Variation of Thermal Infrared Brightness Temperature Anomalies in the Madoi Earthquake and Associated Earthquakes in the Qinghai-Tibetan Plateau (China)

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.

Analytical Study of the Changes in Brightness Temperature Based on the Tectonic Field Associated With Three Earthquakes in the Eastern Tibetan Plateau

“…3(i)), the BT radiation intensified again, predominantly in the eastern Qiangtang and eastern Bayan Har blocks, approximately 32% and 14% of which experienced an increase in BT above the threshold, respectively. Available research findings suggest that spatial radiation intensification gradually disappears after an earthquake [40]. However, as seen in Fig.…”

“…Images of each swath were then cropped based on the size of the study area, and the BT was retrieved simultaneously. The cropped images were combined into images with a temporal resolution of 1 day [40]. Since cloud cover is detrimental to the > TGRS-2022-03662 < retrieval of the BT, a cloud removal procedure is also required to process the MODIS BT data.…”

“…Through repeated trials, we found that spatial BT anomalies calculated at time intervals of calendar months could reflect abnormal information to the greatest extent. Therefore, a background BT field was calculated for each of the 12 calendar months based on the data for the 18-year period [40]. Precisely, the spatial BT values for a particular month over the 18-year period were summed and then averaged to produce the background field for the month.…”

Pronounced Changes in Thermal Signals Associated with the Madoi (China) M 7.3 Earthquake from Passive Microwave and Infrared Satellite Data

“…In comparison, lower ILRA values were observed within the five tectonic blocks in 2019 when earthquakes of M > 5.5 did not occur (blue lines in Figure 10). Using MODIS monthly brightness temperature data, Yang et al [37] observed two increased thermal anomaly processes in the Tibetan Plateau prior to the Madoi earthquake, which started from June 2020 and January 2021, and they found that the anomalies moved from west to east with time. Our results based on MWBT and OLR data with higher temporal resolutions shed further light on the thermal evolution within the different scale tectonic units (seismogenic fault and active tectonic block) during the second thermal anomaly process since January 2021.…”

“…The thermal-related signals associated with this earthquake have been reported using the MODIS infrared brightness temperature (IRBT) and AMSR2 microwave brightness temperature (MWBT) data [37,38]. The infrared variation has shown that an increased IRBT has covered most areas of Tibetan Plateau since October 2020 [37], and an enhancement in MWBT within the Bayan Har block, which is more pronounced compared to the outside of this block, has been observed since January 2021 [38]; this may be associated with the localized activities in this block.…”