ISSN (print): 1698-6180. ISSN (online): 1886-7995 www.ucm.es/info/estratig/journal.htm Journal of Iberian Geology 38 (1) 2012: 253-270 http://dx.doi.org/10.5209/rev_JIGE.2012.v38.n1.39218 Active tectonics of the Alhama de Murcia fault, Betic Cordillera, Spain Tectónica activa de la Falla de Alhama de Murcia, Cordillera Bética, España J.J. Martínez-Díaz* 1,2, E. Masana 3, M. Ortuño 4 1 Dpto. de Geodinámica, Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain 2 Instituto de Geociencias IGEO (UCM-CSIC), 28040 Madrid, Spain, [email protected] 3 RISKNAT. Dpt. Geodinamica i Geofisica, Facultat de Geologia, Universitat de Barcelona. c/ Marti i Franques s/n. 08028 Barcelona, Spain, [email protected] 4 Centro de Geociencias, Universidad Nacional Autónoma de México, Blvd. Juriquilla, 3001, 76230 Juriquilla, Querétaro, Mexico. [email protected] *Corresponding author Received: 24/04/12 / Accepted: 10/05/12 Abstract We present an overview of the knowledge of the structure and the seismic behavior of the Alhama de Murcia Fault (AMF). We utilize a fault traces map created from a LIDAR DEM combined with the geodynamic setting, the analysis of the morphology, the distribution of seismicity, the geological information from E 1:50000 geological maps and the available paleoseismic data to des- cribe the recent activity of the AMF. We discuss the importance of uncertainties regarding the structure and kinematics of the AMF applied to the interpretation and spatial correlation of the paleoseismic data. In particular, we discuss the nature of the faults dipping to the SE (antithetic to the main faults of the AMF) in several segments that have been studied in the previous paleoseismic works. A special chapter is dedicated to the analysis of the tectonic source of the Lorca 2011 earthquake that took place in between two large segments of the fault. Keywords: Alhama de Murcia Fault, Betic Cordillera, active faults, slow-moving faults, strike-slip faults. Resumen En este estudio se presenta una revisión del conocimiento que hasta la actualidad se tiene de la estructura y comportamiento sis- mogenético de la Falla de Alhama de Murcia (AMF). Se utiliza un nuevo mapa de la traza de la AMF realizado a partir de un modelo 254 Martínez-Díaz et al. / Journal of Iberian Geology 38 (1) 2012: 253-270 digital del terreno de alta resolución a partir de datos LIDAR, combinado con el análisis del marco geodinámico, la geomorforlogía, la distribución espaciotemporal de la sismicidad, la información geológica de trabajos previos y los datos paleosísmicos existentes, para describir la actividad reciente de la AMF. Se discute la importancia de las incertidumbres que se mantienen en relación con la estructura y la cinemática de la AMF para la correcta interpretación y correlación espacio-temporal de los datos paleosísmicos obtenidos hasta ahora. En particular, se discute la naturaleza de las fallas con buzamiento SE en superficie (antitéticas con las fallas principales de la AMF que bordean las sierras) en varios segmentos que han sido estudiados en análisis paleosismológicos previos. Se dedica un capítulo especial al análisis de la fuente geológica del terremoto de Lorca de 2011 que tuvo lugar en la zona de inter- segmento que separa dos de los segmentos de mayor longitud de la AMF. Palabras clave: Falla de Alhama de Murcia, Cordillera Bética, fallas activas, fallas lentas, fallas de desgarre. 1. Introduction implications and seismogenic behavior of the AMF. We present a new AMF fault trace map from a high resolu- The Alhama de Murcia Fault (AMF) (Bousquet et al., tion DEM, and we utilize the geomorphology, the spatial 1979) is a strike-slip shear zone with reverse component distribution of seismicity, the geological mapping and that crosses the eastern Betic cordillera with a NE-SW the available paleoseismic data to describe the detailed direction (Fig. 1). The AMF accommodates ~ 0.1 – 0.6 geometry of the AMF segments. We interpret the deep mm/yr of the approximately 5 mm/yr of convergence be- structure of the fault that is coherent with the surface ge- tween Nubian and Eurasian plates (Masana et al., 2004) ology and we finally discuss the needs to improve our and is one of the largest faults of the Eastern Betics Shear knowledge of the seismogenic behavior of this fault. A Zone (Silva et al., 1993). Many of the largest damaging special chapter is dedicated to the analysis of the tectonic historical earthquakes occurred in the eastern Betic Cor- source of the Lorca 2011 earthquake that took place in dillera are related to this structure (Fig. 1). between two large segments of the fault. The most damaging earthquake occurred in Spain in the last 50 years took place next to the city of Lorca 2. Geodynamic setting (11/05 2011, Mw 5.2). In spite of its moderate size this earthquake produced massive damage in this city. This The study area is located in the Internal Zones of the earthquake has been related to the activity of the AMF Betic Cordillera (Fig. 1), commonly referred to as the Al- (i. e. IGME, 2011; Vissers and Meijninger, 2011; Lopez- boran Domain (Balanya and García Dueñas, 1987). This Comino et al., 2012; Martínez-Díaz et al., 2012). In re- area is composed of Paleozoic, Meso zoic and Paleogene cent years several studies have focused on the characteri- rocks, which developed as a thrust stack during the Alpine zation of the paleoseismic activity and the determination Orogen (Egeler and Simon, 1969). The Alboran domain of AMF seismic parameters: slip rate, recurrence inter- belongs to the formerly Alpine Orogene that was a con- val, maximum magnitude (Martínez-Díaz et al., 2001; tinuous structure from northwest Africa, along the Betic Masana et al., 2004, 2005, Masana, 2010; Ortuño et al., Cordillera, and to Western Alps during Cretaceous - Neo- 2012). All of these parameters were obtained by the study gene. The thrusts bounding the major tectonic complexes of trenches excavated in sites that were appropriated to (Nevado-filabride, Alpujarride and Malaguide) were later identify recent (preferably later Quaternary) surface rup- reactivated as low-angle normal faults under regional ex- tures. Until now, these studies have been restricted to two tensional tectonics (Aldaya et al., 1991; García-Dueñas of the four segments that form the AMF. The correct in- et al., 1992; Galindo-Zaldívar et al., 1989; Jabaloy et al., terpretation of these data and the correct extrapolation to 1993). Martínez-Martínez and Azañon (1997) inferred the whole fault requires a good knowledge of the deep two nearly orthogonal extension episodes from the Bur- and shallow structure of the fault zone. But this also re- digalian to the Serravalian. The neotectonic period (the quires improving our understanding of the relationships last 9 My) started after this extensional process, and a between the fault structure, the morphology, and the spa- compressional stress field with a NNW–SSE shorten- tial and temporal evolution of historical and instrumen- ing direction became dominant. Deformation under this tal seismicity. We still have significant limitations in the stress field formed high-angle (strike-slip, normal and knowledge of the structure of the AMF that may limit the reverse) faults that have been active since Late Miocene. interpretation of the paleoseismic data. The Lorca earth- The Alhama de Murcia Fault is one of these faults. quake gave us some insights to improve this knowledge. This NNW–SSE shortening direction is driven by plate In this work we present a review of the origin, structure, tectonics (Fig. 2). The Nubia-Eurasia and Eurasia-North Miocene evolution, Quaternary activity, morphotectonic America motions changed significantly approx. 3 Ma Martínez-Díaz et al. / Journal of Iberian Geology 38 (1) 2012: 253-270 255 3°0'W 2°0'W 1°0'W 0°0' 1°0'E A 5º W 4º W 3º W 2º W 1º W 0º IBERIA Iberian Peninsula Magnitude (Mw) 39°N 1.0- 1.9 Betics Ojos 1908 Alacant 2.0 - 2.9 Lorquí 1911 SF Alboran B 3.0 - 3.9 Tell Cehegín 1948 Murcia 38°0'N 4.0 - 4.9 Gulf of Alicante AF C Cadiz Rif AFRICA Mula 1787 Cotillas 1911 AMF > 5.0 F CR Cartagena 38°N External Zones Alboran Domain Torrevieja 1829 Murcia Torrevieja F CA F Lorca PF NB F Cartagena Eastern M ea A Granada S Lorca 1579;1674 a Betics . PF Águilas e an Almería 1522 Vera 1518 S FZ F RF 37°0'N A C ne C Almería 37°N Z n Z F Adra rra AF C a Almería e Intensity ite n (EMS) ed Adra a M rr VI Algero-Balearic Adra 1910 te VII Basin Alboran Sea i ed VIII Mar de Alborán 1804 M IX Fig. 1.- Regional distribution of in- 36°N East Alboran Gibraltar Strait strumental and historical seismicity Africa X 36°0'N Basin Km within the Betic Cordillera. A: epi- 0 60 120 Km 0 50 100 200 centres of earthquakes from the pe- 3°0'W 2°0'W riod1°0'W 0-2010 with horizontal0°0' error of 1°0'E 5º W 4º W 3º W 2º W 1º W 0º location <10 km, data from the “Insti- B tuto Geográfico Nacional”. The AMF IBERIA Iberian Peninsula is framed by the square. MagnitudeB: Historical (Mw) earthquakes with intensity EMS > VI. 39°N 1.0- 1.9 Betics Ojos 1908 Note the significantAlacant alignment of epi- 2.0 - 2.9 centers along the AMF. The structural Lorquí 1911 SF Alboran B 3.0 - 3.9 Tell Cehegín 1948 divisionMurcia of the Betic-Rif Cordillera is 38°0'N 4.0 - 4.9 Gulf of Alicante shownAF for reference in the inset.