Detailed surface maps from satellite studies allowed them to infer which parts of the ground moved where.
They report in Nature Geoscience that those shifts correlate with locations where water has been drained for years.
The study highlights how human activity such as drainage or borehole drilling can have far-reaching seismic effects.
Pablo Gonzalez of the University of Western Ontario and
colleagues used satellite radar data to trace the ground movements of
the Lorca event back to their source, finding that the earthquake
resulted from slippage on a comparatively shallow fault that borders a
large water basin south of the city.
That the slippage happened at a depth of just 3km explains
why the fairly mild Magnitude 5.1 quake caused so much damage in the
area.
The team went on to study potential reasons for the slippage,
finding that the water table in the adjacent Alto Guadalentin basin had
dropped by some 250m over the last 50 years as water was drained for
irrigation in the region.
Their calculations show that this created stresses on the
fault that initially triggered the earthquake and defined its eventual
magnitude.
Geoengineering dreams
However, the area lies on a seismically active region, and the
data suggest only that the water drainage sped up and eventually
triggered a process that would have eventually happened anyway.
Dr Gonzalez stressed the study was specific to the Lorca
earthquake, telling the Reuters news agency that "we cannot set up a
rule just by studying a single particular case".
"But the evidence that we have collected in this study could
be necessary to expand research in other future events that occur
near... dams, aquifers and melting glaciers, where you have tectonic
faults close to these sources."
In an accompanying Nature Geoscience article,
Jean-Philippe Avouac of the California Institute of Technology said:
"It does not take much to trigger an earthquake - even strong rainfall
can do the job".
Continue reading the main story
“We should remain cautious of human-induced stress perturbations, in particular those related to carbon dioxide sequestration projects”
~Jean-Philippe Avouac California Institute of Technology ~
"Numerous examples of seismicity
triggered by the impoundment of reservoir lakes, hydrocarbon
extraction, quarrying and deep well injections have been documented over
the years."
Previous research has suggested that the fluid injection
associated with the controversial practice of gas extraction by
hydraulic fracturing or "fracking" was linked to specific earthquake events.
If science can pin down exactly how stresses from
anthropogenic sources distribute and contribute to seismic events, Prof
Avouac suggested, "we might dream of one day being able to tame natural
faults with geoengineering".
"For now, we should remain cautious of human-induced stress
perturbations, in particular those related to carbon dioxide
sequestration projects that might affect very large volumes of [the
Earth's] crust."
Source: bbc.co.uk (image from bbc.co.uk), link
Source: bbc.co.uk (image from bbc.co.uk), link
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