Earthquakes - Extreme Events: A Physical Reconstruction and Risk Assessment - page 149

detect imminent earthquakes, but there appears to be little doubt that they
are capable of this phenomenon (Robinson, 1993). Catfish for example were
reported to jump agitatedly and could easily be caught immediately prior to
the1923 Tokyo earthquake. Panicked behaviour in rats is an official indication
of an impending earthquake in China. Bryant (2005)provides more detailed
descriptions of this interesting phenomenon.
palaeoearthquakes
Earthquakes cause substantial, localised, changes to the form of the
Earth's surface and near surface. This occurs as:
sediment deformation (warping, microfaulting);
deposition of various sedimentary units;
formation and destruction of landforms; and
deformation and destruction of human built features.
These events can also be recorded in tree rings and speleothems. Analysis of Qua-
ternary sediments and landforms is the most common form of reconstructing
ancient earthquakes.
There are several ways in which an earthquake may affect sedimentation and
ground properties. These include:
rockslides, landslides, mudslides;
deposits falling from steep slopes and distant rolling of blocks and
debris along slopes;
formation of scarps, flexures, ravines and cracks;
displacement of sedimentary and rock layers and bodies vertically and
horizontally;
warping and non-uniform settling or shaking in soils;
cracking of hard or loose sediments;
ejection of loose detrital materials forming local hollows and heaps;
watersaturation and liquefaction flow in soil, mostly clayey and sandy
ones; and
formation of channels and cones of sand eruption (sand blows).
Notall of these features are necessarily unequivocal evidence of a past earth-
quake for other events such as extreme meteorological and climatic changes, as
well as human activities, can result in similar sediment and landscape features.
When these other factors can be eliminated as a potential cause, these features
are useful in locating areas affected by palaeoseismicity.