Abstract
Earthquakes are one of the most threatening natural disasters to human beings, and pre- and post-earthquake microwave brightness temperature (MBT) anomalies have attracted increasing attention from geosciences as well as remote sensing communities. However, there is still a lack of systematic description about how to extract and then discriminate the authenticity of seismic MBT anomalies. In this research, the first strong earthquake occurring near the northern edge of eastern Bayan Har block in nearly 20 years, the recent Mw 7.3 Maduo earthquake in Qinghai province, China on 21 May 2021, was selected as a case study. Based on the monthly mean background of MBT, the spatiotemporal features of MBT residuals with 10.65 GHz before and after the earthquake was firstly revealed. Referring to the spatial patterns and abnormal amplitudes of the results, four typical types of evident MBT positive residuals were obtained, and the time series of intensity features of each category was also quantitatively analyzed. Then, as the most influential factor on surface microwave radiation, air temperature, soil moisture and precipitation were analyzed to discriminate their contributions to these residuals. The fourth one, which occurred north to the epicenter after the earthquake, was finally confirmed to be caused by soil moisture reduction and thus ruled out as being related to seismicity. Therefore, the three retained typical MBT residuals with 10.65 GHz could be identified as possible anomalies associated with the Maduo earthquake, and were further analyzed collaboratively with some other reported abnormal phenomena related to the seismogenic process. Furthermore, through time series analysis, the MBT positive residuals inside the Bayan Har block were found to be more significant than that outside, and the abnormal behaviors of MBT residuals in the elevation range of 4000–5000 m reflected the shielding effect on microwave radiation from thawing permafrost on the plateau in March and April, 2021. This research provides a detailed technique to extract and discriminate the seismic MBT anomaly, and the revealed results reflect well the joint effect of seismic activity and regional coversphere environment on satellite-observed MBT.
Highlights
In mid-late April and early May, significant microwave brightness temperature (MBT) residuals reoccurred around the forthcoming epicenter, and their shapes appeared in strips or spots, but their intensity were slightly weaker than that in late March
The Earth system is far from equilibrium [46], and the seismogenic environment varies with its special spatial location, so the surface microwave radiation observed by satellites is vastly different and inevitably affected by many factors
The major disturbances to the earth’s surface, from which the microwave radiation emits, need to be eliminated one by one before the obtained MBT residuals can be considered to be seismic anomalies, and the MBT anomaly should be analyzed from the perspective of seismogenic process
Summary
At 18:04 on 21 May 2021 (UTC), the Mw 7.3 Maduo earthquake occurred at the southern Qinghai province, China, of which the epicenter was located at 34.59◦ N, 98.24◦ E, with a hypocenter depth of 10 km (USGS). Bayan Har block, which is one of the representative active blocks of lateral extrusion in the Qinghai–Tibet Plateau since Cenozoic and one of the most intense areas of earthquake activity in China [1,2,3]. The Bayan Har block is enclosed by the East Kunlun fault zone as the north boundary, the Longmenshan fault zone as the east boundary, the Ganzi–. For the last 25 years, the strong earthquakes above Mw 6.5
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