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[EN] The north-striking sinistral reverse Papatea Fault ruptured with a very large (up to 12 m) oblique slip as part of the 2016 MW 7.8 Kaikōura earthquake in the northeastern South Island. Paleoseismic studies were undertaken at three sites along the Papatea Fault, named Murray’s roadcut, Jacqui’s Gully (both on the main strand), and Wharekiri trench (western strand). These sites provide evidence for up to three Late Holocene paleoearthquakes prior to 2016 (=E0) on this previously unmapped active fault, with preferred OxCal-modelled timings of 98–149 (E1), 546–645 cal yr BP (E2), and >738 cal yr BP (E3). Event correlations between the sites are generally consistent across these past events, implying that the two strands of the Papatea Fault link at depth and rupture together co-seismically as in 2016. Comparisons of its paleoseismic record with the Kekerengu Fault and uplift data from Waipapa Bay and Kaikōura, suggest that the Papatea Fault may have three distinct rupture modes: (i) Kaikōura-type multi-fault ruptures with multi-metre, anelastic block displacements and associated major landscape change; (ii) multi-fault earthquake ruptures with other regional fault combinations; and (iii) single-fault Papatea ruptures with metre-scale displacement. OxCal models offer the possibility that the E1 fault rupture occurred in 1855 CE.

[EN] The recent update of the Colombian seismic hazard model by Dirección de Geoamenzas of the Colombian Geological Survey (CGS), has identified the necessity of considering fault geological data in future successive updates of the hazard map. At the same time, the faultbased seismic hazard studies developed in the Centro Nacional IGME-CSIC have also identified the need of increasing the available knowledge on recent activity and paleoseismology of Spanish active faults in preparation for a future update of the national seismic hazard. In this frame, both CGS and IGME-CSIC, have formally agreed to collaborate in active faults research as well as their modelling for seismic hazard calculations to improve seismic risk provisions. It has been program firstly a pilot study in the transfer zone between the Algeciras and Guaicaramo faults (Colombia) that could also serve to provide the methodological framework for studying other faults in the country.

[EN] Within the framework of the IGME-CSIC Department of Geological Hazards and Climate Change, the OBTIER research group was created in July 2021 and currently has 22 members, including scientific and technical staff, as well as young people with contracts linked to competitive national and international research projects. The main objective of the group is to provide society with scientific information, methods, tools and solutions to mitigate the impact of geohazards and the effects of Climate Change. OBTIER is currently leading 6 competitive projects (4 European and 2 national), as well as several projects in agreement with other national and international administrations. It is an active member of the EuroGeoSurveys Earth Observation Expert Group and the ASGMI Geological Hazards Group. OBTIER offers society a wide range of capabilities on: earthquakes, tsunamis, landslides, land subsidence, volcanic eruptions, droughts and floods. In 2021, the group published an article in Science entitled: Mapping the global threat of land subsidence with significant media coverage around the world.

La cuantificación de la peligrosidad sísmica guarda una dependencia estrecha con el registro disponible de terremotos pasados. Esto supone un condicionante sustancial en la evaluación del riesgo sísmico, ya que los eventos más devastadores son también los menos frecuentes. En España, los estudios de peligrosidad sísmica más recientes (IGN-UPM, 2013) se basan en el registro histórico e instrumental de terremotos, que recoge un período de aproximadamente 1,000 años. Dado que el régimen tectónico actual está marcado por una deformación lenta, este período de tiempo no es lo suficientemente extenso como para comprender el ciclo sísmico completo de los sistemas de fallas activos (Perea et al., 2006). En el caso concreto del sistema de fallas de la zona de cizalla de las Béticas Orientales, la falta de registro a lo largo del ciclo sísmico completo de las fallas puede inducir a una estimación desacertada de la peligrosidad sísmica. Para compensar este déficit de información, los catálogos sintéticos de terremotos se presentan como una herramienta complementaria a los estudios de peligrosidad, ya que permiten caracterizar los sistemas de fallas en el largo plazo. Partiendo del catálogo sintético de un millón de años generado por Herrero-Barbero et al. (2021) para el sistema de fallas de la zona de cizalla de las Béticas Orientales, se han creado en este estudio diversos subcatálogos, aleatoriamente distribuidos en el tiempo, con una duración equivalente al catálogo histórico e instrumental (ca, 1,000 años). Con ello, se muestra la variabilidad de escenarios que el sistema de fallas es capaz de generar. Cada catálogo es sometido a un estudio probabilista de peligrosidad sísmica o PSHA (Probabilistic Seismic Hazard Assessment), de manera que se comprueba la dependencia que guarda la peligrosidad sísmica con el intervalo temporal de análisis. La dispersión que se observa en parámetros como la magnitud máxima, la tasa anual de terremotos o la relación entre frecuencia de magni

The 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. [...]

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

[EN]: To produce seismic hazard assessments to the current state-of-the-art, it is essential to characterize the active faults in terms of geometry, interrelation and seismotectonic status. The Guadalentin Depression is the main basin within the Eastern Betic Shear Zone, which corresponds to a NE-SW tectonic corridor bounded by the Carrascoy, Alhama de Murcia and Palomares faults, from north to south. Although a number of active tectonics and paleoseismological studies have been carried out in these faults, almost nothing is known about their geometry at depth. To unveil the deep structure, geometry and upper Neogene deformation history of these faults we have carried out a high-resolution seismic reflection survey. The acquired seismic profiles will allow to improve our understanding of the deep geometry of the known active faults (up to 2 km depth), as well as to identify potential buried branches and will help to reduce the uncertainties in seismic hazard assessment., [ES]: Para producir evaluaciones del peligro sísmico actualizadas al estado del arte actual, es esencial caracterizar las fallas activas de una región en términos de geometría, interrelación y estado sismotectónico. La depresión del Guadalentín es la principal cuenca cuaternaria dentro de la Zona de Cizalla de las Béticas Orientales, la cual corresponde a un corredor tectónico con dirección NE-SW delimitado por las fallas de Carrascoy, Alhama de Murcia y Palomares, de norte a sur. Aunque varios estudios de tectónica activa y paleosismología se han centrado en estas fallas, su geometría en profundidad es bastante incierta. Para revelar la estructura profunda, la geometría y el historial de deformación desde el Neógeno superior de estas fallas, hemos llevado a cabo un estudio de sísmica de reflexión de alta resolución. Los perfiles sísmicos adquiridos permitirán mejorar nuestra comprensión de la geometría profunda de las fallas activas conocidas (hasta 2 km de profundidad), así como identificar posibles ramas ciegas, y ayudarán a reducir las incertidumbres en los cálculos de peligrosidad sísmica

[EN]: A seismic profile has been performed across the Algezares-Casas Nuevas fault zone, the SW section of the major Carrascoy Fault, a potential source of earthquakes in the region and hence an important threat to the nearby City of Murcia. The seismic data were processed to obtain a Vp model and provide insight into the depth structure of the fault zone. The Vp model was interpreted according to the local geology and surface data, enabling the location of the Messinian/Tortonian contact, and also the erosive contact of the Red Unit (Pliocene alluvial fan deposits) on the Messinian deposits. Both contacts are offset by two principal thrusts identified in the profile, by a similar amount ca. 135-140 m. Considering the age of the onset of the deformation, quoted in 209 ka in previous studies, a vertical slip rate around double that previously calculated can be estimated. We discuss the different causes for this disagreement and we conclude about the important impact that such a slip rate could have on seismic hazard studies.

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.

The critical zone (CZ) represents the most-shallow subsurface, where the bio-, hydro-, and geospheres interact with anthropogenic activity. To characterize the thickness and lateral variations of the CZ, here we focus on the Eastern Betic Shear Zone (EBSZ), one of the most tectonically active regions in the Iberian Peninsula. Within the EBSZ, the Guadalentín Depression is a highly populated area with intensive agricultural activity, where the characterization of the CZ would provide valuable assets for land use management and seismic hazard assessments. To achieve this, we have conducted an interdisciplinary geophysical study along the eastern border of the Guadalentín Depression to characterize the CZ and the architecture of the shallow subsurface. The datasets used include Electrical Resistivity Tomography (ERT), first-arrival travel time seismic tomography, and multichannel analysis of surface waves (MASW). The geophysical datasets combined help to constrain the high-resolution structure of the subsurface and image active fault systems along four transects. The resulting geophysical models have allowed us to interpret the first ~150 m of the subsurface and has revealed: (i) the variable thickness of the CZ; (ii) the CZ relationship between the fault zone and topographic slope; and (iii) the differences in CZ thickness associated with the geological units. Our results provide a method for studying the shallow subsurface of active faults, complementing previous geological models based on paleo-seismological trenches, and can be used to improve the CZ assessment of tectonically active regions.

La convergencia entre las placas Euroasiática y de Nubia en el Mediterráneo occidental (4,5 - 5,6 mm/a) es absorbida principalmente por el cinturón de deformación del Tell, en el norte de Argelia, y por el Corredor de Cizalla de las Béticas Orientales (CCBO), un conjunto de fallas activas de orientación general NE-SO con velocidades de desplazamiento bajas y ciclos de carga sísmica largos..., The convergence between the Nubian and Eurasian plates in the western Mediterranean (4,5 - 5,6 mm/a) is mainly absorbed by Tell deformation belt in Algeria northern and by the Eastern Betics Shear Zone (EBSZ), a set of NE-SW actives faults with low slip rates and long seismic loading cycles...

In Spring 2011 (11th of May), the vicinity of Lorca city (Murcia, SE Iberian Peninsula) was hit by two main seismic shocks that reach a maximum magnitude of 5.2 Mw. The earthquake caused serious widespread damage in the city and its surroundings. Similar events have affected the area regularly in the past (for example: on May 6,1977, 4.2 mg). These events are distributed along a relatively broad band (roughly NE-SW oriented) parallel to the coast, associated to the activation of the Alhama de Murcia Fault (AMF), an oblique-slip (reverse-strike-slip) fault system located in the Eastern Betics Shear Zone. The current study aims to characterize the shallow subsurface across some of the surface outcrop of a few of the main faults that lie within this seismogenic strike-slip fault system. Six normal-incidence seismic reflection profiles were acquired in the area crossing the AMF and the Carrascoy fault, among others). This study focuses on the determination of the shear-wave velocity depth model by applying Multichannel Analysis of Surface Waves (MASW), using the shot records of the seismic reflection profiles. The 1D velocity-depth functions acquired were pasted together to obtain the final 2D velocity models. The hand-picked dispersion curves were inverted using two different approaches to address the consistency of the inversion schemes. The final models reveal relevant differences across the different fault zones, reflecting the heterogeneity and lateral variability that characterizes a complex seismogenic zone, a most probably, diffuse plate boundary.

A multidisciplinary study unsing a number of different geophysical methodologies forcharacterizing the nature and structure of the shallow subsurface was carried out in an area of activedeformation located in (SE Iberian Peninsula). An approximately 400 km long network of prominentactive faults oriented NE-SW near parallel to the coast line constitute a singular tectonic feature thatcharacterize the southeastern part of the Iberian Peninsula. This transpressive tectonic corridor, knownas the Eastern Betics Shear Zone (EBSZ) is considered one of the longest and most active fault systemin the Iberia Peninsula. The EBSZ system is a strike slip plate boundary, which is accommodating theconvergence within Iberia of the interaction between the Nubian and Eurasian plates. The fault networkfeatures a reverse and left-lateral strike-slip kinematics with a characteristic sigmoidal trend delineatedby a number of major individual faults as well as other less relevant faults. Within and along thislocalized deformation corridor many destructive earthquakes with relative high intensities have affectedthis region since historical times The interdisciplinary geophysical datasets acquired place strongconstraints on the high-resolution structure of the well defi ned fracture system. The datasets reveal thethickness and properties of the critical zone (CZ) layer. The study includs: Electrical ResistivityTomography (ERT), fi rst arrival time seismic tomography, and multichannel analysis of surface waves(MASW). The combination of these three methods yields complementary benchmarks for mappingshallow subsurface fault zones and the physical properties of the CZ layer. The resulting model andinterpretation reveal new information on the relationship between the topographical slope and thethickness of the CZ layer related to the transport process and the accumulation of regolith alteration.The distribution of the CZ layer is characterized by layers with low P-wave & S-wave velocity anomalies(

La convergencia entre las placas Euroasiática y de Nubia en el Mediterráneo occidental (4,5 - 5,6 mm/a) es absorbida principalmente por el cinturón de deformación del Tell, en el norte de Argelia, y por el Corredor de Cizalla de las Béticas Orientales (CCBO), un conjunto de fallas activas de orientación general NE-SO con velocidades de desplazamiento bajas y ciclos de carga sísmica largos...

The deep structure of the Carrascoy Fault (CAF) is characterized by utilizing the analysis of surface waves identified in shallow high-resolution seismic reflection data. The Multichannel analysis of surface waves (MASW) is used to unravel the 2-D Vs wave velocity model and image the depth geometry of the fault system. The study area includes segments of the fault located in the deformation zone in southeastern Iberian Peninsula. Two approaches have been used to achieve a well-constrained velocity model in the CAF fault zone. Conventional seismic reflection processing workflow has been used to clean the seismic data and increase its S/N ratio. And Occam's approach has been used to invert the digitized surface wave dispersion curves. 1D shear wave velocity-depth profiles were estimated in shot and CDP/CMP domains. Relatively well-resolved 2D velocity-depth models were obtained by the composite of the 1D Velocity-depth functions. These composite results of the 2D-velocity models are able to constrain the depth geometry of the fault zone down to 200 m depth. The fault zone is indicated by a relatively broad low-velocity anomaly that correlates with the fault¿s surface expression in CMP number 1201-1281. The low velocities would then be related to fracturing and associated local weathering that would reduce the shear modulus value.