On Dynamic Properties of Reflected and Head Waves in the n-layered Earth's Crust

Abstract

Summary The results of a theoretical investigation of the dynamics of waves reflected from Moho discontinuity and corresponding head waves in the n-layered Earth's crust are given. The validity of the formulae of geometric ray theory (which are usually used for computations) is only limited. For example, it is not possible to use them in the region of the critical angle, which is of basic importance in many practical cases. The amplitude curve of a reflected wave does not reach its maximum directly in the critical point (as it would follow from the geometric ray theory), but somewhere beyond it. Other peculiarities of the critical region are also discussed. Beyond the interference zone of the reflected and head waves the amplitudes of head waves A*w are very small in comparison with the amplitudes of reflected waves Aw (in most cases A*w/Aw<0.1) Hence it would be very difficult to find the pure head waves in the records. The possible causes of the strengthening of the amplitudes of head waves are discussed (mainly the weak velocity gradient below Moho discontinuity).