Magnetic constraints on the spatial distribution of seismic activity

Abstract

The lithospheric magnetic field (LMF) in China and its surrounding are calculated using the spherical harmonic coefficients given by the NGDC-720 model. The LMF comes from the magnetization of minerals in the crust and in the uppermost mantle. It may, therefore, provide unique insight into lithospheric tectonic processes and mechanisms. Here, we study the geomagnetic manifestation of active tectonic blocks, and find a close correlation between the LMF and seismicity. Many large faults are found to closely overlap with magnetic anomalies, or are distributed along the boundaries of magnetic anomalies. Earthquakes in these fault regions have occurred on the boundaries of magnetic anomalies, or in the transition zones between positive and negative anomalies. We analyze the components of the LMF, and the LMFs at different altitudes, finding that the vertical component, B z at 200 km, is the most related to seismic activity. Relevant physical mechanisms are also discussed. We propose that the stress or viscosity differences caused by temperature variations, which manifest in the LMF, may be the predominant reason for the correlation between the LMF and seismic activity along large faults.

Possible correlation between the vertical component of lithospheric magnetic field and continental seismicity

“…B z at this altitude reflects well not only the seismicity, but also the topography (see Additional file 1: Figure S2). The statistical result is similar to our previous visual inspection (Jiao et al 2013), while more accurate.…”

“…To study the distribution of magnetic anomalies with different horizontal wavelengths, we may select different ranges of degree n, as did Kang et al (2012). Since anomalies with different wavelengths have different attenuating characters, an alternative would be to select a different r. In a former study (Jiao et al 2013), we visually compared seismicity to magnetic anomalies at altitudes (H = 0 km, 50 km, 100 km, 200 km and 400 km). We found that B z at 200 km is mostly associated with seismicity.…”

“…2 illustrates four phenomena: (1) More earthquakes have occurred in areas with negative anomalies than in areas with positive anomalies; (2) few earthquakes occurred inside predominant anomalies, either positive (e.g. basin anomalies) or negative (the two obvious anomalies located near the plate boundary of India and Eurasia); (3) numerous earthquakes occurred near zero B z areas (around the Sichuan Basin anomaly), or near boundaries of obvious anomalies (such as the Tarim Basin anomaly); (4) for distributions of earthquakes that deviate from the above three rules, rules 1-3 could be reproduced by selecting earthquakes with magnitude larger than M s 7.0, or by selecting earthquakes with a focal depth deeper than 30 km, such as those near the boundary of the whole Tibetan negative anomaly (Jiao et al 2013).…”

A Continental Model of Curie Point Depth for China and Surroundings Based on Equivalent Source Method

“…Rajaram et al, 2009). Furthermore, the B z at an altitude of 200 km well delineates the geological characteristics such as faults and basins, and exhibits a better correlation with seismicity than the other two components (Jiao et al, 2013;Lei et al, 2018). Hence, the B z calculated at an altitude of 200 km from the EMM2017 model is used (the effects of the other two components are discussed in Supplementary Information) to invert the CPD.…”