Emma Suriñach

Autopsy on a dead spreading center: The Phoenix Ridge, Drake Passage, Antarctica

New bathymetric and magnetic anomaly data from the Phoenix Ridge, Antarctica, show that extinction of all three remaining segments occurred at the time of magnetic chron C2A (3.3 ± 0.2 Ma), synchronous with a ridge-trench collision south of the Hero Fracture Zone. This implies that the ultimate cause of extinction was a change in plate boundary forces occasioned by this collision. Spreading rates slowed abruptly at the time of chron C4 (7.8 ± 0.3 Ma), probably as a result of extinction of the West Scotia Ridge, which would have led to an increase in slip rate and transpressional stress across the Shackleton Fracture Zone. Spectacular, high-relief ridges flanking the extinct spreading center, mapped for the first time using multibeam swath bathymetry, are interpreted as a consequence of a reduction in spreading rate, involving a temporary magma oversupply immediately prior to extinction.

Quantification of vertical movements in the eastern Betics (Spain) by comparing levelling data

Comparison of precision levelling data carried out at diVerent times is a technique that allows the quantification of recent vertical movements. We used the precision levelling data from the Instituto Geografico Nacional of Spain to improve our understanding of the recent tectonic evolution of some areas in the southeastern Iberian Peninsula (eastern Betics), where significant deformation has occurred during the last century. The resulting movements are presented in recent vertical movement profiles. Profiles with significant movements are discussed, taking into account the geologic and seismic features of each zone. These profiles are: Alicante-Albacete, Alicante-Almeria, Larva (near Jaen)-Almeria and Almeria-El Palo (near Malaga). The results obtained point to the existence of important tectonic deformation rates near the main tectonic structures crossing the profiles. The main tectonic anomalies expressed in constant rates of vertical velocity are: a 2 mm/year step near the ENE-WSW-trending Valldigna-Jumilla fault zone (between Alicante and Albacete); a 0.9 mm/year step located in the NNE-SSW-trending Cocon-Terreros fault zone (between Murcia and Almeria); a subsidence of about 1.5 mm/year of the Almeria Basin zone that can be related to NW-SE and E-W faults; a step of 1 mm/year related to the ENE- WSW-trending Guadahortuna fault (between Granada and Jaen); a 1 mm/year step associated with the ENE-WSW- trending Cadiz-Alicante fault zone (near the Granada area); and a 1.4 mm/year step related to the tectonic activity of the NW-SE- and NE-SW-trending system of faults that aVect the Iberian coast of the Alboran Sea (Almeriaa nd Granada zone). The anomalies related to the ENE-WSW- to E-W-trending structures are associated with reverse faults, whereas the anomalies related to the faults oriented in a NE-SW or NW-SE direction are associated with strike-slip faults with a normal component of vertical movement. These movements are consistent with the present-day Betics stress tensor determined with diVerent methodologies, such as the focal mechanism analysis and microstructural and geomorphological studies, that indicate the existence of a maximum horizontal compression in a NNW-SSE direction together with a perpendicular extension. If we consider the rates of vertical deformation to be constant in time and if we consider that all the accumulated stress results in big earthquakes (M

Frequency Content Evolution of Snow Avalanche Seismic Signals

6.0) with no ductile deformation, an estimate of the minimum return periods for major earthquakes can be made. The return periods, which range between 500 and 1200 years, depending on the zone, should be regarded as new information in the assessment of seismic hazard. These values are in agreement with those deduced from the seismic catalogues of the areas where there is suYcient information.

Extensional deformation and development of deep basins associated with the sinistral transcurrent fault zone of the Scotia–Antarctic plate boundary

Seismic signals generated by avalanches have been recorded by theavalanche team of the Universitat de Barcelona at theVallée de la Sionne experimental site (Switzerland) since 1998. During these years avalanches of varying size and flowwere recorded by two sensors located at different positions.In the present paper we show the general features of the running spectra of the seismicsignals for the different type of recorded avalanches. Using this method we are able not only to detect avalanches with low amplitude signals but also to distinguishbetween avalanches and other seismic sources (i.e., local earthquakes) which have thesame frequency content but a different frequency evolution.

Active crustal fragmentation along the Scotia–Antarctic plate boundary east of the South Orkney Microcontinent (Antarctica)

Abstract The Scotia–Antarctic plate boundary extends along the southern branch of the Scotia Arc, between triple junctions with the former Phoenix plate to the west (57°W) and with the Sandwich plate to the east (30°W). The main mechanism responsible for the present arc configuration is the development of the Scotia and Sandwich plates from 30–35 Ma, related to breakup of the continental connection between South America and the Antarctic Peninsula. The Scotia–Antarctic plate boundary is a very complex tectonic zone, because both oceanic and continental elements are involved. Present-day sinistral transcurrent motion probably began 8 Ma ago. The main active structures that we observed in the area include releasing and restraining bends, with related deep extensional and compressional basins, and probable pull-apart basins. The western sector of the plate boundary crosses fragmented continental crust: the Western South Scotia Ridge, with widespread development of pull-apart basins and releasing bends deeper than 5000 m, filled by asymmetrical sedimentary wedges. The northern border of the South Orkney microcontinent, in the central sector, has oceanic and continental crust in contact along a large thrust zone. Finally, the eastern sector of the South Scotia Ridge is located within Discovery Bank, a piece of continental crust from a former arc. On its southern border, strike-slip and normal faults produce a 5500-m-deep trough that may be interpreted as a pull-apart basin. In the eastern and western South Scotia Ridge, despite extreme continental-crustal thinning, the basins show no development of oceanic crust. This geometry is conditioned by the distinctive rheological behaviour of the crust involved, with the bulk concentration of deformation within the rheologically weaker continental blocks.

Seismic images and evolution of the Iberian crust in the Pyrenees

Abstract The structure of the Scotia–Antarctic plate boundary is poorly known east of the South Orkney Microcontinent. New multichannel seismic profiles, together with magnetic, gravity and swath bathymetry data obtained during the SCAN97 cruise, show a complex relief of raised blocks and elongated depressions that may reach more than 6000 m in depth. These depressions develop in relation with extensional active structures and constitute an uncommon feature in the oceans, where most of the trenches are formed in subduction contexts. The main crustal elements of the area include the oceanic crust of the Scotia Plate, the Discovery Bank composed of continental crust, a tectonic domain with intermediate features between continental and oceanic crusts that includes the Southern Bank, and the oceanic crust of the northern Weddell Sea, representing the Antarctic Plate. The Intermediate Domain was probably developed during the Late Cenozoic subduction of the Weddell Sea oceanic crust below the Discovery Bank. The fault zone associated with the plate boundary is characterized at present by sinistral transcurrent and transtensional slips, which develop a NE–SW elongated deep pull-apart basin with extreme crustal thinning and mantle uplift. The complex bathymetry and structure of the plate boundary are consequences of the presence of continental and intermediate crusts – where the deformations are concentrated – between the two stable oceanic domains. The location of a major part of the plate boundaries around the Scotia Arc is probably determined by the position of the continental and intermediate crustal fragments surrounded by oceanic crust, due to the differential behavior experienced during deformation.

REMOTE, a Wireless Sensor Network Based System to Monitor Rowing Performance

Abstract Crustal images of the Pyrenean range based on coincident wide-angle and vertical deep seismic profiles are presented in this study. Wide-angle experiments in the thickened Iberian crust along strike lines have provided no evidence for reflections from interfaces between layers of different velocities in the middle or lower crust. In contrast, reversed sounding on a line across the Pyrenean range shows wide-angle reflectivity. Its unusual reflectivity pattern points to widespread impedance contrasts of localized continuity embedded in the crust. This observation is consistent with a new image of vertical-incidence reflectivity, obtained by coherency-weighted migration of the coincident Ecors traverse. This profile shows numerous discontinuous and dipping reflections from the middle to the base of the crust. The reflections dip towards the axis of the range. The upper limit and the attitude of the reflective zones are so strongly variable that the crust can hardly be envisaged as the simple, continuous three-layered model previously used for geodynamical reconstructions. The reflective zones cannot be brought back to the horizontal image of a layered-lower crust of proposed extensional origin by plate unbending to the pre-Alpine stage. The dipping reflections may result from compressional deformation, as the south Pyrenean deep crustal domain has undergone both Hercynian and Alpine orogenic deformation. If part of the present reflectivity pattern was due to Alpine remobilization, the corresponding lower crustal deformation would have spread out, thereby accomodating convergence by thickening, even outside the axial zone, where the upper crustal deformation appears to be concentrated.

The transition from an active to a passive margin (SW end of the South Shetland Trench, Antarctic Peninsula)

In this paper, we take a hard look at the performance of REMOTE, a sensor network based application that provides a detailed picture of a boat movement, individual rower performance, or his/her performance compared with other crew members. The application analyzes data gathered with a WSN strategically deployed over a boat to obtain information on the boat and oar movements. Functionalities of REMOTE are compared to those of RowX [1] outdoor instrument, a commercial wired sensor instrument designed for similar purposes. This study demonstrates that with smart geometrical configuration of the sensors, rotation and translation of the oars and boat can be obtained. Three different tests are performed: laboratory calibration allows us to become familiar with the accelerometer readings and validate the theory, ergometer tests which help us to set the acquisition parameters, and on boat tests shows the application potential of this technologies in sports.

Recent vertical movements from high-precision leveling data in northeast Spain

Abstract The lateral ending of the South Shetland Trench is analysed on the basis of swath bathymetry and multichannel seismic profiles in order to establish the tectonic and stratigraphic features of the transition from an northeastward active to a southwestward passive margin style. This trench is associated with a lithospheric-scale thrust accommodating the internal deformation in the Antarctic Plate and its lateral end represents the tip-line of this thrust. The evolutionary model deduced from the structures and the stratigraphic record includes a first stage with a compressional deformation, predating the end of the subduction in the southwestern part of the study area that produced reverse faults in the oceanic crust during the Tortonian. The second stage occurred during the Messinian and includes distributed compressional deformation around the tip-line of the basal detachment, originating a high at the base of the slope and the collapse of the now inactive accretionary prism of the passive margin. The initial subduction of the high at the base of the slope induced the deformation of the accretionary prism and the formation of another high in the shelf—the Shelf Transition High. The third stage, from the Early Pliocene to the present-day, includes the active compressional deformation of the shelf and the base-of-slope around the tip-line of the basal detachment, while extensional deformations are active in the outer swell of the trench.

A 3D Gravimetric Crustal Model for the northeastern region of the Iberian Peninsula

Abstract Historical and modern high-precision leveling data are analyzed to measure recent vertical movements in northeast Spain. The recent vertical movements are deduced by comparing the original height differences (taken from the original logbooks) measured in the field in two surveys carried out by the Instituto Geografico Nacional in the periods 1871–1922 and 1925–1974. An exhaustive study of the errors involved in the measurements indicates that some of the observed movements are significant. We present the recent vertical movements along eight profiles with significant uplift rates: a southern anomaly of about 1 mm/yr, observed in two independent profiles, associated with the southern part of the Catalan Ranges frontal thrust; one anomaly between Caldetes and Arenys with an average velocity of about 4 mm/yr, which can be related to the seismic activity of this century; two anomalies of about of 2.5 mm/yr in the north and of about 4 mm/yr in the south associated with the NW-SE striking Amer-Brugent fault system, which has been related to a great seismic crisis in the fifteenth century, and one anomaly of about 0.8 mm/yr associated with the Emporda basin dynamics. Other observed recent vertical movements are mainly related to sediment compaction masking possible tectonic deformations. All the northern anomalies are associated with the NW-SE system of faults considered as a “transfer zone” of the NE-SW striking faults which controlled the formation of the Neogene European rifting. The former shows Plio-Quaternary tectonic activity: folds, faults, volcanism, hydrothermalism and historical seismicity. The low seismicity of this century around the Amer-Brugent fault system contrasts with both the high average velocities estimated here and with the fifteenth century seismic crisis. Therefore, if these high uplift rates are tectonic in origin, they may represent an accumulation of elastic strain which would be released in a future large earthquake rather than in continual small ones. According to this hypothesis, a large part of the stress accumulated since the fifteenth century has yet to be released. Further leveling and neotectonic surveys are needed to test this hypothesis.