GEOMAGNETIC EFFECT OF TURKISH EARTHQUAKE OF JANUARY 24, 2020

Purpose:The main cause of geomagnetic disturbances are cosmic sources, processes acting in the solar wind and in the interplanetary medium, as well as large celestial bodies entering the terrestrial atmosphere. Earthquakes (EQs) also act to produce geomagnetic effects. In accordance with the systems paradigm, the Earth–atmosphere–ionosphere–magnetosphere system (EAIMS) constitute a unified system, where positive and negative couplings among the subsystems, as well as feedbacks and precondition among the system components take place. The mechanisms for the action of EQs and processes acting in the lithosphere on the geomagnetic field are poorly understood. It is considered that the EQ action is caused by cracking of rocks, fluctuating motion in the pore fluid, static electricity discharges, etc. In the course of EQs, the seismic, acoustic, atmospheric gravity waves (AGWs), and magnetohydrodynamic (MHD) waves are generated. The purpose of this paper is to describe the magnetic effects of the EQ, which took place in Turkey on 24 January 2020. Design/methodology/approach: The measurements are taken with the fluxmeter magnetometer delivering 0.5-500 pT sensitivity in the 1-1000 s period range, respectively, and in a wide enough studied frequency band within 0.001 to 1 Hz. The EM-II magnetometer with the embedded microcontroller digitizes the magnetometer signals and performs preliminary filtering over 0.5 s time intervals, while the external flash memory is used to store the filtered out magnetometer signals and the times of their acquisition. To investigate quasi-periodic processes in detail, the temporal variations in the level of the H and D components of the geomagnetic field were applied to the systems spectral analysis, which makes use of the short-time Fourier transform, the wavelet transform using the Morlet wavelet as a basis function, and the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods. Findings: The train of oscillations in the level of the D component observed 25.5 h before the EQ on 23 January 2020 is supposed to be associated with the magnetic precursor. The bidirectional pulse in the H component observed on 24 January 2020 could be due to the piston action of the EQ, which had generated an MHD pulse. The quasi-periodic variations in the level of the H and D components of the geomagnetic field, which followed 75 min after the EQ, were caused by a magnetic disturbance produced by the traveling ionospheric disturbances due to the AGWs launched by the EQ. The magnetic effect amplitude was estimated to be close to 0.3 nT, and the quasi-period to be 700-900 s. The amplitude of the disturbances in the electron density in the AGW field was estimated to be about 8 % and the period of 700-900 s. Damping oscillations in both components of the magnetic field were detected to occur with a period of approximately 120 s. This effect is supposed to be due to the shock wave generated in the atmosphere in the course of the EQ. Conclusions: The magnetic variations associated with the EQ and occurring before and during the EQ have been studied in the 1-1000 s period range. Key words: earthquake, fluxmeter magnetometer, quasi-periodic disturbance, seismic wave, acoustic-gravity wave, MHD pulse

Geomagnetic effect of the Albanian earthquake on November 26, 2019

Background. The main cause of geomagnetic disturbances is known to be space sources, processes acting in the solar wind and in the interplanetary medium, as well as falling large celestial bodies. Earthquakes also give rise to geomagnetic effects. In accordance with the systems paradigm, the Earth–atmosphere–ionosphere–magnetosphere system comprises the single system where direct and reverse, positive and negative coupling take place. The mechanism of the earthquake effect on the magnetic field is poorly understood. A rock cracking, a fluctuating movement of fluids in pores, a corona discharge of the high-voltage static charge, etc., are thought to be the processes that give rise to the geomagnetic effect. In the course of earthquakes, seismic, acoustic, atmospheric gravity, and magnetohydrodynamic waves are generated, which provide for coupling between the subsystems in the Earth–atmosphere–ionosphere–magnetosphere system. Purpose of Work. The paper describes the possible response in the level of the geomagnetic field to the earthquake of 26 November 2019 that took place in Albania. Techniques and Methodology. The measurements were taken with the fluxmeter magnetometer at the V. N. Karazin Kharkiv National University Magnetometer Observatory. It delivers 0.5 – 500 pT sensistivity in the 1–1000 s period range over a quite large frequency band of 0.001 to 1 Hz. To study the quasi-periodic processes in detail, the systems spectral analysis of the temporal dependences of the horizontal (H, D) geomagnetic field components has been employed. It includes the short-time Fourier transform, the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods, and wavelet transform, simultaneously. The wavelet transform employs the Morlet wavelet as a basis function. Results. The quasi-periodic variations in the level of the geomagnetic field observed to appear with a 6 min lag and to last for 70–80 min could be due to the earthquake. These disturbances could be transferred by the magnetohydrodynamic waves. The quasi-periodic variations that were observed to appear with a 97–106 min lag and to last for about 130–140 min were most likely due to the earthquake. They were transferred by the atmospheric gravity waves with a period of 7–14 min. A relative disturbance in the electron density in the atmospheric gravity wave field was observed to be approximately 5.3%. The results obtained from observations of Albanian and Turkish earthquakes show agreement. Conclusions: The magnetic variations in the 1–1000 s period range that were observed to occur before and during the earthquake have been studied.

Geomagnetic effect of earthquakes

Based on the results of instrumental observations carried out at a number of mid-latitude observatories of the INTERMAGNET network and at the Mikhnevo Geophysical Observatory of Institute of Geosphere Dynamics of Russian Academy of Sciences, it is shown that strong earthquakes are accompanied by increased variations of Earth’s magnetic field. In this case, the short-period stage (period ~ 0.5-0.8 min) and long-period stage (period ~ 5-20 min) of increased geomagnetic variations are clearly distinguished. The maximum amplitude of induced geomagnetic variations is 1.5-2 nT and 2- 4 nT, respectively, for short-period and long-period variations. A similar in morphology and almost synchronous nature of the induced geomagnetic disturbances at the observatories located at significantly different distances from the earthquake source is noted.

A new parametrization for the radio emission of air showers applied to LOFAR data

The energy and mass composition of cosmic rays influence how the energy density of the radio emission of air showers is distributed on the ground. A precise description of the radio profiles can, therefore, be used to reconstruct the properties of the primary cosmic rays. Here, such a description is presented, using a separate treatment of the two radio-emission mechanisms, the geomagnetic effect and the charge excess effect. The model is parametrized as a function that depends only on the shower parameters, allowing for a precise reconstruction of the properties of the primary cosmic rays. This model is applied to cosmic-ray events measured with LOFAR and it is capable of reconstructing the properties of air showers correctly.