# Piezomagnetic Anomalies Associated with the 2021 \(M_{\text{W}}\) 7.3 Maduo (China) Earthquake
###### Abstract  
Stress changes due to earthquake rupture can disturb geomagnetic fields significantly. In order to investigate the impact of the 2021 \(M_{\text{W}}\) 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 \(\pm\) 2.2 nanotelsa and +4.3 nanotelsa, 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 \(\times\) 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.  
M\({}_{\text{W}}\) 7.3 Maduo earthquake; piezomagnetic anomalies; coseismic geomagnetic changes Article  
Piezomagnetic Anomalies Associated with the 2021 \(M_{\text{W}}\) 7.3 Maduo (China) Earthquake Applied  
13 December 2021  
Accepted: 16 January 2022  
Published: 19 January 2022  
**Published: 19 January 2022**  
The Bayan Har block, involved in the eastward extrusion of the Tibetan Plateau [27], is a seismically active block [28]. Many strong earthquakes (\(M_{\rm W}>6.5\)) in China occurred in this block and its border faults in past twenty years (Figure 1), including the 2001 \(M_{\rm W}\) 7.9 Kokoxili earthquake, the 2008 \(M_{\rm W}\) 7.8 Wenchuan earthquake, the 2010 Yushu \(M_{\rm W}\) 6.9 earthquake, the 2013 \(M_{\rm W}\) 6.6 Lushan earthquake, and the 2017 \(M_{\rm W}\) 6.5 Jjuzhaigou earthquake. In order to investigate geomagnetic anomalies before, during, and after earthquakes, the China Earthquake Administration operates a geomagnetic network including geomagnetic observatories and geomagnetic repeat stations in the Tibetan Plateau. However, only a repeat station located 26 km from the epicenter of the \(M_{\rm W}\) 6.6 Lushan earthquake recorded PMs [29]. PMs can be neglected if the fault rupture is small [30], unless observations are conducted right on faults [3]. However, PMs must be investigated carefully for earthquakes with ruptures larger than 100 km for their huge energy release and strong impact on local and regional geomagnetic fields.  
The \(M_{\rm W}\) 7.3 Maduo earthquake (herein referred to as Maduo earthquake) occurred at 18:04 UTC on 21 May 2021, with the epicenter located at 98.34\({}^{\circ}\) E and 34.59\({}^{\circ}\) N ([[http://www.csi.ac.cn/](http://www.csi.ac.cn/)]([http://www.csi.ac.cn/](http://www.csi.ac.cn/)), accessed on 10 November 2021). Maduo earthquake caused an about 160 km rupture (Figure 1) along the Maduo-Gande fault [31]; however, the tectonic deformation is significantly weak in the region [32]. How does the earthquake disturb geomagnetic fields in the Bayan Har block? Are the piezomagnetic fields localized? More importantly, how will the earthquake impact observations of piezomagnetic fields in the future? To address these questions, in this study, we construct a piezomagnetic model to calculate the staticoseismic PMs based on a slip model of the Maduo earthquake. Moreover, observed data of 2019 and 2021 on a repeat station are used to examine the PMs.