Gestió d'una xarxa sísmica en temps real localitzada al Pirineu Oriental (La Cerdanya): relocalització hipocentral del període desembre 2019 - juny 2020 i anàlisis sismotectònic

Màster Oficial en Recursos Minerals i Riscos Geològics, Universitat de Barcelona - Universitat Autònoma de Barcelona, Facultat de Geologia. Curs: 2019-2020. Tutor: Mario Ruíz i Cotutora: María OrtuñoSeismicity in the Eastern Pyrenees has shown moderate and diffuse over time. Although, there is evidence of catastrophic historical earthquakes and some of the events in the last decade that have caused considerable damage. This work shows the feasibility to obtain seismic data of best quality in the temporary seismic network installed on Cerdanya Neogene basin. The network has recorded local events that are added to the permanent seismic networks of the ICGC, IGN and RéNaSS distributed region, for the period between December of 2019 and June 2020. Seismic data processing has been performed using the Seiscomp3 seismological software package. A cortical velocity model has been created to improve the accuracy of the location, adjusted to the geology of the Cerdanya basin and the region around it. The catalogue contains 641 seismic events and 251 quarry blasts. The results of the study show that the locations of earthquakes have higher resolution (with vertical errors as low 1 km) in the Cerdanya when including the temporary network as a result of a denser network in this area. Also, it shows that seismicity of Eastern Pyrenees is concentrated in the north and easternmore areas. The recorded data has allowed to discuss the seismotectonic of the Cerdanya, Selva and Fenollet areas, where 202, 158 and 54 earthquakes have been identified, respectively. The hypocentres are distributed in depth from to surface to a maximum of 16 km. In particular, two areas show lineaments that could be related to individual structures: At Meranges (Cerdanya), the events could be grouped in two to three fault planes (dipping NW and SE) perpendicular to Cerdanya fault. In Santa Coloma, (Selva), the network has recorded a seismic cluster (main event 4,2 magnitude) that seems to follow a SE dipping structure. As showed in this study, seismic data in larger periods of time using temporary network could be key for improving the seismotectonic knowledge in some target seismic regions, benefiting the seismic hazard evaluation

Using ultra-high resolution methodologies to imaging active submarine faults: The STRENGTH 2023 cruise in the Alboran sea

8th International Colloquium on Historical Earthquakes, Palaeo- Macroseismology and Seismotectonics, Past earthquakes and advances in seismology for informed risk decision-making, 17-20 September 2023, Lixouri, Kefalonia Island, Greece.-- 4 pages, 2 figuresGreat earthquakes and the possibility to generate destructive tsunamis are geohazards of key societal concern, as they may impact world economies, disturb submarine structures and affect coastal areas with the associated risk for local populations (Bilham, 2010). We still have in our mind catastrophic episodes, such as the giant events of the Sumatra earthquake and tsunami in 2004 in the Indian Ocean of magnitude (Mw) 8.7, and the Tohoku-Oki earthquake and tsunami in 2011 in the northwest of Japan, of magnitude (Mw) 9.0-9.1. Nevertheless, seismic events of moderate to large magnitude (Mw 6-7.3) in areas of low to moderate tectonic deformation, and with long recurrence intervals, such as the Alboran Sea in the Western Mediterranean, might also have a significant effect. Accordingly, during the last decades there has been an expansion of paleoseismology to marine areas, both on-fault and off-fault investigations (Pantosti et al., 2011; Perea et al., 2021a). [...]This research was supported by the grant STRENGTH (PID2019-104668RB-I00) funded by MCIN/AEI/10.13039/501100011033. This project acknowledges the „Severo Ochoa Centre of Excellence‟ accreditation (CEX2019-000928-S), the grant UNrIDDLE (2018-T1/AMB-11039) “Atracción de Talento Investigador” call 2018 funded by Comunidad de Madrid and the Ocean Facilities Exchange Group (OFEG) for allowing us to use the AUV “AsterX” from IFREMERPeer reviewe

Tectonic geomorphology along an active strike-slip fault: the Yusuf fault system (Alboran Sea; Westernmost Mediterranean)

International Conference on Seafloor Forms, Processes and Evolution, 4-6 July 2022, Valletta, MaltaThe NW-SE convergence (4-5 mm/yr) between the African and Eurasian plates controls the present-day crustal deformation in the Alboran Sea (westernmost Mediterranean). Although instrumental seismicity is characterized by low to moderate magnitude events, large earthquakes (I > IX and M > 6.0) have occurred in this region (i.e., 1522 Almeria, 1790 Oran, 1910 Adra, or 2016 Al-Idrissi earthquakes). The dextral strike-slip Yusuf Fault System (YFS) is one of the largest active faults in the Alboran Sea and its seismogenic and tsunamigenic hazard needs to be characterized. The fault system trends WNW-ESE and has a length of ~150 km. Using multi-scale bathymetric data and different morphological analysis tools (i.e., slope or relief image maps), we have characterize the changes in the morphology of the seafloor along the YFS related to its Plio-Quaternary activity. The tectonic evolution of the fault system has resulted in the formation of a large pull-apart basin, which is deeper than the surrounding areas, a topographic ridge, an elongated depression and morphologic lineaments following its trend. The dataset also images several submarine landslides scars, mainly on the steeper slopes surrounding the pull-apart basin. In addition, the analysis of ultra-high resolution bathymetry acquired with AUV has revealed the presence of a series of en-echelon scarps with heights ranging from few centimeters to less than 10 meter. Seismic profiles across these scarps show that they are related to different fault strands of the YFS that are offsetting the seafloor, possibly because of an earthquake occurred in historical timesPeer reviewe

Seismic activity at the eastern Pyrenean termination

13 pages, 6 figures, 2 tables, supplementary data https://doi.org/10.1016/j.tecto.2023.229977.-- Data availability: Data will be made available on requestAlthough the seismic activity at the eastern Pyrenees is nowadays moderate and sparse, with events usually not exceeding magnitudes 4.5, this area has been affected in the past by the most destructive event occurred in the Pyrenees, reaching an intensity of IX, whose seismogenic structure is not well understood and still under debate. In order to progress in the knowledge of these structures, we present here the results derived from a 14 months-long broad-band seismic deployment focused on the Cerdanya Basin, but encompassing the eastern termination of the Pyrenees. The dense station coverage has allowed us to obtain accurate hypocentral locations, as well as up to 23 focal mechanisms from local low-magnitude earthquakes. In addition to a relatively sparse seismicity, several clusters of seismic events located in well-defined, small areas and depth ranges have been identified. The results show a few low-magnitude seismic events located in the southern limit of the Cerdanya Basin that could be related to oblique secondary faults within the footwall of the Têt Fault, the major tectonic structure in the area. Our data shows also that the Capcir Fault has associated seismicity, with some of the events located out of the fault plane, perhaps on secondary fault branches. To the east, a cluster of low-magnitude events is detected in the epicentral area of two relatively large earthquakes occurred recently. Further west, the Maladeta Massif has a sustained seismic activity, although its origin does not seem to be related to the most relevant structure in the area, the North Maladeta Fault. Regarding focal mechanisms, most of them show normal fault solutions with nodal planes NW-SE oriented, which agree with the extensional regime perpendicular to the axis of the chain derived from the seismic and geodetic dataThis research has been supported by the Spanish Ministry of Science, Research and Innovation grant number RTI2018-095594-B-I00. A.C. benefited from a 6 months stage in the GEO3BCN to realize her master thesis. [...] This work has benefited from open-source initiatives such as Seiscomp (Helmholtz-Centre Potsdam - GFZ German Research Centre for Geosciences and gempa GmbH, 2008), GMT (Wessel et al., 2013) and QGis (www.qgis.org)With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)Peer reviewe

Caracterización del sistema de fallas Norte-Sur en el mar de Alborán mediante datos geofísicos de alta-resolución: el inicio de un sistema de fallas transtensional

IV Reunión Ibérica sobre Fallas Activas y Paleosismología, del 7 al 10 de septiembre de 2022 en Teruel.-- 4 pages, 2 figures[EN] A key element in assessing the hazards associated with moderate to high seismic activity is the growth and connections of fault segments. The Alboran Sea is a Neogene basin located in the westernmost Mediterranean Sea and accomodate most of the convergence between the Eurasian and Nubian plates (4 – 5 mm/year) through different fault systems. This study shows the surface and depth characterization of the North-South Fault System in the northern Alboran Sea to understand better the region’s kinematics using ultra-high-resolution geophysical data acquired in the area. The data analyses have revealed the presence of several fault scarps striking N-S, resulting in horst and graben systems and the presence of pockmarks in the area. The identified faults cut the post-Messinian seismostratigraphic units (last 5.3 Ma) up to the seafloor, which supports that the fault system is currently active. Moreover, results suggest that this fault system presents high segmentation and small accumulated displacements supporting that it is in its initial evolution stage of a transtensional system[ES] Un elemento clave a la hora de evaluar los riesgos asociados a una actividad sísmica de moderada a alta es el crecimiento y las conexiones de los segmentos de falla. El mar de Alborán es una cuenca Neógena, situada en el extremo occidental del Mediterráneo, y absorbe la mayor parte de la convergencia entre las placas Euroasiática y Nubia (4 - 5 mm/año) a través de diferentes sistemas de fallas. Este estudio muestra la caracterización en superficie y en profundidad del sistema de fallas Norte-Sur en el norte del Mar de Alborán para comprender mejor la cinemática de la región utilizando datos geofísicos de ultra alta resolución adquiridos en la zona. Los análisis de los datos han revelado la presencia de varias escarpas de fallas con dirección N-S, que dan lugar a sistemas de horst y graben y a la presencia de marcas de viruela en la zona. Las fallas identificadas cortan las unidades sismoestratigráficas post-mesinianas (últimos 5,3 Ma) hasta el fondo del mar, lo que apoya que el sistema de fallas está actualmente activo. Además, los resultados sugieren que este sistema de fallas presenta una alta segmentación y pequeños desplazamientos acumulados que apoyan que se encuentra en su etapa inicial de evolución de un sistema transtensionalThe authors acknowledge the support of the Spanish Ministry of Science and Innovation through National Projects IMPULS (2006), EVENT-SHELF (2009), EVENT-DEEP (2010), TOPOMED (2011), SHAKE (2015), and STRENGTH (2019). Ariadna Canari is supported by the Spanish Science and Innovation Ministry under "Formación de Personal Investigador" programme (grant PREC-C-2020-0031). Hector Perea was partially supported by "Atracción de Talento Investigador - Comunidad de Madrid" fellow Universidad Complutense de Madrid. Sara Martinez-Loriente (ICM-CSIC) is supported by the MICINN "Juan de la Cierva-2017" (IJCI-2017- 33838) and “Severo Ochoa 2020 Postdoctoral Extension” (PEFSO-03) fellowships. The ICM had the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation, of the Spanish “Ministerio de Ciencia, Innovación y Universidades” 2020-2023 (CEX2019-000928-S)Peer reviewe

Seafloor expression of the deep structure during initiation of transtensional fault systems, as seen in the North-South fault system of the Alboran Sea, SE Iberia

European Geosciences Union (EGU) General Assembly, 23-27 May 2022, Vienna, AustriaHow fault segments grow and connect in regions with moderate to high seismic activity is key to assess associated hazards. Earthquakes may affect populated areas and can trigger tsunamis that threaten coastal areas and affect marine infrastructures. Regions accommodating relatively slow tectonic deformation may still enclose active fault systems capable of generating moderate to large magnitude earthquakes, albeit at long recurrence intervals (103 to 104 years). Although the Alboran Sea is currently characterised by slow tectonic deformation and by earthquakes of low to moderate magnitude, large historical and instrumental events have also occurred (i.e., the Almeria 1522 IEMS98 VIII-IX or the Al-Idrissi 2016 Mw 6.4 earthquakes). This Neogene basin located in the westernmost Mediterranean Sea absorbs most of the convergence between the Eurasian and Nubian plates (3 - 5 mm/year) by means of four tectonic-scale fault systems: the Carboneras and Al-Idrissi left-lateral strike-slip faults, the Yusuf right-lateral strike-slip fault and the Alboran Ridge thrust. Our study characterises the North-South fault system on the northern Alboran Sea to better understand the kinematics of the region on a larger scale. This system is proposed as the northern termination of the Al-Idrissi fault, and it may be presently evolving due to the transtensional stress field that affects the area. The first step to characterise the fault system has been to elaborate a detailed geomorphological map of the area to describe the identified scarps, their distribution, and structural relations. To achieve this, we have used very high-resolution bathymetric data (1x1 m pixel resolution) acquired with an autonomous underwater vehicle. The bathymetry shows several fault scarps striking N-S, resulting in horst and graben systems. The second step has involved the interpretation of high-resolution multichannel airgun and sparker seismic profiles running across the N-S faults. The integration of this dataset allows us to relate the morphological scarps with different normal faults interpreted in the seismic profiles. These faults cut the post-Messinian seismostratigraphic units (last 5.3 Ma) up to the seafloor, which supports that the fault system is currently active. Finally, the high segmentation of the North-South fault system and its small accumulated fault displacements supports it is in its initial stage of evolutionPeer reviewe

Accurate seafloor morphology with quantitative relief-processing methods: the growing transtensional north-south fault system (Alboran Sea, Western Mediterranean)

International Conference on Seafloor Forms, Processes and Evolution, 4-6 July 2022, Valletta, MaltaActive fault systems accommodating relatively slow deformation still produce moderate to large magnitude earthquakes, such as those in the Alboran Sea, a Neogene basin that absorbs most of the convergence between the Eurasian and Nubian plates (4-5 mm/ year) in the westernmost Mediterranean Sea (i.e., the Almeria 1522 IEMS98 VIII-IX or the Al-Idrissi 2016 Mw 6.4 earthquakes). Accurate characterisations of how fault segments grow and connect are crucial to better understand tectonic regional processes in this and other regions with slow deformation. We characterise the North-South fault system, which currently evolves due to the transtensional stress field in the northern Alboran Sea, by means of new geomorphologic analyses grounded on quantitative relief-processing methods applied over ultra-high-resolution data acquired by AUV. We modify the Red Relief Image Maps (RRIM, Chiba et al., 2008) with our own new, specific visualisation approach, Red-Blue Relief. This method displays relief accurately and without lighting bias and presents multiscale capabilities that allows coupling with seismic data at adequate scale. As a result, we identify several seafloor morphologies as scarps, pockmarks, horst, and grabens better than previous efforts. Combining the seafloor morphology analyses with high-resolution seismic profiles across the study area, we related morphologic scarps to different normal faults. Concluding, the high segmentation of the N-S fault system and its small cumulative fault displacements suggest that this is an active system presently growingPeer reviewe

Reassessing seismicity and seismic hazard in offshore areas: The case of the Alboran Sea (western Mediterranean)

8th International Colloquium on Historical Earthquakes, Palaeo- Macroseismology and Seismotectonics, Past earthquakes and advances in seismology for informed risk decision-making, 17-20 September 2023, Lixouri, Kefalonia Island, Greece.-- 5 pages, 2 figuresThe potential occurrence of large earthquakes and their capacity to trigger devastating tsunamis poses a significant geohazard that raises crucial societal concerns. Such events possess the ability to disrupt submarine structures, impact coastal regions, and have far-reaching consequences on global economies, thereby posing a risk to local populations (Bilham, 2010). Recent history serves as a stark reminder of the catastrophic nature of these occurrences, exemplified by the colossal Sumatra earthquake and tsunami in 2004 within the Indian Ocean (Mw8.7) or the Tohoku-Oki earthquake and tsunami that struck the northwest region of Japan in 2011 (Mw9.0–9.1). Nonetheless, it is vital to recognize that earthquakes with moderate to large magnitudes (Mw>5.5) in regions characterized by low to moderate tectonic deformation, and featuring long intervals between events, can also exert a substantial impact. The Alboran Sea situated in the Western Mediterranean is one such area of concern. Consequently, in recent decades, there has been a notable expansion in the interest to identify the active faults and to enhance our understanding about their seismic activity and probable aftermaths. [...]This research was supported by the grant STRENGTH (PID2019-104668RB-I00) funded by MCIN/AEI/10.13039/501100011033. This project acknowledges the „Severo Ochoa Centre of Excellence‟ accreditation (CEX2019-000928-S) and the grant UNrIDDLE (2018-T1/AMB-11039) “Atracción de Talento Investigador” call 2018 funded by Comunidad de MadridPeer reviewe

The Plio-Quaternary activity of the Yusuf Fault System (Alboran Sea; Westernmost Mediterranean): From 3D deep structure to seafloor geomorphology

European Geosciences Union (EGU) General Assembly, 23-27 May 2022, Vienna, AustriaThe identification and seismic characterization of the active structures in the Alboran Sea (westernmost Mediterranean) are essential to evaluate better the exposure of the South Iberian Peninsula and Maghreb coasts to different natural hazards. The Alboran Sea accommodates part of the present-day crustal deformation related to the NW-SE convergence (4-5 mm/yr) between the African and Eurasian plates. The area is characterized by low to moderate magnitude instrumental seismicity. However, large earthquakes (I > IX and M > 6.0) have occurred in this region in historical and recent times (i.e., 1522 Almeria, 1790 Oran, 1910 Adra, 1994 and 2004 Al-Hoceima or 2016 Al-Idrissi earthquakes). The dextral strike-slip Yusuf Fault System (YFS) is one of the largest active faults in the Alboran Sea and its seismogenic and tsunamigenic hazard needs to be characterized. The fault system trends WNW-ESE and has a length of ~150 km. Using multi-scale bathymetric (ranging from m to cm) and seismic data and different morphological and seismic analysis tools (i.e., slope or relief image maps), we have imaged and characterized the fault system. The analysis of this dataset reveals that the YFS is a complex structure composed of an array of strike-slip faults. The 3D structural model shows that most of the identified faults reach up and offset the seafloor and the Upper Quaternary sedimentary units. The current morphology of the seafloor is a consequence of the Plio-Quaternary tectonic evolution that have resulted in the formation of a large pull-apart basin, which is deeper than the surrounding areas, a topographic ridge, an elongated depression and morphologic lineaments following its trend. The dataset also images several submarine landslides scars, mainly on the steeper slopes surrounding the pull-apart basin. In addition, the analysis of ultra-high resolution data acquired along the Yusuf lineament with AUV has revealed the presence of a series of en-echelon scarps with heights ranging from few centimeters to less than 10 meter. Seismic profiles across these scarps show that they are related to different fault strands of the YFS that are offsetting the seafloor, possibly because of an earthquake occurred in historical timesPeer reviewe

Enhancing Earthquake Detection and Geomorphological Analysis through AI Integration

ICM-CRM Meeting 2023: New Bridges between Marine Sciences and Mathematics, 2-10 November 2023The field of geophysics has undergone a profound transformation with the emergence of Artificial Intelligence (AI). Deep Learning algorithms (DL), in particular, have demonstrated exceptional capabilities in addressing long-standing challenges and expanding the boundaries of traditional geophysical and geomorphological data analysis. We present two compelling examples that highlight the potential of DL techniques in enhancing earthquake detection and the promising future of DL in geomorphological analysis. In the first example, we delve into the remarkable progress achieved in earthquake detection through the application of DL algorithms. Due to their inherent complexity and unpredictable nature, earthquakes pose substantial challenges for accurate detection and prompt response. However, DL-based approaches have exhibited remarkable efficacy in overcoming these challenges. We have analyzed recent available DL pickers, comparing the results against data picked by a human operator and against non-DL programs. We found that DL algorithms have exhibited proficiency in precisely identifying and distinguishing the arrival times of P and S phases, even in the presence of low signalto- noise ratios and intricate triggering mechanisms. Their ability to effectively filter out transient noise and their efficiency in recognizing S waves, tasks often challenging even for experienced human analysts, positions DL algorithms as powerful tools in earthquake monitoring. Furthermore, their minimal parameter tuning requirements ensure accessibility to geophysicists with varying degrees of expertise in neural networks. The second example explores the potential of AI in geomorphological analysis, specifically by leveraging DL techniques to overcome limitations in traditional methods. Digital topographic and bathymetric models are extensively used in geosciences to describe landscape features. However, these methods often suffer from subjective parameter selection and qualitative assessments, which hinder interpretation accuracy and uncertainty estimation. Integrating mathematical models and DL techniques can enhance interpretations and improve uncertainty estimation. DL algorithms can be trained to identify and quantify specific landscape features like fault scarps or landslides, enabling a comprehensive characterization of the terrain. The integration of DL and mathematical expertise offers a data-driven and objective approach for robust interpretations and uncertainty quantification, leading to a deeper understanding of the landscape and improved resource management. Ongoing research in this area shows promising potential for advancing geomorphological analysis through AIPeer reviewe