[en] The first global maps showing the performance of the infra-sound network of the international monitoring system were set in the nineties. Recent measurement of the background noise by the 36 operating stations combined with advanced models of wind give now a more realistic mapping. It has become possible to validate simulations by measuring real events. For instance the explosion that happened in March 2008 in an ammunition storehouse in Albania was detected till Zalesovo (Russia) 4920 km away. These new simulations confirm the detection capability of the network to detect and localize atmospheric explosions whose energy is over 1 kt. It is also shown that the detection performance are very sensitive to both time and places. (A.C.)

[en] The CEA-DAM Ile-de-France collects and processes data sets from infra-sound, seismic or hydro-acoustic sensors, with an exponentially growing volume. In this complex mass of information, the analysis process consists in a chain of treatments, with as first objective the detection in real time, and continuously, of a signal that may come from an event of interest. By illustrating them with concrete examples, the article presents several methods dedicated to the operational processing, that help detecting events of interest, even those buried in a continuous background noise. The article also shows that these methods lead to more than simple detection. They moreover provide essential information either on the events, or on the detection capabilities of the stations. (authors)

[en] We investigate the possibility to estimate the depths of earthquakes of moderate magnitude (3.5≥M≤5.5) from tele-seismic data, using the Comprehensive Nuclear-Test-Ban Treaty Organization monitoring system. To face new problems that arise from the weakness of the magnitudes we want to deal with, two methods were developed. First, a depth-phase recognition method is applied, based on a new improved cepstral analysis. In addition, we develop a focal mechanism genetic algorithm inversion that focuses on depth resolution through an envelope-fitting procedure and adapted reproduction and mutation functions. Six events of interest were analyzed to validate these new proposed methods. First, the tele-seismic depth of the recent Corsica earthquake (France, 7 July 2011) was estimated at about 26 km, whereas regional inversions do not provide any constraints. This proposed depth has a direct impact for regional tectonic studies, as this implies that this earthquake occurred in the continental crust. In contrast, the shallow Sardinia event (Italy, 3 January 2011) took place in the oceanic crust. The depth of the Virginia event (United States, 23 August 2011) was also constrained using these methods, and we show that it is possible to constrain the focal depth even for weak magnitude events, such as the mb 3.6 Ardeche earthquake (France, 3 August 2011). In the case of the Po Plain earthquake (Italy, 27 January 2012), this provides another example of the great interest in tele-seismic analysis, where the detection of the Moho reflected phase (pmP) shows without doubt an upper-mantle event. Finally, the Murcia event (Spain, 11 May 2011) shows the limits of these methods for very shallow events (≤4-5 km). We show that these new depth determinations improve our ability to understand the geologic processes, as they provide complementary information on the source and are not affected by lateral crustal heterogeneities. (authors)

[en] The International Monitoring System (IMS) for the enforcement of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) been designed to detect and locate nuclear explosions. The global network, which includes radionuclide, hydroacoustic, seismic and infrasound stations, provides an opportunity to monitor human activities and natural phenomena on a global scale. The growing amount of global data available in near real time from IDC and IRIS-Consortium enables to rapidly and accurately determinate the earthquakes source parameters. The first and second order characteristics of the event (location, depth, duration, focal mechanism, and also more refined kinematic parameters for large earthquakes, such as spatial slip distribution on the fault and rupture velocity) are calculated from teleseismic P and SH body waves with various methods. The classical point source and line source inversions are used in order to rapidly provide the main features of the rupture process for intermediate and large earthquakes and also to validate the depth estimation. For large earthquakes, we also look for extended source parameters on the fault (slip and rupture velocity), using a description of the source process in terms of slip patch(es). We also use the estimated infrasonic waves generated by the ground coupling to obtain a 2D image of the radiation of the Rayleigh waves. This image will be introduced to constrain the inversion of the rupture process. (author)