Abstract
We processed MODIS data received from ground receiving stations into the spatial range of the Qinghai-Tibetan Plateau (China) and the eastern margin of the plateau, and then 283 K was set as the threshold value to remove the area covered by clouds. The monthly background field was calculated based on 17 years’ data, then we obtained the spatial Brightness Temperature anomaly of the current month by deducting the background field. Furthermore, the Brightness Temperature anomaly curves for secondary tectonic blocks in the plateau were calculated. The data indicated that since June 2020, the Brightness Temperature radiation within the Qinghai-Tibetan Plateau began to increase abnormally, starting from the western part of the study area and expanding eastward to cover the entire plateau. In January 2021, such an anomaly was seen again, extending to the Sichuan-Yunnan Block in the easternmost part of the study area in april. With the ongoing anomaly, a series of moderate and strong earthquakes occurred in the Qinghai-Tibetan Plateau, and finally, on 22 May 2021, the M7.4 earthquake struck the Madoi County. Moreover, according to the internal Brightness Temperature time series curves of the different secondary tectonic blocks, the Brightness Temperature has increased simultaneously since the beginning of 2020. A twofold standard deviation was found in the middle-east segment of the Bayanhar Block and the Qiangtang Block in October 2020, and an almost twofold standard deviation was found in March, while a twofold standard deviation was found in the Sichuan-Yunnan Block in april 2021. The occurrence of earthquakes in the plateau before the Madoi earthquake coincided with an upward trend of the time series curve. The spatial anomaly of Brightness Temperature over the Qinghai-Tibetan Plateau disappeared and the Brightness Temperature time series curve dropped drastically after the Madoi earthquake. The development of spatial anomaly of Brightness Temperature and the time series curve both coincide with the occurrence of earthquakes and are consistent with the generation of tectonic stress in the Qinghai-Tibetan Plateau. Our study showed that thermal infrared Brightness Temperature radiation reasonably reflects regional stress development and enables the detection of anomalies prior to moderate and strong earthquakes.
Highlights
Since the 1980s, thermal infrared data collected by an observation of the satellite platform was used to obtain abnormal information prior to earthquakes (Gorny et al, 1988)
In May 2021 the spatial Brightness Temperature (BT) radiation anomaly vanished but the Yangbi M6.4 earthquake occurred in the southwestern Sichuan-Yunnan Block, and the Madoi M7.4 earthquake occurred in the eastern Bayankala Block almost in the same time (Figure 4L), with an interval of less than 5 h
Moderate-resolution Imaging Spectroradiometer (MODIS) data were processed by splicing, cloud removal, extraction of the background field of BT, and the monthly calculation of BT anomalies with an independently developed system
Summary
Since the 1980s, thermal infrared data collected by an observation of the satellite platform was used to obtain abnormal information prior to earthquakes (Gorny et al, 1988). Ground surface parameters including temperature, outgoing long-wave radiation, and thermal infrared radiation can be detected (Ouzounov et al, 2004, Ouzounov et al, 2007; Tronin et al, 2002, Tronin et al, 2004; Rawat et al, 2011). Besides those ground surface parameters, atmospheric water vapor, CO2, CH4, CO, and other parameters can be monitored (Cui et al, 2011; Dey et al, 2004; Feng et al, 2020; Hayer et al, 2016; Weiyu et al, 2018; Wang et al, 2015; Zhong et al, 2020). Such an anomaly often occurred several months to several weeks before the earthquake, and in some areas, a sudden rise in the impending stage was recorded (Corradini et al, 2010; Pardini et al, 2017; Theys et al, 2019; Feng et al, 2020)
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