Geography Reference
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and Jones (1996) noted that few data exist on the
relationship between building failure in
earthquakes and the type, severity and distribution
of injuries. If the relationship were better known,
there would be a more adequate basis for locating
survivors and knowing how to rescue and stabilise
them.
A combination of improved geophysical
methods (including the use of magnetometry and
radar surveys) and greater integrated data
processing has enabled the accuracy of epicentral
determinations to be increased (e.g. Qamar and
Meagher 1993). This in turn has given rise to
improved understanding of the distribution of
medium- to long-term seismicity around the
world, including better estimates of the return
period of earthquakes with given magnitudes or
intensities. This in turn has stimulated great
increases in the mapping and differentiation of
regional seismic hazards, which has been done at
various scales. Regional studies have encompassed,
for example, East Africa (Mäntyniemi and Kijko
1991), the Mediterranean (Ambraseys 1992), the
Middle East (Degg 1992) and the USA (Hays
1984). Studies of individual countries have been
published on, among others, Bulgaria (Orozova-
Stanishkova and Slejko 1994), France (Levret et al .
1994), Greece (Papazachos et al . 1993), Iraq (Fahmi
and Alabbasi 1989), Jordan (Yücemen 1992),
Panama (Muñoz 1989), Slovenia (Lapajne et al .
1997), Sweden (Kijko et al . 1993), Syria (Malkawi
et al . 1995) and the United Kingdom (Musson and
Winter 1997). Finally, local studies have been
made of, for instance, Mexico City (Iglesias 1989),
Puget Sound (Ihnen and Hadley 1987), the San
Francisco Bay region (Murphy and Wesnousky
1994) and Utah (Gori and Hays 1992). A global
seismic hazard assessment programme also
promotes mapping initiatives (Giardini 1992).
Hazards can be considered at a variety of scales,
and the nature of the risks thus identified may be
partly determined by the level of detail inherent
in each scale. Regional studies of seismicity are
generally considered to be a form of
macrozonation. This is invaluable as a means of
determining the coefficients needed for local
antiseismic building codes, but adequate
earthquake protection also requires there to be
more detailed studies of the performance of
geological materials, foundations and specific site
factors. This is microzonation. Seismic
microzonation was first developed for the Los
Angeles and San Francisco Bay areas (Kockelman
and Brabb 1979) and for Tarcento in the Friuli
region of Italy (Brambati et al . 1980). It responds
to a number of different exigencies. For instance,
highly seismic areas that have large deposits of
saturated sand or sensitive clay may undergo
liquefaction, a spontaneous change from solid to
liquid behaviour that usually involves loss of
foundation bearing capacity. Liquefaction
potential can be mapped in order to determine
the most susceptible locations (Kotoda et al . 1988).
Debris flows, rapid soil flows, rock falls and rock
avalanches also constitute a hazard in mountainous
areas with large, unstable deposits of clastic
material. Indeed, Kobayashi (1981) reported that
such events account for more than half of all
deaths in earthquakes of magnitude M>6.8 in
Japan, which offers a rather different picture to the
common view that building collapse is the
principal determinant of mortality in earthquakes
(Page et al . 1975). Microzonation of susceptible
areas must therefore involve hypotheses about the
behaviour of unstable rock, soil and debris masses
during seismic loading. In the most complex
situations, this may necessitate a series of maps that
show different hazard levels or effects with
different degrees of seismic acceleration of the
ground.
The methodology of volcanic hazard zonation
is well developed and has been tested for several
decades on the Cascades volcanoes of western
North America (Crandell and Mullineaux 1975).
Smith (1996: pp. 179-81) showed that 1970s maps
of Mount St Helens were generally accurate
guides to the spatial distribution of impacts of the
18 May 1980 eruption, with allowance for more
severe landslides and blast effects than had been
predicted. Complex hazard assessments have also
been devised for other volcanoes, including Etna
(Chester et al . 1985) and Vesuvius (see Box 5.1).
The former involves a recurrent lava flow hazard
that has necessitated a spatial analysis of the density
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