קולוקוויום בחוג לגאופיזיקה: Application of the technique of Fracture Induced Electromagnetic Radiation (FEMR) as a precursor to geohazards: An emphasis on the Dead Sea Transform fault before the Syrian-Turkey earthquake (Mw-6.3) on 20.2.2023

Zoom: https://tau-ac-il.zoom.us/j/83294569872?pwd=WmdPUWRPdGVQejIvcXhsQmFJY094UT09

Abstract:

The Fracture Induced Electromagnetic Radiation (FEMR) method has emerged as a prolific geophysical tool over the past decade, offering insights into recent crustal stresses, stress concentration within underground tunnels, the identification of landslide-prone slip planes in unstable regions, and earthquake (EQ) forecasting. The physical foundation of the phenomenon consists of geogenic electromagnetic radiation emanating from fractured brittle rock bodies subjected to an incremental increase in differential stress in the near-surface of the Earth's crust. 

The “Process zone” at the fractured rock contains numerous microcracks-dipoles created due to the polarization of charges on such microcrack surfaces rapidly oscillate, emitting FEMR waves of frequencies between kHz to MHz range. The coalescence of the microcracks eventually leads to a macro failure, dampening the amplitude of the FEMR pulses. Notably, FEMR pulses attenuate less than seismic waves, rendering them more efficient precursors to potential tectonic activities, often suggesting an impending EQ several hours or days in advance. Abnormal increases in FEMR pulse amplitude signify the accumulation of strain in brittle rocks, indicating an upcoming tectonic episode. The FEMR technique has been successfully applied in Central India to identify potential active faults and determine stress azimuths along the Narmada-Son Lineament (NSL).

Additionally, a pilot study employed FEMR to predict weak slip planes prone to small-scale landslides. Regions with high FEMR parameter amplitudes, indicating high "activity," were correlated with weak slip planes, highlighting potential landslide zones. Further applications of FEMR include stress magnitude calculations in the Darjeeling-Sikkim-Himalayas region, where 11 cross-sectional measurements inside a tunnel revealed a normal stress regime in contrast to the reverse stress regime prevalent in the Himalayas. The observed systematic variation in the direction of maximum FEMR emission along the tunnel trajectory led to the postulation of a reactivated thrust plane with variable dip angles in the normal stress regime. In our current study, a recent FEMR investigation along the active Dead Sea transform (DST) segment from Sodom to Jericho shortly preceded a 6.3 magnitude aftershock earthquake in the Turkey-Syrian region on February 20, 2023. The last FEMR measurement, taken two hours before the earthquake, allowed for analyzing FEMR parameters, including Benioff strain release, frequency, rise time, hits or activity, and energy. Based on the comprehensive analysis of these parameters, our study delved into three consecutive stages of EQ nucleation leading to the event itself, providing valuable insights into the modulation of FEMR parameters preceding seismic events. The results from these analyses hold the potential to bridge the knowledge gap between lab-scale and large-scale studies of stress-induced rock collapses, serving as a cost-effective and timely precursor to natural calamities. Researchers are encouraged to embrace the novel FEMR technique for its speed, costeffectiveness, and accessibility in surveying the active tectonics of a region, which is complementary to conventional techniques.

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מארגן האירוע: ד"ר רועי ברקן