Bobrovskiy, Vadim (2018): Electrical intensity (mV) measured as the electromotive force across many electrodes subsurfaces at station S1-SEP, Petropavlovsk-Kamchatskiy, Kamchatka, from 01 January 2016 to 03 February 2016 [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.889724

In geophysical exploration and geomagnetic monitoring, the self-potential method examines slowly varying electric potentials measured across horizontally extended electrodes. Subsequently, electric methods were applied in earthquake precursor studies facing significant troubles such as the unknown source of precursory electric parameters changes and potential effects mainly of magneto-ionosphere origin. There is urgent request to update the mechanism explaining a promising number of observations since attempts to focus on stress and strain changes and fluid flow have not yet yielded useful results. Theoretical and experimental work has reinvestigated the conditions of how measurements should be made using a new class of sensor. The methodology relies on long-range couplings in the Earth's core - Earth's mantle - Earth's crust - ionosphere system evolving in an impulsive manner globally in space and time. The aim of proposed approach consists in the detection of electrical contrasts within the vertical and lateral zones subsurface (channels and layers). Proton migration develops DC and AC electromotive force registered as electrical intensity across arrays of vertical sequences of subsurface electrodes. Field measurements present observational characteristics of measured time series using the multielectrode method. Clearly visible contrasts above slow-changing signals even without post-processing noise reduction procedures are emphasized. Main results presented are detailed observations of incoherent occurrence of underground electrical signals which were followed by major earthquakes occurred at various distance.

The location of sensor station S1-SEP is 100 meters to the south-west of river flow and 2.7 km to the south-west of Avacha Bay in Petropavlovsk-Kamchatskiy, Kamchatka peninsula (53°3'9.98"N, 158°39'9.70"E). The sensor is located on a hillside at 105 meters elevation. Sensor station S1-SEP is equipped with three shallow pits: north-east (NE), central (C) and south-west (SW), which are spaced 10 meters apart (see Fig. 1). The set of 3-in line holes has 45 degrees offset from geomagnetic North for minimization of the influence of geomagnetic activity (Fig. 2). NE-pit has a depth of 1.5 meters. Two electrodes having typical sizes of 300x300x3mm are horizontally arranged in the NE-pit in the intimate contact with the soil thickness of ~500 mm. C-pit and SW-pit have a depth of 2 meters. Six electrodes of 300x300x3 mm size are horizontally arranged in the C-pit and SW-pit in the intimate contact with the soil thickness of ~300 mm.

Three measurement schemes are used (see Fig. 3-5): between electrodes in a single pit (electrode-electrode scheme), between the second electrode in the NE-pit and each electrode in SW-pit (subhorizontal scheme) and between each electrode and GND (the local electrical ground). Electrodes in pits are marked by increasing sequential numbers from uppermost to lowermost. Mains neutral wire or local earthing system or steel water pipeline having electrical contacts with the ground are used as the local electrical ground. Zero (labelled in Fig. 2) electrode is GND.

Measured EMF values are denoted using pit name and electrode numbers, i.e. channel NE2C5 means EMF values between the second electrode of the NE pit and the fifth electrode of the C pit; SW04 means EMF values between GND and the fourth electrode of the SW pit; SW12 means EMF values between the first electrode and the second electrode of the SW pit.

Full set of measuring parameters at S1-SEP sensor station includes (Fig. 3-5):

- eleven EMF values in electrode-electrode scheme (NE12, C12, C23, C34, C45, C56, SW12, SW23, SW34, SW45, SW56).

- six EMF values in subhorizontal scheme between the second electrode of the NE pit and each electrode of the C-pit (NE2C1, NE2C2, NE2C3, NE2C4, NE2C5, NE2C6).

- twelve EMF values between each electrode of C-pit and GND, each electrode of SW-pit and GND (CO1, CO2 CO3, CO4, CO5, CO6, SWO1, SWO2, SWO3, SWO4, SWO5, SWO6).