Abstract
Abstract. Satellite passive microwave radiative signals are considered to reflect thermal radiation and energy exchange of the Earth’s surface, and the microwave brightness temperature (MBT) has been preliminary adopted for pre-earthquake thermal anomaly monitoring in recent decades. Based on the spatio-temporally weighted two-step method (STW-TSM), this paper aims to uncover the evolution characteristics of MBT anomaly prior to typical earthquakes (EQs), i.e. the Mw7.9 Wenchuan EQ in May 2008, the Nepal EQs in April and May 2015, and the Mw5.8 Yibin EQ in June 2019, and to explore and recognize their differences and commonalities. The results are summarized as: 1) significant MBT positive anomalies appeared east and southwest close to the epicenter before the Wenchuan EQ, and the east anomaly migrated northeastward along Longmenshan faults with aftershocks, then the two anomalies dissipated subsequently with the ceasing of large aftershocks (Mw > 5.5). 2) the MBT positive anomalies of Nepal EQs firstly appeared along the Himalayas and became most obvious 1 day before the main shock, and dissipated subsequently after the first shock, and that of the second shock behaved in the same spatiotemporal patten. 3) regional positive MBT anomalies appeared around the epicenter a half month before the Yibin EQ and diminished over time, and the most obvious abnormal area transferred from the central and northwest to the southwest study area. It exhibited that MBT positive anomalies prefer to appear at the mechanically relaxed zones, such as the loose Quaternary with Wenchuan EQ, the cliff peaks with Nepal EQs, and the mountains surrounding Yibin EQ’s epicenter, which can be attributed to the declining of ground surface microwave dielectric caused by stress activated P-holes during the period of seismogenic preparation. This research provides a novel insight into mining MBT anomalies associate with large earthquakes and a possibility to explore the potential mechanism of such abnormal phenomena.
Highlights
Earthquake (EQ) is one of the most destructive natural hazards, and the remote sensing study on monitoring abnormal preearthquake signals has been conducted for many decades (Gornyi et al, 1988; Tronin, 1996; Qiang et al, 1997; Saraf and Choudhury, 2004; Tramutoli et al, 2005; Wu et al, 2012, 2016; Qin et al, 2013)
In the last twelve years, satellite passive microwave remote sensing was becoming an indispensable aspect in detecting seismic-related signals for its effective observations on the Earth surface and capability of indicating potential precursors, and its application has achieved some remarkable results and greatly promoted the remote sensing research on earthquake monitoring as well as forecasting (Maeda and Takano, 2008, 2010; Takano and Maeda, 2009; Singh et al, 2010; Chen and Jin, 2011; Jing et al, 2018; Qi et al, 2020)
The Mw7.9 Wenchuan earthquake is the worst disaster in recent decades of China, which happened in Sichuan Province, China, at 14:28 pm on May 12, 2008 (Beijing Time)
Summary
Earthquake (EQ) is one of the most destructive natural hazards, and the remote sensing study on monitoring abnormal preearthquake signals has been conducted for many decades (Gornyi et al, 1988; Tronin, 1996; Qiang et al, 1997; Saraf and Choudhury, 2004; Tramutoli et al, 2005; Wu et al, 2012, 2016; Qin et al, 2013). The emission and transmission of microwave radiation signals are closely related to the physical properties of coversphere (sands, soil, water, ice, snow, forest and vegetation on the Earth’s surface) and atmosphere, and strongly influenced by numerous geographical, meteorological and geophysical factors that change with time and space. These diversiform effects in time and space domains should be fully considered when processing and applying microwave images, but the existing researches do not pay enough attention to them. How to retain and obtain the abnormal signals related to EQs by excluding a variety of non-seismic factors and explore the mechanism of the abnormal phenomena through comparative analysis is a very critical problem
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