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

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80T00246A004400140002-6
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 5
• Document Creation Date: December 21, 2016
• Document Release Date: January 15, 2009
• Sequence Number: 2
• Content Type: REPORT

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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
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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
???
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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
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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.
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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.
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