Bisztricsány, E

Kiss, Z

English

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A COMPUTATION OF AVERAGE CRUSTAL THICKNESS FROM LOVE-WAVE DISPERSION, FOR A EURASIAN WAVE PATHE. BISZTRICSÁNY and Z. KISS Geophysical Institute, Eötvös University, Budapest and. State Geophysical Survey, Budapest(Received 24"* September, 1959)SUMMARYThe thickness of the crust was determined by analyzing the dispersion curve of the Love-waves of two Southern Chinese earthquakes. The crustal thickness obtained is 33 kilometres, in spite of the fact tha t one third of the wave path has traversed mountains of high elevation.For the determination of crustal thickness several methods may be adopted. One of them is the analysis of the dispersion of the L o v e-wave.Assuming the crust to be homogeneous and to be limited by plane pa­rallel surfaces, the thickness of the crust along the wave path may be calcu­lated from( 1 )the period equation of the L o v e-wave. The letters denote the following quantities:#  being the thickness of the crust, p, the density of the rocks of the crust, p^  the density ol rock below the A l o h o r o v i c  i c interface, T the period of the L o v e-wave, tq the velocity of the transverse wave in the crust, ^  the velocity of the transverse wave along the M o h o r o v i c  i 6 inter­face, c the phase velocity of the L o v e-wave.Dilferentiating graphically the function obtained from (1) we have¿7 being the group velocity of the Love-wave.By the aid of this graph the theoretical and actual curves can be com­pared.15We have investigated two Asian shocks for which the wave path was nearly identical (Fig. 1.)In Hungary horizontal seismographs are set up only. Therefore, the L o v e  and R a y l e i g h  wave types can he distinguished in the record only in case the surface waves arrive perpendicularly to the plane of oscilla­tion of one of the components of the horizontal seismograph. This condition is fulfilled for the two shocks treated.The measured values of T, the period, and (7, the velocity, are listed as below.The above data are also shown in Fig. 2. Of the curves computed by the aid of the equation only those two are shown which do best approximate the points.The data of the two curves are:1. /мй Кие #2 — 4,3 km sec"' R  — 34 kmaq =  3,35 km sec"'^  =  1,923 Ж2. йялйей &2 =  4,3 km sec"' R  =  32 km.=  3,32 km sec"'йп16Time of retease Epkentratcoordinates "  -  maenitud,1931. 1. 27. 20 19 13 25,0 X 96,8 E 7,6 7041,51934.1XII. 15. 01 57 37 31,3 N 89,3 E 7,1 6073,8Shock ol 1. 27, 193!. Shock ot Xll. 15, 1931.7* Г u49 3,71 34,5 3,4044,5 3,65 30,2 3,3744,2 3,62 29,8 3,33{ 41,5 3,57 30,1 3,3240,1 3,53 27,4 3,3038,1 3,5 27,4 3,2835,5 3,47 27,4 3,2634,9 3,43 23,9 3,2320,8 3,217 (7 Г U40,3 3,51 29,6 3,3431,6 3,46 28,0 3,3136,6 3,43 26,8 3,2935,3 3,40 24,4 3,2629,2 3,36 20,8 3,24Fry. 1. Epicenters of two Southern Chinese Shocks wit It wave paths to Budapest. The epicenters are designated by circlesfry.  Dispersion curves ot tire D ove-waves oi two ¡Southern thrnese Shocks. The full and dashed lines indicate, respectively, tho theoretical curves computed from the data shown in the figure. The empty circles designate the observed data of the shock of 1. 27, 1931, the full circles those of the shock of X II., 15, 1934.It can he seen on the map that one-third of the L o v e-wave path cros­ses mountains of high eievation, which ought to he characterized hy a deep root according to the principle of isostasy. The results obtained do not re­flect this crustal thickening. Maybe this is due to the circumstance that in the path sector off the mountains the crustal thickness is very small.2 Sectio Geotogica  ^y

A computation of average crustal thickness from Love-wave dispersion, for a Eurasian wave path

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A computation of average crustal thickness from Love-wave dispersion, for a Eurasian wave path

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