2008年新疆乌恰M6.7地震多参量时空变化特征研究

Temporal and spatial characteristics of the 2008 Wuqia, Xinjiang M6.7 earthquake multiple parameters

研究与孕震过程相关的多种地球物理和地球化学参量的变化特征,可为进一步理解孕震过程中不同圈层多参数的耦合机理提供依据。基于NOAA卫星观测资料分析了2008年乌恰M6.7级地震前后长波辐射异常变化,根据异常时空特征与地震时空窗的对应关系检测到震前的长波辐射异常信息。结合卫星观测获得的地气系统地表温度、大气温度、大气相对湿度、大气压力、一氧化碳含量等地球物理和地球化学参量,基于DTS(DeviationTime-Space)准则开展了多参量综合分析。结果表明,长波辐射异常点位上的地表温度、大气温度及大气相对湿度在地震前存在耦合关系,而检测到的一氧化碳异常出现在震后4 d,这可能与本次地震的断层特性及震后余震频发有关。此外,震前5—10 d出现的大气压力突变也可能对地震发生起到触发作用。因此,建议将地气系统中长波辐射的异常变化看作与地震活动相关的重要参量,其他地气系统参量作为辅助参量,在未来的地震监测研究中应重视多参量间的耦合及关联性研究。

Seismic thermal anomalies have attracted increasing attention from the scientific community since they were proposed in the mid-1980 s. A long-term Outgoing Longwave Radiation(OLR) data set from 2007 to 2016 was used to analyze thermal anomalies in the magnitude 6.7 earthquake that hit Wuqia, China, on October 5, 2008. To identify the earth–atmosphere system’s multiple parameter variations related to earthquakes, other surface and atmospheric multi-parameter data were processed over the critical region of Thermal Infrared Radiation(TIR) anomalies.Nighttime NOAA OLR data were selected because capturing seismic anomalies at night is easier than in the daytime considering the effect of artificial anomalies and solar radiation. The vorticity method was used in this study. To reliably detect seismic precursory information, 2009—2011 data on the absence of significant seismic activity in the Xinjiang region were calculated as background field. Apart from vorticity spatial analysis, time series analysis was utilized in this study. Then, the coupling variation of multi-parameter data was analyzed according to the Deviation–Time–Space(DTS) method. The 10-day average OLR vorticity analysis shows a sudden increase of OLR in mid-September 2008. Moreover, a long-term OLR data analysis showed that the anomalies existed prior to the seismic case only, which can be considered a unique variation. The OLR anomalies were not observed in aseismic years, thereby showing that OLR anomalies were related to the Wuqia earthquake. The OLR anomaly is located on the boundary of the Tarim active block. Therefore, distinguishing the seismic precursor is important. The strong-body earthquakegenerating model indicates that the irregular boundary of a solid block is likely to accumulate stress. The Tarim tectonic block has been stable since the Cenozoic era and can be classified as a solid body. Previous studies have shown a strong correlation between stress changes and TIR. The enhanced TIR between the active blocks was due to non-continuous stresses and high energy accumulation induced by the interaction of the active blocks and the strong differential movement between them. The increasing TIR anomalies prior to the earthquake led to heat accumulation on the near-surface and the near-ground air, resulting in the variation of skin temperature, air temperature at the lower height pressure levels, and relative humidity of air. The behavior indicates the coupling relationship between the lithosphere and the atmosphere in the seismogenic region. We deduce that air pressure is one of the external trigger factors of earthquakes. The dramatic variation of air pressure during the seismogenic process might affect the critical state. As soon as all internal conditions(the active seismic structure, the nature of the seismogenic zone, the crustal stress environment, and the focal mechanism) exist, some external conditions may trigger an earthquake. The increase in CO degasing in this case is only at the 800 hPa pressure level, thereby indicating that the source of CO variation is mainly the near-ground surface over the seismogenic zone and appears four days after the shock. The post-seismic variation might be related to the nature of seismogenic structure(locked and extrusion pressure-controlled) and the aftershocks. The surface and atmosphere multi-parameter variations associated with the 2008 M6.7 Wuqia earthquake were analyzed to detect precursor information related to the earth–atmosphere system. OLR anomalies were detected on the boundary of the Tarim active block because stress easily accumulated along a solid block boundary. The enhanced TIR emissions are reflected in anomalous OLR data. Results showed that the spatial location of OLR anomalies could reflect the crustal stress accumulation. Furthermore, OLR, skin temperature, air temperature, and relative humidity showed quasi-synchronous variations before this case. Results supported the seismic multi-sphere coupling model. The multi-parameter coupling between the surface and the atmosphere is an important precursor indicator in the short-term and immediate periods, and should be considered in future seismic infrared monitoring.