Stress changes due to earthquake rupture can disturb geomagnetic fields significantly. In order to investigate the impact of the 2021 M_W 7.3 Maduo earthquake on geomagnetic fields, a piezomagnetic model is constructed based on the coseismic slip to calculate the static coseismic piezomagnetic anomalies (PMs). The PMs are considerable in near-field. However, the PMs are negligible in regions tens of kilometers from the fault rupture. The PMs of our model are consistent with those of other strike-slip earthquakes, indicating that our piezomagnetic model is reasonable. The east component of observed coseismic geomagnetic changes and calculated PMs on a geomagnetic repeat station located about 6 km from fault trace are +4.8 ± 2.2 nanotesla and +4.3 nanotesla, respectively. It seems that the piezomagnetic model can explain the observed data. The PMs are up to 10 nanotesla in the near-field with the initial magnetization of 3 A/m and stress sensitivity of 2 × 10⁻³ MPa⁻¹. Consequently, considerable coseismic geomagnetic changes that are above error could be observed along the fault, especially at locations with geometrical complexities.

To understand the deep tectonic environment at the origin of strong earthquakes along the northern section of the North-South seismic belt and the central continental block of Mongolia, large-scale gravity and geomagnetic surveys and rock sample collection were carried out along the Suhbaatar-Ulaanbaatar-Dalandzadgad profile in Mongolia. The spatial distribution characteristics of the lithospheric magnetic field at 160 geomagnetic measuring points along the profile were then systematically analyzed and summarized. Based on the composition of the lithospheric magnetic field from different sources at different depths combined with the regional geological structure and collected rock sample lithology, the lithospheric magnetic field was further decomposed into different components—the basement, middle layer, and shallow surface—by the upward continuation method. The results show that these components have obvious zoning characteristics and that the lithospheric magnetic field distribution of the Suhbaatar-Ulaanbaatar-Dalandzadgad profile is related to the geological structure, rock lithology, seismic activity, natural remanent magnetization, and magnetic susceptibility. Many destructive earthquakes have occurred in the area where the lithospheric magnetic field changes dramatically, the lithologies are dominantly igneous, and the magnetic susceptibility and natural remanent magnetization are high. In contrast, the lithologies in the area with moderate variation in the lithospheric magnetic field are mostly sedimentary, the magnetic susceptibility and natural remanent magnetization are low, and destructive earthquakes are rare. Since the lithospheric magnetic field reflects the magnetic characteristics of the rocks above the Curie interface, its spatial distribution not only corresponds to the geological structure but also predicts the depth and location of faults. Therefore, it is significant to carry out geomagnetic surveys and rock sampling to analyze the characteristics of geological structures and research regional seismicity.

Although coseismic geomagnetic signals accompanying seismic waves have been observed previously, static coseismic changes in the geomagnetic field throughout China have hardly been elucidated. The static coseismic geomagnetic changes associated with the 2017 M_W 6.5 Jiuzhaigou earthquake were investigated to evaluate the monitoring ability of geomagnetic stations in China. Precise geomagnetic field measurement data were obtained from the Songpan (SPA) geomagnetic station located 65 km from the epicenter. The static coseismic variation was below the background noise level. Piezomagnetic models were constructed from two non-uniform slip models, illuminating the possible geomagnetic changes caused by static stress changes due to fault slip. The piezomagnetic anomalies around the fault segment were 0.2 and 0.4 nT with a uniform rock magnetization of 1 A/m. The piezomagnetic anomaly at SPA was insignificant, indicating that no observable static geomagnetic signals were detected by the stations during the Jiuzhaigou earthquake. Given the higher rock magnetization of 2–3 A/m, the near-field piezomagnetic anomalies would tend to exceed 1 nT. Consequently, there would have chance to observe considerable piezomagnetic signals in the localized area of the fault segment.