2021年5月22日2时4分青海省玛多县发生M7.4地震。四川地震预警台网成功地处理并产出了本次地震预警结果。本文针对四川地震预警系统产出的8次地震预警处理结果及预警减灾效能进行了分析。此次地震震中距四川地震预警网55km，首台触发后12.19s发布首次预警处理结果，前5次预警处理结果用时距离首台触发时间均小于35s。与正式地震目录对比，第1次预警处理结果震中位置偏差为17.1km，震级偏差为-1.8，盲区半径为121km。随着参与计算台站数量增多，震中位置偏差和震级偏差不断减小，盲区半径不断增大。由于地震破裂时间长和台站限幅等原因，8次预警震级均偏小。本次地震预警的有效获益区为震中距121～324km的环形区域，此区域内减灾效能显著。本次地震预警结果表明，四川地震预警系统在本次地震中预警产出效果较好，对于网外大地震预警有重要参考意义。

An M7.4 earthquake occurred in Maduo county, Qinghai Province. the Sichuan Earthquake Early Warning System(EEWS) successfully captured this earthquake and output the early warning results. In this paper, we analyzed the eight early warning processing results and the effectiveness of disaster reduction of this earthquake. the epicenter distance of the earthquake is 55km from the Sichuan Earthquake Early Warning Network(EEWN). the first warning processing result was released 12.19s after the first station was triggered, and the first 5 warning processing results took less than 35s to the triggering time of the first station, which meets the timeliness requirements of early warning. Compared with the official earthquake catalog, the first warning processing results show that the deviation of the epicenter position is 17.1km, the magnitude deviation is -1.8 with the blind zone of 121km. As more stations involved in the calculation, the deviations of both the epicenter position and magnitude are getting smaller and smaller, but the blind zone radius is increasing. Due to the long rupture time of the earthquake and the waveform clipping of the seismic stations, the magnitudes from eight early warning are all smaller than the catalog value.the effective beneficiary area of this earthquake early warning is the circular area with an epicenter distance of 121~324km so that the effectiveness of disaster reduction in this area is remarkable. the results of this earthquake early warning show that the Sichuan EEWS is of a good capability for early warning output in this earthquake outside the Sichuan EEWN, which has an important significant reference for the early warning of large earthquakes outside the earthquake early warning network.

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国家重点研发计划（2018YFC1504003）、地震科技星火计划项目（XH19038Y）、北京市自然科学基金（8202051）共同资助