Wang Qing-Yu, Frank William B, Abercrombie Rachel E, Obara Kazushige, Kato Aitaro
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
Department of Earth and Environment, Boston University, Boston, MA, USA.
Sci Adv. 2023 Aug 9;9(32):eadh3688. doi: 10.1126/sciadv.adh3688.
Low-frequency earthquakes, atypical seismic events distinct from regular earthquakes, occur downdip of the seismogenic megathrust where an aseismic rheology dominates the subduction plate boundary. Well situated to provide clues on the slip regime of this unique faulting environment, their distinctive waveforms reflect either an unusual rupture process or unusually strong attenuation in their source zone. We take advantage of the unique geometry of seismicity in the Nankai Trough to isolate the spectral signature of low-frequency earthquakes after correcting for empirically derived attenuation. We observe that low-frequency earthquake spectra are consistent with the classical earthquake model, yet their rupture duration and stress drop are orders of magnitude different from ordinary earthquakes. We conclude their low-frequency nature primarily results from an atypical seismic rupture process rather than near-source attenuation.
低频地震是有别于常规地震的非典型地震事件，发生在地震成因大逆冲断层的下倾部位，那里无震流变学主导着俯冲板块边界。它们所处位置得天独厚，能够为这一独特断层环境的滑动状态提供线索，其独特的波形要么反映了异常的破裂过程，要么反映了震源区异常强烈的衰减。我们利用南海海槽地震活动的独特几何形态，在校正根据经验得出的衰减后，分离出低频地震的频谱特征。我们观察到，低频地震频谱与经典地震模型相符，但其破裂持续时间和应力降与普通地震相差几个数量级。我们得出结论，它们的低频特性主要源于非典型的地震破裂过程，而非震源附近的衰减。
