强震前的“干热异常”与地温、降水波及应变弱停

The Abnormal High Soil Temperature,Less Precipitation and Weakening of Stress Wave before Strong Earthquake

对近30年出现在中国西部及邻区的14次MS≥6.9强震前1年多内的地温场和降水场进行了分析。发现有如下共同规律：①在震前1年左右东亚地区会出现干热异常（3.2 m地温升高,同时降水距平为负值）,持续时间约为2-6个月,最大干热面积可达2-4×106km^2;②在震前0.5-1年左右我国的月降水距平%图和3.2 m地温距平的月际变温图上,可看到波长小于1 000 km的地温波和降水波,可称为＂超低频应力密度波（应变波）＂,它是致使岩石破裂的力源;③在震前0-2个月应变波的波长会停止缩短,振幅变小,且波动方向可有一个近90°的旋转,是＂应变弱停＂的表现。以上可视为孕震三步曲。依据上述统计事实本文提出了强震成因的假设：地外核中有一股热力极不稳定的Benard上升流体对其上的壳幔层形成顶托,造成地温升高,对流热传导系数变小,形成干热异常;岩石圈中脆性层的应力不断增大,致使出现不稳定波（应变波）;出现＂应变弱停＂时意味着强震即将爆发。

The relationship between the ground temperature field and the precipitation field within one year before the occurrence of strong earthquake（MS≧6.9,14 times in total） in western China over the past 30 years are analyzed.It is found that： ①A large area with abnormal high soil temperature at 3.2 m are identified one year before the occurrence of earthquake accompanied by less precipitation in this area.The abnormal mentioned could last for 2 to 6 months with a maximum dry area of 2-4×106 km2.② The fluctuation in both the soil temperature and precipitation fields with the wavelength less than 1 000 km are appeared 0.5-1 year before earthquake occurrence,namely,the so called ＂ultra low frequency stress wave＂.The wave is responsible for break of the curst.③ The stress wave weakens with a shorter wavelength and lower intensity,as well as a sharp turning of the propagation direction by nearly 90°.The above three stages could be called ＂the three stages for earthquake gestation＂.A hypothesis is proposed on the mechanism of strong earthquake based on the above mentioned facts as follows： There is a kind of unstable uplifting Benard convection in outer layer of the earth core with a horizontal scale of 106 km^2.The uplifting action push up the crust and the mantle.When arrives at the boundary layer between the earth core and the mantle.Following results are expected consecutively： The higher soil temperature field and the heat conductivity decreasing cause less rainfall.With the stress in the crust keeping increase a kind of unstable wave（strain wave） appears.The weakening of the stress wave happens right before the occurrence of the strong earthquake.