Detection and interpretation of precursory magnetic signals preceding October 30, 2020 Samos earthquake

Authors: İLKİN ÖZSÖZ, OYA ANKAYA PAMUKÇU

Abstract: A major earthquake (M_w=7.0) occurred in the Samos Island on the 30th of October 2020 at 11:51 UTC. Swarm satellite magnetic data were analysed for 153 days before and 46 days after the earthquake. Preearthquake and postearthquake anomaly search is constrained within the Dobrovolsky's Circular Area. Fundamentally, there are 5 steps for processing satellite magnetic data to interpret the earthquake preparation phase. The first step is converting geographical coordinates to geomagnetic latitude and longitude. Secondly, intensity of the external magnetic field should be evaluated by magnetic indices (Ap, Kp and |Dst). Thirdly, preearthquake and postearthquake magnetic anomaly should be constrained through magnetic indices (Ap < 20, Kp ≤ 3 and |Dst|<10) and Dobrovolsky's Circular Area. The following step is filtering short-wavelength magnetic anomalies using first time derivative and trend removal (de-trend). Finally, anomalous residual magnetic variations of the satellite tracks are classified through RMS analysis. The cumulative number of anomalous points (y-axis) is plotted versus the date (x-axis). R² values denote the degree of linear distribution of the anomalous tracks. For X, Y, Z, and F components of the magnetic field, R² is computed as 0.9038, 0.8697, 0.8490, and 0.9694, respectively. Y component of the magnetic field provided the best results in terms of interpretation. Regarding the results of the Y component, linear distribution and deviation from this distribution are fairly distinguishable.

Keywords: Satellite magnetic data, precursory earthquake signals, Swarm satellite constellation, magnetic field components, Samos 2020 earthquake

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