Remote sensing applied to litho-structural and regolith mapping of the SW of Angola (PLANAGEO Project)

ABSTRACT: IGEO (Geological Institute of Angola) has developed the sosubprograms was focused on the remote sensing survey of the country. The main objective of the study is the use of satellite Earth Observation data in order to support preliminary geological and regolith mapping. This allows us to obtain a first approximation to cartography 1:250.000. Litho-structural and regolith maps are elaborated over eight blocks, covering one-third of the country area and including different geological contexts.info:eu-repo/semantics/publishedVersio

Estimation of vertical slip rate in an active fault-propagation fold from the analysis of a progressive unconformity at the NE segment of the Carrascoy Fault (SE Iberia)

Many studies have dealt with the calculation of fault-propagation fold growth rates considering a variety of kinematics models, from limb rotation to hinge migration models. In most cases, the different geometrical and numeric growth models are based on horizontal pre-growth strata architecture and a constant known slip rate. Here, we present the estimation of the vertical slip rate of the NE Segment of the Carrascoy Fault (SE Iberian Peninsula) from the geometrical modeling of a progressive unconformity developed on alluvial fan sediments with a high depositional slope. The NE Segment of the Carrascoy Fault is a left-lateral strike slip fault with reverse component belonging to the Eastern Betic Shear Zone, a major structure that accommodates most of the convergence between Iberian and Nubian tectonics plates in Southern Spain. The proximity of this major fault to the city of Murcia encourages the importance of carrying out paleosismological studies in order to determinate the Quaternary slip rate of the fault, a key geological parameter for seismic hazard calculations. This segment is formed by a narrow fault zone that articulates abruptly the northern edge of the Carrascoy Range with the Guadalentin Depression through high slope, short alluvial fans Upper-Middle Pleistocene in age. An outcrop in a quarry at the foot of this front reveals a progressive unconformity developed on these alluvial fan deposits, showing the important reverse component of the fault. The architecture of this unconformity is marked by well-developed calcretes on the top some of the alluvial deposits. We have determined the age of several of these calcretes by the Uranium-series disequilibrium dating method. The results obtained are consistent with recent published studies on the SW segment of the Carrascoy Fault that together with offset canals observed at a few locations suggest a net slip rate close to 1 m/ka

Slip Rate Variation During the Last ∼210 ka on a Slow Fault in a Transpressive Regime: The Carrascoy Fault (Eastern Betic Shear Zone, SE Spain)

Fault slip rate variability over time is a crucial aspect for understanding how single faults interact among each other in fault systems. Several studies worldwide evidence the occurrence of high activity periods with clustering of events and synchronization among faults, followed by long periods of low activity (super-cycles). The increasing gathering of evidence of these phenomena is making fault hazard models quickly evolving and challenging seismic hazard assessment. However, in moderately active fault systems, a determination of fault slip rates can present large uncertainties, that have to be carefully considered when slip rate histories are determined. In this work, we estimate the variation of slip rate in the last ∼210 ky of the NE segment of the left-lateral reverse Carrascoy Fault, one of the main faults forming the Eastern Betic Shear Zone in SE Spain. We study two selected field sites where we have been able to measure offsets and date the sediments along with uncertainties. The first site shows a progressive discordance drawn by different calcretes developed on alluvial deposits. The vertical throw is calculated by modeling the growth of the discordance. The vertical slip rates are estimated dating the deformed calcretes by Uranium Series and by comparing them with a complete regional calcrete dates database compiled from the literature. On the second site, we analyze the geomorphology of different Upper Pleistocene alluvial fans, where three incised channels are offset by the fault, providing the net slip for the last ∼124 ky. We discuss the influence of different factors on the estimate of net slip rates using data from different sources. This analysis highlights the importance of determining an accurate fault geometry and how local data can provide misleading deformation rates. Our results suggest the existence of long periods of low activity disturbed by short high activity periods. Such a pattern of activity along time is defined for the first time in the Eastern Betic Shear Zone, with interesting implications in the seismogenic behavior of the rest of the slow faults within the region

Active fault databases and seismic hazard calculations: a compromise between science and practice. Review of case studies from Spain

Since the Quaternary Active Faults Database of Iberia (QAFI) was released in February 2012 a number of studies aimed at producing seismic hazard assessments have made use of it. We will present a summary of the shortcomings and advantages that were faced when QAFI was considered in different seismic hazard studies. These include the production of the new official seismic hazard map of Spain, performed in the view of the foreseen adoption of Eurocode-8 throughout 2017. The QAFI database was considered as a complementary source of information for designing the seismogenic source-zone models used in the calculations, and particularly for the estimation of maximum magnitude distribution in each zone, as well as for assigning the predominant rupture mechanism based on style of faulting. We will also review the different results obtained by other studies that considered QAFI faults as independent seismogenic-sources in opposition to source-zones, revealing, on one hand, the crucial importance of data-reliability and, on the other, the very much influence that ground motion attenuation models have on the actual impact of fault-sources on hazard results. Finally, we will present briefly the updated version of the database (QAFI v.3, 2015), which includes an original scheme for evaluating the reliability of fault seismic parameters specifically devised to facilitate decision-making to seismic hazard practitioners

Nuevos eventos deformacionales registrados en el Segmento SO de la Falla de Carrascoy (Murcia, España): implicaciones en el modelo de crecimiento

La Falla de Carrascoy es una falla de desgarre sinestral que forma parte del Corredor de Cizalla de las Béticas Orientales. Con dos segmentos solapados (SO y NE) controla el borde norte de la Sierra de Carrascoy y su articulación con la Depresión del Guadalentín. El segmento SO está formado por la zona de Falla de Algezares – Casas Nuevas, un sistema de pliegues y cabalgamientos que conforman relieves de tipo foreberg dispuestos en échelon, mostrando la migración progresiva de la deformación hacia el NO desde el frente montañoso controlado por la falla de desgarre sinestral (Falla de Carrascoy s.s.). Estudios previos sitúan el inicio de la formación de la Falla de Algezares – Casas Nuevas en el Pleistoceno medio. En el presente trabajo se han identificado nuevos eventos de deformación tectónica en el extremo NE de la falla que pliegan y cabalgan los sedimentos de abanicos aluviales del Pleistoceno superior. Estos eventos posteriores a los registrados en localizaciones más occidentales en los trabajos previos, se ajustan a un modelo de crecimiento en el que la longitud de la falla aumenta gradualmente con cada terremoto

New deformational events recorded in the SW Segment of the Carrascoy Fault (Murcia, Spain): Implications in the growth model

La Falla de Carrascoy es una falla de desgarre sinestral que forma parte del Corredor de Cizalla de las Béticas Orientales. Con dos segmentos solapados (SO y NE) controla el borde norte de la Sierra de Carrascoy y su articulación con la Depresión del Guadalentín. El segmento SO está formado por la zona de Falla de Algezares – Casas Nuevas, un sistema de pliegues y cabalgamientos que conforman relieves de tipo foreberg dispuestos en échelon, mostrando la migración progresiva de la deformación hacia el NO desde el frente montañoso controlado por la falla de desgarre sinestral (Falla de Carrascoy s.s.). Estudios previos sitúan el inicio de la formación de la Falla de Algezares – Casas Nuevas en el Pleistoceno medio. En el presente trabajo se han identificado nuevos eventos de deformación tectónica en el extremo NE de la falla que pliegan y cabalgan los sedimentos de abanicos aluviales del Pleistoceno superior. Estos eventos posteriores a los registrados en localizaciones más occidentales en los trabajos previos, se ajustan a un modelo de crecimiento en el que la longitud de la falla aumenta gradualmente con cada terremoto.The Carrascoy Fault is a left-lateral strike-slip fault belonging to the Eastern Betic Shear Zone. With two overlapping segments (SW and NE), this fault controls the northern edge of the Carrascoy Range and its linkage with of the Guadalentín Depression. The SW segment is formed by the Algezares – Casas Nuevas Fault zone, a fold-and-thrust system constituting foreberg-type, en-echelon-arranged reliefs that show the progressive northwestward migration of deformation from the front controlled by the left-lateral strike-slip (s.s. Carrascoy Fault). Prior studies locate the onset of the Algezares – Casas Nuevas Fault in the middle Pleistocene. In this paper we have identified new tectonic events at the NE fault tip, which fold and thrust the sediments of late Pleistocene alluvial fans. These events are younger than those recorded westernmost in previous studies, and they support a growth model in which the length fault gradually increases with each earthquake.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Active fault databases: building a bridge between earthquake geologists and seismic hazard practitioners, the case of the QAFI v.3 database

Active fault databases are a very powerful and useful tool in seismic hazard assessment, particularly when singular faults are considered seismogenic sources. Active fault databases are also a very relevant source of information for earth scientists, earthquake engineers and even teachers or journalists. Hence, active fault databases should be updated and thoroughly reviewed on a regular basis in order to keep a standard quality and uniformed criteria. Desirably, active fault databases should somehow indicate the quality of the geological data and, particularly, the reliability attributed to crucial fault-seismic parameters, such as maximum magnitude and recurrence interval. In this paper we explain how we tackled these issues during the process of updating and reviewing the Quaternary Active Fault Database of Iberia (QAFI) to its current version 3. We devote particular attention to describing the scheme devised for classifying the quality and representativeness of the geological evidence of Quaternary activity and the accuracy of the slip rate estimation in the database. Subsequently, we use this information as input for a straightforward rating of the level of reliability of maximum magnitude and recurrence interval fault seismic parameters. We conclude that QAFI v.3 is a much better database than version 2 either for proper use in seismic hazard applications or as an informative source for non-specialized users. However, we already envision new improvements for a future update

Unidades litológicas del Neógeno en el extremo oeste de la Cuenca del Guadalquivir y su correlación con el sondeo Huelva-1 (Huelva - España)

A detailed surveying and a new geological map of the sheet at 1:50.000 number 999/1016 (Huelva - Los Caños), located at the west end of the Guadalquivir Basin, has been carried out. This data allows us to propose a new organization of the lithological units present at the west side of the Odiel River. These units include all the sedimentary record in this sector of the Guadalquivir Basin, ranging from Tortonian to Pliocene, but with shallower and coarser facies that are only present in this part of the basin. This fact is due to the location of the area, probably less subsiding due to a longer distance from Betic-Rif orogen. The lithological units are described concisely and a correlation with the core of the Huelva-1 borehole and with the outcrops of Huelva – Palos de la Frontera area is also proposed. The units are organized in a stack of sequences with a progradational pattern, typical of a basin margin, and highlighting a gradual reduction of the accommodation space in the late Messinian and during the Pliocene.Se ha realizado un reconocimiento detallado y un nuevo mapa geológico de la hoja a 1: 50.000 número 999/1016 (Huelva - Los Caños), situada en el extremo oeste de la Cuenca del Guadalquivir. Estos datos nos han permitido proponer una nueva organización de las unidades litológicas presentes en el lado oeste del río Odiel. Estas unidades incluyen el registro sedimentario completo de este sector de la Cuenca del Guadalquivir, que va desde Tortoniense al Plioceno, pero mostrando unas facies más someras y gruesas que solo están presentes en esta parte de la cuenca. Este hecho se debe a la ubicación de la zona, probablemente menos subsidente debido a su mayor distancia con respecto al orógeno Bético-Rifeño. Las unidades litológicas se describen de forma concisa y se propone también su correlación con el testigo del sondeo Huelva-1 y los afloramientos de la zona de Huelva - Palos de la Frontera. Las unidades litológicas se organizan formando un apilamiento de secuencias con un patrón progradacional, típico de un borde de cuenca, y ponen de manifiesto una reducción gradual del espacio de acomodación a finales del Messiniense y durante el Plioceno.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Economía y Competitividad (MINECO)Plan de Edición de Cartografía Geológica y Geomorfológica del IGME 2013-2016pu

Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

Acknowledgement. The authors would like to acknowledge the project INTERGEO (CGL2013-47412-C2-1-P) GEO3BCNCSIC for the data access. Data are public access through SeisDARE (DeFelipe et al., 2021), dataset Martí et al.(2015). The Ministry of Education and Culture of the Republic of Indonesia is thanked for the main author's Ph.D. scholarship (D3.2/KD.02.01/2019). JA is funded by MICINN (IJC2018-026335-I). I.P. is funded by the Spanish Government and the Universidad de Salamanca (Beatriz Galindo grant BEGAL 18/00090). IDF is funded by a FEDER-Junta de Castilla y León Postdoctoral contract (SA0084P20). We thank the GIPP-GFZ, (Germany) and Lisbon University (Portugal) for the instrumentation provided. Generalitat de Catalunya (AGAUR) grant 2017SGR1022 (GREG); EU (H2020) 871121 (EPOSSP); and EIT-RawMaterias 17024 (SIT4ME). We sincerely thank Seismic Unix CWP (Center for the Wave Phenomena, Colorado School of Mines (Cohen and Stockwell, 2019)). We also thank all the people involved directly or indirectly in this work.The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world