In terms of the geological record, microorganisms such
as foraminifera play an important role since these indicator
species are readily preserved, providing evidence of prehistoric earthquake changes. Estuarine foraminifera are
sensitive to salinity and tidal exposure (Hayward et al.,
1999a). Specific taxa indicate salt marsh environments
and have been used to track gradual Holocene sea-level
changes (Hayward et al., 1999b; Gehrels, 2000). They
can also record sudden changes such as earthquakeinduced bed level changes and, along with diatoms and
other microorganisms, have been sampled from estuarine
cores to determine the recurrence intervals of seismic
events (Cochran et al., 2007; Hayward et al., 2010). Analysis of floral and faunal data collected from cores, combined with sediment dating, can indicate both the scale
and recurrence intervals of seismic changes in estuary
beds. This provides vital background information for
planning development around estuaries since building
foundations and lifeline networks above- and belowground, including roads, bridges, water, gas, and sewerage
systems, are very vulnerable to earthquake-induced soft
sediment disturbances. Catastrophic lifeline network failures that have resulted from the disturbance of soft sediments around coastal and estuarine margins include the
destructive effects of the 1886 M L Charleston earthquake,
the 2011 Tōhoku earthquake, and the 2010–2012 Canterbury, New Zealand, earthquake sequence.
Soft sediment disturbances can also provide
a geological record of seismic events in estuaries. During
the 2010–2012 Canterbury, New Zealand, earthquake
sequence, each seismic event that exceeded 5.2 M w produced extensive sand volcanoes (Reid et al., 2012;
Quigley et al., 2013). At the surface, the sand volcanoes
were quickly modified by tide and winds, resulting in
broad sandy hummocks, whereas in the subsurface, small
but distinctive pipes were produced that remain preserved
despite the surface reworking of the estuary bed (Reid
et al., 2012). The preserved pipe structures of sand volcanoes may be associated with other types of soft sediment
folding and distortion (see Montenat et al., 2007).
Seismic events, either in nearby coastal regions or far
field, may also produce tsunami depending on the earthquake magnitude and the geometry of fault rupture and
seafloor change. Tsunami may be recorded as distinct
horizons within estuarine sediments, with signature
marine micro- and macrobiota and outsized clasts
transported by the tsunami and left relict and unable to
be remobilized by estuarine hydrodynamics. The ongoing
influence of the influx of marine water can include elevated salinity levels and the physical removal of surface
plants and organisms.
Summary
There is no dispute that earthquakes and their associated
tsunamis and mass movements affect estuarine ecosystems. The effects are often dramatic. While some
habitats are lost, new habitats may be made available.
The recovery of estuarine communities following an
extreme earthquake disturbance will generally follow a
successional sequence according to the physical and
chemical conditions in the environment, the local hydrodynamic conditions, and the availability of potential
recruits.
Earthquakes and their associated tsunami and mass
movements are natural events, and when human environment interactions are minor, recovery of most estuarine
systems is predicted to occur within 4–10 years (Borja
et al., 2010), probably more quickly than in the slowergrowing habitats of tropical reefs (Phongsuwan and
Brown, 2007). This was the case, for example, for the
estuarine habitats affected by the 1964 Alaskan earthquake and tsunami and for the 1960 Chilean events
(Reinhardt et al., 2010). It is, however, not the case for
the earthquake, tsunami, and subsequent nuclear disaster
that occurred along the Tōhoku coast of eastern Japan in
2011, including some of the most heavily modified and
populated coastal landscapes of the early twenty-first century (Gomez et al., 2012). Given current global trends
toward the coastal concentration of human populations,
industry and infrastructure including seawalls and nuclear
power plants, and the associated modification of catchments, and coastal plains and margins, the effects on estuaries of earthquakes and their associated natural and
human-induced events are likely to be more pronounced
and endure within the landscape for decades to centuries
(Hart, 2011).
Some scientists suggest that recovery from natural disturbances will be faster than those caused by anthropogenic changes. Determining the time scale of recovery
from earthquake disturbances continues to be
a challenge, with reported estimates varying from days
for some species to years and decades and periods up to
25 years. Long-term studies have been unable to quantify
this. Moreover, the challenge is likely to grow as earthquake, tsunami, and mass movement events interact with
increasingly human modifications to coastal and linked
environments worldwide over the twenty-first century,
mixing the natural and human-produced effects of these
events. It is clear, however, that from the evolution of estuarine habitats, the new restored habitat may be different
from that originally damaged by earthquake activity.
One important feature of this is whether this is a natural
result or one produced by human activity restricting the
ability of an estuary to recover. Nevertheless it would be
expected that the mosaic of communities formed after
the disturbance would maintain species diversity.
Bibliography
Alongi, D. M., 2008. Mangrove forests: resilience, protection from
tsunamis, and responses to global climate change. Estuarine,
Coastal and Shelf Science, 76, 1–13.
Baxter, R. E., 1971. Earthquake effects on clams of Prince William
Sound. In NRC (ed.), The Great Alaska Earthquake of 1964.
Committee on the Alaska Earthquake, National Research Council. Washington, DC: National Academy Press, pp. 238–245.
212
EARTHQUAKE DISTURBANCES
as foraminifera play an important role since these indicator
species are readily preserved, providing evidence of prehistoric earthquake changes. Estuarine foraminifera are
sensitive to salinity and tidal exposure (Hayward et al.,
1999a). Specific taxa indicate salt marsh environments
and have been used to track gradual Holocene sea-level
changes (Hayward et al., 1999b; Gehrels, 2000). They
can also record sudden changes such as earthquakeinduced bed level changes and, along with diatoms and
other microorganisms, have been sampled from estuarine
cores to determine the recurrence intervals of seismic
events (Cochran et al., 2007; Hayward et al., 2010). Analysis of floral and faunal data collected from cores, combined with sediment dating, can indicate both the scale
and recurrence intervals of seismic changes in estuary
beds. This provides vital background information for
planning development around estuaries since building
foundations and lifeline networks above- and belowground, including roads, bridges, water, gas, and sewerage
systems, are very vulnerable to earthquake-induced soft
sediment disturbances. Catastrophic lifeline network failures that have resulted from the disturbance of soft sediments around coastal and estuarine margins include the
destructive effects of the 1886 M L Charleston earthquake,
the 2011 Tōhoku earthquake, and the 2010–2012 Canterbury, New Zealand, earthquake sequence.
Soft sediment disturbances can also provide
a geological record of seismic events in estuaries. During
the 2010–2012 Canterbury, New Zealand, earthquake
sequence, each seismic event that exceeded 5.2 M w produced extensive sand volcanoes (Reid et al., 2012;
Quigley et al., 2013). At the surface, the sand volcanoes
were quickly modified by tide and winds, resulting in
broad sandy hummocks, whereas in the subsurface, small
but distinctive pipes were produced that remain preserved
despite the surface reworking of the estuary bed (Reid
et al., 2012). The preserved pipe structures of sand volcanoes may be associated with other types of soft sediment
folding and distortion (see Montenat et al., 2007).
Seismic events, either in nearby coastal regions or far
field, may also produce tsunami depending on the earthquake magnitude and the geometry of fault rupture and
seafloor change. Tsunami may be recorded as distinct
horizons within estuarine sediments, with signature
marine micro- and macrobiota and outsized clasts
transported by the tsunami and left relict and unable to
be remobilized by estuarine hydrodynamics. The ongoing
influence of the influx of marine water can include elevated salinity levels and the physical removal of surface
plants and organisms.
Summary
There is no dispute that earthquakes and their associated
tsunamis and mass movements affect estuarine ecosystems. The effects are often dramatic. While some
habitats are lost, new habitats may be made available.
The recovery of estuarine communities following an
extreme earthquake disturbance will generally follow a
successional sequence according to the physical and
chemical conditions in the environment, the local hydrodynamic conditions, and the availability of potential
recruits.
Earthquakes and their associated tsunami and mass
movements are natural events, and when human environment interactions are minor, recovery of most estuarine
systems is predicted to occur within 4–10 years (Borja
et al., 2010), probably more quickly than in the slowergrowing habitats of tropical reefs (Phongsuwan and
Brown, 2007). This was the case, for example, for the
estuarine habitats affected by the 1964 Alaskan earthquake and tsunami and for the 1960 Chilean events
(Reinhardt et al., 2010). It is, however, not the case for
the earthquake, tsunami, and subsequent nuclear disaster
that occurred along the Tōhoku coast of eastern Japan in
2011, including some of the most heavily modified and
populated coastal landscapes of the early twenty-first century (Gomez et al., 2012). Given current global trends
toward the coastal concentration of human populations,
industry and infrastructure including seawalls and nuclear
power plants, and the associated modification of catchments, and coastal plains and margins, the effects on estuaries of earthquakes and their associated natural and
human-induced events are likely to be more pronounced
and endure within the landscape for decades to centuries
(Hart, 2011).
Some scientists suggest that recovery from natural disturbances will be faster than those caused by anthropogenic changes. Determining the time scale of recovery
from earthquake disturbances continues to be
a challenge, with reported estimates varying from days
for some species to years and decades and periods up to
25 years. Long-term studies have been unable to quantify
this. Moreover, the challenge is likely to grow as earthquake, tsunami, and mass movement events interact with
increasingly human modifications to coastal and linked
environments worldwide over the twenty-first century,
mixing the natural and human-produced effects of these
events. It is clear, however, that from the evolution of estuarine habitats, the new restored habitat may be different
from that originally damaged by earthquake activity.
One important feature of this is whether this is a natural
result or one produced by human activity restricting the
ability of an estuary to recover. Nevertheless it would be
expected that the mosaic of communities formed after
the disturbance would maintain species diversity.
Bibliography
Alongi, D. M., 2008. Mangrove forests: resilience, protection from
tsunamis, and responses to global climate change. Estuarine,
Coastal and Shelf Science, 76, 1–13.
Baxter, R. E., 1971. Earthquake effects on clams of Prince William
Sound. In NRC (ed.), The Great Alaska Earthquake of 1964.
Committee on the Alaska Earthquake, National Research Council. Washington, DC: National Academy Press, pp. 238–245.
212
EARTHQUAKE DISTURBANCES