Dept. Natural History Sci., Hokkaido University, N10W8, Kita-ku, Sapporo 060-0810, Japan.
Sci Rep. 2012;2:931. doi: 10.1038/srep00931. Epub 2012 Dec 5.
Day-scale Earth's free oscillation after large earthquakes has been detected by underground instruments such as strainmeters, gravimeters and seismometers, to investigate Earth's internal structure, geodynamics, and source properties of earthquakes. Here we show that Global Positioning System (GPS) can also detect the signals of the Earth's free oscillation. A dense GPS array in Japan (GEONET) recorded the surface deformation following the 2011 Tohoku megathrust earthquake. A simple array analysis over 300 stations reduces local noise in GPS time series. We find that the dense GPS array truly detected both spheroidal and toroidal fundamental modes in three-direction displacement. This new tool has a strong potential to investigate the free oscillations particularly in low-frequency bands.
利用应变仪、重力仪和地震仪等地下仪器检测到了大地震后的日地自由振荡，以研究地球内部结构、地球动力学和地震的震源特性。在这里，我们表明全球定位系统（GPS）也可以检测到地球自由振荡的信号。日本密集的 GPS 阵列（GEONET）记录了 2011 年东北Mw9.0 地震后的地表变形。对 300 多个台站进行简单的阵列分析可以降低 GPS 时间序列中的局部噪声。我们发现，密集的 GPS 阵列确实在三个方向的位移中检测到了球型和环型基本模式。这种新工具具有特别在低频带中调查自由振荡的强大潜力。
