A. Calahorrano - Academia.edu (original) (raw)

Papers by A. Calahorrano

ABSTRACT Five major geological domains form the Gibraltar Arc System (GAS). The GAS is fronted in... more ABSTRACT Five major geological domains form the Gibraltar Arc System (GAS). The GAS is fronted in the Gulf of Cadiz by a large imbricated wedge of tectonically piled rock slices. A extended terrain forms the backstop of the wedge. The structural Gibraltar arc is formed by thrust and fold belt that overlays the edge of the extended terrain. To the east there are several extensional basins, in the Mediterranean portion of the system. The West Alboran Basin has subsided by almost 10 km but the sediment infill appears largely unrelated to normal faulting. The East Alboran Basin seafloor contains ridges and promontories that, where dredged and drilled, contain abundant volcanic rocks. Further east the South Balearic – North Algerian Basin is believed to be characterized by backarc oceanic basin. However, the different tectonic elements of the GAS have regionally poorly characterized basement, and their age, evolution and geodynamic origin are highly debated. Part of this uncertainty arises from the scarcity of deep-penetration modern geophysical data in most of the system. The goal of this contribution is to present a summary of results recently produced from models and images from the data collected in 4 recent marine experiments. We present P-wave velocity models across key areas of the system and new reflection images of the tectonic and sediment structures of the crust. Further we present magnetotellutic 3D models of the lithospheric structure. These results are use to interpret the Miocene formation of the GAS and Plio-Pleistocene continent collision that might explain the crustal-lithospheric structure. We conclude that a geodynamic process that is no longer active formed the geological domains of the GAS, and that a new deformation regime -active since about the Pliocene times-is controlling the currently active deformation.

International Journal of Greenhouse Gas Control, 2013

Geophysical Research Letters, 2008

This work illustrates the great potential of multichannel seismic reflection data to extract info... more This work illustrates the great potential of multichannel seismic reflection data to extract information from the finestructure of meddies with exceptional lateral resolution (10-15 m). We present seismic images of three meddies acquired in the Gulf of Cadiz (SW Iberian Peninsula), which consist of concentric reflectors forming oval shapes that sharply contrast with the background oceanic structure. The seismic images reveal the presence of different regions within the meddies that are consistent with those observed in historical temperature (T) and salinity (S) data. The core region, characterized by smooth T and S variations, is weakly reflective. The double-diffusive upper and lower boundaries and the lateral-interleaving outer edges, characterized by stronger T and S contrasts, display strong reflectivity bands. These new observations clearly show differences between layers developed at the upper and lower boundaries that can contribute to the knowledge of mixing processes and layering formation in oceans. Citation: Biescas,

Y., Sallares, V., y …, 2009

A compilation of swath bathymetric data available along the Ecuador South-Colombia subduction zon... more A compilation of swath bathymetric data available along the Ecuador South-Colombia subduction zone allows describing the detail morphologic characters of the trench and margin seafloor, and evaluating the effects and the age of the Carnegie ridge subduction, as well as the modes of mass transfer. The outer trench wall shows a welldeveloped bend-fault pattern that cuts across the Carnegie Ridge, and progressively rotates clockwise from south to north, thus accompanying the trench curvature from N to NE-trending. The first order segmentation of the Nazca plate due to the Carnegie Ridge and Grijalva Fracture Zone reflects on the inner trench wall geomorphology, thus delimiting southern, central and northern margin segments. The overall morphologic character of the central margin segment, which is characterized by a generally steep slope, intensive mass wasting and a small frontal prism is compatible with an erosive margin, thus supporting negative mass transfer. Tectonic accretion is however active in the southern and northern margin segments in the form of the Guayaquil and Colombia accretionary wedges thus indicating positive mass transfer that contributes to continental growth. Sediment transfer from the Andes to the trench is accommodated through the Guayaquil canyon across the southern margin segment, and the Esmeraldas and Patia-Mira canyon systems across the northern margin segment, providing 0.8 km and 2.0-4.8 km trench fill, respectively. In contrast, very few terrestrial sediment has deposited in the shallow trench of the central margin segment. According to the plate kinematics pattern, we interpret the areas of extensively eroded margin slope between Cabo Pasado and the Galera seamounts and between Puerto Lopez and the Guayaquil canyon to result from the southward migration of the Carnegie Ridge flanks along the trench. Accordingly, the Carnegie Ridge has been subducting for ~4-5 Myr. Our geomorphologic analysis indicates that the mouths of the major canyons and the trench segments adjacent to highly unstable slopes are major areas of potential hazards that should be avoided for the emplacement of submarine infrastructures.

$Research paper thumbnail of Multifractal dimension and b value analysis of the 1998–1999 Quito swarm related to Guagua Pichincha volcano activity, Ecuador$

Journal of Geophysical Research, 2004

Temporal variations of spatial multifractal dimensions of Quito swarm seismicity (Ecuador) are re... more Temporal variations of spatial multifractal dimensions of Quito swarm seismicity (Ecuador) are related to the August 1998 to December 1999 Guagua Pichincha volcanic activity. Multifractal dimensions decrease a few days before the five main seismic energy peaks and increase again before or just after these peaks. This behavior reveals a selforganization of earthquakes that precedes main seismic energy peaks. The Quito swarm is also characterized by a bimodal Gutenberg-Richter law with two b values: b 1 = 0.95 ± 0.15 and b 2 = 1.48 ± 0.15. This bimodality may reveal the superposition of two different processes: one related to a classical elastic rupture and the other related to hydraulic fracture (leading to high b values) resulting from magma and overpressurized groundwater movements. Groundwater expulsion may be driven by heat released from deeper upgoing magma and manifested on the surface by the occurrence of phreatic explosions (beginning 7 August 1998) and by the formation of eight dacitic lava domes (beginning

ABSTRACT A detailed image of the internal structure and the distribution of the physical properti... more ABSTRACT A detailed image of the internal structure and the distribution of the physical properties of the future Spanish technological laboratory for the geological storage of CO2 has been obtained using seismic data. This acquisition experiment located in Hontomin (Burgos, Spain) consists of a multi-seismic characterization of the site including a 35 km2 3D seismic survey and a couple of 3 component orthogonal profiles. Here we focused on the seismic images and the tomographic velocity models resulting from the EW profile. This line consists of 230 new generation 3-component receivers with 25 m interval. A mixed seismic source were used including a 4 15-Tn M22 vibroseis trucks with a 16-sec sweep and 450 gr of explosives for difficult access areas. The distance between consecutive shots was also 25 m. Seismic data processing included static corrections, spherical divergence correction, airwave muting, deconvolution, bandpass time-variant filtering, stack and time migration. The seismic data show two main characteristics related 1) with the presence of a shadow zone, typically related to low velocity layers, where first P-wave arrivals disappear at ~800-1000 m from the shot point, and 2) the presence of a continuous high amplitude reflection at ~400 twts below the shadow zone. This reflection is related to the high impedance contrast between the Purbeck formation and the Middle Jurassic carbonated marine deposits of the Dogger formation that corresponds to the top of the reservoir seal. In order to improve the seismic image a preliminary 3D velocity model has been obtained using the data set recorded in the 3 component EW profile using the shot points of the 3D seismic survey. The final seismic image outlines this Purbeck-Dogger contact and the dome-shape of the reservoir. Toward the West, a ~100-twts thick package with high-amplitude reflections are interpreted as the Lower Jurassic carbonate sequence of the Lias formation, where is planned to inject the CO2.

We applied 2D preserved amplitude prestack depth migration to obtain a quantitative velocity mode... more We applied 2D preserved amplitude prestack depth migration to obtain a quantitative velocity model along the Multi Channel Seismic (MCS) reflexion profile SIS-72, collected across the Ecuadorian subduction zone during the SISTEUR marine cruise (2000). The method was divided in three main steps : (1) forward modelling, which was solved by the Born approximation and an asymptotic ray tracing algorithm.

A detailed 3D seismic characterization of a future scientific plant for carbon dioxide capture an... more A detailed 3D seismic characterization of a future scientific plant for carbon dioxide capture and storage (CSS) was carried out this summer in Hontomin (Burgos, Spain). This is part of a multidisciplinary experiment funded by the Spanish Government and the European Union, by means of the state-own foundation CIUDEN, that aims to demonstrate that CCS is technologically feasible and the most suitable strategy of reducing global warming caused by greenhouse gases emissions. The pilot test site is located in a dome shape structure. The reservoir is a saline aquifer (1500 m depth), confined within Lower Jurassic limestones and sealed by Lower Cretaceous detritic formations. The seismic survey consisted on: 1) a 30 km2 3D seismic survey; 2) 2 three-component 2D seismic cross profiles and 3) a CGGVeritas' seismovie device, composed by two 60m depth sources and a linear array of 80 receivers, 10 meters depth, separated 25 meters between each other. The preliminary seismic results show an accurate 3D image of the internal structure and the distribution of the physical properties of the study area. Through this information, the preferential displacemet of the CO2 plume has been inferred, which is mandatory to determine the location of the injection and monitoring well and to evaluate the possible escape pathways.

$Research paper thumbnail of The Structure of the Continent‐Ocean Transition in the Gulf of Lions From Joint Refraction and Reflection Travel‐Time Tomography$

Journal of Geophysical Research: Solid Earth

PVG) es resultado de la interacción entre el punto caliente de Galápagos y la dorsal de Cocos-Naz... more PVG) es resultado de la interacción entre el punto caliente de Galápagos y la dorsal de Cocos-Nazca durante los últimos ~20 m.a. Esta interacción ininterrumpida ha producido un exceso de magmatismo de variable intensidad que ha originado las cordilleras submarinas de Carnegie, Cocos y Malpelo, y su producto actual, la plataforma insular de Galápagos. En este trabajo mostramos que la combinación de observaciones geofísicas, en este caso sísmicas, gravimétricas y batimétricas, permite no sólo determinar la estructura interna y propiedades físicas de la corteza, sino también restringir notablemente la naturaleza y funcionamiento del punto caliente. La estructura cortical obtenida con datos sísmicos muestra una gran uniformidad confirmando que toda la provincia es producto de un único proceso. Las variaciones laterales de densidad cortical asociadas a la presencia de las cordilleras explican las anomalías batimétricas y gravimétricas observadas, lo cual implica que el manto bajo las cor...

We use two high quality MCS lines (SIS-72 and SIS-18) acquired during the SISTEUR survey to 1) im... more We use two high quality MCS lines (SIS-72 and SIS-18) acquired during the SISTEUR survey to 1) image the subduction channel (SC) across the southern Ecuadorian convergent margin off the Gulf of Guayaquil, and 2) estimate its physical properties and related mechanical behaviour. P-wave velocity analysis performed during pre-stack depth migration provided accurate velocity models over the first ~32 km of subduction down to a 8-km-depth. The SIS-72 model revealed that the velocity within the SC (2800 m/s +/- 150 m/s) is significantly lower than that of the overriding plate basement (~3800 m/s). The low velocity uncertainties allowed calculating porosity and fluid pressure in the SC. The ~constant low velocity in the SC associated with the landward increase in overburden pressure, reflects fluid overpressures as high as ~40 MPa at 25 km from the trench, down to a 7-km-depth. The overpressure parameter (lambda*), defined as the ratio of fluid overpressure over overburden pressure allowed...

In this work we present new results on the structure and activity of the imbricated wedge of the ... more In this work we present new results on the structure and activity of the imbricated wedge of the Gulf of Cadiz based on ∼ 3000 km of multichannel (MCS) profiles acquired off NW Moroccan margin. Seismic images indicates that the imbricated wedge is bounded between the Gulf of Cadiz margin at the north, the Kenitra margin at the south and the Rharb margin at the east. It is imaged as a sedimentary body with variable seismic amplitude, and structured by imbricated thrust sheets similar to an accretionary prism. Its maximum thickness is located at the east region of the gulf. It gradually thins toward the center and south of the gulf, where it is buried by ∼0.3 twts of sedimentary deposits, indicating that the imbricated wedge is actually not growing. It probably stops it s activity at ∼5-6 Ma. The imbricated wedge is overlaid by sedimentary sequences whose oldest unit is uppermost Tortonian. No evidences of gravitational (olistostrom) origin were founded. Active deformation related to ...

Article 76, paragraph 1, of the United Nations Convention for the Law of the Sea (UNCLOS) establi... more Article 76, paragraph 1, of the United Nations Convention for the Law of the Sea (UNCLOS) establishes the entitlement of a coastal State to determine the outer limits of its continental shelf, and defines two different criteria to delimitate these outer limits based on either distance or nature of the submerged landmass. By default, the Convention states that the outer edge of the continental margin corresponds to a line delineated at a distance of 200 nautical miles from the baselines from which the breadth of the territorial sea is measured (the “reference distance” from here on). But this provision can be overcome in the case that the coastal State is able to demonstrate that the submerged land territory beyond this distance is a “natural prolongation” of the emerged landmass. This entitlement is evaluated by the Commission in reference to a “test of appurtenance” that consists on the factual demonstration of the natural prolongation of its land territory to the outer edge of the...

The city of Quito (1.5 million pop.), Ecuador, located in the interandean valley, is lirnited on ... more The city of Quito (1.5 million pop.), Ecuador, located in the interandean valley, is lirnited on the west side by Guagua Pichincha Volcano and on the east side by a series of slopes aligned NNE, in accordance with the Andean trend. This latter morphological feature is the superficial expression of the Quito Active Fault System. Since June 1998, an anomalous increase of seismic activity was registered in the northern part of Quito, and two months later, an increase of volcanic and seismic activity at Guagua Pichincha Volcano (located 16 km SW of the swarm) was registered. Characterization and relationship between these two seismic activities are important to understand both processes and to advise people living in Quito and its surrounding areas

In this work we quantify the physical properties variations of underthrust sediments along the fi... more In this work we quantify the physical properties variations of underthrust sediments along the first tens of km of subduction of the non-accretionary sourthern Ecuadorian margin using high-quality multichannel seismic data. Two pre-stack depth-migrated profiles (SIS-72 and SIS-18) have revealed the presence of three zones along the subduction channel (SC) characterized by contrasting velocity and velocity-derived physical properties. These variations

Multichannel seismic lines acquired during the SISTEUR cruise (2000) provide new constraints on t... more Multichannel seismic lines acquired during the SISTEUR cruise (2000) provide new constraints on the structure and deformation of the subduction zone at the southern Ecuadorian margin, from the deformation front to the continental shelf of the Gulf of Guayaquil. The pre-stack depth migrated images allows to characterise the main structures of the downgoing and overriding plates and to map the

Tectonics, 2015

Interpretation of new multichannel seismic reflection profiles indicates that the Palomares margi... more Interpretation of new multichannel seismic reflection profiles indicates that the Palomares margin was formed by crustal-scale extension and coeval magmatic accretion during middle to late Miocene opening of the Algero-Balearic basin. The margin formed at the transition between thinned continental crust intruded by arc volcanism and back-arc oceanic crust. Deformation produced during the later positive inversion of the margin offshore and onshore is partitioned between~N50°E striking reverse faults and associated folds like the Sierra Cabrera and Abubacer anticlines and N10-20°E sinistral strike-slip faults like Palomares and Terreros faults. Parametric subbottom profiles and multibeam bathymetry offshore, structural analysis, available GPS geodetic displacement data, and earthquake focal mechanisms jointly indicate that tectonic inversion of the Palomares margin is currently active. The Palomares margin shows a structural pattern comparable to the north Maghrebian margins where Africa-Eurasia plate convergence is accommodated by NE-SW reverse faults, NNW-SSE sinistral faults, and WNW-ESE dextral ones. Contractive structures at this margin contribute to the general inversion of the Western Mediterranean since~7 Ma, coeval to inversion at the Algerian margin. Shortening at the Alboran ridge and Al-Idrisi faults occurred later, since 5 Ma, indicating a westward propagation of the compressional inversion of the Western Mediterranean.

Bulletin de l’Institut français d’études andines, 2003

Les variations temporelles des dimensions multi-fractales spatiales de l'essaim de séismes tecton... more Les variations temporelles des dimensions multi-fractales spatiales de l'essaim de séismes tectoniques de Quito (Équateur) sont corrélées à l'activité du volcan Guagua Pichincha. Les dimensions multi-fractales diminuent avant les 5 pics d'énergie. Ces valeurs réaugmentent avant ou juste après le pic d'énergie. L'essaim de Quito est également caractérisé par de fortes valeurs du facteur b (variant de 1,12 +/-0,05 à 1,43 +/-0,28). Une rupture dans la courbe de la loi de Gutenberg-Richter est observée qui implique la présence de deux valeurs du facteur b. Nous supposons qu'il puisse s'agir d'un comportement catastrophique, où une bifurcation se produit et conduit à deux scenari volcaniques différents : un épisode éruptif ou un épisode de calme du Guagua Pichincha. Ce comportement peut dépendre de petites variations de conditions internes, telles que des variations du champ de contraintes et/ou de pression de pores associées à des mouvements de fluides (gaz, eau souterraine et/ou magma). Mots clés : Dimensions multi-fractales, physique non linéaire du chaos, volcan Guagua Pichincha, essaim de Quito.