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High-velocity friction experiments were conducted on two natural fault gouges retrieved from the Yingxiu-Beichuan fault zone (Sichuan, China), which accommodated the 2008 Wenchuan Mw 7.9 earthquake. The experiments simulate large earthquake slip; the rotary shear apparatus enables to gather information as a function of shear displacement (and slip velocity) in a single experiment. The two starting fault gouges are essentially paramagnetic with one containing goethite. The experimentally sheared gouges both show a significant magnetic enhancement and softening with increasing slip distance. Rock magnetic measurements reveal that magnetite was formed during the experiment due to thermochemical reactions of iron adsorbed on clay minerals (smectite, chlorite). Scanning electron microscope observations showed that the new magnetite occurs as spherical and sintered irregular aggregates. This implies a high-temperature origin. The peak temperatures are estimated numerically to range from~260 to~440°C. Also, during the experiment on the goethite-bearing fault gouge, goethite was altered, reduced to magnetite due to the decomposition of trace organic matter present in the starting material. Magnetic susceptibility and magnetization of sheared samples are linearly increasing with the temperature rise induced by frictional heating; coercivities are decreasing. The grain size of the newly formed magnetite increases with heating temperature. This demonstrates that short-duration frictional heating generated by fast seismic slip induces thermal alteration: neoformation of ferrimagnetic minerals leads to magnetic enhancement and softening of slip zones. Thus, rock magnetic methods are a useful tool for diagnosing the earthquake slip and estimating the temperature rise of coseismic frictional heating.

This study analyzed the total electron content (TEC) observed by 337 ground‐based Global Navigation Satellite System (GNSS) receivers over China and South Asia, the critical frequency of the ionospheric F2 layer (foF2) and its height (hmF2) recorded by the ionosonde at Puer (22.7°N, 101.05°E, 72% obscuration), Yunnan province, during and after the annular solar eclipse on June 21, 2020. The observations show that the eclipse induced not only a daytime major depression but also nighttime perturbations in the ionosphere. The TEC perturbed intermittently from noon to midnight between 85° and 125°E on the eclipse day. The positive and negative changes of the prereversal enhancement respectively occur in the nearby longitudinal sectors of 100°and 115°E. The TEC perturbations behave as a terminator wave that propagates in a northwestward direction after sunset.

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The sudden eruption of the Tonga underwater volcano (20.53°S, 175.38°W) on 15 January 2022 generated explosions that triggered blast waves traveling away from the eruption. In this study, the analysis of the geomagnetic field observations on the ground shows that the eruption perturbed the E‐region current density by 22–55 mA/m within a radius of 8,000 km away from the eruption. The perturbation evolved into large scales of ∼5 hr and thousands of kilometers as it traveled away. The traveling speed of the leading front is ∼740 m/s that is near acoustic in the ionosphere. The magnetic fields and total electron content observations suggest that the dynamics changes further induced significant ionospheric disturbances that lasted ∼10 hr after the eruption. The examination of the Tonga volcanic eruption inspires us that a near‐surface perturbation can change the dynamics of the upper atmosphere.

Recognition of coring‐induced disturbance, which is essential for magnetic fabric and paleomagnetic studies of poorly lithified sediments, is generally not straightforward. Here, we report on anisotropy of magnetic susceptibility (AMS) and paleomagnetic data of the sediments from Holes U1480E and U1480H, IODP Expedition 362, west of the Sumatra subduction zone. AMS is characterized by steep minimum principal axes (Kmin) in undisturbed sediments. However, a considerable portion of the recovered sediments are affected by significant coring‐induced disturbance. In these cases, we observed three AMS patterns: (1) AMS principal axes are randomly distributed for sediments with mingling and distortion of beds, (2) Kmin axes of sediments with upward‐arching beds are deflected out of the splitting face of the working half, and (3) suck‐in sediments are characterized by vertical Kmax axes. These deformation‐dependent AMS patterns can be attributed to the realignment of mineral particles caused by the coring process and subsequent sampling procedures. Besides a low‐coercivity, vertical, drilling‐induced overprint, we observed a high‐coercivity component that is likely a composite of the primary magnetization with a demagnetization‐resistant portion of the drilling overprint. After accounting for the disturbed intervals, several polarity transitions can be identified in the undisturbed sediments which correlate well with the Pleistocene geomagnetic polarity timescale. These observations demonstrate that great caution is required when attributing geological significance to AMS and paleomagnetic data obtained from soft sediment cores, which are highly susceptible to coring‐induced disturbance. In addition, AMS measurements provide a potential tool for identifying core deformation for further paleomagnetic studies.

The North China craton is encircled by four successive triple-conjugated rifts, which are respectively centers of large igneous provinces (LIPs) of bimodal compositions, i.e., Xiong'er rift (south, ca. 1.78 Ga Taihang LIP), Yanliao rift (north, ca. 1.32 Ga Yanliao LIP), Xuhuai rift (east, ca. 1.23 Ga Licheng and ca. 0.92 Ga Dashigou LIPs), and Langshan rift (west, ca. 0.82 Ga Qianlishan LIP). These rifts are genetically related with their contemporaneous LIPs based on their consistent geometry. Spatial migration of these rifts and LIPs indicates their propagation from along one marginal side to the opposite side of the craton, which may results in the sequential breakup of the proto-North China craton from one side to another during 1.8-0.8 Ga. However, the observation that the lithosphere under the LIP-associated rift regions is less destructed (decratonized) in the Mesozoic indicates a possible role of LIPs in strengthening intracratonic steady state. This study shows that LIPs may change craton stability in either direction.