Multi-mode pre-seismic geomagnetic anomalies reveal potential mechanisms of the August 15, 2007, Mw8.0 Pisco earthquake: Pressure-stimulated rock current

Abstract

This study investigates multi-type pre-seismic geomagnetic anomalies observed before the August 15, 2007, M_w 8.0 Pisco earthquake, and proposes Pressure-Stimulated Rock Current (PSRC) as an underlying mechanism. Using time-domain and frequency-domain analyses, the research identifies ultra-low frequency (ULF) emissions and magnetic vector deflections related to the earthquake. Based on the diurnal variation anomalies across multiple stations, a novel algorithm, the Forward Intersection of Magnetic Disturbance Vector (FIMDV), was developed to estimate the location of the seismogenic zone by analyzing the magnetic vector deflection. The FIMDV algorithm integrates the magnitude and directional information of magnetic disturbance vectors to pinpoint rock currents, providing new insights into geomagnetic anomalies and earthquake preparation. The study identifies two key phases of potential PSRC generation: the crack coalescence phase, associated with ULF emissions detected a month before the earthquake, and the crack interconnection phase, which corresponds to diurnal anomalies observed on the earthquake day. The former involves microcrack formation and positive hole activation, leading to varying electromagnetic fields that propagate as low-frequency waves detectable at the ground surface. The latter involves cracks interconnection facilitating the propagation of direct rock currents to the ground surface and inducing stable magnetic disturbance vectors. Geological validation confirmed that the local lithology, rich in silicate minerals, enables positive holes activation and propagation, further supporting PSRC as a driving mechanism of the observed multi-mode geomagnetic anomalies, including diurnal variation, vector deflection, Z/H polarization ratio, and horizontal polarization ellipse.