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The understanding of the dynamical behavior of seismic phenomena is currently an open problem, mainly because seismic series can be considered to be produced by phenomena exhibiting dynamic phase transitions; that is, with some complexity. For this purpose, the Middle America Trench in central Mexico is considered a natural laboratory for examining subduction because of its heterogenous natural structure. In this study, the Visibility Graph method was applied to study the seismic activity of three regions within the Cocos plate: the Tehuantepec Isthmus, the Flat slab and Michoacan, each one with a different level of seismicity. The method maps time series into graphs, and it is possible to connect the topological properties of the graph with the dynamical features underlying the time series. The seismicity analyzed was monitored in the three areas studied between 2010 and 2022. At the Flat Slab and Tehuantepec Isthmus, two intense earthquakes occurred on 7 and 19 September 2017, respectively, and, on 19 September 2022, another one occurred at Michoacan. The aim of this study was to determine the dynamical features and the possible differences between the three areas by applying the following method. First, the time evolution of the a- and b-values in the Gutenberg–Richter law was analyzed, followed by the relationship between the seismic properties and topological features using the VG method, the k–M slope and the characterization of the temporal correlations from the γ-exponent of the power law distribution, P(k) ∼ k−γ, and its relationship with the Hurst parameter, which allowed us to identify the correlation and persistence of each zone. [ABSTRACT FROM AUTHOR]

Non-extensive statistical mechanics (or q-statistics) is based on the so-called non-additive Tsallis entropy. Since its introduction by Tsallis, in 1988, as a generalization of the Boltzmann–Gibbs equilibrium statistical mechanics, it has steadily gained ground as a suitable theory for the description of the statistical properties of non-equilibrium complex systems. Therefore, it has been applied to numerous phenomena, including real seismicity. In particular, Tsallis entropy is expected to provide a guiding principle to reveal novel aspects of complex dynamical systems with catastrophes, such as seismic events. The exploration of the existing connections between Tsallis formalism and real seismicity has been the focus of extensive research activity in the last two decades. In particular, Tsallis q-statistics has provided a unified framework for the description of the collective properties of earthquakes and faults. Despite this progress, our present knowledge of the physical processes leading to the initiation of a rupture, and its subsequent growth through a fault system, remains quite limited. The aim of this paper was to provide an overview of the non-extensive interpretation of seismicity, along with the contributions of the Tsallis formalism to the statistical description of seismic events. [ABSTRACT FROM AUTHOR]

We applied multi–temporal 1D magnetotelluric (MT) surveys to identify space–time anomalies of apparent resistivity ( ρ a ) in the upper lithosphere in the Antarctic Peninsula (the border between the Antarctic and the Shetland plates). We used time series over several weeks of the natural Earth's electric and magnetic fields registered at one MT station of the Universidad Nacional de Colombia (RSUNAL) located at Seymour–Marambio Island, Antarctica. We associated resistivity anomalies with contrasting earthquake activity. Anomalies of ρ a were detected almost simultaneously with the beginning of a seismic crisis in the Bransfield Strait, south of King George Island (approximately 85.000 events were reported close to the Orca submarine volcano, with focal depths < 20 km and MWW < 6.9). We explained the origin of these anomalies in response to fluid migration near the place of the fractures linked with the seismic swarm, which could promote disturbances of the pore pressure field that reached some hundreds of km away. [ABSTRACT FROM AUTHOR]

In this work, we apply multi-temporal 1D-magnetotelluric (MT) surveys to estimate the space–time variations of the apparent resistivity ρ a and correlate these changes with seismic activity in the central part of Colombia (South America). We use the time series of the Earth's natural electric and magnetic fields registered at two MT stations of the National University of Colombia Seismological Network (RSUNAL), located in the Eastern Andean Cordillera, in the central part of Colombia, over several days. Assuming that large earthquakes may generate these types of anomalies, we identified positive results for the Mesetas earthquake (Mw6.0, Lon = 74.184° W, Lat = 3.462° N, H = 13 km-depth, 24 December 2019, UTC 19:03:55), with anomalies registered eight hours before the mainshock. The depth at which the resistivity anomaly was identified coincides with the depth of the earthquake hypocenter. The origin of these anomalies may be associated with the migration of fluids due to the change in the stress regime before, during, and after the earthquake. We hypothesize that before the occurrence of an earthquake, the stress field generates pore pressure gradients, promoting alterations in fluid migration that change the resistivity of the upper crust. [ABSTRACT FROM AUTHOR]

Since 2013 to date more than 1000 seismic events have been recorded by the Servicio Geologico Colombiano (Colombian Geological Survey, SGC) in the municipality of Puerto Gaitán (Colombia). A total of 14 earthquakes are moment magnitude M w > 4.0. The largest event ever recorded in the area occurred in November 2015 with M w 4.8. It seems like the case of Puerto Gaitán is associated with the deep injection of coproduced wastewater from oil and gas extraction. The data presented in this work suggests a close relationship in space and time between injection operations and seismicity. An analysis of temporality between both data sets resulted in a time lag equivalent to about 218 d. For this paper, we computed the input and output energy during injection operations from 2013 to 2015 in order to estimate the fraction of total input energy that is radiated as seismic waves. Our results suggest that the seismic energy is only a small fraction of the total energy into the system. Although Puerto Gaitan is one of the places with the most significant volume of wastewater injected among the ones reported in the literature, the energy efficiency of the system is the lowest reported to date in comparison with other applied technologies. The low efficiency seems to be associated to the aseismic deformation of the reservoir rocks. The observed clustering of earthquakes is delimited by the basement crystalline depth. From an operational point of view, we determine that, like most cases associated with fluid injection, volume of fluid is the variable that determines change in the seismic moment released. Furthermore, the sequence of events in Puerto Gaitán may not fit into a well-known correlation between the volume of fluid injected and the maximum expected magnitude. The observed magnitudes in Puerto Gaitan are well bellow compared to those reported in the literature for similar volumes of injected fluid. [ABSTRACT FROM AUTHOR]

A three-dimensional estimation of the Vp, Vs and Vp/Vs ratio structure at Galeras volcano was conducted by means of passive local earthquake tomography. 14,150 volcano-tectonic events recorded by 58 stations in the seismological network established for monitoring the volcanic activity by the Colombian Geological Survey – Pasto Volcano Observatory between the years 1989 and 2015, were inverted by using the LOTOS code. The seismic events are associated with shear-stress fractures in solid rock as a response to pressure induced by magma flow. Tomography resolution tests suggest a depth of imaging that yield 10 km from the summit of the main crater, illuminating a large portion of the volcanic structure and the interaction of tectonic features like the Buesaco and Silvia-Pijao faults. Full catalog tomographic inversion, that represents the stacked image of the volcanic structure or the most permanent features underneath the volcano, shows vertical structures aligned with seismicity beneath the main crater. We hypothesize that these structures correspond to a system of ducts or fractures through which magma and fluid phases flow up from deeper levels toward the top and related with the intersection of the surface traces of the Silvia-Pijao and Buesaco faults. [ABSTRACT FROM AUTHOR]

Central Cordillera of Colombia near to the Nevado del Ruiz volcano is a seismically active area above the subducting slab of the Nazca plate and deforming upper crust of the Andes. Buildings in the region require strengthening against the effects of both types of hazards: earthquakes and volcanoes. During these trips, we will discuss the 13 November, 1985, Nevado del Ruiz Volcano eruption that destroyed the Armero city with about 22,000 deceases, as well the 25 January, 1999. Armenia earthquake (M 6.2) that killed about 2000 people and injured 4000 largely as the result of older, poorly constructed buildings. The economic impact of the quake on the region was significant with about 8000 coffee farms either completely or partially destroyed and over 13,000 structures either partially damaged or completely destroyed. Both phenomena are associated to a large-transversal structure termed Caldas tear, which is controlling strong motion earthquakes and the Quanternary volcanism of the northern Andes. [ABSTRACT FROM AUTHOR]

Abstract: The Abanico del Quindío (AQ) fan, a volcaniclastic deposit from the Ruiz–Tolima volcanic complex (RTVC), Colombia, provides insight into recent deformation in the Central Andes. The use of geological observations, geophysical measurements, and estimates of fault-scarp ages constrain timing of recent tectonic activity. Gravity and magnetic analyses, along with geomorphologic cartography, allow the detection of lateral variations in basement distribution and at least three structural trends that cut the AQ: the Armenia fault (NNE), El Danubio fault (NNW), and Hojas Anchas fault (E–W). Recent deformation in the zone results from slip on the Armenia and El Danubio faults and suggests a maximum interval magnitude of 5.1< M w <6.3, with ages ranging between 2560±480yr B.P. and 4120±780yr B.P. Although no surface ruptures are associated with historical events on the fault segments in this zone, blind structures may have influenced the hypocentral distribution of events recorded after the Armenia Earthquake (M w 6.2, 25-01-1999). Further geophysical studies are needed to understand the Romeral Fault System and assess the earthquake hazard for the city of Armenia. [Copyright &y& Elsevier]

A geometric model for the subduction of the Nazca plate beneath the South American plate in southwestern of Colombia is proposed based on the relocation of hypocenters of local and distant earthquakes. By means of the simultaneous inversion of teleseismic P and SH body waves, the depths of the 15 events with Mw = 5.8 were constrained, and the hypocenters of the 250 earthquakes recorded between 1990 and 2005 by the International Seismological Centre (ISC) and U.S. Geological Survey, National Earthquake Information Center (NEIC) were constrained and relocated. A model is proposed for the hypocentral sections taking into account the trench along of the Earth and Colombia-Ecuador. Three different possible shapes of subduction of the Nazca plate in the Colombia-Ecuador trench were obtained: The first configuration, in the Cali A segment, the dip angle changes from17° to 45° down to a maximum depth of 100km; the second configuration, in the Popayán B and Nariño C segments, the dip angle holds approximately constant at 30° down to a maximum depth of 200 km; and the third configuration, in the Quito D segment, the dip angle changes of 9° to 50° to a maximum depth 220 km. The maximum depth of seismicity along the Colombia-Ecuador trench shows two increases, the first between latitudes 4.5°N-5°N and the second between the latitudes 1°S-2°S, which suggest that the presence of the Malpelo and Carnegie Ridges may generate a differential blockage at the Pacific Colombia-Ecuador basin. [ABSTRACT FROM AUTHOR]

The space variation of the parameter of attenuation Q - Coda in a sector of the Piedemonte Llanero is studied using the Coda waves. The estimation of the attenuation of the amplitude of coda is calculated by means of the Model of simple Isotropic Dispersion of Sato (1977), from seismograms of earthquakes located in the region, between September of 1993 to June 2002. Following the methodology used by Aki and Chouet (1975) we analyzed seismograms in four bands centered to 1. 5, 3, 6 and 12 Hz with respective bandwidths of 1, 2, 4 and 8 Hz. By linear regression Qc value were calculated at 1 Hz. From the expression proposed by Pull (1984) to model the amplitude of the coda waves by means of ellipses, we extended this expression to calculate the space variation of the Q-1c, for three-dimensional analysis (anelastic tomography). By means of a square minimum inversion the value of attenuation for each cell of the three-dimensional model was calculated. Their results were correlated with the regional tectonic frame and found that when the attenuation increases with the depth, it correspond to zones with Tectonics of thick layers and on the contrary, where the attenuation diminishes with the depth corresponds to zones with tectonics of thin layers. [ABSTRACT FROM AUTHOR]

The space-time variation of the parameter of attenuation Q-Coda in a sector of the Piedemonte Llanero was studied using the Coda waves. The estimation of the attenuation of the amplitude of coda is calculated by means of the Model of simple Isotropic Dispersion of Sato, from earthquakes seismograms happened in the region from September 1993 to June 2002. Following the methodology used by Aki and Chouet (1975), they analyzed seismograms in four centered bands to 1.5, 3, 6 and 12 Hertz with its corresponding bandwidths of 1, 2, 4 and 8 Hertz. And by regression to linear calculated the value of Qc to 1 Hertz. From the expression proposed by Puli to model the amplitude of the waves coda by means of ellipses, this expression was extended to calculate the space variation of the Qc-1, (anelastic tomography). And by inverse square minimums, the value of attenuation for each cell of the three-dimensional model was calculated. Their results were correlated with the regional tectonic frame showing that when the attenuation increases by depth, it corresponds to zones with Tectonics of thick skin and, on the contrary, where the attenuation diminishes by depth, it corresponds to zones with Tectonics of thin skin. On the other hand, the temporary variation of minimum values of Qc (maximum attenuations) was correlated to qualitatively earthquakes of magnitude greater to 3,5 and, in addition, the temporary distribution of Qc was quantified by dimension fractal showing that the grouping of the minimum values of Qc increases before ocurring a main event and its grouping decreases after occurring the main event. [ABSTRACT FROM AUTHOR]

As a comment on Seismic Electric Signals (SES) and earthquakes: A review of an updated VAN method and competing hypotheses for SES generation and earthquake triggering, herein we present the analysis of time series gathered by three MT stations located in the Eastern Cordillera of Colombia, for evaluating the electric and magnetic fields during an interval of several days. Records allow estimating multi-temporal apparent resistivity profiles in each station. Then, we correlate possible resistivity anomalies with seismicity, assuming that large earthquakes generated those anomalies. As an example, we identified a change in the apparent resistivity 7-h previous to the Mesetas earthquake (Mw6.0, December 24th, 2019). We would like to highlight that the resistivity anomaly was identified at the same depth as the earthquake hypocenter, and by more than one station. [ABSTRACT FROM AUTHOR]

At least 156 earthquakes (Mw 2.8–4.4) were detected in Puerto Gaitán, Colombia (Eastern Llanos Basin) between April 2013 and December 2014. Out of context, this figure is not surprising. However, from its inception in 1993, the Colombian National Seismological Network (CNSN) found no evidence of significant seismic events in this region. In this study, we used CNSN data to model the rupture front and orientation of the highest-energy events. For these earthquakes, we relied on a joint inversion method to estimate focal mechanisms and, in turn, determine the area's fault trends and stress tensor. While the stress tensor defines maximum stress with normal tendency, focal mechanisms generally represent normal faults with NW orientation, an orientation which lines up with the tracking rupture achieved via Back Projection Imaging for the study area. We ought to bear in mind that this anomalous earthquake activity has taken place within oil fields. In short, the present paper argues that, based on the spatiotemporal distribution of seismic events, hydrocarbon operations may induce the study area's seismicity. [ABSTRACT FROM AUTHOR]

The Mutatá earthquake is a M w 6 earthquake which occurred in northwestern Colombia on September 14, 2016. This region is located at the junction between three tectonic plates, namely the South American, Nazca and Caribbean plates, and the Chocó-Panamá and Northern Andes Blocks. This event took place in the Murindo seismic zone, a zone characterized by a high seismic activity involving the Uramita fault zone, which defines the contact between the two blocks. In this study, we relocate the mainshock – aftershocks sequence and analyze the source characteristics of the Mutatá earthquake. Using data from the Colombian Seismological National Network, and after re-picking the 411 events, we obtain absolute locations exhibiting a NW-SE oriented cloud, with the mainshock being located 8 km away from its original location and at a depth of 17.6 km. The event cloud is situated at the intersection of three faults with different orientations, the NNW-SSE Uramita Fault, a NW-SE fault, and a NNE-SSW inferred fault. Using data coming from 8 broad-band seismographs within 300 km of the mainshock, we perform moment tensor and kinematic slip distribution inversions. The moment tensor inversion points to an event centroid at 20 km depth, with a predominantly double-couple mechanism. The fault orientations in the area, NW-SE orientation of the event cloud, and hypocenter – centroid technique, indicate that the NW-SE nodal plane likely corresponds to the fault plane giving a right-lateral strike-slip mechanism on a SW dipping plane. The rupture model estimated on this plane shows different slip patches, one being close to the mainshock centroid, and few other patches distributed around the mainshock except to the southeast where most of the aftershocks are located. The maximum slip for this model is approximately 0.16 m. The source characteristics of the 2016 Mutatá earthquake suggest then that secondary faults within the Murindo seismic zone can generate large earthquakes, potentially consisting in an important source of seismic hazard in this region. • Mainshock – aftershocks sequence forms a NW-SE elongated cluster. • Double-couple moment tensor showing a mostly right-lateral mechanism. • Slip distribution in all directions around the centroid location except to the southeast. • Highlight the necessity of regional studies to obtain reliable source characteristics. • Secondary faults in Murindo seismic cluster seem able to generate high magnitude events. [ABSTRACT FROM AUTHOR]