Rayleigh waves from small explosions

Dobrin, Milton B.; Simon, R. F.; Lawrence, P. L.

doi:10.1029/tr032i006p00822

Cited by 47 publications

(8 citation statements)

References 9 publications

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“…This accounts also for the fact that the major axis is not parallel to the vertical. An inclination of the major axis of ellipses has indeed been found from observed seismograms (Dobrin et al 1951). The ratio of axes of the curves changes both with depth of source and with distance from the source.…”

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confidence: 53%

Effect of Depth of a Point Source on the Motion of the Surface of an Elastic Solid Sphere

Alterman

Abramovici

1966

Geophys J Int

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An exact solution, obtained previously for the displacement of the surface of a uniform elastic solid sphere due to an impulsive compressional pulse from a point-source situated at depth d below the surface of a sphere of radius a is applied here to the problem of propagation from a source at d = aJ32 and a16400 and compared with results for d = aJ8. Theoretical seismograms, radial and angular component, are given at distances 0 < 6 < 7c from the source.Rayleigh waves are found due to all sources. In the high frequency limit they have the velocity of Rayleigh waves in a homogeneous half space. There is dispersion towards higher velocities. The Rayleigh waves from the shallow source have amplitudes more than ten times the amplitude of body waves. In the seismograms from the medium and deep sources their amplitude is smaller, they have less high-frequency components and show more dispersion. The amplitude of Rayleigh waves has a minimum at 90" and 270". At 180" and 360" the radial component has a maximum of ten, seventeen and forty times the radial component at 90" for the deep, medium and shallow sources respectively. The ratio of angular to radial amplitude is largest at 90" and 270", decreasing to zero at 180" and 360". The Rayleigh waves show phase shift, almost elliptical retrograde particle motion, change in form of ellipses with depth of source and deviations of the direction of the major axis from the vertical direction similar to results in observed seismograms. Higher modes of surface waves are found and their connection with groups of reflected pulses of mixed types given. As in several observed seismograms the second mode is especially predominant in the angular component. Whereas diffracted pulses connected with p times reflected P, are encountered mainly in deep-focus events, diffraction phenomena connected with the transformed phases P,S, are found here at all depths and have in several cases amplitudes comparable to, or larger than, the reflected pulses.

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confidence: 53%

Effect of Depth of a Point Source on the Motion of the Surface of an Elastic Solid Sphere

Alterman

Abramovici

1966

Geophys J Int

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“…The group velocity of this pulse is approximately 0.16 kin/s, and its dominant period is about 0.3 s. This is virtually the same as the dominant group velocity and period associated with the microseismic noise in the east part of Long Valley described by lyer and Hitchcock [1976] in their investigation of geothermal noise. Published dispersion curves from surface wave studies of shallow and sedimentary structures [Dobrin et al, 1951] suggest that these waves may be an Airy phase of fundamental mode Rayleigh waves propagating in the lake and marsh deposits (the 0.5-kmthick layer with P wave velocities of 1.5-1.9 km/s).…”

Section: Indicates a Vertical Offset In The Basement Of About 15 Km mentioning

confidence: 99%

Structure of Long Valley Caldera, California, from a seismic refraction experiment

Hill¹

1976

J. Geophys. Res.

117

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Two seismic refraction profiles crossing the Long Valley caldera in approximately east and north directions indicate that the crystalline basement with P wave velocities of 6.0±0.4 km/s has been downdropped by 2.5–3 km across normal faults along the north and northwest sides of the caldera and 1–2 km along the south and east sides. Basement depths beneath the caldera floor range from between 3 and 4 km in the north and east sections to about 2 km in the central and south sections. Relief on the basement within the caldera suggests that the caldron block was partially disrupted during collapse, although a steplike offset in the eastern part of the basement may be due in part to precollapse displacement along the Hilton Creek fault. The distribution of P wave velocities in the caldera fill suggests that the Glass Mountain rhyolite and Bishop tuff have velocities of 4.0–4.4 km/s and the postcollapse rhyolite, rhyodacite, and basalt flows have velocities of 2.7–3.4 km/s. Domelike relief on the 4.0‐ to 4.4‐km/s horizon indicates that postcollapse resurgence elevated the west central part of the caldera by about 1 km. Evidence for the roof of the magma chamber is contained in later arrivals tentatively identified as reflections from a low‐velocity horizon at a depth of 7–8 km. Evidence for anomalous scattering or absorption properties associated with the region of shallow hydrothermal alteration and hot spring activity is contained in relative attenuation of high frequencies in a guided wave propagating through this region.

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“…Some of the earliest such measurements of phase velocity, for periods <1 s, can be found in the oil exploration literature (e.g., Dobrin et al, 1951). Early works suggested that in the two-station approach, phase estimated from a cross correlogram of the two seismograms yields more stable estimates than from phase differences .…”

Section: Phase Velocitymentioning

confidence: 99%