Abstract
In 2003 hydraulic stimulations were carried out in a geothermal field
in eastern El Salvador, Central America, as part of a project to
explore the feasibility of commercial hot fractured rock energy generation.
A key requisite for this environmentally friendly energy source is
that the fracturing of the hot rocks at depths of 1-2 km must not
produce levels of ground shaking at the surface that would present
a serious disturbance or threat to the local population. Thresholds
of tolerable ground motion were inferred from guidelines and regulations
on tolerable levels of vibration and from correlations between instrumental
strong-motion parameters and intensity, considering the vulnerability
of the exposed housing stock. The thresholds were defined in terms
of peak ground velocity (PGV) and incorporated into a 'traffic light'
system that also took account of the frequency of occurrence of the
induced earthquakes. The system was implemented through a dedicated
seismograph array and locally derived predictive equations for PGV.
The 'traffic light' was used as a decision-making tool regarding
the duration and intensity of pumping levels during the hydraulic
stimulations. The system was supplemented by a small number of accelerographs
and re-calibrated using records obtained during the rock fracturing.
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