Marta Ferrater (1), Maria Ortuño (1), Eulàlia Masana (1), Giorgi Khazaradze (1), Anna Echeverria (1), Raimon Pallàs (1), Eduardo García-Melendez (2), José J. Martínez Díaz (3), Stéphane Baize (4), Héctor Perea (5), Pedro P. Cunha (6), Thomas Rockwell (7) (1) RISKNAT Group, GEOMODELS, Departament de Geodinàmica i Geofísica, Facultat de Geologia,Universitat de Barcelona, c/ Martí i Franquès s/n, 08028 Barcelona, Spain (marta.ferrater@ub.edu) (2) Área de Geodinámica Externa, Facultad de CC. Ambientales, Universidad de León, Campus de Vegazana s/n 24071 León, Spain (3) Departamento de Geodinamica, Universidad Complutense, Instituto de Geociencias IGEO (UCM,CSIC), C/ Jose A. Novais 2, 28040 Madrid, Spain (4) Institut de Radioprotection et Sûreté Nucléaire - Seismic Hazard Division (BERSSIN), BP 17, 92262 Fontenay-aux-Roses, France (5) Barcelona Center for Subsurface Imaging (B-CSI), de Geociències Marines - Institut de Ciències del Mar - CSIC, Psg. Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain (6) Departamento de Ciências da Terra, IMAR-CMA, Universidade de Coimbra; Largo Marquês de Pombal, 3000-272 Coimbra, Portugal (7) Department of Geological Sciences, San Diego State University, San Diego, CA 92182, USA Departament The Alhama de Murcia fault slip-rate: first constraints from updated data UNIVERSITAT DE BARCELONA U B A Z-Present day soil B C D F G H E I J K W X Z: Current soil. Very dark silts. With very few floating clasts. A: Dark silts with few granules and pebbles. Local concentrations of angular pebbles in lenticular bodies. Interpreted as the base of a present-day channel. The upper part show incipient development of a soil. B: Dark matrix-supported gravels with angular and poorly sorted pebbles. Soil is developing a top of unit C: Paleosoil composed of yellow silts with carbonatic nodules. Few pebbles (up to 5 cm in diameter) are present. Gradual base. D: Clast-supported gravels. This unit show two subunits in some walls. The upper unit is composed by granules and pebbles (in some cases imbricated), forming tractive structures and lamination. The lower unit has heterometric clasts (granules to boulders), with no sorting nor tractive structures and a highly erosive base E: Paleosoil composed of yellow silts with carbonatic cementation. This soil is less continuous than soil at unit C. Few pebbles (up to 5 cm in diameter) are present. Gradual base. F: Clast-supported gravels with some parts being matrix supported. Clasts are heterometric and angular, and no tractive structures are observed. G: Orange silts and clays with variable thickness. Some very few clasts float within this unit. Gradual but no erosive base. H: Heterometric clast-supported gravels containing pebbles to boulders. Poorly sorted and angular clasts. In the lower part, some grey and laminated sands crop out locally as well as local orange silty layers. I: Pink sands with lamination in the lower part of H. J: Orange silts with very few floating clasts. K: Grey clast-supported heterometric and angular gravels with no sorting nor tractive structures. W : Gravels and yellowish silt X : Clast supported heterometric and angular conglomerates. The top of the unit is red. Tr13 Tr11 Tr7 Tr12 Tr6 SE-NW Channel 1 Channel 2 Channel 1 Channel 2 Channel 1 Channel 2 Channel 1 Channel 2 18m 8m FE CRF BSF CRF CAF CF Granada a d a v e S N i err a CC S S S S Nf Nf Nf Nf Nf A A A A A A A A A A A M M M M P P N N N N N N N N N N Murcia Alicante Lorca Almeria Adra PF AMF Iberian Massif 50 km V Neogene and Quaternary basins (V: volcanic rocks) Prebetic units Subbetic units Malaguide complex Alpujarride complex Nevadofilabride complex Iberian massif EXTERNAL ZONES INTERNAL ZONES N V P S M A Nf IBERIAN PENINSULA Betics Alboran basin Rif Tell EBSZ Figure 4. Examples of some offsets. A detailed geomorphic analysis has been carried out along AMF. 1956 aerial photographs, present day orthophotographs of 0.25m cell and Digital Elevation Models (of 1m, 0.5m and 0.25m cell based on a recent LiDAR adquisition) analysis and field work support this evidence. Figure 2. CuaTeNeo GPS network velocities with 95% confidence error ellipses with respect to western Europe.. Figure 1. Geological map of Eastern Betics. Legend: CRF, Crevillente fault; AMF, Alhama de Murcia fault; CAF, Carrascoy fault; PF, Palomares fault; CF, Carboneras fault; EBSZ, Eastern Betics Shear Zone. Modified from Masana et al., 2004. Figure 3. A-A' profile parallel and normal velocities with 1 sigma uncertainties (vertical bars). Location of the profile is shown in Fig. 2. Dashed straight gray lines show linear regression fit for the individual group of stations, used to estimate the offsets. Topography is represented with an irregular line with a vertical exaggeration of 1:9. Stations on the NW side of the AMF are plotted as circles and as triangles on the SE side. The intersections with the AMF and PF are shown as short vertical lines on the bottom. Top: Profile parallel (AMF normal) velocities. ΔVc is the compressive differential motion (velocity offset) between the two blocks. Bottom: Profile normal (AMF parallel) velocities. ΔVss is the strike-slip differential motion between the two blocks. Figure 7. 3D model of the trenches 5, 10 and 13 (Fig. 5) created with GoCAD software. This ongoing work interpretation allows the measurement of channels offsets. (Channel 1: 3D distance =17.7 m, Map distance (XY) = 17.6m, Vertical distance = 1.4 m; Channel 2: 3D distance = 7.7 m, Map distance = 7.6 m, Vertical distance = 1.3 m. Figures 5 and 6. Aerial photo with the location of the trenches, of the 2001 and 2013 campaigns in El Saltador site (results of TR3 and TR4 are published in ; and panoramic view of 2013 trenches. Further discussion is focused on trenches 5, 10 and 13. Martínez-Díaz et al., 2003; Masana et al., 2004) REFERENCES Echeverria, A., Khazaradze, G., Asensio, E., Gárate, J., Martín Dávila, J., Suriñach, E. (2013). Tectonophysics 608, 600–612. López-Comino, J.-Á., Mancilla, F. D. L., Morales, J., Stich, D. (2012). Geophysical Research Letters 39(3), 1–5. Martínez-Díaz, J. J., Masana, E., Hernández-Enrile, J. L., Santanach, P. (2003). Annals of Geophysics 46(5), 775–791. Martínez-díaz, J.J., Masana, E., Ortuño, M. (2012a). Journal of Iberian Geology 38(1), 253-270. Martínez-Díaz, J.J., García-Mayordomo, J., Jiménez-Díaz, A. (2012b). Alhama de Murcia: ES627. In Quaternary Active Faults Database of Iberia v.2.0 - December 2011 (García-Mayordomo et al., eds.), IGME, Madrid. Masana, E., Martínez-Díaz, J. J., Hernández-Enrile, J. L., Santanach, P. (2004). Journal of Geophysical Research 109, 1–17. Moreno, X. (2011). Tesi doctoral, Universitat de Barcelona. Ortuño, M., Masana, E., García-Meléndez, E., Martínez-Díaz, J.J., Štěpančíková, P., Cunha, P.P., Sohbati, R., Canora, C., Buylaert, J.P., Murray, A.S., 2012. Geol. Soc. Am. Bull. 124 (9–10), 1474–1494. CONCLUSIONS The higher slip rate that we infer from new work presented here implies that: a) the AMF is far more active than previously believed; and b) the seismic hazard associated with this fault should be thoroughly revised (net slip rate is considered 0.3mm/yr; Martínez-díaz et al., 2012b). This is particularly important in light of the recent 2011 Lorca earthquake (Mw5.2; López- Comino et al., 2012) that caused 9 fatalities, along with major structural damage to local buildings. INTRODUCTION The Alhama de Murcia fault (AMF) is one of the most active faults of the Eastern Betics Shear Zone (EBSZ; Fig. 1). This system absorbs most of the NNW-SSE shortening between Eurasian and African plates in the Iberian region. Previous studies suggest a slip rate between 0.1 and 0.6 mm/yr for AMF (Martínez-Díaz et al., 2003; Masana et al., 2004; Martinez Díaz et al., 2012a). New geologic and geodetic investigations suggest that the slip rate could be significantly higher, in accordance with the slip rate of the Carboneras fault (Moreno, 2011), which is also part of the EBSZ. In this poster, we present three lines of evidence of a higher slip rate for the AMF. ACKNOWLEDGEMENTS The authors were supported by research projects: CGL2011-30005-C02-02 SHAKE, CSD2006-00041 TOPOIBERIA, CGL2006-12861-C02-01 EVENT and CGL2004-21666- E CuaTeNeo from the Spanish Ministry of Science and Innovation; PTDC/GEO- GEO/2860/2012 from Fund. Ciência e Tecnologia; Project LE311A12-2 from Junta de Castilla y León. Fundings for the postdoctoral and doctoral fellowships were provided by Spanish Ministry of Economy and Competitivity (Juan de la Cierva fellowship for H. Perea), Spanish Ministry of Education, Culture and Sport (FPU fellowship for M. Ferrater) and by the University of Barcelona (APIF fellowship for A. Echeverria ). We are very grateful to Òscar Gratacós for his help with the GoCAD program. EVIDENCE 3: Paleoseismological 3D trenches (first estimations of lateral offsets) EVIDENCE 2: Surface channels offset EVIDENCE 1: GPS measurements (slip rate = 1.5mm/yr) A reverse-sinistral geodetic slip rate of 1.5mm/yr (Echeverria et al., 2013) is estimated between the northern block of the AMF and the southern block of Palomares fault (PF in Fig.1). This value would be the sum of the slip-rates of both EBSZ faults. The more conspicious geomorphic expression of the AMF with respect to the PF suggests that the former is responsible of more than a half of this value (i.e. 1mm/yr approx.). Current work is focused on: 1) dating the sedimentary units using C14, TL, quartz-OSL, post-IRIR and U- series; and 2) determining the errors on the offset measurement. We have identified some offseted channels incided on alluvial fan surfaces deposited between middle Pleistocene to Holocene (Martínez-Díaz et al., 2003; Ortuño et al., 2012). The offsets range between some tenths to some hundreds of meters allowing us to estimate lateral slip rates between 0.1 and 2.5 mm/yr. Current work is focused on dating this surfaces by U-series in pedogenic carbonate. Identified channels on both blocks of the fault are being used to calculate the net slip rate. Here we show two of them (channels 1 and 2, Fig. 7). Considering: 1) a maximum age for the channels of 30ka (Masana et al., 2004) and 2) the firsts offset measurements of the channels (17.7m and 7.5m), the minimum estimated slip rate would range between 0.25 and 0.57 mm/yr. min. slip rate = 0.25-0.57 mm/yr.