Long-period ocean-bottom motions in the source areas of large subduction earthquakes

Abstract

Long-period ground motions in plain and basin areas on land can cause large-scale, severe damage to structures and buildings and have been widely investigated for disaster prevention and mitigation. However, such motions in ocean-bottom areas are poorly studied because of their relative insignificance in uninhabited areas and the lack of ocean-bottom strong-motion data. Here, we report on evidence for the development of long-period (10–20 s) motions using deep ocean-bottom data. The waveforms and spectrograms demonstrate prolonged and amplified motions that are inconsistent with attenuation patterns of ground motions on land. Simulated waveforms reproducing observed ocean-bottom data demonstrate substantial contributions of thick low-velocity sediment layers to development of these motions. This development, which could affect magnitude estimates and finite fault slip modelling because of its critical period ranges on their estimations, may be common in the source areas of subduction earthquakes where thick, low-velocity sediment layers are present.

Systematic difference between first-motion and waveform-inversion solutions for shallow offshore earthquakes due to a low-angle dipping slab

“…Although the velocity model in the offshore region has relatively large uncertainties, upper surface of the PHS from JIVSM is consistent with other models (e.g., Hirose et al 2008;Citak et al 2012;Nakamura et al 2015). …”

Structural Characteristics of the Nankai Trough Shallow Plate Boundary Inferred From Shallow Very Low Frequency Earthquakes

“…We evaluated Green's functions for CMT inversion via numerical simulations of seismic wave propagation based on the parallel staggered-grid finite-difference method (FDM; Furumura & Chen, 2004;Takemura et al, 2015). The accretionary prism model is important for modeling surface wave propagation in subduction zones (e.g., Furumura et al, 2008;Nakamura et al, 2015;Shapiro et al, 1998;Takemura et al, 2019;Volk et al, 2017). We employed the reliable 3-D velocity structure model including a realistic accretionary prism structure (Takemura et al, 2019).…”

Synthesizing ocean bottom pressure records including seismic wave and tsunami contributions: Toward realistic tests of monitoring systems

“…It would be important in near future to synthesize the observed record by using more realistic and diverse earthquake rupture scenarios [e.g., Hok et al, 2011;Ma, 2012;Kozdon and Dunham, 2014;Xu et al, 2015;Kim et al, 2016]. Also, it would be useful to use more realistic subsurface structure in calculating the seismic wave propagation [e.g., Nakamura et al, 2015;Noguchi et al, 2016]. Although we focus on tsunamigenic earthquakes, landslide can contribute to tsunami excitation [e.g., Tappin et al, 2014].…”