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在日本伊豆半岛的伊东近海1998年4月震群期间,我们在近场地区观测到了地面旋转和平移运动的6个分量。为了检验我们使用MotionPack传感器观测结果的可靠性,我们安装了8301F传感器,即灵敏度比MotionPack传感器高的惯性角位移传感器。MotionPack的噪声水平远高于8301F的噪声水平,但这些信号分量的波形却相互相当相似,说明MotionPack记录旋转速率正确,但噪声较高。我们的观测使人们知道了垂直轴周围最大旋转位移和最大平移速度之间的线性相关。围绕垂直轴旋转运动的波形与平移水平速度的波形类似,说明最大值之间线性相关。这些旋转运动远大于由圣安德烈斯断层台阵数据计算的旋转运动。这种大差异可由下列一种或一种以上作用来解释:单一回转仪测量和台阵观测所得旋转运动空间尺度的差异;记录伊东近海震群的台站受陡峭地形的影响;圣安德烈斯断层和伊东近海震群区之间成熟度的差异。
During the April 1998 earthquake swarm in the Ito Peninsula, off the Izu Peninsula, Japan, we observed six components of ground rotation and translational motion in the near field. To test the reliability of our observations with the MotionPack sensor, we installed the 8301F sensor, an inertial angular displacement sensor with higher sensitivity than the MotionPack sensor. The noise level of the MotionPack is much higher than the noise level of 8301F, but the waveforms of these signal components are quite similar to each other, indicating that the MotionPack record rotates at the correct rate but at a higher noise level. Our observations have made people aware of the linear correlation between the maximum rotational displacement and the maximum translational velocity around the vertical axis. The waveform of the rotation around the vertical axis is similar to the waveform of the pan horizontal velocity, indicating a linear correlation between the maxima. These rotational movements are much larger than the rotational motion calculated from the San Andreas fault array data. This large discrepancy can be explained by one or more of the following: differences in the spatial dimensions of the rotational motion measured by the single gyrometer and by the array observations; by the steep terrain at the stations recording the swarm of the Ito-Seashore; Differences in maturity between the Reese Fault and the near-epicenter of Ito East.