DOREL ZUGRAVESCU, MARIN IVASCU, DUMITRU STANICA, MIRCEA PAUCA
(ABSTRACT)
The possibilities of the present theoretical models and experimental measurements
to explain long term process and short-term triggers of earthquakes has been
studied. The conclusion is that: although the basic process is well understood
and accurately measured, its details are quite complex. For example, the stress
accumulation rate is not uniform over time. A large earthquake on a segment
of a fault changes the stress on the adjacent segments, either statically or
dynamically, and accelerates or decelerates seismic activity, depending on
the fault geometry. Migrating fluids may weaken Earth’s crust significantly,
altering the times at which earthquakes occur. The overall long-term process
is regular, but considerable temporal fluctuation of seismicity occurs, making
accurate prediction of earthquakes extremely difficult. Fortunately the mechanical
processes of earthquake preparation are always accompanied by deformations,
afterwards complex short or long-term precursory phenomena can appear. In this
condition, temporal variation of radon in soil or water can give an evidence
that the emanation of this gas in some cases is in a relation to tectonic disturbance
in the Earth’s crust. Soil-gas observation on radon anomalies can be
used for earthquake prediction though the radon chance are also influenced
by meteorological parameters. Further studies are needed to differentiate the
changes, and to reduce the effect of meteorological parameters on the measured
radon concentration. Anomalies of radon concentrations in soil gas were registered
a few week or months before several earthquakes.
Key words: long-term processes, short-term triggers, strain drop, plate-tectonics,
exhumed faults, radiated energy, precursory phenomena, radon anomalies.