11:30 〜 11:45
[SVC34-09] Dyke swarms in the oceanic lithosphere beneath the Ontong Java Plateau as inferred from Po/So waves
キーワード：Po/So波、海洋リソスフェア、オントンジャワ海台
The Ontong Java Plateau (OJP) is an oceanic large igneous province (LIP) in the southwest Pacific. The OJP is estimated to be formed at 120 and 90 Ma by massive volcanism based on petrological and geochemical studies, however, the formation process is still under discussion. To explore the origin of OJP, we investigate the seismic structure of the oceanic lithosphere beneath the OJP region by analyzing Po/So waves.
The Po/So waves are P and S waves which travel over great distances through the oceanic lithosphere, and are characterized by high-frequency content and long-duration developed by the multiple forward scattering due to small-scale stochastic random heterogeneities.
We used broadband seismic wave data from campaign observation named “OJP array” conducted in 2014-2017. The campaign seismic network consisted of ocean bottom stations and islands stations in and around the plateau.
Through the waveform analysis, we found that the Po/So waves traveling in the OJP attenuate more rapidly compared to those in the typical oceanic region (e.g., the North Western Pacific). In particular, the propagation efficiency of So waves in the OJP is much less than the NWP. We investigate the cause of the difference in propagation efficiency of the Po/So waves using numerical Finite Difference Method simulations of 2-D seismic wave propagation. We found that a dyke-like structure developed in the oceanic lithosphere produces the characteristic Po/So waves observed in the OJP, while lamina structure produces Po/So waves in the typical oceanic region. Our preferred model of the heterogeneity in the OJP lithosphere has vertically elongated scatterers described by a von Karmann function with a vertical correlation length of about 5 km and horizontal correlation length of about 0.05 km. The standard deviation of wave speed fluctuations from the averaged background model is about 2%. The results suggest that the oceanic lithosphere beneath the OJP had been altered by massive volcanism.
The Po/So waves are P and S waves which travel over great distances through the oceanic lithosphere, and are characterized by high-frequency content and long-duration developed by the multiple forward scattering due to small-scale stochastic random heterogeneities.
We used broadband seismic wave data from campaign observation named “OJP array” conducted in 2014-2017. The campaign seismic network consisted of ocean bottom stations and islands stations in and around the plateau.
Through the waveform analysis, we found that the Po/So waves traveling in the OJP attenuate more rapidly compared to those in the typical oceanic region (e.g., the North Western Pacific). In particular, the propagation efficiency of So waves in the OJP is much less than the NWP. We investigate the cause of the difference in propagation efficiency of the Po/So waves using numerical Finite Difference Method simulations of 2-D seismic wave propagation. We found that a dyke-like structure developed in the oceanic lithosphere produces the characteristic Po/So waves observed in the OJP, while lamina structure produces Po/So waves in the typical oceanic region. Our preferred model of the heterogeneity in the OJP lithosphere has vertically elongated scatterers described by a von Karmann function with a vertical correlation length of about 5 km and horizontal correlation length of about 0.05 km. The standard deviation of wave speed fluctuations from the averaged background model is about 2%. The results suggest that the oceanic lithosphere beneath the OJP had been altered by massive volcanism.