地球内核时变现象的性质探究及差速旋转的速率测定

地球的内核在几年的尺度上存在着明显的时变现象。重复地震产生的内核信号在固定路径上的变化为此提供了有力证据。然而时变的机制仍有一定的争议：内核相对于地幔的差速旋转是常见的一种解释，但不同研究测定的转速并不一致，甚至相差几个量级，因而也有研究认为时变来自内核边界的快速变化。本项目的研究目标是解决现阶段时变机制的争议，并对内核的旋转速率进行高精度的可靠测定。申请人将会利用近几十年的全球地震波形数据，扩充此前建立的高质量的重复地震数据库；并从中提取内核震相，得到时变现象的时空分布模式，从而据此剖析时变现象的成因。前人不同研究得到的转速难以吻合，很可能是误差较大所致。本项目将聚焦于采样到小尺度内核结构的关键数据，并结合内核的时变模式得到内核的运动模式和旋转速率。研究结果不仅能帮助我们进一步认识地球深部的运行方式，也会对磁场的产生机制等重要问题带来一定的启发。

Temporal changes of the Earth’s inner core over decadal time scales have been well observed by different seismic studies, especially those using high-quality repeating earthquakes. The phenomenon has commonly been interpreted as the differential rotation of the inner core shifting its interior heterogeneities, but estimates of the inner-core rotation rate vary by several orders of magnitude. Moreover, an alternative interpretation, the rapid growing or shrinking at the inner core boundary, is favored by some studies. The proposal aims at resolving the debates about the mechanisms of the temporal changes and determining the rate of the differential rotation with unprecedentedly high precision and reliability. I will use all available strong earthquakes over the globe to expand the database of high-quality repeating earthquakes and extract the signals of temporal change to further analyze the spatiotemporal patterns. The inconsistent estimates of rotation rate from previous studies seem to contradict the rigid inner-core rotation, but it could also be from poorly constrained inner-core structures by previous studies. Thus, I will focus on some key data, which help resolve some fine-scale lateral structures of the inner core. The rotation rate of the inner core would be easily estimated from the lateral structures and the patterns of the temporal change. The investigations on the mechanism of the temporal change and rate of the differential rotation of the inner core shed light on understanding the inner workings of our planet, especially the operation of the geodynamo.