Abstract
Hydrothermal anomalies related to the Ms8.0 Wenchuan earthquake (EQ) on May 12, 2009, have been widely reported. However, the reported anomalies have not been associated with multi-geosphere analysis, and space–time analysis with crustal seismicity is lacking. In this paper, the space–time variation of hydrothermal parameters, including soil moisture, soil temperature, near-surface relative humidity (RHsig995) and air temperature (TMPsfc), was first extracted and analyzed with the NCEP-FNL reanalysis dataset. The b-value (a seismic parameter from the Gutenberg–Richter law) was calculated and mapped to unravel the crustal stress and rock rupture. Our results reveal a similar time window for hydrothermal anomalies on April 20 and April 30, 2008, and these anomalies are mainly distributed along the southern and middle parts of the Longmenshan fault zone. The surface temperature anomalies lag behind the humidity anomalies, and the accelerating stress accumulation started since June 2007 and lasted for eight to nine months before the mainshock. The b-value mapping shows a segmented difference along strike of the Longmenshan fault, and that regional stress accumulated mainly in the southern parts of the F2 and F3 faults. We propose the occurrence of a complex coupling process led by crustal stress buildup before the Wenchuan EQ. The anomalies are concentrated in the southern part of the surface rupture zone. The prolonged crustal stress accumulation corresponds to the short intermittent hydrothermal response on the Earth’s surface before the Wenchuan EQ. Our findings reveal new hydrothermal anomalies in the Earth’s surface and atmosphere and explore direct link with seismogenic processes in the crust.
Highlights
Monitoring and early warning of tectonic earthquake (EQ) has become a research hot spot in seismology
It is noteworthy that this EQ happened on the active fault boundary around the Bayan Har fault block in the Tibetan plateau (Fig. 1b)
The results show that OLR presented an anomaly in the wider areas in the Sichuan Basin from April 29 to April 30, and it turned into an anomalous stripshaped area concentrating on the Longmenshan fault zone on May 5
Summary
Monitoring and early warning of tectonic earthquake (EQ) has become a research hot spot in seismology. The epicenter (31°N, 103.4°E) is located at the middle part of the Longmenshan fold belt (eastern Tibetan Plateau) with the hypocenter depth of about 19 km (Fig. 1a). This earthquake was one of the worst in modern Chinese history, causing over 80,000 fatalities and severe damages to infrastructure (Fu et al 2011a, b). Thermal anomalies observed in the tectonic fault intersecting zone or around the epicenter before the Wenchuan mainshock include surface temperature, surface latent heat flux, thermal infrared radiation and outgoing long-wave radiation (Huang et al 2008; Jing et al 2013; Li et al 2010; Singh et al 2010; Wu et al 2012; Xiong et al 2009; Yang and Mi 2009; Liu et al 2020). This study aims to identify the hydrothermal anomaly responses to the Wenchuan EQ and analyze the space–time correlation with seismicity to understand the geosphere coupling mechanism of earthquake precursors
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