Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

Fig. 3: Relationships among magnitude assessments of different
kinds for palaeoerathquakes: ML (dots), Ma (stars) and Mf
(crosses). Blank stars are for magnitudes, which do not follow the
correlation relationship. See text for details.
THE MUYA, 1957, EARTHQUAKE
The Muya, 1957 (M=7.6) earthquake is the largest
instrumentally recorded seismic event in the region. A
complex set of surface ruptures was associated with it.
They were studied and reported by the special expedition
of Solonenko et al. (1966). We can use detailed
information on this earthquake to understand if there are
some specific regional conditions, which cause the
unusual relationships between PSS length and the offset.
Finding of this cause is the goal of the paper.
Location of the Muya earthquake and seismic source
mechanisms in the region according to (Global Centroid
Moment Tensor Catalog, 2009) are shown in Fig. 4. There
are no focal mechanism solutions reported immediately
in the epicentral area of the Muya earthquake but in its
vicinities normal faulting were observed; to the east
strike‐slip faulting dominates.
Fig. 4: Epicentre of the Muya, 1957, earthquake and source
mechanisms in the Baikal region according to (Global Moment
Tensor Catalog, 2009). Mechanisms for seismic events with
Mo10 24 dyncm (Mw5.3) are plotted.
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
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Materials of field studies clearly show that complex set of
surface faulting can be grouped in three main segments:
western, central, and eastern, with different parameters
of faulting (Fig. 5a, b). The segments compose en echelon
system WNW trending. In the western segment surface
faulting outlines small graben (3 km length and 1.3 km
width). The southern boundary of the graben is controlled
by a normal fault with right‐lateral slip component.
Horizontal slip is 1.05 m and vertical offset is between 1.2
– 1.3 m (Solonenko et al., 1966). Left‐lateral slip (0.3 m)
accompanied with some normal faulting was observed
close to the northern boundary (Kurushin, 1963). In the
central part of the graben 8 meter wide through was
reported (Solonenko, 1965).
A transition zone of NW trending links Western and
Central segments. It is composed from two brunches.
Northern brunch striking WNW is a normal fault (1.4 m
offset) with left‐lateral slip component (0.25 m)
(Kurushin, 1963). Southern brunch is a pressure zone of
NNW trending. It is most probably associated with
thrusting; the amplitude of the vertical offset is either 2.4
m (Kurushin, 1963) or 4 m (Solonenko, 1965).
Fig. 5: Geological manifestations, instrumental epicenter, and
mechanism of the Muya earthquake. a) surface faulting;
epicenter locations (1) by Vvedenskaya, Balakina, 1960, (2) by
Balakina et al., 1972; Sub1, Sub2, Sub3 are mechanisms of sub‐
events. Arrows show slip direction. Question mark is for doubtful
part of the surface faulting. b) generalized scheme of the surface
faulting.