Hydroacoustic effects in the 2003 Tokachi-oki tsunami source

Abstract

We process the JAMSTEC ocean-bottom pressure gauges and ocean-bottom seismometers datasets obtained during the 2003 Tokachi-oki tsunamigenic earthquake-the first records which have ever been obtained in a large tsunami source. On these records, we discover the unique phenomenon in tsunami source-hydroacoustic resonance, i.e. manifestation of long-lasting elastic oscillations of water column at the minimal normal frequency (≈ 0.14 Hz). The concept of a weakly coupled system is applied in 3D numerical simulation of the Tokachi-oki event. First, we simulate earthquake ground motion due to seismic fault rupturing. Then, compressible water column disturbance resulting from the dynamic seismic ground motion is simulated using the velocity of bottom deformation as an input to the water column. Comparison between JAMSTEC in-situ measurements and synthetic signals is carried out.

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

“…Assuming acoustic plane wave propagation along the z axis ( v z = exp [ i ( kz − ωt )]), equations and yield the following relation: where v z is the particle velocity in the z component and is the phase velocity of the acoustic wave. Some studies used the relation of equation to interpret the high‐frequency ocean bottom pressure records [e.g., Bolshakova et al ., ; Matsumoto et al ., ]. Although equation was used for an explanation here, we will use the equations of motions in the elastic medium to calculate the pressure change at the sea bottom instead of equation in order to include an appropriate boundary condition between the fluid and elastic media.…”

Estimation of Seismic Centroid Moment Tensor Using Ocean Bottom Pressure Gauges as Seismometers

“…The pressure changes can be interpreted based on two different relationships according to their frequency range, defined by the fundamental acoustic resonant frequency f 0 = c 0 /(4 h 0 ) ( h 0 is the water depth and c 0 is the velocity of the ocean acoustic wave). When the frequency of the seafloor motion is sufficiently low compared to the fundamental acoustic resonant frequency f 0 ( f < f 0 ), the seafloor pressure change can be approximated as and when the frequency is high ( f > f 0 ) as where ρ 0 is seawater density and a z and v z are the vertical acceleration and velocity of the seafloor motion (hereafter, pressure‐acceleration relationship and pressure‐velocity relationship), respectively (e.g., Bolshakova et al, ; Matsumoto et al, ). Numerical simulation is useful for investigating these relationships (e.g., Kozdon & Dunham, ; Maeda et al, ; Saito, ; Saito & Tsushima, ).…”

“…The dynamic pressure change associated with seismic motion has been previously studied (e.g., Bolshakova et al, 2011;Filloux, 1982;Matsumoto et al, 2012;Nosov & Kolesov, 2007;Saito, 2013). The pressure changes can be interpreted based on two different relationships according to their frequency range, defined by the fundamental acoustic resonant frequency f 0 = c 0 /(4h 0 ) (h 0 is the water depth and c 0 is the velocity of the ocean acoustic wave).…”

“…where ρ 0 is seawater density and a z and v z are the vertical acceleration and velocity of the seafloor motion (hereafter, pressure-acceleration relationship and pressure-velocity relationship), respectively (e.g., Bolshakova et al, 2011;Matsumoto et al, 2012). Numerical simulation is useful for investigating these relationships (e.g., Kozdon & Dunham, 2014;Maeda et al, 2013;Saito, 2017;Saito & Tsushima, 2016).…”

Pressure field induced in the water column by acoustic‐gravity waves generated from sea bottom motion

“…All these effects may act to reduce the dynamic pressure variations induced by AGW far from the epicenter. However, AGWs can travel a distance of O(10 3 ) km with a negligible damping [Bolshakova et al, 2011;Kadri and Stiassnie, 2012] Despite the recent advances in the theoretical understanding of AGWs, it is essential to address the link between the detection of AGWs and the actual generation of a conspicuous tsunami in future work based on field data analysis.…”