[1] The shortening between the African and the Iberian plates is absorbed by a number of faults distributed over a very wide zone with very low slip rates and long periods of seismic loading. Thus a seismotectonic map based only on faults associated with seismicity or with expressive geomorphic features is incomplete. It is possible to characterize seismogenic faults using paleoseismology. First, paleoseismological results based on trenching analysis in the eastern Betics (Lorca-Totana segment of the Alhama de Murcia fault) are presented. The main paleoseismic parameters of this fault segment are (1) a minimum of two to three M w 6.5-7 earthquakes in the last 27 kyr (shortly before 1650 A.D., between 830 and 2130 B.C. and shortly before 16.7 ka, respectively), with a mean recurrence period of 14 kyr, and a very short elapsed time, and (2) a net slip rate of 0.07-0.6 mm/yr during the last 30 kyr. These results were extrapolated to the rest of the known active faults in the eastern Betics and were added to the slip rates of the active faults at the African margin. The total slip rate of the transect, which crosses de Alhama de Murcia fault in Spain and reaches the Cheliff basin (Algeria), would represent 21-82% of the total shortening between Africa and Eurasia estimated from plate motion models and seismic moment summation. A number of factors could account for this discrepancy: (1) hidden seismogenic faults in the emerged areas, (2) absence of correlation between current and late Pleistocene slip rates, (3) extensive small faults that are undetected and that absorb a significant amount of the deformation, and (4) possible overestimation of the convergence rates.

The northeast-striking, dextral-reverse Alpine fault transitions into the Marlborough Fault System near Inchbonnie in the central South Island, New Zealand. New slip-rate estimates for the Alpine fault are presented following a reassessment of the geomorphology and age of displaced late Holocene alluvial surfaces of the Taramakau River at Inchbonnie. Progressive avulsion and abandonment of the Taramakau fl oodplain, aided by fault movements during the late Holocene, have preserved a left-stepping fault scarp that grows in height to the northeast. Surveyed dextral (22.5 ± 2 m) and vertical (4.8 ± 0.5 m) displacements across a left stepover in the fault across an alluvial surface are combined with a precise maximum age from a remnant tree stump (≥1590-1730 yr) to yield dextral, vertical, and reverse-slip rates of 13.6 ± 1.8, 2.9 ± 0.4, and 3.4 ± 0.6 mm/yr, respectively. These values are larger (dextral) and smaller (dip slip) than previous estimates for this site, but they refl ect advances in the local chronology of surfaces and represent improved time-averaged results over 1.7 k.y. A geological kinematic circuit constructed for the central South Island demonstrates that (1) 69%-89% of the Australian-Pacifi c plate motion is accommodated by the major faults (Alpine-Hope-Kakapo) in this transitional area, (2) the 50% drop in slip rate on the Alpine fault between Hokitika and Inchbonnie is taken up by the Hope and Kakapo faults at the southwestern edge of the Marlborough Fault System, and (3) the new slip rates are more compatible with contemporary models of strain partitioning presented from geodesy.

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Most catastrophic earthquakes occur along fast-moving faults, although some of them are triggered by slow-moving ones. Long paleoseismic histories are infrequent in the latter faults. Here, an exceptionally long paleoseismic record (more than 300 k.y.) of a slow-moving structure is presented for the southern tip of the Alhama de Murcia fault (Eastern Betic shear zone), which is characterized by morphological expression of current tectonic activity and by a lack of historical seismicity. At its tip, the fault divides into a splay with two main faults bounding the Góñar fault system. At this area, the condensed sedimentation and the distribution of the deformation in several structures provided us with more opportunities to obtain a complete paleoseismic record than at other segments of the fault. The tectonic deformation of the system was studied by an integrated structural, geomorphological, and paleoseismological approach. Stratigraphic and tectonic features at six paleoseismic trenches indicate that old alluvial units have been repeatedly folded and thrusted over younger ones along the different traces of the structure. The correlation of the event timing inferred for each of these trenches and the application of an improved protocol for the infrared stimulated luminescence (IRSL) dating of K-feldspar allowed us to constrain a paleoseismic record as old as 325 ka. We identifi ed a minimum of six possible paleoearthquakes of M w = 6-7 and a maximum mean recurrence interval of 29 k.y. This provides compelling evidence for the underestimation of the seismic hazard in the region.

We have developed an elastic finite element model in order to study the role of the different forces acting on the northwestern part of the Central American Volcanic Arc and the Chortis Block. We present synthetic focal mechanisms, maps of tectonic regime, and strain crosses to analyze the results. The models show that to achieve the observed state of stress on the volcanic arc, the arc must be modeled as a lithospheric weak zone. Also, the forces related to the eastward drift of the Caribbean plate must be higher than those related to the subduction of the Cocos plate. The coupling on the subduction interface must be low, with or without slip‐partitioning due to the obliquity of the subduction at the trench. At Guatemala the western edge of the Chortis block is pinned against North America, even with low trench‐normal forces, making the triple junction between the Cocos, North American, and Caribbean plates a zone of diffuse deformation. The extension in the western part of the Chortis block, from Guatemala to the Honduras depression, is explained by the geometry of the North American‐Caribbean plate boundary and the direction of motion of the Caribbean plate with respect to North America. The direction of extension in the Chortis block is always E‐W regardless of the magnitude of the applied forces, and the main part of the deformation is absorbed between the Ipala graben and the Honduras depression, both features being consistent with our models.

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 describe 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. ResumenEn este estudio se presenta una revisión del conocimiento que hasta la actualidad se tiene de la estructura y comportamiento sismogenético 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 -Díaz et al. / Journal of Iberian Geology 38 (1) 2012: 253-270 Martínez IntroductionThe Alhama de Murcia Fault (AMF) (Bousquet et al., 1979) is a strike-slip shear zone with reverse component that crosses the eastern Betic cordillera with a NE-SW direction ( Fig. 1). The AMF accommodates ~ 0.1 -0.6 mm/yr of the approximately 5 mm/yr of convergence between Nubian and Eurasian plates (Masana et al., 2004) and is one of the largest faults of the Eastern Betics Shear Zone (Silva et al., 1993). Many of the largest damaging historical earthquakes occurred in the eastern Betic Cordillera are related to this structure (Fig. 1).The most damaging earthquake occurred in Spain in the last 50 years took place next to the city of Lorca (11/05 2011, Mw 5.2). In spite of its moderate size this earthquake produced massive damage in this city. This earthquake has been related to the activity of the AMF (i. e. IGME, 2011;Vissers and Meijninger, 2011; LopezComino et al., 2012;. In recent years several studies have focused on the characterization of the paleoseismic activity and the determination of AMF seismic parameters: slip rate, recurrence interval, maximum magnitude Masana et al., 2004, 2005, Masana, 2010Ortuño et al., 2012). All of these parameters were obtained by the study of trenches excavated in sites that were appropriated to identify recent (preferably later Quaternary) surface ruptures. Until now, these studies have been restricted to two of the four segments that form the AMF. The correct interpretation of these data and the correct extrapolation to the whole fault requires a good knowledge of the deep and shallow structure of the fault zone. But this also requires improving our understanding of the relationships between th...

Betic Cordillera INSAR Coulomb stress transfer Seismic hazard Active tectonics Intersegment zoneOn May 11 th 2011, a Mw 5.2 earthquake stroke the city of Lorca in the SE Spain. This event caused 9 fatalities, 300 injuries and serious damage on the city and the surrounding areas. The Lorca earthquake occurred in the vicinity of a region bounding two well-known segments of a large active fault, the Alhama de Murcia fault (AMF). The Lorca earthquake offers a unique opportunity to study how strain is accommodated in an inter segment region of a large strike slip fault. We map recent tectonic structures in the epicentral region and we use radar interferometry to analyze the coseismic deformation. Combining these data with seismological ob servations of Lorca seismic sequence we first model the source of the earthquake. Then we analyze the influ ence of our preferred model in the adjacent segments by Coulomb failure stress modeling. The proposed earthquake source model suggests that this event ruptured an area of -4x3 km within the complex structure that limits the Gofiar-Lorca and Lorca-Totana segments of the AMF. The induced static stress change on the adjacent segments of the fault represents a seismic cycle advance equivalent to 200 to 1000 years of tectonic loading.