Modelling Ground-to-Air Coupling for the Shallow ML 4.3 Folkestone, United Kingdom, Earthquake of 28 April 2007
Modelling Ground-to-Air Coupling for the Shallow ML 4.3 Folkestone, United Kingdom, Earthquake of 28 April 2007
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DOI：
10.1785/0120080236
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发表时间：
2009-08
影响因子：
3
通讯作者：
D. N. Green;J. Guilbert;A. Pichon;O. Sèbe;D. Bowers
中科院分区：
文献类型：
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作者：
D. N. Green;J. Guilbert;A. Pichon;O. Sèbe;D. Bowers
英国沿海城镇福克斯顿地下3公里处发生震级为4.3级的地震，产生了带宽为2-5 Hz的大气声波（次声）。这些都是在法国的FLERS微气压计阵列上记录的，距离为284公里。地震产生的次声通常与靠近大山脉的大地震有关；突出地形点的震动充当次声源，将地震能量耦合到大气中。在这个例子中，除了平均高度为75米的海岸悬崖外，源区几乎没有明显的地形。我们通过将23公里长的海岸模拟为一系列305个独立产生声波的活塞，探索了地震-次声耦合发生在悬崖上的可能性。模拟悬崖运动的合成地震图使用距离震中4公里的三分量加速度计的记录进行约束。结合微气压计记录的阵列处理，表明声能在对流层内传播到FLERS。合成微气压图与观测结果吻合较好；模拟的到达时间比观测到的早5秒，峰对峰幅度和信号持续时间在记录的2倍之内。该研究表明，如果靠近震中的地形条件有利，中等大小的浅层地震扰动可以产生可观测的次声。
Abstract An earthquake that occurred with a local magnitude of 4.3 and at a depth of 3 km beneath the coastal town of Folkestone, United Kingdom, generated atmospheric acoustic waves in the 2–5 Hz bandwidth (infrasound). These were recorded at the FLERS microbarometer array in France at a range of 284 km. Earthquake-generated infrasound is often associated with large earthquakes close to large mountain ranges; the shaking of prominent topographic points act as infrasound sources, coupling seismic energy into the atmosphere. In this example there is little prominent topography in the source region apart from the coastal cliffs, which have an average height of 75 m. We explore the possibility that the seismic-to-infrasound coupling occurs at the cliffs by modelling a 23 km length of coast as a series of 305 pistons independently generating acoustic waves. Synthetic seismograms modelling the motion of the cliffs are constrained using recordings from a three-component accelerometer located 4 km from the epicenter. Meteorological data, combined with array processing of the microbarometer records, suggest that the acoustic energy propagated to FLERS within the troposphere. The synthetic microbarograms show close agreement with the observations; the modelled arrival time is 5 sec earlier than that observed, and the peak-to-peak amplitude and signal duration are within a factor of 2 of those recorded. This study shows that moderately sized, shallow seismic disturbances can generate observable infrasound if the topographic conditions close to the epicenter are favorable.