Abstract
On 3 August 2014, an Mw 6.2 earthquake occurred in Ludian, Yunnan Province, China (27.245° N 103.427° E). This damaging earthquake caused approximately 400 fatalities, 1800 injuries, and the destruction of at least 12,000 houses. Using air temperature data of the National Center for Environmental Prediction (NCEP) and the tidal force fluctuant analysis (TFFA) method, we derive the temperature variations in multiple air layers between before and after the Ludian earthquake. In the spatial range of 30° × 30° (12°–42° N, 88°–118° E) of China, a thermal anomaly appeared only on or near the epicenter before earthquake, and air was heated from the land, then uplifted by a heat flux, and then cooled and dissipated upon rising. With the approaching earthquake, the duration and range of the thermal anomaly during each tidal cycle was found to increase, and the amplitude of the thermal anomaly varied with the tidal force potential: air temperature was found to rise during the negative phase of the tidal force potential, to reach peak at its trough, and to attenuate when the tidal force potential was rising again. A significance test supports the hypothesis that the thermal anomalies are physically related to Ludian earthquakes rather than being coincidences. Based on these results, we argue that the change of air temperature could reflect the stress changes modulated under the tidal force. Moreover, unlike the thermal infrared remote sensing data, the air temperature data provided by NCEP are not affected by clouds, so it has a clear advantage for monitoring the pre-earthquake temperature variation in cloudy areas.
Highlights
In the past thirty years, there have been numerous reports about surface temperature changes prior to earthquakes [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
The vertical characteristic of those thermal anomalies is consistent with the results of the Mw 5.7 Jiujiang earthquake, and coincide with the principle of atmospheric thermal dynamic diffusion along the vertical: air heated by land, uplifted by heat flux, cooled and dissipated in the sky [26]
Based on the high spatial–temporal correlation between thermal anomalies and the Ludian earthquake, high consistency between spatial–temporal variation of thermal anomalies and tidal force potential, and the strong evidence provided by the significance test, it can be concluded that the thermal anomalies in periods A, B, and C are caused by the Ludian earthquake
Summary
In the past thirty years, there have been numerous reports about surface temperature changes prior to earthquakes [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. Using various thermal infrared (TIR) remote sensing data, researchers have proposed several methods for extracting thermal anomalies before earthquakes. The MeteoSat Second Generation–Spinning Enhanced Visible and Infrared Imager (MSG–SEVIRI), Advanced Very High Resolution Radiometer (AVHRR) loaded on the National Oceanic and Atmospheric Administration (NOAA) satellite, Chinese Feng Yun (FY) meteorological satellite, and so on [2,16,17,18,19,20,21,22,23,24,25] These methods are based on the statistical processing of multiyear remote sensing data, and they usually could not reliably measure small but significant thermal changes occurring prior to single earthquakes [26]. The results of thermal anomalies before the Ludian earthquake and the long-term significance test for determining the relation between earthquakes and thermal anomalies are shown in Section 4, while the discussion and conclusion are presented in Sections 5 and 6
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