Abstract
Abstract. We present a different view of secular variation of the Earth's magnetic field, through the variations in the threshold rigidity known as the variation rate of geomagnetic cutoff rigidity (VRc). As the geomagnetic cutoff rigidity (Rc) lets us differentiate between charged particle trajectories arriving at the Earth and the Earth's magnetic field, we used the VRc to look for internal variations in the latter, close to the 70° south meridian. Due to the fact that the empirical data of total magnetic field BF and vertical magnetic field Bz obtained at Putre (OP) and Los Cerrillos (OLC) stations are consistent with the displacement of the South Atlantic magnetic anomaly (SAMA), we detected that the VRc does not fully correlate to SAMA in central Chile. Besides, the lower section of VRc seems to correlate perfectly with important geological features, like the flat slab in the active Chilean convergent margin. Based on this, we next focused our attention on the empirical variations of the vertical component of the magnetic field Bz, recorded in OP prior to the Maule earthquake in 2010, which occurred in the middle of the Chilean flat slab. We found a jump in Bz values and main frequencies from 3.510 to 5.860 µHz, in the second derivative of Bz, which corresponds to similar magnetic behavior found by other research groups, but at lower frequency ranges. Then, we extended this analysis to other relevant subduction seismic events, like Sumatra in 2004 and Tohoku in 2011, using data from the Guam station. Similar records and the main frequencies before each event were found. Thus, these results seem to show that magnetic anomalies recorded on different timescales, as VRc (decades) and Bz (days), may correlate with some geological events, as the lithosphere–atmosphere–ionosphere coupling (LAIC).
Highlights
The arrival of charged particles to the Earth can be estimated from their trajectories
We seek to find a relation with the Chilean flat slab trench, due to the fact that significant topographic conditions in the active convergent Chilean margin are capable of altering the genesis of the secular varia
Starting with the variations of the total magnetic field and its components, we verified the increasing influence of the phenomenon known as South Atlantic magnetic anomaly (SAMA), with the decrease in the rate of change in rigidity cutoff obtained along the 70◦ W meridian, between the 18 and 42◦ S latitude (Fig. 3)
Summary
The arrival of charged particles to the Earth can be estimated from their trajectories. Cordaro et al.: Variations of the geomagnetic rigidity tions in the core–mantle boundary (CMB), as is the case of the subduction of the Nazca plate under the South American plate, which reaches the CMB and produces a downwelling at the CMB (Yoshida, 2008; Lassak et al, 2010; Soldati et al, 2012) This extension of the Chilean flat slab trench towards the CMB is important because the latest research shows that the role played by CMB topography is closely related to the evolution of geodynamic and in particular to the existence of SAMA (Gubbins, 1988; Olsen et al, 2014; Tarduno et al, 2015; Pavón-Carrasco and De Santis, 2016).
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