Possible Cosmic Influences on the 1966 Tashkent Earthquake and its Largest Aftershocks

Transcription

1 Geophys. J. R. mtr. Sac. (1974) 38, Possible Cosmic Influences on the 1966 Tashkent Earthquake and its Largest Aftershocks G. P. Tamrazyan (Received 1971 August 13)* Summary I present evidence to support the hypothesis that the Tashkent earthquake of 1966 April 25 and the largest (intensity V or greater) earthquakes in its aftershock sequence tended to occur under similar 'cosmic' conditions, namely, the relative position and orientation of the Sun, Moon and Earth. Introduction In general it is knon that basic regularities or periodicities in the occurrence of earthquakes are related to various phenomena and processes in complicated ays (Tamrazyan 1968). It is suspected that there is some pattern in the spatial and temporal distribution of earthquakes of a given magnitude. For example, there is a distinct correlation beteen the orldide occurrence of large earthquakes (magnitude 8.4 to 8.9) and some process related to the rotation of the Earth, as shon by the time variation of the 'V numbers' (the product of the absolute value of the first difference of the polar co-ordinates and the first difference of the Wolf numbers, averaged over intervals of one-tenth year (Tamrazyan 1968). For earthquakes of slightly loer magnitude (7.9 to 8.3) this correlation is not present, although correlation exists ith other forces such as the tidal forces hich also influence the larger earthquakes. In this paper e sho that there may be additional influences hich depend on the relative position of the Earth, Moon and Sun. Fig. I (from Tamrazyan 1968) shos the number and energy release of all orldide earthquakes (M 2 7-9) from 1903 to 1956 as a function of the orientation of the Earth ith respect to the Sun, i.e. the spatial orientation of the Greenich meridian. There is a clear pattern in the intradiurnal distribution of these large earthquakes, namely, to maxima and to minima occur. During the 6hr of maximum seismic activity (0000 to 0300 and 1500 to 1800 GMT), the average rate of energy release is approximately 1-74 x lo2' erg hr-', hich exceeds the average rate of energy release during the 4 hr of minimum seismic activity (4 x erg hr-' in the period 0700 to 1100 GMT) by a factor of four. This strongly suggests a regular and periodic variation in the rate of release of global seismic energy, hich in turn implies a similar variation in the stress state of the Earth's crust. In this paper e discuss the correlation beteen different measures of the relative position and orientation of the Earth, Moon and Sun, and the aftershock sequence folloing the earthquake of 1966 April 25 (the epicentre of this earthquake as actually ithin the city of Tashkent: see event data in Table 1). Within a 5-month * Received in original form 1968 March 7 423

2 424 G. P. Tamrazyan 4 1: x) T FIG. 1. The intradiurnal distribution of the largest earthquakes (M < 7.9) orldide, as a function of Greenich mean time. ( ; see Tamrazyan 1968). Top, histogram of the number of earthquakes during each hour. Bottom, energy release in units of loz3 erg. The curved line and shaded area shos a running average over a 3-hr time interval. period folloing the main shock there ere numerous aftershocks, including 15 earthquakes hose intensity at Tashkent as V or more. These 15 largest aftershocks released slightly more than 98 5 per cent of the total energy of Tashkent earthquakes in the entire year 1966, the 40 aftershocks of intensity IV or V accounting for 1 * 5 per cent of the remainder. Moreover, only one earthquake of intensity V or greater occurred in the entire year (see belo). The main shock of 1966 April 25, and its aftershock sequence thus totally dominate the seismicity of the region. Date: Origin time: Latitude: Longitude: Depth of focus: Magnitude: Apparent surface faulting: Table 1 Focal data on the Tashkent earthquake Depth to bedrock at the epicentre: 1966 April GMT North East 8 km North-est to southeast, ith the northeastern block uplifted 2.5 km

3 Tashkent earthquake, S FIG. 2. Top, relation beteen the main shock (and the largest aftershocks) and the day of the synodic month, starting from the ne moon. Bottom, relation beteen the main shock (and the largest aftershocks) the day of the sidereal month, starting ith the time of the Moon s passing through the perigee of its orbit. Symbols: One, denotes the main shock, 1966 April 25; To, denotes aftershocks of intensity VI-VII at Tashkent; Three, denotes aftershocks of intensity V-VI at Tashkent. Results and Discussion The aftershock sequence e consider here occurred in a period of about three months after the main shock, beteen April 25 and August 15. During this period the largest interval beteen aftershocks of intensity V or greater at Tashkent as less than 1 month. We therefore exclude from consideration the only other earthquake of

4 Table 2 Event data for the Tashkent earthquake of 1966 April 25 and its largest aftershocks Date Origin time (1966) (GMT) No. (day) (month) (hr) (min) 1 25 April 2 07 May 3 09 May 4 09 May 5 09 May 6 22 May 7 24 May 8 25 May 9 04 June June June July July July August Magnitude (MI Intensity (1) VII V-VI V-VI VI VI- VIII Local solar Lunar time after Local lunart Age* Age? declination midnight (day) (day) (deg) (mid Q (mi "45' '54' "23' '20' " $26'33' "56' "14' "36' "Ol' " 19' '28' "12' "02' "03' time (hr) Synodic age of the earthquake. f Reduced anomalistic age of the earthquake. $ Measured from lunar upper culmination on local meridian. 4, 'd

5 Tashkent earthquake, t I I I I I I I l l I i I I I I I I I N V VI VI I Vlil FIG. 3. Relation beteen the main shock together ith the largest aftershocks (intensity V or greater at Tashkent) and the apparent declination of the Moon. The vertical scale is apparent declination in degrees; horizontal scale is calendar time (IV = April, V = May, etc.). Symbols: Annulus denotes the main shock: large circles denote aftershocks of intensity V1 to MI at Tashkent: small circles denote aftershocks of intensity V to VI at Tashkent. intensity V or greater at Tashkent hich occurred in 1966-that of 1966 October 13- since it appeared to be clearly separate in time from the others. Data on the aftershocks is given in Table 2. Fig. 2 at the top shos the relation beteen the aftershocks and the phase of the Moon. Most of the earthquakes took place ithin to opposite quadrants, the nemoon quarter and the full-moon quarter. The main shock and six out of seven aftershocks of intensity VI or greater all lie ithin these quadrants. This correlation definitely suggests the possibility of a physical influence of the Moon's position on the seismic activity ithin the Earth's crust beneath Tashkent. There is also a correlation beteen the aftershock occurrences and the orbital position of the Moon. The bottom part of Fig. 2 shos the distribution of aftershocks by day of the sidereal month, i.e. days after the passage of the Moon through the perigee of its orbit. All the 15 largest aftershocks fall in to opposite quadrants. This strongly suggests that there may be extraterrestrial influences on the aftershock occurrences in addition to the Moon. This possibility is very markedly supported by a plot of aftershock activity vs the apparent declination of the Moon (Fig. 3). Not only all the aftershocks but the main shock itself occurred hen the Moon's apparent declination as near its extrema: for the main shock and 11 of the 15 aftershocks, ithin three degrees from the extrema of 27", and in no case less than eight degrees from the extrema. The regularity of these occurrences is most striking. Fig. 4 shos aftershock activity plotted vs local solar time beginning at midnight. There seems to be strong correlation beteen aftershock activity and the position of the Sun ith respect to the local meridian io FIG. 4. Intradiurnal relation beteen the main shock (and the largest aftershocks) and local solar time, beginning at midnight. Each bar denotes an individual event.

6 428 G. P. Tamrazyan ~ FIG. 5. Distribution of the main shock and the largest aftershocks as a joint function of the apparent lunar declination and the reduced lunar time. Horizontal scale is the absolute value of apparent lunar declination in degrees; vertical scale is reduced lunar time measured from the Moon s upper transit through the local meridian. The shaded section contains shocks hich account for 99 per cent of the seismic energy release in the Tashkent region during Fig. 5 shos the distribution of aftershocks as a joint function of lunar apparent declination and reduced lunar time. From the standpoint of uniformity it is convenient to use the reduced lunar day conjugated in duration ith the solar day instead of the lunar day ith a duration of 24 hr 50 min. We find here also a regularity to the pattern, ith the earthquakes being largely concentrated ithin about one-fifth of the total area of the diagram. The frequency of occurrence of aftershocks ithin this region of the diagram is 16 times the frequency of occurrence in the remaining four-jiflhs of the diagram, and more than 99 per cent of the energy release during 1966 in Tashkent is accounted for by the events falling ithin this region. It should be noted that the numerous smaller aftershocks (M = 4.0 to 5.0) sho no correlation ith any of these variables ith hich the stronger events are so notably correlated. Hoever, the seismic energy release of the area is almost entirely determined by the larger events. Conclusions It ould appear, then, that the Tashkent earthquake of 1966 April 25 and its strongest aftershocks are related in some ay to cosmic conditions involving at least the relative position and orientation of the Sun, Moon and Earth. It ill be most

7 Tashkent earthquake, interesting to determine hether similar correlations exist for earthquakes in other areas of the Earth. Institute of Geology, Academy of Sciences of the Azerbaydzhan SSR, P.O. Box 189, Baku-Centre, USSR References Anon., Communications of the Central Seismic Station, Tashkent. Tamrazyan, G. P., Origin time of earthquakes in the Kurile-adjoint-to- Kamchatka region, and local lunar and solar time, J. Phys. Earth, 14, 41. Tamrazyan, G. P., Principal regularities in the distribution of major earthquakes relative to solar tides, lunar tides, and other cosmic forces, Int. J. Solar System, 9, 574. Ulomov, V. I., Zakharov, A. L. & Ulomova, N. V., 1967: The Tashkent earthquake of 1966 April 26, and its repeated shocks, Dok. Akad. Nauk USSR, 177,567.