Some characteristics of the seismicity of the Tyrrhenian Sea Region



In the first p a r t of the paper the seismic strain release
of the T y r r h e n i a n Sea Region (including Italy), as the function of time,
is examined on the basis of t h e d a t a of the e a r t h q u a k e s t h a t took place
f r om 1901.01.01 to 1970.12.31, between the northern l a t i t u d e s of 34° and
44° and between the eastern longitudes of 8° and 18.5°, respectively. All
registered shocks with a R i c h t e r - m a g n i t u d e of 5.5 or over it were considered,
i n d e p e n d e n t l y f r om t h e focal d e p t h . Three periods were recognized in the
a c t i v i t y ; t h e lengths of which are not t h e same, however.
I n the second p a r t the elastic strain release in accordance with the
focal d e p t h of t h e same e a r t h q u a k e s is t r e a t e d briefly. It was found t h at
t h e t o t a l strain-release had a maximum value in t h e depth between 0 and
74 kms and there was a minimum between the depth of 300 and 524 kins
with an interval between 375 and 449 kms within which no earthquakes
occurred at all. The general p a t t e r n of the d i s t r i b u t i o n of seismicity as
t h e f u n c t i o n of hypocentral d e p t h reminds to the well-known picture, one
can experience in other regions where i n t e r m e d i a t e and deep shocks occur.
This s t a t e m e n t is consistent w i t h t h e idea, according to which t h e seismicity
of t h e Tyrrhenian Sea Region can be discussed and explained in t h e light
of t h e theory of new global tectonics.
F i n a l l y , in the t h i r d p a r t of the study, the authors have s t a t e d t h at
in some cases multiple events occurred b e n e a t h t h e Tyrrhenian Sea Region.
Such multiple seismic events were detected in the case of other areas, such
as the Fiji-Tonga-Kermadec Region, the seismic belt of South America
etc., — but, according to the knowledge of t h e authors, this is t h e first occasion
when multiple seismic events are demonstrated in the Tyrrhenian
Sea Region.

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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X