Surface Wave Tomographic Study of Central Asia Tectonic Regimes

A suite of 33 Asian earthquakes and 36 Central Asia and Novaya Zemlya underground explosions are used to define the minimum detection levels in terms of surface-wave and body-wave magnitudes and the discrimination thresholds of the M versus m discriminant for the Canadian seismograph network. Under low microseismic noise conditions surface-waves can be observed for earthquakes down to m 4.9 and explosions down to m 5.9 for the region near the central Asia test sites. For events above these magnitudes, the M versus m relationships provide reliable discrimination between earthquakes and explosions. Comparison with an intracontinental study leads to the conclusion that the discrimination threshold is limited by path effects and greater distances to events about m 1.0 larger near the Asian test sites than near the Nevada test site.

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Exit-surface wave reconstruction using a focal series

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100129577 ◽

1992 ◽

Vol 50 (2) ◽

pp. 988-989

Author(s):

W.J. de Ruijter ◽

M.R. McCartney ◽

David J. Smith ◽

J.K. Weiss

Keyword(s):

Surface Wave ◽

Spherical Aberration ◽

Data Extraction ◽

High Sensitivity ◽

Geometric Distortion ◽

Variation Method ◽

Objective Lens ◽

Immediate Reconstruction ◽

Exit Surface ◽

Electron Microscopes

Further advances in resolution enhancement of transmission electron microscopes can be expected from digital processing of image data recorded with slow-scan CCD cameras. Image recording with these new cameras is essential because of their high sensitivity, extreme linearity and negligible geometric distortion. Furthermore, digital image acquisition allows for on-line processing which yields virtually immediate reconstruction results. At present, the most promising techniques for exit-surface wave reconstruction are electron holography and the recently proposed focal variation method. The latter method is based on image processing applied to a series of images recorded at equally spaced defocus.Exit-surface wave reconstruction using the focal variation method as proposed by Van Dyck and Op de Beeck proceeds in two stages. First, the complex image wave is retrieved by data extraction from a parabola situated in three-dimensional Fourier space. Then the objective lens spherical aberration, astigmatism and defocus are corrected by simply dividing the image wave by the wave aberration function calculated with the appropriate objective lens aberration coefficients which yields the exit-surface wave.

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