[ES] La Sima del Vapor, localizada en Alhama de Murcia, presenta unas características ambientales que la hacen única en su género. A su elevada temperatura, 40ºC y su escasez en oxígeno, 17%, hay que sumarle una elevada cantidad de CO2, 10.900 ppm, en sus escasos 85 metros de desarrollo vertical. En este trabajo, hemos llevado a cabo un muestreo del aire en el interior de la sima para estudiar la traza isotópica del CO2 y del CH4 y poder determinar su origen. Por otro lado, al estar desarrollada a favor de la Falla de Alhama de Murcia, hemos introducido una serie de registradores en continuo de temperatura y CO2, para analizar su variabilidad en el tiempo y su potencial relación con la sismicidad asociada a dicha falla, y registrada entre septiembre del año 2015 y enero del 2016. En concreto, la cueva se desarrolla en el segmento de Alhama - Alcantarilla, con 21 km de longitud media y apareciendo como una falla en desagarre con componente inverso. Los perfiles de temperatura en profundidad indican un gradiente geotérmico subsuperficial de 3,2ºC/100m., [EN] The Vapor cave, located within the Murcia province (SE of Spain), exhibits a peculiar environmental
parameters, high temperature (40ºC), scarce oxygen (17%) and high values of CO2 (>10,000 ppm).The depth reaches
80 m and it is constrained by the Alhama de Murcia Fault, one of the most seismically active faults in the Iberian
Peninsula.In this work, we have carried out a gas content analysis for the atmosphere inside the cave, mainly CO2 and
CH4, and their isotopic analysis. Moreover, a set of loggers were placed at different depths with the aim to get a
temporal series of temperature and carbon dioxide. The correlation between these parameters and the earthquakes
recorded in the vicinity brings us an opportunity for understanding the dynamics of this fault. The trace of this fault,
approximately 21 km, with geometry of oblique sinistral fault, suggests a potential earthquake of M6. The estimated
vertical geothermal gradient is 3.2ºC/100m., Este trabajo ha sido financiado
parcialmente por los proyectos SISMOSIMA,
CGL2013-47412-C2-2-P, INTERGEO CGL2013-
47412-C2-1-P y el proyecto CGL2013-43324-R en los
análisis isotópicos del C., Peer Reviewed

[EN] We present the results of the mechanical parameters of natural clay rich
fault-rock (fault gouge) from one of the most active faults in the Iberian Peninsula, Alhama de Murcia Fault (FAM). FAM shows segments partially formed by exhumed fine grained fault gouge (FG) with a 50-80 m thickness
developed mainly in a brittle regime. It is composed mainly by mica (muscovite and paragonite) and quartz, the clay minerals are mainly illite with some
caolinite. The FG shows a notable tectonic fabric characterized by the preferred orientation of plate-like minerals arranged in an anastomosing texture
which controls the mechanical behavior of the fault. Undisturbed samples,
taken from two fault observatory boreholes, have been used for laboratory
tests. The result of the study shows that there is important variability in
strength properties depending on the stress orientation in relation to fabric.
The friction angle (φ) varies between very low values (16ᵒ-26ᵒ) for planes
oriented favorably to the tectonic fabric to very high values (>50ᵒ) for planes
unfavorably oriented. This high value of friction angle was also obtained in
reconstructed and not oriented FG samples., [ES] En este trabajo se presenta el estudio de los parámetros mecánicos de la
roca de falla (fault gouge) de la falla de Alhama de Murcia (FAM) próxima al
bloque levantado. Esta falla es una de las más activas de la Península Ibérica y
destaca por tener segmentos con un espesor de roca de falla (FG) exhumada
de 50-80 m de espesor en régimen frágil. Su composición mineralógica se compone mayoritariamente por minerales del grupo de la mica (moscovita y
paragonita) y cuarzo; en la fracción arcillosa predomina la illita acompañada
por caolinita. Muestra una marcada fábrica tectónica caracterizada por la orientación preferente de los minerales laminares según una textura anastomosada
que controla la resistencia mecánica de la falla. Para este estudio se han tomado
muestras inalteradas procedentes de dos sondeos sobre los que se han realizado distintos ensayos de esfuerzo-deformación considerando diferentes
orientaciones de los esfuerzos respecto a la fábrica. El ángulo de fricción (φ)
varía desde valores mínimos (16ᵒ-26ᵒ) para los planos de rotura orientados
favorablemente a la fábrica tectónica hasta valores máximos (>50ᵒ) para los
planos orientados desfavorablemente. Estos elevados valores fueron obtenidos
también en muestras remoldeadas de FG sin orientaciones preferentes., Este trabajo ha sido financiado por el
proyecto INTERGEO (CGL2013-47412-C2-
1-P)., Peer reviewed

[EN] We present here a geometrical analysis of a structure related to the
reactivation of the NE end of the Alhama de Murcia Fault (Eastern Betic
Shear Zone, SE Spain) due to the NW-SE convergence initiated iin the Upper
Miocene. Conventional techniques of structural analysis have been used to
estimate a net slip rate of 0.13 – 0.18 mm/yr in the Alhama de Murcia –
Alcantarilla segment. The maximum expected magnitude of earthquakes
from the fault segment dimensions is between MW 6.5 - 6.6, following
empirical regressions, with a recurrence interval between 7,300 - 14,100
years for the slip rate obtained. The low geomorphologic expression observed
in this sector of the Alhama de Murcia Fault compared to other segments
shows a lower activity rate as well as the results obtained suggest the
influence of the Carrascoy Fault on the regional shortening rate distribution, [ES] En este trabajo se presentan los resultados del análisis geométrico de una
estructura asociada a la reactivación del extremo NE de la Falla de Alhama de
Murcia (Zona de Cizalla de las Béticas Orientales) por la convergencia NO-SE
iniciada en el Mioceno Superior. A partir de técnicas de análisis estructural convencionales se ha estimado una tasa de deslizamiento neto de entre 0,13 y
0,18 mm/año en el segmento Alhama de Murcia – Alcantarilla. La magnitud
máxima de un terremoto cuya fuente fuese este segmento se encuentra entre
MW 6,5 - 6,6, estimada mediante correlaciones empíricas, con un periodo de
recurrencia comprendido entre 7300 y 14100 años para la tasa de deslizamiento obtenida. La menor expresión geomorfológica observada en este sector
de la Falla de Alhama de Murcia en comparación con otros segmentos de la
misma evidencia un menor grado de actividad, al mismo tiempo que los resultados obtenidos sugieren la contribución de la Falla de Carrascoy en la
repartición de la tasa de acortamiento regional entre ambas estructuras., Trabajo financiado por el proyecto
CGL2013-47412-C2-1-P (Ministerio de
Economía y Competitividad)., Peer reviewed

IX Congreso Geológico de España, 12-14 septiembre 2016, Huelva, [ES] El terremoto principal de la serie sísmica tuvo lugar el 25 de enero de 2016, con una magitud Mw 6.3, que
fue precedido por un premonitorio de magnitud Mw 5.1 el día 21 de enero. Hemos utilizado 41 mecanismos focales
para analizar las características sismotectónicas y estructurales de la serie. Para agrupar los mecanismo focales hemos
utilizado un algoritmo de agrupamiento jerárquico espacial y por el tipo de rotura del mecanismo. De cada agrupación
hemos obtenido el mecanismo focal medio y lo hemos asociado a una estructura o familia de estructuras. Hemos
comprobado la compatibilidad mecánica de estas estructuras mediante transferencia de esfuerzos de Coulomb. El
evento principal de la serie se produjo en la Falla de Al Idrisi intersectando la cresta de Alborán. Este evento disparó
réplicas y series independientes en fallas de desgarre asociadas al sistema de Falla de Al Idrisi hacia el sur, pero también
en fallas inversas asociadas al levantamiento de la Cresta de Alborán hacia el este; produciendose una partición de la
deformación entre ambos tipos de estructuras interaccionando por transferencia de esfuerzos., [EN] The mainshock of seismic series took place on January 25, 2016, with a Mw 6.3 magnitude, which was
preceded by a premonitory of magnitude Mw 5.1 on 21 January. We have used 41 focal mechanisms to analyze the
seismotectonics and the structural characteristics of the series. To cluster the focal mechanisms we used a hierarchical
clustering algorithm using the spatial distribution of the events and also the type of rupture mechanism. For each
cluster we have obtained the average focal mechanism and have been associated with a structure or family of
structures. We have tested the mechanical compatibility of these structures by Coulomb stress transfer modelling. The
mainshock of the series occurred in the Al Idrisi Fault intersecting the Alboran Ridge. This event triggered aftershocks
and independent series in strike-slip faults associated with the Al Idrisi Fault System towards the south, but also in
reverse faults associated with the lifting of the Alboran Ridge eastward; producing a strain partitioning between both
types of structures interacting by stress transfer., Esta investigación es parte de los proyectos CGL2013-
47412-C2-1-P y CGL2015-67130-C2-2-R., Peer reviewed

[EN] [Aims and Methods] The structural evolution of the western boundary of the Chortis Block, particularly in the Central America Volcanic Arc crossing El Salvador is poorly known. We have done a kinematic analysis from seismic and fault slip data and combined our results with a review of previous regional studies. This approach allowed us to constrain the tectonic evolution and the processes that control the deformation in northern Central America., [Results] Along the active volcanic arc we identified active transtensional deformation. On the other hand, we have identified two deformation phases in the back arc region: A first one of transpressional wrenching close to simple shearing (Miocene); and a second one characterized by almost E–W extension coincident with the extensional direction of the Honduras grabens opening. Our results reveal a change from transpressional to transtensional shearing coeval with a migration of the volcanism towards the trench in Late Miocene times., [Implications] The strain change could be related to a transition from coupled to decoupled interface on the Cocos—Caribbean subduction, which could be caused by a slab roll-back of the Cocos Plate beneath the Chortis Block. The combination of different degrees of coupling on the subduction interface, together with a constant relative eastward drift of the Caribbean Plate, control the deformation style along the western boundary of the Chortis Block., [ES] [Objetivos y metodología] La evolución estructural del límite oeste del Bloque de Chortís, particularmente en la región del arco volcánico centroamericano cruzando El Salvador, ha sido muy poco estudiada. En este artículo presentamos los resultados de un análisis cinemático junto con una revisión de estudios regionales previos., [Resultados] Esta aproximación nos ha permitido arrojar luz sobre la evolución tectónica y los procesos que controlan la deformación en el norte de Centroamérica. A lo largo del arco volcánico activo hemos identificado deformación transtensiva. Por otro lado, hemos identificado dos fases de deformación en la zona de retro-arco: una primera fase de cizalla transpresiva cercana a la cizalla simple (Mioceno); y una segunda fase caracterizada por una extensión cercana a la dirección E–W que coincide con la dirección de apertura de los grábenes de Honduras. Los resultados de nuestros análisis revelan un cambio de cizalla transpresiva a cizalla transtensiva coetáneo con la migración del arco volcánico hacia la fosa durante el Mioceno Superior., [Implicaciones] El cambio en el estilo de la deformación podría estar relacionado con un decrecimiento en el grado de acoplamiento de la inter-fase Cocos—Caribe, que podría deberse a un proceso de roll-back de la placa del Coco bajo el Bloque de Chortís. La combinación de diferentes grados de acoplamiento en la inter-fase de la subducción, junto con una deriva constante de la placa de Caribe, controlan el estilo de la deformación a lo largo del límite oeste del bloque de Chortís., This research was supported by the project “INTERGEO” (CGL2013-47412-C2-1-P), “Study of the seismic potential of inter-segment regions in strike-slip active faults using Geological, Geophysical and Geodetic analysis: Applied to the Alhama de Murcia Fault and the El Salvador Fault Zone”., Peer reviewed

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., The authors would like to thank the following: The project INTERGEO (CGL2013-47412-C2-1-P) GEO3BCN-CSIC for providing access to the data. SeisDARE provides public access to the seismic data [86]. The KEMDIKBUDRISTEK of the Republic of Indonesia for providing a Ph.D. scholarship to the first author. The GIPP-GFZ (Germany) and Lisbon University (Portugal) provided the instrumentation. Additionally, we sincerely thank Seismic Unix CWP (Center for Wave Phenomena, Colorado School of Mines) for allowing us to use the free academic license software, and we also thank everyone who was directly or indirectly involved in this work.
J.A. is funded by grant IJC2018-036074-I and by MCIN/AEI /10.13039/501100011033. I.P. is funded by the Spanish Government and the Universidad de Salamanca (Beatriz Galindo grant BEGAL 18/00090). This project was funded by Grant 2017SGR1022 (GREG) from the Generalitat de Catalunya (AGAUR); EU (H2020) 871121 (EPOS-SP); and EIT-RawMaterias 17024 from the European Institute of Technology (EIT) (SIT4ME)., Peer reviewed

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 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). W, Peer reviewed

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.