a deep Geophysical Observatory at the North Anatolian Fault
The principal objective of the GONAF project is to install a downhole seismic observatory to monitor the microseismic activity in direct vicinity to the fault under low-noise conditions. Present seismic monitoring efforts throughout the eastern Sea of Marmara rely on recordings obtained at the surface, and presently the closest sensors are deployed on the Prince Islands (PIRES seismic array, see pdf
). The array consists of two 5-seismograph sub-arrays on Yassiada and Sivriada Islands that are the closest offshore locations to main branch, and single stations deployed on other Princes Islands. The improved signal-to-noise ratio resulting from the deployment of GONAF downhole instrumentation will significantly lower the magnitude-detection threshold for small-scale microseismicity at the fault and reduce the source-receiver distance . This will therefore improve the hypocentral map characterizing the physical setup of the critically-stressed Prince Island segment of the NAFZ.
We intend to deploy the following seismic instrumentation along the GONAF boreholes (long-term deployment):
- Vertical chains of up to ten tubing-deployed three-component short-period borehole seismometers at a constant spacing along the entire depth extent [primary objective: monitoring of microseismicity].
- One three-component broadband borehole seismometer at the deepest part of the boreholes [primary objective: monitoring of low-frequency seismic events].
- Vertical chains of up to five borehole accelerometers at a constant spacing along the entire depth extent [primary objective: determination of depth-depending changes of seismic ground deformation].