Seismic Ray

seismic ray

[′sīz·mik ′rā]
(geology)
The path along which seismic energy travels.

Seismic Ray

 

a line normal to the front of a seismic wave propagating from the focus of an earthquake. The direction of a ray changes with a change in the velocity of seismic waves along the path of propagation. In a homogeneous, isotropic elastic medium with a constant velocity of wave propagation, a ray is a straight line. In a first approximation for the earth, velocity is taken to be a function of depth; as velocity increases with depth, the paths of the rays become curved, turning convexly downward symmetrically relative to the apexes of the rays. The equation for a ray is

where T is the ray’s travel time, Q is the epicentral distance in radians, R is the radius of the earth, Vr is the velocity of seismic waves along the ray, e(r) is the angle of inclination of the ray to the horizon at a depth corresponding to the radius r, e0 is the angle of emergence of the seismic ray on the earth’s surface, and V0 is the velocity at the earth’s surface.

Each ray has a deepest point with radius rp. At this point, e = 0, cos e(r) = 1, and p = rp/ Vrp.

I. V. GORBUNOVA

References in periodicals archive ?
Wide-azimuth is an advanced seismic data acquisition technique that gives more refined imaging from the recorded seismic ray paths.
If the measuring base is long, there is indeed much more scope for the shortest "source--sensor" join in a velocity inhomogeneous medium to differ from the seismic ray which propagates along the path of shortest time.
Optimization of a seismic ray tracing with globalization method in anisotropic medium 3D
On tracing seismic rays with specified end points".
The azimuth and apparent velocity of P-wave enable us to determine the direction of a seismic ray approaching the array.
This method assumes linear propagation of a seismic ray of a direct wave, which is refracted at a distinctive refraction boundary.
The travel times of seismic rays are affected not only by the surface ellipticity bulges at the end of rays but also by the ellipticity of each internal surface of constant seismic velocity encountered by the ray.
Seismic rays were computed using the package BEAM87, which has been modified for the so called '2.
In case of the central seismic source, whose distance from the geophone is 1 to 2 m, one may consider relatively shallow penetration of seismic rays into the rock massif, and the seismic wave then propagates mostly through the disturbed part of the massif.
However, for deeper layers the resolution is not really good, because most earthquakes located at shallow levels and there are not many seismic rays that cross those regions (Espinosa and Monsalve 2002).

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