青藏高原东南缘热流估算及与地震活动相关性分析

青藏高原东南缘地区内部构造运动强烈,是地热资源发育与地震事件频发的活动地区.大地热流记录了发生在地球深部各种作用过程的热学信息,可以作为地质构造活动和地震活动研究的有效约束,但是大范围的热流数据测量很难实现,因此,本文根据居里面深度结合放射性元素分布等计算了青藏高原东南缘的大地热流分布.首先,通过地表放射性元素的分布计算出地表产热量的分布,然后,利用相关地热参数之间的关系迭代计算出该地区地壳上下层的热导率分布,最终估算出地表热流及地下不同深度处热流值的分布.本文结果表明:(1)青藏高原东南缘的大地热流位于44～108mW·m~(-2)之间,平均75mW·m~(-2),符合研究地区西南高、东北低的背景趋势,地壳内部热流值随深度的增加而降低.大部分地区地表热流异常与实际地热带分布相吻合,如川西、藏东南与滇西地区等地为地热高值区,川东和楚雄等地为热流低值区.(2)结合其他地球物理探测结果,总结了地壳内部热流与地震事件的联系:在地热梯度带地区,当两侧地层在一定深度范围内存在明显物性差异时,地震事件高发.

Estimation of heat flow in southeastern margin of Tibetan Plateau and its analysis of the correlation with earthquake activity

The southeastern margin of Tibetan Plateau is an area where geothermal resources are developed and earthquakes occur frequently due to the complete and intense geotectonic activities. Heat flow records the geothermic information about various tectonic movements that occur in the deep earth. It can be used as an effective constraint on geological tectonic activities and seismic activity studies. However, the heat flow data for large areas is difficult to achieve through logging technology. Hence, this paper estimates the surface heat flow and its value underground based on the Curie depth combing the radioactive elements distribution of the study area. Firstly, we calculate the surface heat production from the radioactive elements distribution. Secondly, we obtain the thermal conductivities of upper and lower layers of the crust by an iterative approach based on the relation between geothermal parameters. Finally, we obtain the surface heat flow and its value underground. The results show that:(1) The variation range of surface heat flow of southwestern margin of Tibetan Plateau is 44~108 mW·m^-2, and the mean is 75 mW·m^-2. It is in line with the background trend of high in southwest and low in northeast. The crustal heat flow value decreases as the depth increases. The majority of local high and low anomalies of surface heat flow are corresponding to the previous researches, such as west of Sichuan province, southeast of Tibet and west of Yunnan province are with high heat flow value; east of Sichuan province and Chuxiong are with low heat flow value. (2) Combined with other geophysical findings, the connection between the crustal heat flow at different depth and earthquake events is:earthquakes tend to occur in geothermal gradient zones where exist apparent differences of physical properties within a certain depth range on both sides of the gradient zone.