[S-SS07] Seismic wave propagation: Theory and Application

[SSS07-P10] An enigmatic tremor occurred in Greenland on September 16, 2023

*Kiwamu Nishida¹, Kazushige Obara¹, Takanori Matsuzawa², Takeshi Kimura² (1.Earthquake Research Institute, University of Tokyo, 2.National Research Institute for Earth Science and Disaster Resilience)

Keywords:single force source , A very low-frequency monochromatic tremor

Broadband seismic stations worldwide observed an enigmatic tremor from September 16, 2023. After an initial wave packet with a dominant period of 20-50 s arrived, a monochromatic tremor with a dominant period of about 100 s was excited and continued for several days. To emphasize the initial event, a 20-50 mHz bandpass filter was applied, and both Rayleigh and Love waves were found to be excited. No significant P waves were observed, but S wave propagation was identified in the radial component. The hypocenter was determined by measuring the Rayleigh wave travel time from the envelope. The tremor is located on the east coast of Greenland. To determine the radiation pattern of the monochromatic tremor, we analyzed broadband seismic data of IRIS stations. We plotted the mean squared amplitudes of the radial, transverse, and vertical components ( a time window of about 2000 s after the Rayleigh wave arrival) by applying a bandpass around 10 mHz. The result shows that the horizontal single force (e.g., Kanamori and Given, 1982) can explain the azimuthal dependency of the Love and Rayleigh wave amplitudes. Although this report is preliminary, based on the observed results, we consider a possibility that they are excited by seiche trapped in a fjord bay. We are considering the possibility that a landslide initially occurred, then ice entered into the bay and excited the seiche. A single force by the seiche was applied to the wall in the horizontal direction. We will address a more quantitative estimation, including other possibilities.