Nicole Béthoux

• Nice Sophia Antipolis University

A new seismically active zone is found in the southern part of the Ligurian basin, 80-km west of Corsica (western Mediterranean). The activity began in February 2011 with a foreshock (ML 4) and a mainshock (ML 5.3) 5 days later, followed by numerous aftershocks. We first analyze the fore- and mainshock in detail. We compare the results obtained usi...

The aim of the SI-Hex project (acronym for « Sismicité Instrumentale de l’Hexagone ») is to provide a catalogue of seismicity for metropolitan France and the French marine economic zone for the period 1962–2009 by taking into account the contributions of the various seismological networks and observatories from France and its neighbouring countries...

The North-Andean subduction zone generates recurrent tsunamigenic earthquakes. The seismicity is usually considered to be segmented because of different specific morphological features of the Nazca Plate driving the subduction motion. Most of the recent powerful earthquakes in the margin were located in its northern part. To the south, the region o...

Volcano-tectonic processes in the central part of Iceland, covered by the Vatnajökull glacier, are investigated by inversion of focal mechanisms. Working on a large catalog of focal mechanisms determined by the Icelandic Meteorological Office (IMO), we used a damped regional-scale stress inversion method to obtain an insight of kilometric variation...

The SW Alps are an active orogen undergoing intra-mountainous extension and peripheral compression. We discuss the significance of syn-orogenic extension based on a comparison of paleo-stress derived from fault-slip data inversion reflecting long-term (<12 Ma) evolution of SW Alps and the present-day stress state obtained by inversion of the focal...

The seismological study of recent seismic crises near Oleron Island confirms the coexistence of an extensional deformation and a transtensive regime in the Atlantic margin of France, which is different from the general western European stress field corresponding to a strike-slip regime. We argue that the switch of the principal stress axes σ1/σ2 in...

We document a one week long slow-slip event (SSE) with an equivalent moment magnitude of 6.0-6.3 which occurred in August 2010 below La Plata Island (Ecuador), south of the rupture area of the Mw=8.8 1906 megathrust earthquake. GPS data reveal that the SSE occurred at a depth of about 10km, within the downdip part of a shallow (<15km), isolated, lo...

The Jia-Shian earthquake (Mw=6.3) occurred on 04th March 2010 in the southwestern Taiwan. We used the waveforms of teleseismics to identify the strike, dip and rake of focal mechanism are 311/33/37. Furthermore, we explored the strike, dip and rake are 316/40/44 on the first pulse of the teleseismic P wave. We also took account of the Continuous Gl...

Seismic hazard assessment of active faults in slow orogenic domains is a challenging issue and even more in regional with polyphase tectonic history. We present a multi-disciplinary approach combining geological observations and sismological analysis along the south-western flank of the Alpine arc (France and Italy). Statistical analysis of strieat...

On 1 April 2006, the Taitung earthquake (M w 6.1) occurred in Taiwan at the boundary between the Philippine Sea and Eurasian Plates, where high conver-gence rates contributed to the development of Plio-Pleistocene orogeny in the region. From the joint inversion of seismic and geodetic data, we identified the event's fault geometry and reconstructed...

Comparison of the eroded off-rift zone left inactive by plate motion with the inner active seismic rift zone allows us to constrain the fracturing mechanisms. In eastern off-rift zone, we measured 423 fault slips (including normal and strike-slip faults). Inversion of fault slip data reveals the parallelism of the minimum stress (σ3) computed for t...

The deep structure of the North Ligurian margin and its contiguous Ligurian basin as well as the seismicity recorded in these zones are neither well understood nor precisely constrained. In order to better address these questions, there is a need for offshore instrumenting, which was realised for a duration of nearly 6 months during the GROSMarin (...

Along strike variation of interplate seismic activityNo evidence of flat slab in Ecuador facing the Carnegie RidgeThick brittle crust and tectonic segmentation in the overriding plate

A seismic study of a segment of the convergent margin of Ecuador is presented. During the SISTEUR campaign a network of 24 Ocean Bottom Seismometers (OBS) was deployed on the Carnegie Ridge, one line along the main axes of the ridge and two lines across the strike of the edge of the ridge, during one month. This marine network was complemented with...

The GROSMarin experiment, held in 2008, investigates the structures of the seismically active North Ligurian rifted margin. An array of 21 Ocean Bottom Seismometers was deployed offshore a region spanning from Nice to Imperia and recorded seismic refraction shots as well as microseismicity for a duration of more than 5 months. It was extended onlan...

The orogen of Taiwan emerges east of the Pacific seaside of Mainland China. This ongoing mountain building is the result of the active collision between the Eurasian Plate to the West and the Philippine Sea Plate to the East. In the eastern part of the island, the plate boundary lays inside a narrow North-South valley, the Longitudinal Valley. In t...

The orogen of Taiwan emerges east of the Pacific seaside of Mainland China. This ongoing mountain building is the result of the active collision between the Eurasian Plate to the West and the Philippine Sea Plate to the East. In the eastern part of the island, the plate boundary lays inside a narrow North-South valley, the Longitudinal Valley. In t...

The subduction of the Nazca plate beneath South America has caused one of the largest megathrust earthquake sequence during the XXth century with three M>7.7 earthquakes that followed the great 1906 (Mw = 8.8) event. Better understanding the processes leading to the occurrence of large subduction earthquakes requires to monitor the ground motion ov...

The North-Ligurian rifted margin is singular in that it lies immediately next to the Alpine orogenic arc. It is furthermore seismically active and can experience destructive earthquakes such as in 1887 in the region of Imperia—an event that resulted in a tsunami and more than 600 casualties in spite of a coastal area that was much less densely popu...

The seismic background noise observed on the OBS (ocean-bottom seismometer) recordings is well known to be strong. With the recent appearance of broadband OBS, the background noise in the extended frequency range is even more significant. By taking into account the various degrees of freedom of the seismic sensors, it has been shown that the seismo...

The aftershock sequence of the 1999 Chi-Chi earthquake (Mw = 7.6) provided a large number of focal mechanisms recorded with BATS Centroïde Moment Tensors (CMT) which allowed us to perform reliable stress tensor inversions in North Central Taiwan. These inversions were done for three time-periods corresponding to the post-seismic phase of the 1999 C...

The seismic activity of the Ligurian Basin, the northeastern termination of the western Mediterranean basin, is larger than in surrounding regions, even though recent geodetic studies attest that this area is subject to very low levels of deformation. This basin is an example of a type of passive margins that cannot be considered solely as inert si...

The western Provence in southern France is an intraplate low deforming region, cut by large sinistral strike-slip faults as the Nîmes Fault. The deformation rate of this fault was estimated at 0.1 mm yr-1 from geological and morphological observations. Nevertheless, some large earthquakes occurred in this area in historical times inducing well-docu...

A full-scale mechanical prototype line was deployed to a depth of 2500 m to test the leak tightness of the electronics containers and the pressure-resistant properties of an electromechanical cable under evaluation for use in the ANTARES deep-sea neutrino telescope. During a month-long immersion study, line parameter data were taken using miniature...

full-scale mechanical prototype line was deployed to a depth of 2500 m to test the leak tightness of the electronics containers and the pressure-resistant properties of an electromechanical cable under evaluation for use in the ANTARES deep-sea neutrino telescope. During a month-long immersion study, line parameter data were taken using miniature a...

The Moho preserves imprints of the regional geodynamic evolution of the lithosphere. As such, its detailed topography in divergence or convergence zones has a strong bearing on any geodynamic model. This is still more critical where 3D effects are expected, as in the case of the Alpine chain which exhibits in its western part a short radius of curv...

We present here a detailed analysis of a seismic data set recorded by a dense seismological network installed over 6 months in the southeast of France. This experiment was set-up at the boundary between the Ligurian basin and the southern subalpine thrust belt (the Nice arc), which is a complex tectonic region that undergoes low to moderate seismic...

We present here a detailed analysis of a seismic data set recorded by a dense seismological network installed over 6 months in the southeast of France. This experiment was set-up at the boundary between the Ligurian basin and the southern subalpine thrust belt (the Nice arc), which is a complex tectonic region that undergoes low to moderate seismic...

We investigate how focal solutions and hypocenter locations may depend on the ray tracing algorithm and the strategy of velocity inversion. Using arrival times from a temporary seismological network in the south-western Alps, a local earthquake tomography has been performed by Paul et al. [Paul, A., Cattaneo, M., Thouvenot, F., Spallarossa, D., Bét...

A full-scale mechanical prototype line was deployed to a depth of 2500 m to test the leak tightness of the electronics containers and the pressure-resistant properties of an electromechanical cable under evaluation for use in the ANTARES deep-sea neutrino telescope. During a month-long immersion study, line parameter data were taken using miniature...

A geotransect across the south-western Alps from the Pelvoux Massif (external French Alps) to the Dora-Maira massif (internal Italian Alps), through the Monviso ophiolitic complex, was investigated in the framework of the ‘Géo-France 3D Alpes’ programme. A new interpretative crustal-scale section across the south-western Alps is proposed, combining...

We analyzed the seismicity of central and western France, using historical data, a compilation of all recorded earthquakes from 1962 to 2002 (4574 events, relocated), and all published focal mechanisms (119 focal solutions). The aim is to understand what are the causes of earthquakes and stress accumulation in a slowly deforming intraplate region....

We present a lithospheric section of the northern Tyrrhenian basin based on principal observations along a transect from Corsica Island to Tuscany margin. Offshore, crustal structure observations come from the LISA deep seismic cruise, composed by Multi-Channel Seismic profiles and wide angle reflection/refraction seismic data. Other parts of the s...

Refinement of the seismicity distribution (4574 events) in western and central France, has been done by synthesis of seismological bulletins. Earthquakes have then been relocated by joint hypocentre and velocity structure inversion. The new hypocentre distribution indicates that the seismicity of those regions is much less diffuse than previously t...

1] The deep structure of the Ecuador subduction zone and adjacent Carnegie Ridge (CR) was investigated using on-shore off-shore wide-angle seimics. A crustal model obtained by 2-D inversion of traveltimes reveals the overthickened (14 km) oceanic crust of the CR that underthrusts the high velocity (>6 km/s) basement of the upper plate margin wedge,...

From Nov. 2002 to March 2003, the CHARSME project (CHile ARgentina Seismological Measurement Experiment) took place in Chile and Argentina in order to analyze the regional seismotectonic characteristics and to map the change of the subducted Nazca plate from a flat-slab to an inclined geometry. Local seismological and gravimetric data were collecte...

In the orogenic belt, the combination of the geological data (tectonic, petrologic and kinematic analysis) with the geophysical imagery of the crust (regional seismicity, local earthquake tomography and gravimetry) allows to obtain crustal scale models coherent with the present-day deformation. In this way, the recent pluridisciplinary studies perf...

We perform a spatial and temporal analysis of the instrumental seismicity of the Western Alps, between latitude 41°–48° N and longitude 5°–10° E, using a recently revised catalogue available for the period 1962–1995 containing 7500 events in the magnitude range 2–5.9. Taking into account the fact that the major difficulty of such an analysis in an...

The February 25th 2001 event (Ml=4.6), occurred offshore, 25-30 km south of Nice, near the location of the December 1989 event (Ml=4.6). Both events can be related to the structures observed at the southern Alps and Ligurian Sea margin and their charac- terisation is fundamental in the estimation of the seismic hazard on the French Rivera. The last...

Subduction of the Nazca Plate beneath of Ecuadorian margin is influenced by the Carnegie Ridge, a major E-W volcanic relief related to Cocos spreading center and Galapagos hotspot activity. During the Sisteur experiment (September-October 2000), 9 OBSs (Ocean Bottom Seismometer) and 2 land-stations recorded wide angle arrivals from 128 litres airgu...

During the SALIERI cruise conducted by GEOMAR and Géosciences Azur 4000 nautical miles of multibeam bathymetry were acquired together with magnetics on the Carnegie Ridge and the convergent margin of Ecuador and Colombia. The Carnegie Ridge is a highly asymmetric dome feature with a steep, faulted northern flank and a gently sloping southern one in...

Understanding the conditions of occurrence of major earthquakes in intraplate regions of low deformation is a long-standing question. As a particular example, this study attempts to understand the relationships between the location of the seismicity and the mechanical behaviour of the Lig urian Basin. Indeed, this northern eastern part of the weste...

The Southern Alps – Ligurian basin junction is one of the most active seismic areas in Western Europe countries. The topographic and the structural setting of this region is complex because of (i) its position between the high topography of the Southern Alps and the deep, narrow Ligurian oceanic basin, and (ii) the large number of structures inheri...

Data from a new deep-penetration seismic reflection line (LISA cruise 1995), onland seismic recording (LISA) and marine ESPs (expanding spread profiles, CROC II cruise 1981) are integrated to study the crustal structure of the north Ligurian basin. The correlation of these different seismic data, located along an Antibes-Ile Rousse transect, provid...

Owing to the apparent deformation field heterogeneity, the stress regimes around the Provence block, from the fronts of the Massif Central and Alpine range up to the Ligurian Sea, have not been well defined. To improve the understanding of the SE France stress field, we determine new earthquake focal mechanisms and compute the present-day stress st...

To investigate the influence of inherited inhomogeneity in a lithosphere under extension, we studied the deep structure of Corsica, an island in the Mediterranean sea, at the boundary of the extensional Tyrrhenian basin, using a temporary array of eight broad-band seismographs. Between the stations in the western Hercynian part of the island and th...

For two months, ground motions induced by natural seismicity were recorded by 4 dense arrays, each of them including 9 seismological receivers. The target zone is a 400 km2 area and displays a characteristic topographic organization. The sites correspond to flat valleys filled with surficial soft sediments. The data recorded during this experiment...

The western Alpine regions have been instrumented since the beginning of the century, and the number of seismological stations largely increased since 1980. This dense network has allowed an important improvement in the hypocentral determination, even for low magnitude events. This condition was a good opportunity to perform a synthesis of 32 years...

The Ligurian Sea (West Mediterranean) is an example of a narrow oceanic basin which stops Lg wave propagation. Locating the exact point of Lg extinction was one of the goals of the SISBALIG II seismological experiment, which deployed both inland stations in Provence and Corsica and Ocean Bottom Seismometers (OBS) in the Ligurian Sea. A precise anal...

A detailed analysis of 16 new earthquake mechanisms, followed by a synthesis of available focal solutiones in the southwestern Alps, allows to characterize the various present-day defomation regimes within the pre-Triassic basement of this region. We define 4 areas of deformation, 3 of which are mainly compressional and one of which is is extension...

The establishment of a permanent 4-station network and a temporary 10-station network during the SISBALIG II survey, has allowed clarification of the microseismicity affecting Corsica. The epicentral map (61 events) indicates a microseismic zone oriented in a NNE-SSW direction that stretches from Zicavo region, in the south, to the eastern plain an...

The current and historical seismicity of the Ligurian Sea and surrounding regions has been analyzed in order to obtain closer seismotectonic correlations. The seismicity and focal mechanisms indicate particular differences between the different sectors of the Ligurian Basin. The aseismicity of the eastern side of the basin, corresponds to an active...

The analysis of recorded seismic data to quantify the magnitude of the anomalous propagation of Lg waves across the southwestern part of the Alpine region, and to map the spatial extension of the region where the extinction of Lg occurs, is proposed. This mapping is used to define the geological structure specifically responsible for the sudden var...

Two earthquakes occurred in the Ligurian Sea in December 1989 and April 1990. Both were widely felt along the French and Italian Rivieras, thus reminding us of the seismic risk in this region. The significant increase in the number of seismic stations in the area facilitated the study of these two shocks and their related aftershocks. Using differe...

Recent marine and onland geophysical and geological investigations along the northern Caribbean plate boundary call for a review of its tectonic interpretation, in the light of a new compilation of the seismological data avalaible from Cuba to Puerto Rico. We show that the shallow seismicity in the northeastern Caribbean is concentrated along an ea...

A partir des sismogrammes enregistres en differentes stations sismologiques, on peut determiner la direction et le pendage de la faille qui a joue pendant le seisme; on peut egalement caracteriser la nature du mouvement le long de cette faille (en compression, en distension, en coulissage). Le calcul des mecanismes au foyer est donc un moyen a la f...

Nous présentons les résultats d'une première expérience d'utilisation conjointe de stations sismologiques sous-marines (OBS) et terrestres pour l'étude de la sismicité de la mer Ligure. Durant cette campagne, un réseau de 11 stations temporaires, dont 4 sous-marines, a été déployé. On a pu ainsi préciser les conditions expérimentales nécessaires au...

Four ocean bottom seismometers (OBS) and seven land seismological stations were deployed in order to study the seismicity of the Ligurian Sea. Location and focal solutions of regional events have been improved by the OBS data. Furthermore, a strong attenuation of seismic energy is suspected through the continental slope: the use of OBS to analyze t...

New microtectonic and seismological data allow us to deduce the stress field associated with a great active lithospheric strike-slip fault, the northern Caribbean transcurrent plate boundary. Since we know from other data the kinematics of the Caribbean plate relative to North America, we try to connect stress field and kinematics. We show that the...

In numerous regions, the focal depths are not precisely determined from standard location methods because of the poor azimuthal coverage by the seismic network or because of the important geological complexity. In this study, we attempt to refine the determination of the focal depth of some events by analyzing the waveforms of the seismograms and t...

Fault plane solutions for 20 earthquakes which occurred recently (1981-1987) in the Ligurian Sea and the SW Alps have been investigated allowing for the conclusion of different regional stress fields. Nevertheless, it seems possible to assume that these local responses are the consequence of the same general trend ie the vergent motion of the Apuli...

During the EGT survey, 50 underwater shots were detonated on a N-S section through the Gulf of Genoa running from the northern margin (44.12°N) towards Corsica (42.90°N) along the 9°E meridian. The aim of this work is, in a first stage, to establish the propagation model of regional phases in this region and. consequently, to improve the location o...

In order to provide more insight into land propagation of T phases, signal analysis of these phases recorded inland has been carried out. We found that the wave train is composed mainly of Pg and Sq waves which reach the seismic station from different azimuths. With the hypothesis that the signal is the sum of discrete arrivals due to different ray...

Relocated epicenters are computed with a model based on complex local structure, i.e. oceanic floor in the central Ligurian Basin and thinned continental margins. By superposing these relocated earthquakes on a basement bathymetric map, the structural relations are clearly demonstrated. Compressive stress towards the west-northwest is confirmed in...

The Ecuadorian margin located between 2.5oS and 1oN is underthrust by the Carnegie Ridge (CR), a prominent volcanic relief on the Nazca Plate. According to its history of great subduction earthquakes, the margin in contact with CR can be divided in two segments. Immediately north of 0.5oS, the 1906 and 1942, earthquakes ruptured the plate boundary...

The researches of Arctic region is necessary for beginning from delimitation of Arctic. Geographically concept "Arctic" uncertain enough. There is a set of approach to definition of its borders and set the variants of these borders (eternal permafrost, boreal tayga, drifting ice, temperature, etc.). Most correct the point of view of Ecology is real...

An unresolved p roblem in seismology concerns the occurrence of unexpectedly strong earthquakes within intraplate slow deforming regions s uch as Central Asia, Western United States and Western Europe. These earthquakes can b e damaging as the 1811 and 1 812 New Madrid events of Mw = 8.1 and 8.2, in a region where the instrumental seismicity level...

Summary