Interference among seismic waves radiated by multiple but identical sources arranged in a tight pattern can alter the individual radiation signatures, which can mask the original nature of the source. The pattern for the combined events may even resemble the pattern for a different type of source. Another mechanism to change the signature of a seismic event is scattering near the source. For example, manmade sources embedded in the subsurface need some means of access and placement, such as a tunnel or borehole. Additional hollows may be located nearby to site instruments or other sources. Relative to the surrounding material, all of these cavities may constitute large impedance contrasts that very efficiently scatter and convert seismic waves of comparable wavelengths.
To examine these effects, we calculate radiation patterns for a number of models consisting of two or three cavities with one or multiple explosive sources located inside the cavities. We illustrate the importance of distance between the cavities and exemplify the effect of synchronized sources by time-delaying multiple explosions. We observe that careful selection of distance and delays alters the radiation pattern, which might allow synthesis of a radiation pattern, to boost radiation in a predetermined direction or to make the pattern resemble the radiation from another type of source.