Regionalization and dependence of coda Q on frequency and lapse time in the seismically active Peloritani region (northeastern Sicily,Italy)     

Elisabetta Giampiccolo  Tiziana Tuvè 《Journal of Seismology》2018,22(4):1059-1074

The Peloritani region is one of the most seismically active regions in Italy and, consequently, the quantification of attenuation of the medium plays an important role for seismic risk evaluation. Moreover, it is necessary for the prediction of earth ground motion and future seismic source studies. An in depth analysis has been made here to understand the frequency and lapse time dependence of attenuation characteristics of the region by using the coda of local earthquakes. A regionalization is likewise performed in order to investigate the spatial variation of coda Q across the whole region. Finally, our results are jointly interpreted with those obtained from recently published 3D velocity tomographies for further insights.  相似文献   

The sediment-fill of Pago Pago Bay (Tutuila Island,American Samoa): New insights on the sediment record of past tsunamis     

Brieuc Riou  Eric Chaumillon  Jean-Luc Schneider  Thierry Corrège  Catherine Chagué 《Sedimentology》2020,67(3):1577-1600

Extensive bathymetric and two-dimensional seismic surveys have been carried out and cores collected in Pago Pago Bay (Tutuila, American Samoa) in order to describe and gain a better understanding of the sediment fill of the bay, which was affected by the 2009 South Pacific Tsunami. Eight sedimentary units were identified over the volcanic bedrock. The basal transgressive unit displays retrograding onlaps towards the shore, whereas the overlying seven aggradational layers alternate between four draping units and three pinching out seaward units. ‘Core to seismic’ correlation reveals that draping units are composed of homogeneous silts, while pinching out units are dominated by very coarse coral fragments showing fresh cuts, mixed with Halimeda plates. The basal unit is attributed to transgressive sedimentation in response to flooding of the bay after the last glacial maximum, followed by the upper aggradational units corresponding to highstand sedimentation. The changeovers in these upper units indicate an alternation between low-energy silt units and high-energy coral debris units interpreted as tsunami-induced deposits. The ¹⁴C dating reveals that high-energy sedimentation units can last up to approximately 2000 years while low-energy sedimentation units can last up to approximately 1000 years. This alternation, deposited during the last highstand, may be explained by cycles of tectonic activity and quiescence of the Tonga Trench subduction, which is the main source of tsunamigenic earthquakes impacting the Samoan archipelago. In the uppermost silt unit, only the geochemical signature of the terrestrial input of the 2009 SPT backwash deposits was detected between 7 cm and 9 cm depth. Hence, Pago Pago Bay offers a unique sediment record of Holocene bay-fill under the impact of past tsunamis intermittently during the last 7000 years.  相似文献   

A Sunspot Catalog for the Period 1952 – 1986 from Observations Made at the Madrid Astronomical Observatory     

Aparicio  A. J. P.  Lefèvre  L.  Gallego  M. C.  Vaquero  J. M.  Clette  F.  Bravo-Paredes  N.  Galaviz  P.  Bautista  M. L. 《Solar physics》2018,293(12):1-23

The Spectral Irradiance Monitor (SIM) instrument on board the Solar Radiation and Climate Experiment (SORCE) performs daily measurements of the solar spectral irradiance (SSI) from 200 to 2400 nm. Both temporal and spectral corrections for instrument degradation have been built on physical models based on comparison of two independent channels with different solar exposure. The present study derives a novel correction for SIM degradation using the total solar irradiance (TSI) measurements from the Total Irradiance Monitor (TIM) on SORCE. The correction is applied to SIM SSI data from September 2004 to October 2012 over the wavelength range from 205 nm to 2300 nm. The change in corrected, integrated SSI agrees within \(0.1~\mbox{W}\,\mbox{m}^{-2}\) (\(1\sigma\)) with SORCE TIM TSI and independently shows agreement with the SATIRE-S and NRLSSI2 solar models within measurement uncertainties.

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The path towards high-contrast imaging with the VLTI: the Hi-5 project     

D. Defrère  O. Absil  J.-P. Berger  T. Boulet  W. C. Danchi  S. Ertel  A. Gallenne  F. Hénault  P. Hinz  E. Huby  M. Ireland  S. Kraus  L. Labadie  J.-B. Le Bouquin  G. Martin  A. Matter  A. Mérand  B. Mennesson  S. Minardi  J. D. Monnier  B. Norris  G. Orban de Xivry  E. Pedretti  J.-U. Pott  M. Reggiani  E. Serabyn  J. Surdej  K. R. W. Tristram  J. Woillez 《Experimental Astronomy》2018,46(3):475-495

The development of high-contrast capabilities has long been recognized as one of the top priorities for the VLTI. As of today, the VLTI routinely achieves contrasts of a few 10^??3 in the near-infrared with PIONIER (H band) and GRAVITY (K band). Nulling interferometers in the northern hemisphere and non-redundant aperture masking experiments have, however, demonstrated that contrasts of at least a few 10^??4 are within reach using specific beam combination and data acquisition techniques. In this paper, we explore the possibility to reach similar or higher contrasts on the VLTI. After reviewing the state-of-the-art in high-contrast infrared interferometry, we discuss key features that made the success of other high-contrast interferometric instruments (e.g., integrated optics, nulling, closure phase, and statistical data reduction) and address possible avenues to improve the contrast of the VLTI by at least one order of magnitude. In particular, we discuss the possibility to use integrated optics, proven in the near-infrared, in the thermal near-infrared (L and M bands, 3-5 \(\upmu \)m), a sweet spot to image and characterize young extra-solar planetary systems. Finally, we address the science cases of a high-contrast VLTI imaging instrument and focus particularly on exoplanet science (young exoplanets, planet formation, and exozodiacal disks), stellar physics (fundamental parameters and multiplicity), and extragalactic astrophysics (active galactic nuclei and fundamental constants). Synergies and scientific preparation for other potential future instruments such as the Planet Formation Imager are also briefly discussed. This project is called Hi-5 for High-contrast Interferometry up to 5 μm.  相似文献   

Prospects for the characterisation of exo-zodiacal dust with the VLTI     

S. Ertel  O. Absil  D. Defrère  J.-C. Augereau  B. Mennesson 《Experimental Astronomy》2018,46(3):401-411

Exo-zodiacal dust, exozodi for short, is warm (～300 K) or hot (up to ～2000 K) dust found in the inner regions of planetary systems around main sequence stars. In analogy to our own zodiacal dust, it may be located in or near the habitable zone or closer in, down to the dust sublimation distance. The study of the properties, distribution, and evolution of exozodis can inform about the architecture and dynamics of the innermost regions of planetary systems, close to their habitable zones. On the other hand, the presence of large amounts of exo-zodiacal dust may be an obstacle for future space missions aiming to image Earth-like exoplanets. The dust can be the most luminous component of extrasolar planetary systems, but predominantly emits in the near- to mid-infrared where it is outshone by the host star. Interferometry provides a unique method of separating the dusty from the stellar emission. We discuss the prospects of exozodi observations with the next generation VLTI instruments and summarize critical instrument specifications.  相似文献