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International audience; The Vanuatu arc in the southwest Pacific Ocean is one of the world's most seismically active regions, with almost 39 magnitude 7+ earthquakes in the past 43 years. Convergence rates are around 90–120 mm/yr along most of the arc, but drop to 25–43 mm/yr in the central section, probably due to the subduction of the d'Entrecasteaux ridge. We characterize the slab geometry and tectonic state in this central section by analyzing data from a 10 month deployment of 30 seismometers over this section. We located more than 30,000 events (all less than magnitude 5.5), constructed an improved 1-D velocity model, calculated focal mechanisms and cluster geometries, and determined the 3-D geometry of the interplate seismogenic zone. The seismogenic zone has a shallow bulge in front of the d'Entrecasteaux ridge, which could be explained by the ridge's buoyancy contributing to the uplift of the fore-arc islands. The seismogenic zone extends to ~45 km depth, significantly below the 26–27 km depth of the fore-arc Moho, indicating that the upper mantle wedge is not significantly serpentinized, which is consistent with the relatively high thermal parameter of the subducting plate. The maximum width of the seismogenic zone is 80 km, indicating an upper earthquake magnitude limit of Mw 7.85 ± 0.4, assuming standard rupture zone aspect ratios. The data also reveal a double seismic zone, 20 to 30 km below the seismogenic zone, which is presumably caused by flexure of the downgoing plate.

© 2014 Biophysical Society. During β-adrenergic stimulation, cardiac troponin I (cTnI) is phosphorylated by protein kinase A (PKA) at sites S23/S24, located at the N-terminus of cTnI. This phosphorylation has been shown to decrease KCaand pCa50, and weaken the cTnC-cTnI (C-I) interaction. We recently reported that phosphorylation results in an increase in the rate of early, slow phase of relaxation (kREL,slow) and a decrease in its duration (tREL,slow), which speeds up the overall relaxation. However, as the N-terminus of cTnI (residues 1-40) has not been resolved in the whole cardiac troponin (cTn) structure, little is known about the molecular-level behavior within the whole cTn complex upon phosphorylation of the S23/S24 residues of cTnI that results in these changes in function. In this study, we built up the cTn complex structure (including residues cTnC 1-161, cTnI 1-172, and cTnT 236-285) with the N-terminus of cTnI. We performed molecular-dynamics (MD) simulations to elucidate the structural basis of PKA phosphorylation-induced changes in cTn structure and Ca2+binding. We found that introducing two phosphomimic mutations into sites S23/S24 had no significant effect on the coordinating residues of Ca2+binding site II. However, the overall fluctuation of cTn was increased and the C-I interaction was altered relative to the wild-type model. The most significant changes involved interactions with the N-terminus of cTnI. Interestingly, the phosphomimic mutations led to the formation of intrasubunit interactions between the N-terminus and the inhibitory peptide of cTnI. This may result in altered interactions with cTnC and could explain the increased rate and decreased duration of slow-phase relaxation seen in myofibrils.

Protein kinase A (PKA) phosphorylation of myofibril proteins constitutes an important pathway for β-adrenergic modulation of cardiac contractility and relaxation. PKA targets the N-terminus (Ser-23/24) of cardiac troponin I (cTnI), cardiac myosin-binding protein C (cMyBP-C) and titin. The effect of PKA-mediated phosphorylation on the magnitude of contraction has been studied in some detail, but little is known about how it modulates the kinetics of thin filament activation and myofibril relaxation as Ca2+ levels vary. Troponin C (cTnC) interaction with cTnI (C-I interaction) is a critical step in contractile activation that can be modulated by cTnI phosphorylation. We tested the hypothesis that altering C-I interactions by PKA, or by cTnI phosphomimetic mutations (S23D/S24D-cTnI), directly affects thin filament activation and myofilament relaxation kinetics. Rat ventricular myofibrils were isolated and endogenous cTn was exchanged with either wild-type cTnI, or S23D/S24D-cTnI recombinant cTn. Contractile mechanics were monitored at maximum and submaximal Ca2+ concentrations. PKA treatment of wild-type cTn or exchange of cTn containing S23D/S24D-cTnI resulted in an increase in the rate of early, slow phase of relaxation (kREL,slow) and a decrease in its duration (tREL,slow). These effects were greater for submaximal Ca 2+ activated contractions. PKA treatment also reduced the rate of contractile activation (kACT) at maximal, but not submaximal Ca 2+, and reduced the Ca2+ sensitivity of contraction. Using a fluorescent probe coupled to cTnC (C35S-IANBD), the Ca2+-cTn binding affinity and C-I interaction were monitored. Ca2+ binding to cTn (pCa50) was significantly decreased when cTnI was phosphorylated by PKA (ΔpCa50 = 0.31). PKA phosphorylation of cTnI also weakened C-I interaction in the presence of Ca2+. These data suggest that weakened C-I interaction, via PKA phosphorylation of cTnI, may slow thin filament activation and result in increased myofilament relaxation kinetics, the latter of which could enhance early phase diastolic relaxation during β-adrenergic stimulation. © 2014 Biophysical Society.

International audience; This study investigates a microseismic swarm induced by injection operations in the Arkema-Vauvert salt field. The seismic activity in this field is monitored only by two permanent 3-component stations deployed in two wells. This study focuses on a period of 21 months (2004 January-2005 September) during which 1214 seismic events are located. The seismic activity is divided into three periods correlating with the water injection operations, highlighting a migration of the seismicity toward a thrust fault connecting the injection well and the production well. A waveform analysis reveals S-wave anisotropy, and focal mechanisms are computed using P, Sv and Sh amplitudes manually measured on anisotropy-corrected seismograms. First, synthetic resolution tests assess the reliability of the focal mechanisms determination from the two 3-component stations deployed in the field. Synthetic data are generated for 1056 earthquakes with various focal mechanisms and are perturbed with noise. The results indicate that the type of focal mechanism is correctly retrieved for 74 per cent of the synthetic earthquakes, but the uncertainties of the strike and rake are significant (from 15 to 45inline image). Next, the focal mechanisms are computed for 532 real earthquakes. The solutions primarily correspond to a dip-slip/thrust fault type with subvertical NE-SW and subhorizontal N-S to NW-SE nodal planes. Correlations between the focal mechanisms and the spatio-temporal distribution of the seismic activity are noteworthy. The study shows it is possible to reliably retrieve double-couple focal mechanisms for some faulting geometries with two 3-component seismological stations. However, the reliability of the focal mechanism retrieval depends on the station configuration. Therefore, the addition of further stations would improve the results.

International audience; The North Ecuadorian-South Colombian subduction zone was the site of the 1906 Mw 8.8 megathrust earthquake. This main shock was followed by three large events in 1942, 1958, and 1979 whose rupture zones were located within the 500 km long 1906 rupture area. A combined onshore and offshore temporary seismic network covering from the trench to the Andes was deployed during 3 months in the area of large earthquakes, in order to obtain a detailed knowledge of the seismic background activity. Resulting earthquakes location and mechanisms bring new insights on interseismic active deformation distribution in the three main tectonic units of the margin, namely, the Interplate Seismogenic Zone, the fore-arc region which is part of the North Andean Block and the downgoing oceanic Nazca plate. The interplate seismic activity presents along strike variations, suggesting that the seismicity and the associated stress buildup along the plate interface depend on the time elapsed since the last large earthquakes. According to our results, the updip and downdip limits of the seismogenic zone appear to be located at 12 and 30 km depth, respectively. Shallow to intermediate depth seismicity indicates a slab dip angle of ≈25°. North of the Carnegie Ridge, the Wadati-Benioff plane is defined beneath the fore arc down to ≈100 km depth. Facing the ridge, the Wadati-Benioff plane extends beneath the Andes, down to ≈140 km depth. This observation conflicts with the hypothesis of the presence of a flat slab at a depth of 100 km facing the ridge. In the overlying fore-arc region, the crustal seismicity occurs down to 40 km depth and is mainly concentrated in a roughly NW-SE 100 km wide stripe stretching from the coast, at about 1°N, to the Andes. The location of this active deformation stripe coincides with observed tectonic segmentation of the coastal domain as evidenced by the presence of an uplifting segment to the south and a subsiding segment to the north of the stripe. It also corresponds to a ≈30° change in the trend of the Andes, suggesting that the curvature of the volcanic arc might play an important role in the deformation of the fore-arc region.

International audience; We have developed a method that enables computing double-couple focal mechanisms with only a few sensors. This method is based on a non-linear inversion of the P, Sv and Sh amplitudes of microseismic events recorded on a set of sensors. The information brought by the focal mechanism enables determining the geometry of the rupture on the associated geological structure. It also provides a better estimate of the conventional source parameters. Full analysis has been performed on a data set of 15 microseismic events recorded in the brine production field of Vauvert. The microseismic monitoring network consisted of two permanent tools and one temporary borehole string. The majority of the focal mechanisms computed from both permanent tools are similar to those computed from the whole network. This result indicates that the double-couple focal mechanism determination is reliable for both permanent 3C receivers in this field.

13 pages, 5 figures, 2 tables, La localización exacta de los terremotos costa afuera y en tierra es un desafío a largo plazo para la comunidad científica, y este problema es de particular interés en las regiones de subducción como el margen activo de Ecuador-Colombia, donde grandes terremotos y tsunamis han ocurrido. En el norte de Ecuador, la sismicidad no está bien precisada debido a la ausencia de registros sísmicos entre la costa y los Andes. Por lo tanto, algunos problemas importantes, como la geometría del slab, no están resueltos aún. Nosotros proponemos aquí estudiar la sismicidad de la región de Esmeraldas (norte de Ecuador), usando datos de dos experimentos sismológicos locales, SUBLIME y ESMERALDAS, llevados a cabo en esta parte de Ecuador. Estos fueron conducidos respectivamente en 1998 y 2005, y durante ambos experimentos, estaciones en tierra y OBS (Sismómetros de Fondo Oceánico) fueron desplegados simultáneamente. Las redes de SUBLIME y ESMERALDAS cubrieron juntas una gran área, extendiéndose desde el margen hasta la Cordillera. Hemos localizado eventos registrados usando diferentes modelos de velocidad de acuerdo a las áreas geológicas y topográficas. Los modelos de velocidad usados fueron derivados a partir de perfiles sísmicos de gran ángulo a través del margen norte ecuatoriano, y de un modelo de velocidad terrestre global. Nuestros resultados muestran que el Límite Superior pendiente arriba (UdL) de la zona sismogénica está localizado a una profundidad superficial de ~10 Km, 40 Km al Este de la Fosa. Utlizando resultados anteriores de sísmica activa y nuestras localizaciones, determinamos una inclinación del slab de 10° al nivel de la fosa que aumenta a 25°-30° en la parte profunda hasta 120km de profundidad por debajo de la Cordillera Occidental. Hemos también notado la presencia de una intensa y densa deformación en la parte superior, desde los 40Km al Este de la Fosa hasta la Cordillera. El conocimiento de los patrones de sismicidad en las zonas de subducción, como la localización del UdL, es un parámetro clave para la determinación de los riesgos sísmicos y de tsunamis, [EN] Accurate location of offshore and onshore earthquakes is a long-time challenge in the scientific community and this problem is of particular interest in subduction regions like the active Ecuador Colombian margin, where great earthquakes and tsunamis occurred. In the north of Ecuador, the seismicity is not well constrained because of a lack of recorded seismicity between the coast and the Andes. Therefore, some major problems, like geometry of the slab, are not resolved yet. We propose here to study the seismicity of the Esmeraldas region (north Ecuador), using data of two local seismological experiments, SUBLIME and ESMERALDAS, carried out in this part of Ecuador. They were conducted respectively in 1998 and in 2005 and during both experiments, land stations and OBSs (Ocean bottom seismometers) were deployed simultaneously. Together SUBLIME and ESMERALDAS networks cover a large area, stretching from the margin up to the Cordillera. We locate recorded events using different velocity models according to geological and topographical areas. The velocity models used were derived from wide-angle seismic profiles across the north Ecuadorian margin, and from a global earth velocity model. Our results show that the Updip Limit (UdL) of the seismogenic zone is located at a shallow ~10 km depth, 40 km east of the trench. Using active seismic tomography of previous study and our location results we show a 10° dipping slab in the trench area, increasing to 25°-30° down to 120km depth beneath the western Cordillera. We also note the presence of an intensive thick deformation in the upper, from 40km east of the trench until the cordillera. Knowledge of seismicity patterns in subduction zones, like the UdL location, is a key parameter for seismic and tsunami risk determination

International audience

International audience