Geoscience Reference
In-Depth Information
essential differences in the physical processes controlling one or another stage. Nat-
urally, the description of all the stages is based on general principles of the me-
chanics of continuous media; however, application of complete three-dimensional
(3D) equations for describing concrete tsunamis is not only irrational, but also just
impossible at the present-day stage of development of computational technologies.
The only possible way consists in the development of an inter-related complex of
models, each of which will adequately describe a certain stage in the evolution of
the wave. Strong underwater earthquakes are the most widespread cause for the rise
of tsunami waves. Part of the energy of a seismic source is captured by the wa-
ter column and is transferred, primarily, to various wave motions. The number of
works devoted to investigation of the tsunami formation mechanism by a seismo-
tectonic source is incredibly large. Without claiming to present a full list, we shall
only mention several publications: [Takahasi (1934, 1963); Miyoshi (1954); Kajiura
(1963, 1970); Van Dorn (1964); Kanamori (1972); Hammack (1973); Abe (1978);
Levin, Soloviev (1985); Kowalik, Murty (1987); Dotsenko, Soloviev (1988); Nosov
(1999); Ohmachi et al. (2001); Yagi (2004); Okal, Synolakis (2004); Satake et al.
(1995)]. The physical processes taking place at a seismotectonic tsunami source
and at an earthquake focus represent a unique whole. Therefore, studies of tsunami
and of earthquake sources mutually complement and enrich each other. In spite of
the significant progress achieved in this direction in the past decades, both tsunami
and earthquake sources still remain 'terra incognita'.
2.1 Seismotectonic Source of a Tsunami: The Main Parameters
and Secondary Effects
2.1.1 The Main Parameters
According to modern ideas, an earthquake is the abrupt release of strain accumulated
in the Earth's crust, resulting from the relatively slow motion of lithosphere plates
[Kanamori, Brodsky (2004)]. The source of an earthquake can be represented as
a displacement that occurs owing to a fault along one or several planes. In the case
of large shallow events the rupture speed amounts to 75-95% of the velocity of
S-waves. An earthquake is characterized by the seismic moment
M
0
=
µ
DS
[N
·
m]
,
where
is the rigidity coefficient of the medium,
D
is the displacement amplitude
between the opposite edges of the fault, and
S
is the area of the fault surface.
The earthquake's magnitude is related to the seismic moment by the following
relationship:
µ
M
w
=
log
10
M
0
1
.
5
−
6
.
07
.
