No abstract

The present study deals with rapid, automatic, estimation of some earthquake parameters (location, focal depth, and magnitude) in a region of rather high seismic activity, in quasi-real time, through the analysis of incoming broadband records. The method can be applied, in particular, in poorly instrumented countries with high seismic-risk potential. It can also be applied when the analysis of a very important flow of data requires rapid, sophisticated, preferably automatic, data processing. The method requires, as a minimum, a three-component broadband seismographic station and a sufficiently populated database, that is, an instrument operating for a time long enough to have accumulated an appropriate data set, used to construct the knowledge base. The more extensive the knowledge base, the better the accuracy of the method. We proceed in several steps. First, applying the SPARS algorithm to the only vertical component, available waveforms are classified according to the source location taken from National Earthquake Information Center (NEIC) catalog; it results in the sorting out of a subset of waveforms/events which will not be included in the knowledge base. Second, each element of the knowledge base is validated according to the epicentral distance with respect to the reference station (and eventually the azimuth of the corresponding source). Third, new input waveforms are analyzed and compared with one or more elements of the knowledge base to estimate their source location and size. The method can be used to search for doublets (or multiplets); if multiplets are found, their location and focal depth can be determined by using a fuzzy event relocation method. We have tested the capability of the proposed algorithms, processing (broadband) waveforms collected during four and half years at the GEOSCOPE broadband station PVC, operated by Institut de Recherche pour le Développement, formerly ORSTOM (IRD) at Port Vila, Vanuatu. Among 650 events recorded at this station, 254 ones, meeting a good criterion of quality, have been sorted. The results show that, in a range of distances up to 1000 km, the method is capable of yielding, in a very short time, the location of the input event, the accuracy depending on the local density of known events in the vicinity. We also obtain a reliable estimation of the energy by measuring the maximum surface wave (or S-wave) amplitude, related to the classical magnitude MSZ.

We have studied the photoluminescence (PL) of titanium dioxide nanocrystalline powders (TiO2) synthesized by the thermal hydrolysis in the form of anatase (A), whose surface has been modified by the adsorption of chromium ions (Cr 3+ ). The samples are characterized by X-ray diffraction, X-ray fluorescence, and Raman spectroscopy. PL spectra were excited by a nitrogen UV laser. The Cr 3+ ion doping in А/TiO2 leads to short-wave and long-wave shifts of the PL peaks due to the Burstein-Moss effect and due to the contribution of radiation "tails" of the electron density of states, respectively. The PL intensity of Cr 3+ -doped A/TiO2 at low concentration of Cr 3+ (up to 0.5 at.%) increases in comparison with the undoped A/TiO2 due to the formation of additional centers of radiative recombination of carriers. With increasing the concentration of Cr 3+ (∼1.0 at.%), the A/TiO2 PL intensity decreases due to the concentration quenching. K e y w o r d s: titanium dioxide, anatase, Cr-doping, photoluminescence.

Deghosting of pressure‐only data has become a routine in marine seismic processing. Most existing techniques suffer from noise susceptibility or excessive simplification of the used ghost model, which leads to difficulties in removing the ghost waves. The algorithm presented in this paper is based on the wavefield extrapolation theory, and is capable of taking into account arbitrary streamer shapes and rough sea surfaces. The computations are performed in the frequency domain and come down to solving systems of linear equations. Regularization and data‐adaptive statistical optimization of the parameters prevent noise amplification. We describe the theory of the method and test it against synthetic and field datasets with different streamer shapes for both rough and flat sea surfaces.