Theoretical seismic wave propagation

Richards, Paul G.

doi:10.1029/rg017i002p00312

Cited by 7 publications

(1 citation statement)

References 288 publications

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“…While many methods for computing synthetic seismograms exist, only a few have thus far been applied to the synthesis of body waves in marine seismology. Chapman [1978] has categorized the methods mathematically, Richards [1979] has reviewed them extensively, and our discussion will elaborate on the utility of the various methods.…”

Section: Synthetic Methodsmentioning

confidence: 99%

A new look at the seismic velocity structure of the oceanic crust

Spudich¹,

Orcutt²

1980

Reviews of Geophysics

283

168

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Within the last decade a new picture of the oceanic crust has emerged from advances in seismic experimental design, instrumentation, and analysis techniques. In this new picture, layer 2 is a region in which velocity increases rapidly with depth. While there is evidence of finer structure within layer 2, the exact nature of this structure is still poorly resolved. Layer 3 is much more homogeneous vertically than layer 2 and appears to have gentle vertical velocity gradients and occasional low-velocity zones in v•, and vs. Although it has been observed at several sites, the widespread existence of a high-velocity basal crustal layer is in doubt. The thickness of the crust-mantle transition has been observed to vary between 0 and 2 km from site to site, and even at fiat lying, uncomplicated sites, seismic evidence for lateral heterogeneities on a scale of a few kilometers can be found. This seismic picture of the crust is in good agreement with the seismic velocities of rocks from ophiolite complexes and is consistent with the theoretically expected behavior of seismic velocities in porous, water-saturated rocks at elevated pressures. A review of velocity results obtained from use of synthetic seismogram modeling techniques is given, and the types of synthetic techniques suitable for marine work are described. anic crust and comment on both its current limitations and its advantages over the classical thick layered view of the crust. As useful companions to this paper we suggest the works of Kennett [1977] and Lewis [1978].Our main points in this paper are as follows: 1. Although the travel time data from marine refraction experiments can generally be well explained by oceanic crustal velocity models consisting of a small number of homogeneous layers, this cannot be construed to imply the necessary existence of homogeneous layers, velocity interfaces, or reflectors within the crust. Crustal velocity models in which velocity varies smoothly with depth in most depth regions generally explain seismic wave amplitude variations better than the classical thick homogeneously layered models.3. In oceanic 'layer 2,' seismic velocities increase quite rapidly with depth (velocity gradients are -1-2 s-'). Finer structure has been observed within layer 2, but it appears to be highly variable laterally. The layer 2-layer 3 transition may be a velocity discontinuity at some sites and a broad gradient zone at other sites. The finer structure of layer 2 is only • Now at U.S. Geological Survey, marginally within the ability of explosion seismology to resolve. Oceanic 'layer 3' has more gentle vertical seismic velocity gradients (---0.1 s-') and possible low-velocity zones inboth compressional (P) and shear (S) wave velocity. While a high-velocity (vp = 7.2-7.7 km/s) basal crustal layer may exist at some sites, there is little clear evidence that such a layer is widespread throughout the oceans. 5. The width of the crust-mantle transition is quite variable._6. Velocity gradients within the crust are more naturally interpreted petrol...

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Section: Synthetic Methodsmentioning

confidence: 99%

A new look at the seismic velocity structure of the oceanic crust

Spudich¹,

Orcutt²

1980

Reviews of Geophysics

283

168

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Effects of causal absorption on seismic body waves

Červený

Frangié

Vaněk³

1982

Stud Geophys Geod

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A computer model study of the propagation of the long‐range Pn phase

Gettrust¹,

Frazer²

1981

Geophysical Research Letters

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Synthetic long‐range (high‐frequency) Pn phases that fit both the arrival times and, more importantly, the characteristic long coda duration of this phase are generated using a velocity‐depth model consistent with long‐range refraction and surface wave observations. These synthetics show that a crustal guided‐wave plays an important part in the character of "typical" long‐range Pn coda; in particular, the largest amplitude arrivals at ranges greater than about 8° propagate through the crustal wave guide. Comparison of a synthetic long‐range Pn signal with an observation of this phase at 8° range suggests that any P‐velocity inversion at the base of the lithosphere must be small. This result is consistent with the anomalously high Q values for Sn reported by Walker et al. [1978] since a P‐velocity inversion much smaller than the associated S‐velocity inversion means that tunneling would extract much more low‐frequency energy from long‐range Sn than it would from long‐range Pn.

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Theoretical seismic wave propagation

Cited by 7 publications

References 288 publications

A new look at the seismic velocity structure of the oceanic crust

A new look at the seismic velocity structure of the oceanic crust

Effects of causal absorption on seismic body waves

A computer model study of the propagation of the long‐range Pn phase

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