COMPLEX GEOLOGICO-GEOPHYSICAL INVESTIGATIONS OF THE CRUSTAL STRUCTURE IN THE ZONE OF TRANSITION BETWEEN THE ASIATIC CONTINENT AND THE PACIFIC OCEAN

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CIA-RDP80T00246A004400140002-6
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RIFPUB
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K
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5
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December 21, 2016
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January 15, 2009
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2
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REPORT
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Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6 VaVeFEDINSLIs ? COMPLEX GEOLOGICO-G.J.PHYSICAL INVEc.TIGATIJNS OP THE CRUSTAL ST;,,UCTUIRE IN THE Z,.,NE ? TRANSITION BETWEEN THE ASIATIC 1. Thu striking difference in the crustal structure under - as well as continents and oceans - in made the investigation of the transition zone between them of great importance. The USSR nrogram for the IGY includes the ? ? the ? ? ? ? transition. The Kurile-K,,mchatka zone of transition between continent and the P,,cific ocean is one of the geologico-geophysically most interesting ? regions of the ?, we have the Kurile island are includes which is bordered froin south-east by the deep Kurile trough. also the ?belt of the strongest in the USSR seism- ic ? - of earthquakes arising at depths ranging from the smallest down to 600 km. In this region of the USSR volcanism is also most strongly developed. The natural geophysical fields ? and magnetic) in this zone show sharply pronounced anomalies. ? ? ? ingular feature ? the work of the P:cific expedition is the use of a wide complex of methods of investigation as well as comparatively ? -? ??- ? (for regional work), The ? s s t carried ? by seismic, gravimet- ric and ? methods. Seismic shootin7, measurements were combined with observ- ations of weak local earthquakes. At sea acoustic and hydro- determinations added. G..,ophysical investigations of the crustal structure are comDlemented by geologic observationr and laboratory ? ? samples ? rocks. The region undor Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6 Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6 OYhotsk sea with its north-west c6asts _nve2tigation includes the the island of S--khalint the ? the Komandor and Ku ile islands and the adjacent parts of the Pacific ocean including the Kurile trough and also the south-west part of the B,aring sea. Tine . for two seasonse se Si~ismic obser- vations method . 1 Seismic were carried out by the Sounding (DSS). The main features of this work are: 1) The use ? mobile shooting points stationary recording points, combination 2) A of sea and land observations. 1957 two ! profiles crossing were made part of - Okhotsk - running from S,-,khalin to the islands of Iturup and Urup nnd three profiles crossin-7 the Kurile trough ? from the islands of Iturupt ocean Urup and Simushir and extend into the about In the region of the island of Iturup an area survey was alio carried out consistinz of a fan-shaped system Of profiles made from sea and . observations. 700 rhots were fired and profiles general about ? ? x., were made. Along each profile systerns ? -? reversed ond overtaking distance-time curver were obtained. F-,,om the DSS records waves were picked out corresponding to the 11-rranitic"o ? subcrustal layers. ! ? ? i on the ? location of tho profiles, three types of distance-time for these waves differing in the absolute arriv,il time's ? out: the Pacificithe ? - sea ? ? ieland- types (the last for S~khalin and the Kurile islands). ? n s. Along the lines of the ! profiles gravimetric observations were also carried out ? ? special gravimeters with hi.'Thly damped S. ? ?: ships on three gravi- materF and correlated with the ? obser- vf-ttions. were ? ? ? above ?? and then sharply increases above the Kurile trough reachin--, qt the ? of the deep-water plateau a value of ??? Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6 Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6 These were carried out as 5. M$aZU112M? an aeromagnetic area survey. The survey was made by means of hydroplane flying a ? ??? above the sea level. ? i these observations a diagram anomalies was drawn. Above Okhotsk between S juth Sakhalin and South Kurile islands9 the magnetic field is little disturbed and mainly positives Above the Kurile are, against a background ? negative values local poeitive appear. ? ? of the Kurile anomalies. deep- water ridge there is a zone of large positive ? is reached, abrupt change the a magnetic field takes ? ? onomilies north-eastern ? runs ? ? 3 ? ? 3 ? n so . to investigate the weak local earthquakes of the Kurile i~-lands, a net of 5 provizi.-n,l regional seismic stations of hi-,,,h%.r sensitivity 3 ? by the expedition island ? Iturup, where the 1 detailed obtained. equipped with ? of the VEGIK . r a natural ? ? . ? see. The magnification of the apparatus ? 16000. believed thl--t -i joint treatment ? and the . ? earthquakes should Five _i mort ? ? picture of the crustal structure. The ob- st.rvations of earthquakes will also enable us to investigate the the connection ? ? opace as well as butwec;n the island regicn and the deep crustal seismicity etructure, volcanism and tectonics. ? ? ? Geologic wDrk ? throw upon ? structural conditi-.,ns in th,.; ' investigation, the history of its tectonic and, in particular, upon its ? to date hic-toryp ? ? ? drawn which will enable us to cl:~rify the history of the vibrational movements of parts of the land -~idj!icent to the ocean and deccribe more accurately the Okhotsk and ~istory of firmjn~; the depressions of the Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6 Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6 as Tell as of the adjacent portions of the Pneific ocean. Diagrams are being drawn of the present crustal structure in the region under investigation and an attempt is being made to establish connection between and present day movements ? ? - hnnd and seismicity on the other. The treatment Ct the ? a obtained by the expedition is not yet finished nnd only ? results can be communicated. Preliminary date ? the structure crustal the direc- tion S.S-,akhalin- : islands - the ocean. The crustal structure in the region investigated by the expedition in 1957 can ? : described ? ? w 1) The thickness of the crust increases ? under the Kurile islands and the adjacent shallow p a r t s of the Okhotsk - and Pacific ocean. The crust here is close in structure to thet of the continental type and consists of three layers: the sedimentary, granitic and ? basnltic.2) In the e a s t e r n part ? the western slope of the Kurile ? wedging ? of the granitic place. Further into the ocean the crust consists only of n basrltic layer thinly covered by sediments. In the ocenn the thickness of the crust, including the column of rater, is of the order of struc- 12-17 ?km. 3) In the Okhotsk sea there ? ture between profiles and VI. ? the southern profile (I) we have a continental ? a maximum thickness nbout 28 km consisting of three layers, - : along northern profile thinner-maximum (IV) the crust is thickness 5I ?m and contains no distinct granitic layer. The ? ? z? results are in ??? qualitative agreement data. The . ? ' ? data show that the crustal structure in the trnnsitizn zone is extremely complicated. 7le have here in fact three types of crust: a properly continentel crust observed under the islands and adjacent shallow parts of the sea ? ? ocenn; a ocennic crust which Is typical ? the ocean bed and a intermediate characteristic for the southern deep-rater part of the Okhotsk see. Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6 Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6 In 1958 the volume of work of the expedition by all above mentioned methods is almost doubled, At the present time sea and land observations are being carried out by the expedition. Approved For Release 2009/01/15: CIA-RDP80T00246AO04400140002-6