利用sPn和Pn震相走时差计算的2014年2月28日石嘴山M_L4.4地震的震源深度为7.21±0.277km；分析不同震源深度下民勤台的理论波形与观测波形拟合结果，得到震源深度为7~8km。研究认为，石嘴山M_L4.4地震属于浅源地震，震源浅和沉积层较厚是此次地震震感较强的主要原因。另外，合理选取地震波形数据和震相识别方法，可有效提高sPn震相测定震源深度的可靠性。为便于应用，本文还给出了宁夏地区地震震源分别位于上地壳和下地壳时sPn和Pn震相走时差与震源深度的对应关系表。

We calculated the focal depth of the Shizuishan earthquake by using arrival-time difference of seismic phase sPn and Pn,which is 7.21±0.277km. The depth of earthquake is 7~8km by comparing the synthetic seismograms and the observed seismogram at different depths. Two results show that the sPn phase can determine reliable source depth,sPn and Pn in the upper and lower crust of the border area between the upper and the lower crust and the source depth of the upper and lower crust are obtained. According to the regional velocity model,we obtained the corresponding table of arrival-time difference and focal depth when earthquakes occur in the upper and lower crust in the border area of Ningxia and Inner Mongolia. The Shizuishan earthquake occurred in the north boundary of the Yinchuan Basin. Shallow source is one of the important reasons for feeling strongly in source region.

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国家自然科学基金-青年科学基金项目（41604015）和宁夏回族自治区重点研发计划（2016KJHM135）联合资助