador earthquake in 1906 (Mw 8.4) and the Tumaco earthquake in 1979 (Mw 8.3) generated destructive tsunamis. Therefore, it is important to characterize the seismic rupture processes and their relation with interplate coupling along the CESZ. We searched for repeating earthquakes by performing waveform similarity analysis. Cross correlation (CC) values were computed between earthquake pairs with hypocenter differences of less than 50 km that were located in the northern CESZ (1°–4°N) and that occurred from June 1993 to February 2018. We used broadband and short-period seismic waveform data from the Servicio Geológico Colombiano (SGC) seismic network. A CC threshold value of 0.90 was used to identify the waveform similarity and select repeating earthquakes. We found repeating earthquakes distributed near the trench and the coast. Our estimated repeating earthquakes near the trench suggest that the interplate coupling in this region is low. This is in clear constrast to the occurrence of a large slip in the 1906 Colombia-Ecuador earthquake along the trench in the southern part of the CESZ, and suggests that rupture modes are different between the northern and southern parts of CESZ near the trench.

DOI: https://www.issmge.org/publications/publication/risk-management-in-volcanic-chains-of-the-circum-pacific-belt

Resumen

The Circum-Pacific Belt, also called the Pacific rim of fire, is an area around the Pacific Ocean characterized by intense seismic and volcanic activity as evidence of a living and dynamic Earth / Planet. This is the reason, which explains the presence of large numbers of earthquakes and volcanoes around the borders of the Pacific Ocean. It concentrates a large percentage of the world's earthquakes and volcanoes, also some of the countries with dense population are located in these areas. Based on assessment of the volcanic hazard and activity of the volcano, local authorities should proceed to develop in a consulting and coordinated manner with their communities contingency plans and response strategies; which include alert levels, evacuation routes and exercises, such drills for those who permanently reside in areas where such dangerous volcanic phenomena can occur, such as lahars or pyroclastic flows. As an example of risk reduction experience during a volcanic eruption, the Nevado del Huila volcano in Colombia is presented..

DOI: https://doi.org/10.3389/feart.2020.611320

Resumen

Understanding the relationship between degassing, crystallization processes and eruption style is a central goal in volcanology, in particular how these processes modulate the magnitude and timing of cyclical Vulcanian explosions in intermediate magmas. To investigate the influence of variations in crystal micro-textures on magma rheology and eruption dynamics, we conducted high-temperature (940°C) uniaxial compression experiments at conditions simulating a shallow volcanic conduit setting on eight samples of high-crystallinity andesite with variable plagioclase microlite populations from the 2004 to 2010 Vulcanian explosions of Galeras volcano, Colombia. Experiments were conducted at different strain rates to measure the rate-dependence of apparent viscosities and assess the dominant deformation processes associated with shear. Variations in plagioclase micro-textures are associated with apparent viscosities spanning over one order of magnitude for a given strain rate. Samples with low numbers of large prismatic microlites behaved consistently with published rheological laws for crystalline dome samples, and displayed extensive micro-cracking. Samples with high numbers of small tabular microlites showed a lower apparent viscosity and were less shear-thinning. The data suggest a spectrum of rheological behavior controlled by concurrent variations in microlite number, size and shape. We use previously published micro-textural data for time-constrained samples to model the apparent viscosity of magma erupted during the 2004–2010 sequence of Vulcanian explosions and compare these results with observed SO2 fluxes. We propose that variations in magma decompression rate, which are known to produce systematic textural differences in the plagioclase microlite cargo, govern differences in magma rheology in the shallow conduit. These rheological differences are likely to affect the rate at which magma densifies as a result of outgassing, leading to magmatic plugs with a range of porosities and permeabilities. The existence of magmatic plugs with variable physical properties has important implications for the development of critical overpressure driving Vulcanian explosions, and thus for hazard assessment during volcanic crises. We suggest a new conceptual model to explain eruption style at andesitic volcanoes based on micro-textural and rheological differences between “plug-forming” and “dome-forming” magma. We advance that existing rheological laws describing the behavior of andesitic magma based on experiments on dome rocks are inappropriate for modeling large Vulcanian explosions (∼106 m3), as the magma involved in these eruptions lacks the characteristics required to form exogenous lava domes.

DOI: https://doi.org/10.1016/j.cretres.2021.105122

Resumen

-Kronosaurus boyacensis is the most famous and most important Lower Cretaceous marine reptile fossil recovered from the Villa de Leyva region of Boyacá, Colombia, northern South America. To the local population it has become iconic as The Fossil (‘El Fósil’) of Colombia. Here we provide a detailed re-description of the holotype of the pliosaurid sauropterygian Kronosaurus boyacensis, and designate it a new genus, Monquirasaurus. Redescription of Monquirasaurus boyacensis required detailed consideration of the genus Kronosaurus, the Albian holotype of which is non-diagnostic at the taxonomic level of genus and species so the name Kronosaurus queenslandicus is thereby restricted to the holotype only. Aptian specimens currently assigned to Kronosaurus queenslandicus, and housed in the University Museum in Harvard, USA, are designated as the holotype and referred specimen of the new genus and species Eiectus longmani, which also provisionally includes all Albian material formerly referred to the genus Kronosaurus. The two pliosaurid marine reptiles from the Cretaceous of Colombia and Australia do not fit well into the current phylogenetic framework proposed for these gigantic marine reptiles, highlighting the importance of both northern and southern peri-Gondwanan specimens for the study of Lower Cretaceous Gap pliosaurids.