利用连续重力观测约束2014智利Iquique地震的震源机制解

2014年4月1日,智利北部Iquique地区近海发生MW8.1地震,地震发生之后,国际上一些著名的地震科研机构和学者采用不同的数据和方法计算得到此次地震的震源机制解,但这些结果存在较大差异.地球长周期自由振荡的振幅主要依赖于地震矩的大小及地震断层的破裂方式,可以很好地约束地震震源机制.因此,本文根据2014年Iquique地震现有的6个不同震源机制解模拟计算了该地震激发的自由振荡信号,并与全国连续重力台网中16个弹簧重力仪的观测结果进行比对,基于1.5~5.3mHz的球型简正模分析和约束了Iquique地震的震源机制解.研究发现,基于美国地质调查局WPhase Moment Tensor Solution反演的震源机制解的自由振荡模拟值与实际观测符合最好,其相应的震级能较好反映Iquique地震释放的总能量,而利用海啸数据反演的标量地震矩偏小,联合远场和近场长周期观测数据反演可显著改善震源机制解.另外,还基于格尔木重力台站的模拟值与观测值定量分析了不同震源机制解参数对自由振荡振幅的影响.结果表明地震的标量地震矩M0对自由振荡振幅的影响最大,而断层走向、倾角、滑动方向角和震源深度对自由振荡的振幅影响相对较小.

Constraining the focal mechanism of the Iquique earthquake with observations of the continuous gravity stations

On 1 April 2014, a magnitude M_W8.1 interplate thrust earthquake ruptured a densely instrumented region of Iquique seismic gap in northern Chile. After Earthquake, the focal mechanism solutions of Iquique earthquake were provided by well-respected international earthquake research institutions and scholars based on different data and methods, which were quite different. The amplitudes of the Earth's free oscillations have a close relationship to earthquake focal mechanisms. Focal mechanisms of large earthquakes can be well analyzed and constrained with observations of long period free oscillations. We compared free oscillations observed by 16 spring gravimeters of continuous gravity stations with synthetic normal modes corresponding to six different focal mechanisms for the Iquique earthquake, and the focal mechanisms solutions of Iquique earthquake were analyzed and constrained by spherical normal modes in a 1.5 to 5.3 mHz frequency band. It's found that the synthetic modes corresponding to the focal mechanism determined by the United States Geological Survey WPhase Moment Tensor Solution show agreement to the observed modes, suggesting that earthquake magnitudes predicted in this way can reflect the total energy released by the earthquake. The scalar seismic moment obtained by tsunami data inversion is significantly underestimated. Focal mechanism solutions can be improved by joint inversion of far-and near-field data. In addition, based on the synthetic and observed normal modes at Golmud station, quantitative analysis was carried out to research the influences of free oscillation's amplitudes caused by different focal mechanism parameters. The results show that scalar seismic moment M₀ has a major influence on the amplitudes of free oscillations, and the strike, dip, rake and depth of the hypocenter have minor influences.