Drilling for a seismic monitoring network recently started on the Marmara Sea near Istanbul. Specially designed seismic sensors in eight boreholes on the outskirts of Istanbul and around the eastern Marmara Sea will monitor the seismic activity of the region with high precision. In each of the respective 984-foot-deep holes several borehole seismometers will be permanently installed at various depths. These detect even barely perceptible earthquakes with very small magnitudes at a high resolution, and thus can provide information about the associated earthquake rupture processes.
To determine and monitor the seismic
hazard of the region and the processes occurring in the fault zone beneath the
Marmara Sea off Istanbul with the latest earthquake monitoring technology, the
GONAF plate boundary observatory (Geophysical Observatory at the North
Anatolian Fault) was set up under the auspices of the GFZ German Research
Centre for Geosciences. "Istanbul, with its more than 13 million
inhabitants, is located in a region that is extremely vulnerable to
earthquakes. A high probability of a strong earthquake of magnitude up to 7.4
is assumed for the region," explains Professor Georg Dresen from the GFZ,
one of the organizers of the project GONAF. "The data of small earthquakes
in the region that are measured in the borehole can provide important
information about the processes before a major earthquake."
The data is continuously transmitted in
real time to Potsdam and Ankara and evaluated there. A particular difficulty is
that the earthquake zone to be monitored lies under the seabed of the Marmara
Sea, about 12 miles off Istanbul. Only monitoring below ground in boreholes
ensures the required precision of the measurements, due to the much lower noise
level. "This means we have to get as close as possible to the quake source
region," explains GFZ researcher Professor Marco Bohnhoff, director of the
project. "With our new, specially developed borehole seismometers the
ratio of signal to background noise can be improved by at least a factor of 10,
and therefore achieve a much higher resolution."
The project involves close cooperation
with the Disaster and Emergency Management Presidency of Turkey (AFAD). The
drilling is implemented as part of the International Continental Scientific
Drilling Program (ICDP). Engineers and scientists at the GFZ supervise the
construction and installation activities. Upon successful completion and
handover of the fully equipped pilot borehole on the peninsula Tuzla, just off
Istanbul, a first test phase will commence before the remaining seven wells
will be drilled.
"An earthquake prediction is not
the goal of the project," clarifies Marco Bohnhoff. "Earthquake
prediction is still not possible. But the data gathered in our project of the
seismic activity before, during and after the expected strong quake will mean a
great advance in the study of earthquakes."