GaiaCode has delivered a second batch of three multiparameter geophysical borehole instruments to the Turkish National Disaster and Emergency Management Authority (AFAD) in Ankara. Together with three previously installed similar instruments, these new devices will augment an existing seismic monitoring network in the country, which has one of the highest earthquake hazards in the world.
GaiaCode will install these new instruments in boreholes in the western part of the country, near the cities of Edirne, Kirklareli and Eskisehir (see yellow markers on the map). They add to three previous stations, in which GaiaCode installed similar borehole instruments in the fall of 2022. These locations are marked with red pointers on the map.
Each instrument consists of a set of three ALPHA broadband sensors, three SIGMA accelerometer sensors and a newly designed single jaw hole-lock to anchor the instrument in the borehole. These sensor elements and the hole-lock are stacked in a 316 stainless steel tube with a diameter of 89 millimeters. The whole system is pressure rated to a water depth of 900 meters.
Wide bandwidth and high dynamic range
The combination of Alpha and Sigma sensors in one borehole unit allows for the recording of seismic signals over a wide frequency range, from 120 second to 250 Hertz for the broadband sensor and DC to 350 Hertz for the Sigma accelerometers. The Sigma accelerometers are set to record strong ground motion of up to 4 g. Data will be transmitted in analogue form to a GaiaCode TAU digitizer at the respective wellheads.
Single Jaw Hole-Lock
The sensor stack is combined with a powerful single arm hole-lock, which locks the sensor system against the borehole casing with a force exceeding 30 kilogram. Together with the hole-lock two sets of “ears” (skids) at the top and bottom of the sensor stack force the sensor against the borehole casing. This geometry shifts possible parasitic resonances of the locked instrument package in the borehole far out of the seismic band. One of the main features of this hole-lock design is that the instrument package can be removed from the borehole without retracting the hole-lock arm.
