## 2 Experimental Set-Up  
Multi-parametric Geophysical Observatory resides at the two high-altitude experimental sites of the Institute of Ionosphere and of the Tien Shan Research Station of the Lebedev Physical Institute, both hosted in mountain at the altitudes between 3340 and 3400 m above the sea level, far away from any technogenic interference. The uniqueness of the Observatory lies in its location in vicinity to the epicenters of two catastrophic earthquakes, the Verny \(M7.3\) (13.3 km) and Kemin \(M8.2\) (16.3 km) ones, and also not far from the sources of about ten other major earthquakes, which have occurred on the territory of Kazakhstan during the last century. The experimental base of the Observatory comprises complex equipment for simultaneous monitoring the processes proceeding in the lithosphere, atmosphere, and ionosphere.  
A multi-channel geophysics recorder MGR-02-16 is installed at an altitude of 3400 m. The device is designed for monitoring the temporal changes in ENPEMF, which is measured here continuously, and simultaneously at the two frequencies of VLF band, 7.5 kHz and 10.0 kHz, in accordance with the method proposed in [2; 3; 4; 5]. Two mutually orthogonal ferrite antennas of the geophysical recorder are set in the north-south (7.5 kHz) and West-East (10.0 kHz) directions. The counting rate of electromagnetic pulses is defined over 10 s long time intervals.  
Next to the recorder resides an IMS-008 magnetic sensor of inductive type, which registers the strength variation of the horizontal component of the Earth's magnetic field in an ULF band, 0.001-20 Hz, with a sampling rate of 66.6 Hz. The magnetic sensor is oriented in the north-south direction. To ensure registration of the electromagnetic signals only in the ULF band, a 12-order Chebyshev low-pass filter with a cut-off bandwidth of 20 Hz is applied. A notch filter is also used for better suppression of the interference from the 50 Hz industrial main.  
At the territory of Geophysical Observatory there exists a 300 m deep borehole, which is also used for the study of seismogenic effects. Up to the depth of (150 \(\pm\) 5) m, the borehole is filled with water. At the depth of 100 m it is installed a gamma ray detector, which is based on a \(\diameter\)40 mm sized NaI(Tl) scintillation crystal. The detector was especially designed for the measurement of the flux of gamma rays from tens of keV to some MeV in borehole.  
The gamma detector was calibrated using the reference gamma sources \({}^{241}\)Am (with the energy of emitted radiation \(\simeq\) 60 keV) and \({}^{137}\)Cs (660 keV). The rate of output pulsesobtained from the detector is registered with a 10 s periodicity in the four energy ranges: 30-150 keV, 150-250 keV, 250-500 keV, and \(\geqslant\)500 keV.  
Besides the gamma detector, three temperature sensors are also installed in the borehole at the levels of 1 m, 24 m, and 39 m; one more sensor is placed on the surface near the upper borehole orifice. It was found that below 24 m under the surface, the air temperature varies only by a few hundredths of a centigrade throughout a year, providing stable operation conditions for the electronic circuitry and scintillation crystal of the gamma detector, which generally could be affected by temperature variation. The on-ground part of all geophysical recorders is kept under temperature stabilization in the limits of (\(20\pm 0.25\)) \({}^{\circ}\)C.  
The mutual disposition of the mentioned detectors at the Geophysical Observatory is listed in Table 1 and illustrated by a picture in Figure 1.  
All observations made at Geophysical Observatory are analyzed with regard to the current geomagnetic situation. For the purpose, we use the \(Ap\) and \(Kp\) indices of geomagnetic activity obtained at the website of the World Data Center for Geomagnetism in Kyoto [35].