Abstract
The tectonic processes leading up to an earthquake and the occurrence of the earthquake itself will cause local changes in the geophysical field (geomagnetic field, stress field, etc.). In this paper, the variation characteristics of the tectonic stress field (TSF) and local geomagnetic field (LGF) before and after the Yangbi Ms 6.4 earthquake are studied. The regional stress tensor damping inversion method was used to invert the TSF using focal mechanism solutions (FMSs). The change characteristics of the TSF before and after the earthquake were analyzed. An annual variation model of the LGF was constructed, and the variation of the horizontal vector was analyzed. The azimuth and plunge of the maximum principal compressive stress axis of the TSF in the epicentral region before and after the earthquake were −4.4° and 2.7°, 172.7° and 6.6°, respectively. The variations in the declination, inclination and total intensity of the epicenter one year before and one month after the earthquake were −0.20′ (0.07′), 0.29′ (−0.12′), and −1.7 nT (−1.9 nT), respectively. The epicenter is located at the boundary of the “weak variation region” of the horizontal vector. This research is of great significance concerning the TSF background and incubation mechanism of earthquakes.
Highlights
The geomagnetic field and stress field are important geophysical fields
Of a single earthquake cannot be used to define the actual direction of the tectonic stress applied underground, the characteristics of the tectonic stress field (TSF) in the region can be inferred through many focal mechanism solutions (FMSs) in a given area [8,9,10]
The number marked on the right of the circle in the figure is the value of the damping coefficient, and the cross is the calculated optimal damping coefficient
Summary
The geomagnetic field and stress field are important geophysical fields Changes in these fields caused by tectonic activities such as earthquakes have long been central issues in geophysical research [1,2]. Because these fields are associated with two different disciplines, little research on the relationship between the geomagnetic field and the stress field has been published [3,4]. The inversion of the tectonic stress field (TSF) based on the earthquake focal mechanism solution (FMS) is an effective method to study the process and mechanism of earthquake initiation and occurrence [6,7]. The FMS of a single earthquake cannot be used to define the actual direction of the tectonic stress applied underground, the characteristics of the TSF in the region can be inferred through many FMSs in a given area [8,9,10]
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