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地震波速度是认识地球深部状态和过程的主要观测参数.利用地震观测获得的速度结构图像讨论地球深部动力学过程,首先需要确定地震波速度图像能反映哪个时期构造事件的影响,这是地震波速度结构图像的时效性问题.立足于岩石物理实验依据,本文建立了上地幔温度-速度对应关系模型,利用数值方法模拟上地幔高温和低温异常的演化过程,并对中国东部上地幔动力学过程进行探讨.模拟结果显示,高温异常体的演化时间受异常体尺寸和上地幔黏滞系数控制,而低温异常的演化时间受尺度控制,与上地幔黏滞系数几乎无关.温度异常尺度越大,可被追溯的时间越久;但高温异常的保留时间远小于低温异常.考虑地震学观测的分辨率为100km,尺度为500km×300km的高温异常能持续被地震学观测20Myr,表明中国东部上地幔地震波低速异常可能反应新生代以来的热事件;而300km×120km尺度的低温异常持续时间可达~192Myr,表明中国东部地幔转换带地震波高速异常可能代表停滞的古太平洋俯冲板片.
Seismic wave velocity is the main observation parameter for understanding the state and process of deep Earth. Using the velocity structure images obtained from seismic observations to discuss the deep dynamical processes of the Earth, we first need to determine the influence of the seismic events on the seismic events during which time the seismic velocity images Based on the experimental data of rock physics, this paper establishes a temperature-velocity correspondence model of the upper mantle, simulates the evolution of the high-temperature and low-temperature anomalies in the upper mantle using numerical methods, and discusses the dynamics of the upper mantle in eastern China. The simulation results show that the evolutionary time of high temperature anomalous body is controlled by the size of anomalous body and the upper mantle viscous coefficient, while the evolution time of low temperature anomalous is controlled by scale and has little relation with the upper mantle viscous coefficient.The larger the temperature anomaly scale can be traced back However, the retention time of high-temperature anomalies is far less than that of low-temperature anomalies. Considering the resolution of seismological observation is 100km, the high-temperature anomaly of 500km × 300km can be continuously observed by seismology for 20Myr, indicating that the low- Response to Cenozoic thermal events; and 300km × 120k The low-temperature anomaly duration of m-scale can reach ~ 192Myr, indicating that the high-speed anomalous seismic waves in the mantle transition zone in eastern China may represent stagnant paleo-Pacific subduction plates.