On the distribution of energy and number of earthquakes in accordance with the focal depth P . T I E D E R V A R I ( * ) R i c e v u t o il 30 Marzo 1964 SUMMARY. — A n investigation is presented here concerning the distribu- tion of earthquake energy and number of shocks in accordance with the focal depth. T h e global distribution of these quantities according to the depth of hypocentres can be approached by an exponential curve between 0 and about 500 km under the Earth's surface. RIASSUNTO. — Viene presentato d a l l ' A . , in questa nota, uno studio sulla distribuzione dell'energia dei terremoti e il numero di scosse nei con- f r o n t i della p r o f o n d i t a focale. L a distribuzione nel mondo di queste quan- t i t y nei confronti della profondita ipocentrale, puo essere rappresentata da una curva esponenziale compresa f r a lo 0 e i 500 km al disotto della su- perflcie della terra. Eitsema (') emphasized the importance of studies concerning the connection between strain- (or energy-)release and focal depth of earth- quakes. In his quoted paper he mentioned that the strain-release/' depth diagram of the Sunda Arc and the same diagram of the Earth as a whole show surprisingly similar characteristics in the period of 1904-1946. This extraordinarily interesting recognision induced the author of the present paper to extend the investigations for a larger scale of time. Gutenberg and Bichter (s.3) published the magnitude-data of the greatest shocks between 1896 and 1904; on the other hand the data of all shocks of magnitude 6,9 and over it are at our disposal from 1904 till about the middle of 1962, due partly to the common work of Gutenberg and Bichter (4) and partly to the Bulletin of the Seismological Society of America (5). Altogether we have the data of 1389 earthquakes occured between the beginning of 1896 and about the middle of 1962. W e calculated the energy-release instead of the strain-release. ( * ) F . R . A . S . - Vice-President of International Lunar Society. 3 8 2 P . H l S D E R V A R I Table I I I . Depth, km Number of shocks Depth, km Number of shocks 0 - 49 50- 74 75- 99 100-124 125-149 790 181 73 94 30 400—124 425-149 450-174 475-199 500-524 6 1 4 2 4 150-174 175-199 200-224 225-249 250-274 43 18 37 11 13 525-549 550-574 575-599 600-624 625-649 2 3 6 26 6 275-299 300-324 325-349 350-374 375-399 2 6 6 9 4 650-674 675-699 700-724 725-749 750-774 11 0 1 0 0 Table I V Depth, km Total energy, 1020 ergs ' Depth, km Total energy, 1020 ergs" 0 - 49 50- 74 75- 99 100-124 125-149 3915110,9 485432.5 178412.6 254351,6 10265,5 400-424 425-149 450-474 475-499 500-524 16515,4 158,5 2488,0 268,1 1046,2 150-174 175-199 200-224 225-249 250-274 161739,9 38446.5 50046.6 23893,3 3221,0 525-549 550-574 575-599 600-024 625-649 588,2 5174,7 1807,0 17480,7 4195,9 275-299 300-324 325-349 350-374 375-399 219,2 1465.4 34469,5 6992.5 905,2 650-674 675-699 700-724 725-749 750-774 7280,5 0 109,6 0 0 T o t a l energy: 5,222085.1026 ergs. D I S T R I B U T I O N OF E N E R G Y A N D N U M B E R OF E A R T H Q U A K E S 3 8 3 10 e r g s b.) = N r i g . I - The distribution of eartliquake-energy in accordance with the focal depth, between the period 1896-19(33. all over the world, for shocks between magnitude range of 6,9-8,9 (according to the present author). a) between the depth of 0 and 175 km; b) between the depth of 125 and 750 km. 3 8 4 P . I I E D E R V A R I The Table I shows the number of the above mentioned earthquakes according to their magnitude and focal depth respectively (see on tho next pages together with its continuation, Table I I ) . The total number of shocks in the different levels may be seen in Table I I I . According to the Table I I I , we may state the fact that the number of earthquakes, regardless of their magnitude, reached a maximum between the depth of 0 and 49 km and the second greatest maximum is between 50 and 74 km under the surface of the Earth. Further maxima are between 100 and 124 km, 150 and 174 km, 200 and 224 km, 600 and 624 km and between 650 and 674 km respectively. Fig. 2 - Strain release - depth diagram of the earthquakes of the Sunda Arc for the period 1904-1953, after Ritsena. For the relation between earthquake-energy and magnitude we used the following expression: where E is the energy in ergs and M is the magnitude. Using this formule, we got for the energy-distribution according to depth, the results of Table I V . W e state the fact that the total energy of shocks as a function of depth reached a maximal height between 0 and 49 km under the surface o 1 0 o Zbo 5 o o 4 0 0 6 DO tfoo too log E = 11 + 1,6 M D I S T R I B U T I O N OF E N E R G Y A N D N U M B E R OF E A R T H Q U A K E S 3 8 5 and the second greatest maximum could be found immediately under this level, that is between the depth of 50 and 74 km. There are several other maxima, too, namely between the depth of 150-174 km and of 325-349 km respectively. The global distribution of total energy ac- cording to the focal depth can be approached by an exponential curve between 0 and about 500 km under the Earth's surface. Between 450 and 550 km we can experience a wide minimum-zone in the total energy of shocks. Throughout the deeper layers in the mantle of the Earth the total energy of shocks begin slowly to grow again. A newer, smaller maximum is to be seen about the depth of 600-675 km. This drawing reminds us to the distribution of strain release ac- cording to the depth on the territory of Sunda Arc, as Ritsema showed (Figure 1 and 2). R E F E R E N C E S ( ' ) RITSEMA A . R., The Seismicity of the Sunda Arc in Space and Time. « Indonesian Journal for Natural Science », 1-3, January-June (1954). (2) GUTENBERG B., Great Earthquakes 1S90-1903. Transactions of American Geophysical Union, 37, 5, (1956). (3) RICHTER C. F., Elementary Seismology. San Francisco, 1958. ( ' ) GUTENBERG B., RICIITER C. F., Seismicity of the Earth. Second edition. Princeton, 1954. (5) Bulletin of the Seismological Society of America. 43-52, ( 1 9 5 3 - 1 9 6 2 ) . ( 6 ) EATON J. P . , TAKASAKI K . J., Seismological Interpretation... ((Bulletin of the Seism. Soc. A m . », 49, (1959). (7) GUTENBERG B., Major and Great Earthquakes of 1957 and 1958. « Bulletin of the Seism. Soc. A m . », 49. 50, [(1959, 1960). (8) ROTIIE J. P., Les seismes du Chili. « Revue pour l'etude des calamites », 37, 1961. (') Preliminary Determinations of Epicentres, 1962 and 1963. U.S. Dept. of Commerce Coast and Geodetic Survey.