Steady late quaternary slip rate on the Cinarcik section of the North Anatolian fault near Istanbul, Turkey

The distribution of plate motion between multiple fault strands and how this distribution may evolve remain poorly understood, despite the key implications for seismic hazards. The North Anatolian Fault in northwest Turkey is a prime example of a multistranded continental transform. Here we present the first constraints on late Quaternary slip rates on its northern branch across the Cinarcik Basin in the eastern Marmara Sea. We use both deep penetration and high‐resolution multichannel seismic reflection data with a stratigraphic age model to show that a depocenter has persisted near the fault bend responsible for that transform basin. Successively older depocenters have been transported westward by fault motion relative to Eurasia, indicating a uniform right‐lateral slip rate of 18.5 mm/yr over the last 500,000 years, compared to overall GPS rates (23–24 mm/yr). Thus, the northern branch has slipped at a nearly constant rate and has accounted for most of the relative plate motion between Eurasia and Anatolia since ~0.5 Ma

Limits of the seismogenic zone in the epicentral region of the 26 December 2004 great Sumatra-Andaman earthquake: Results from seismic refraction and wide-angle reflection surveys and thermal modeling

The 26 December 2004 Sumatra earthquake (Mw = 9.1) initiated around 30 km depth and ruptured 1300 km of the Indo-Australian Sunda plate boundary. During the Sumatra OBS (ocean bottom seismometer) survey, a wide angle seismic profile was acquired across the epicentral region. A seismic velocity model was obtained from combined travel time tomography and forward modeling. Together with reflection seismic data from the SeaCause II cruise, the deep structure of the source region of the great earthquake is revealed. Four to five kilometers of sediments overlie the oceanic crust at the trench, and the subducting slab can be imaged down to a depth of 35 km. We find a crystalline backstop 120 km from the trench axis, below the fore arc basin. A high velocity zone at the lower landward limit of the raycovered domain, at 22 km depth, marks a shallow continental Moho, 170 km from the trench. The deep structure obtained from the seismic data was used to construct a thermal model of the fore arc in order to predict the limits of the seismogenic zone along the plate boundary fault. Assuming 100C-150C as its updip limit, the seismogenic zone is predicted to begin 530 km from the trench. The downdip limit of the 2004 rupture as inferred from aftershocks is within the 350C 450C temperature range, but this limit is 210-250 km from the trench axis and is much deeper than the fore arc Moho. The deeper part of the rupture occurred along the contact between the mantle wedge and the downgoing plate

The Grosmarin experiment

The GROSMARIN (which stands for GrandROSMARIN) cruise is proposed by UMR Géosciences Azur (with fellow french and italian research groups). Its goals are to better characterize active structures along this zone and to assess the resulting seismic hazard in a sort of continuation with respect to the MALISAR experiment, which has already surveyed some active structures through shallow observations. The GROSMARIN cruise is in fact the necessary counterpart to characterize them at depth

Verso una migliore conoscenza delle strutture del margine Ligure: il progetto GROSMARIN

(English Abstract) The Ligurian margin, that is the junction area located between the Ligurian basin and the Southwestern Alps, is a passive margin, seismically active and subjected to gravitative movements. The active deformation in this sector is among the strongest ever experienced in Western Italy and Southern France. The current geodynamics of the basin is not completely understood yet, and somewhat under interest and debate of the scientific community. The latest results on the recent evolution of the Alps-Mediterranean system suggest that the area under study lay close to a domain under extension. The interest for the area is reinforced by its seismic activity that, although of low to moderate energy, acts in an area of high vulnerability. Some historical events involved in fact dramatic social and material damages. The growth of population (that now accounts for more than 2.500.000 inhabitants between Cannes and Genoa), the setting of numerous industries and the tourist business of the area are additional motivation for monitoring the area from the seismic point of view and especially to make specific studies on the seismogenic structures of this sector. Events with magnitude greater than 4.5 to 5.0 are in fact recorded every 5 years, but the area undergoes a rather weak microseismicity that often remains undetected and always poorly located by land seismic networks. The natural risks associated to this sector cannot neglect the presence of steep canyons that incise the offshore margin and favour gravitative slopes. The sediment masses accumulate on top of these canyons and may slip even after an earthquake of moderate magnitude. The GROSMARIN (which stands for GrandROSMARIN) cruise is proposed by UMR Géosciences Azur (with fellow french and italian research groups). It aims at (1) studying the microseismicity along a part of the northern margin of the Ligurian Basin, offshore France and Italy and (2) to realise a 3D tomography by wide-angle seismics. The goal is to better characterize active structures along this zone and to assess the resulting seismic hazard.Published359-360N/A or not JCRope

Combined traveltime and frequency-domain seismic waveform inversion: : a case study on multi-offset ultrasonic data

Geophysical Journal International, v. 154, n. 1, p. 117-133, 2003. http://dx.doi.org/10.1046/j.1365-246X.2003.01956.xInternational audienceWe present the acquisition and processing of a multi-offset ultrasonic tomography experiment in which we aim to precisely reconstruct the image and kinematic properties of two scatterers that contrast strongly with the water background. The resultant non-linearity causes the failure of a frequency-domain waveform fitting strategy for retrieving the whole range of experimentally covered wavenumbers. A mixed tomographic approach is instead adopted in which traveltime and waveform inversion are combined iteratively. This strategy helps in overcoming the waveform inverse problem non-linearity and the data computed in our final tomographic model match most of the observed features in the experimental seismograms. This model is in good agreement with what is known concerning the properties of the scatterers and it is characterized by both the high focusing of waveform tomography and the accurate kinematics of traveltime tomography. These achievements are reached in spite of a limited, but nevertheless uniform, geometric coverage. Our strategy of using two different tomographic tools sequentially therefore appears to be a possible solution to addressing the issue of highly non-linear seismic inverse problems

Infrasound modeling in a spherical heterogeneous atmosphere

International audienceThe deployment of a worldwide network for infrasound detection requires numerical methods for modeling these signals over long distances. A ray theoretical approach appears robust and efficient. It furthermore allows a straightforward interpretation of recorded phases. We have developed a three-dimensional Hamiltonian ray tracing for modeling linear acoustic waves in the atmosphere. Propagating over distances superior to 500 km requires the curvature of the Earth to be considered, which is achieved by using spherical coordinates. High atmospheric winds are properly handled through a modified Hamiltonian. These winds as well as sound velocity can change significantly during long-lasting propagations; these variations are also included in our modeling. Finally, the amplitude of infrasonic signals is computed by concomitantly solving for paraxial rays and assessing the evolution of the ray tube thus defined. We present the theory for this atmospheric infrasound modeling and some simple applications that establish its robustness and potential

Frequency-domain full-waveform inversion of OBS wide-angle seismic data

International audienceIn deep offshore, crustal-scale seismic imaging is classically performed by traveltime tomography applied to wide-angle seismic data recorded by a network of Ocean Bottom Seismometers (OBS). The resulting velocity model is of limited resolution. If the wide-angle experiment is multifold thanks to densely sampled OBSs, this large-scale velocity model can be used as a starting model for full-waveform inversion. Considering the full wavefield recorded over a broad range of apertures is expected to provide a significant resolution improvement in the velocity models. We applied 2D frequency-domain full-waveform inversion to wide-angle data recorded by 100 OBSs deployed perpendicular to the trench axis of a subduction zone, offshore Japan. The full-waveform modelling/inversion are entirely implemented in the frequency domain. Thirteen frequencies ranging from 3 to 15 Hz were inverted sequentially with a weighted least-square method, the velocity model obtained for each frequency being used to start the inversion of the next one. The resolution of the velocity models inferred from traveltime and full waveform tomographies were estimated to be ~10 km and 500 m respectively at 10 km depth suggesting a resolution improvement by an over order of magnitude. The relevance of the structures was assessed by ray tracing and full-waveform modelling

Paraxial ray tracing for atmospheric wave propagation

Geophysical Research Letters, v. 31, p. L20106, 2004. http://dx.doi.org/10.1029/2004GL020514International audienc