| The feasibility of
an earthquake early warning Shield in Greece is being explored as a
European demonstration project. This will be the first early warning
system in Europe. The island of Revithoussa is a liquid natural gas
storage facility near Athens from which a pipeline runs to a gas
distribution centre in Athens. The Shield is being centred on these
facilities. The purpose here is to analyze seismicity and seismic hazard
in relation to the Shield centre and the remote sensor sites in the Shield
network, eventually to help characterize the hazard levels, seismic
signals and ground vibration levels that might be observed or create an
alert situation at a station. Thus this paper mainly gives estimation of
local seismic hazard in the regional working area of Revithoussa by
studying extreme peak ground acceleration (PGA) and magnitudes.
Within the Shield region, the most important zone to be
detected is WNW from the Shield centre and is at a relatively short
distance (50 km or less), the Gulf of Corinth (active normal faults)
region. This is the critical zone for early warning of strong ground
shaking. A second key region of seismicity is at an intermediate distance
(100 km or more) from the centre, the Hellenic seismic zone south or
southeast from Peloponnisos. A third region to be detected would be the
northeastern region from the centre and is at a relatively long distance
(about 150 km), Lemnos Island and neighboring region. Several parameters
are estimated to characterize the seismicity and hazard. These include:
the 50-year PGA with 90% probability of not being exceeded (pnbe) using
Theodulidis & Papazachos strong motion attenuation for Greece, PGANTP;
the 50-year magnitude and also at the 90% pnbe, M50 and MP50,
respectively. There are also estimates of the earthquake that is most
likely to be felt at a damaging intensity level, these are the most
perceptible earthquakes at intensities VI, VII and VIII with magnitudes
MVI, MVII and MVIII. Example results (from many) include the corresponding
parameters describing the hazard for Revithoussa as follows: PGANTP:
203 cm s- 2 , M50: 6.5, Mp50: 6.9, MVI:
5.8, MVII: 6.1 and MVIII: 6.4. These data are also
useful in selecting expected alert-signals i.e. examples of strong ground
vibration histories that might be expected at a Shield station in the
alert situation. |