INTRO | HIGHLIGHTS | FEATURES | FOCUS | PERSPECTIVES | BIOS
From
Around
the
World
Detecting landslides
with earthquake
monitoring networks
Large, fast landslides, especially
those formed from hard rock,
generate earthquake waves that
can be recorded remotely. This
provides the potential to detect
remotely large landslides as
they occur and to determine
parameters such as the speed of
movement.
A recent study published in the
Journal of Geophysical Research
investigated these seismic
signals, focusing on whether
properties of a landslide, such
as volume, can be derived from
the seismic signals recorded
remotely. To do this, 20 known
rockslides from the Alps were
compiled, and the data recorded
in the regional seismic network
was analysed for each event.
The research demonstrates
that these events are indeed
detectable and that they tend
to have a characteristic set of
waveforms – a landslide ‘finger
print’ – that allows them to
be distinguished from other
events that generate seismic
signals. The research shows that
scientists are one step closer
to remote monitoring of large
landslide events, especially
those in high mountain areas,
which may allow both a better
understanding of the frequency
of these large landslides, and the
hazards themselves in
real time.
Dammeier, F., Moore, J.,
Haslinger, F., & Loew, S.
(2011). Characterization
of alpine rockslides using
statistical analysis of seismic
signals. Journal of Geophysical
Research, 116 (F4) DOI:
10.1029/2011JF002037
New model for understanding
rock fall behaviour
No increase in global
risk for big earthquakes
Rockfalls kill hundreds of people per year worldwide, and they cause
severe economic disruption along railway lines and roads. During the
winter of 2011-12 in Scotland, a series of rockfalls on the A890 between
Lochcarron and Kyle led to its closure for over two months causing long
detours (in some cases over 200 km) and serious economic disruption to
local communities. Over the last decade, there have been many studies
that have tried to relate rates of rockfall activity to environmental drivers
such as rainfall, frost and strong winds. Perhaps surprisingly, these studies
have shown poor correlations between these environmental drivers and the
rockfalls themselves. Recent research published in Earth Surface Processes
and Landforms provides a spectacular set of laser scan datasets to look at
the evolution of rockslope failure in Yosemite National Park. In particular,
it showed that 14 rockfalls in late 2010 occurred in a sequence and
suggests that it was caused by stress redistributions associated with each
rockfall event. Researchers have developed a mechanical model to explain
this process. Whilst it has long been suggested that the development of
cracks might be the controlling process for rockfalls, (explaining why they
do not respond to environmental drivers) this study is the first to propose
a direct mechanical model for explaining how these events occur.
Despite the large magnitude earthquakes that have occurred in Japan,
New Zealand, Sumatra, Chile and other parts of the world, the global risk
of big earthquakes is no higher today than in the past, according to a study
published in PNAS. Researchers examined the timing of large earthquakes
with a magnitude of 7 or higher from 1900 to present, after removing local
clustering related to aftershocks, in order to identify any anomalies when
comparing present and past earthquake records. While the global rate of
earthquakes 8 or higher in magnitude is at a record high since 2004, rates
have been nearly as high in the past, and the rate of smaller quakes is close
to the historical average. Any global rate changes in earthquake risk would
require the existence of actual physical mechanisms that could cause such
changes in the first place. While it is possible for large earthquakes to trigger
other earthquakes, this process increases the earthquake risk regionally,
not globally. The s