Last week a second observation drill hole was drilled to about 50 m depth only a couple of metres away from the first one. The two holes will form a single observational entity equipped with 3-component geophones. The shallower (second) hole to 50 m depth, and the deeper (first) hole to 100 m depth contain together 9 geophones with a spacing of 10 m in depth. Two holes were used since a single drill hole was considered too risky for the number of geophones being employed since each geophone is connected to its own cable. Yesterday and today, the two geophone chains were installed and cemented at 100 m, 90 m 80 m, 70 m and 60 m in the deep hole and at 50 m, 40 m, 30 m and 20 m in the shallower hole. The geophones will be connected to a recording system when power is installed on-site next Spring. The purpose of the observation system is threefold (i) to investigate if it is possible to record useful drill-bit noise from the drilling of COSC-1, (ii) to passively record potential local earthquakes and (iii) to act as calibration sensors for future VSP measurements in COSC-1 after drilling is completed. (Photo: Christopher Juhlin)