Downhole geophysical observatories: best installation practices and a case history from Turkey

作者：Prevedel Bernhard^*; Bulut Fatih; Bohnhoff Marco; Raub Christina; Kartal Recai F; Alver Fatih; Malin Peter E

来源：International Journal of Earth Sciences, 2015, 104(6): 1537-1547.

DOI：10.1007/s00531-015-1147-5

• Downhole observatory
• Permanent monitoring
• Seismometer
• Fault system
• North Anatolian Fault Zone
• Earthquake research

Downhole sensors of different types and in various environments provide substantial benefit to signal quality. They also add the depth dimension to measurements performed at the Earths' surface. Sensor types that particularly benefit from downhole installation due to the absence of near-surface noise include piezometers, seismometers, strainmeters, thermometers, and tiltmeters. Likewise, geochemical and environmental measurements in a borehole help eliminate near-surface weathering and cultural effects. Installations from a few hundred meter deep to a few kilometer deep dramatically reduce surface noise levels-the latter noticeably also reduces the hypocentral distance for shallow microearthquakes. The laying out of a borehole network is always a compromise of local boundary conditions and the involved drilling costs. The installation depth and procedure for a long-term downhole observatory can range from time limited installations, with a retrieval option, to permanently cemented sensors. Permanently cemented sensors have proven to be long-term stable with non-deteriorating coupling and borehole integrity. However, each type needs to be carefully selected and planned according to the research aims. A convenient case study is provided by a new installation of downhole seismometers along the shoreline of the eastern Marmara Sea in Turkey. These stations are being integrated into the regional net for monitoring the North Anatolian Fault Zone. Here we discuss its design, installation, and first results. We conclude that, despite the logistical challenges and installation costs, the superior quality of downhole data puts this technique at the forefront of applied and fundamental research.

• 出版日期2015-9