Traveltime curves for various events

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Problem

Draw arrival-time curves for the five events in Figure 6.14a.

Figure 6.14a.  Events involving a mesa.
Figure 6.14b.  Arrival times of events. (i) Geometry; (ii) traveltimes.

Solution

We have for the depth to the mesa, 1900 m; height of mesa, 900 m. The traveltime curves were obtained graphically. We let stand for receiver locations.

For the reflected diffraction from (diffracted at A), the virtual source (see problem 4.1) for the event is in Figure 6.14b(i) (note that traveltime increases upward), so that

For the reflection from , we use the virtual source . We will also have a diffraction from the source (paths not shown).

For the reflected refraction from (reflected at C), we find two traveltimes and then draw a straight line through them.

For the diffraction at from ,

For the diffracted reflection from (diffracted at C), we use the image point of (not shown) so that

which gives the same curve as for the diffraction from except that it is displaced towards increased time by the difference in traveltimes for and .

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Geometry of seismic waves Characteristics of seismic events

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