Reconstruction of a 2D seismic wavefield by seismic gradiometry

Abstract

We reconstructed a 2D seismic wavefield and obtained its propagation properties by using the seismic gradiometry method together with dense observations of the Hi-net seismograph network in Japan. The seismic gradiometry method estimates the wave amplitude and its spatial derivative coefficients at any location from a discrete station record by using a Taylor series approximation. From the spatial derivatives in horizontal directions, the properties of a propagating wave packet, including the arrival direction, slowness, geometrical spreading, and radiation pattern can be obtained. In addition, by using spatial derivatives together with free-surface boundary conditions, the 2D vector elastic wavefield can be decomposed into divergence and rotation components. First, as a feasibility test, we performed an analysis with a synthetic seismogram dataset computed by a numerical simulation for a realistic 3D medium and the actual Hi-net station layout. We confirmed that the wave amplitude and its spatial derivatives were very well-reproduced for period bands longer than 25 s. Applications to a real large earthquake showed that the amplitude and phase of the wavefield were well reconstructed, along with slowness vector. The slowness of the reconstructed wavefield showed a clear contrast between body and surface waves and regional non-great-circle-path wave propagation, possibly owing to scattering. Slowness vectors together with divergence and rotation decomposition are expected to be useful for determining constituents of observed wavefields in inhomogeneous media.

Seismic Wavefield Reconstruction based on Compressed Sensing using Data-Driven Reduced-Order Model

“…Although it requires assumptions and constraints, traditional methods have achieved some success (Kawakami, 1989;Vanmarcke & Fenton, 1991;Kameda & Morikawa, 1994, 1992Sato & Imabayashi, 1999). The constraint on the reconstruction have been much reduced in the modern method of the seismic-wave gradiometry (SWG) method (e.g., Langston, 2007a,b;Liang & Langston, 2009;Maeda et al, 2016;Shiina et al, 2021). This method is based on the idea that the amplitudes of seismic waves and their spatial gradients at an arbitrary point can be interpolated from the observed amplitudes at surrounding stations without making assumptions concerning velocity structures and locations of earthquakes.…”

Seismic Azimuthal Anisotropy for the Southeastern Tibetan Plateau Extracted by Wave Gradiometry Analysis

“…They discussed the radial anisotropy based on the Love and Rayleigh wave velocity based on the WG analysis. In addition, the WG method has been applied for wavefield reconstruction (Maeda et al, 2016), and the vertical WG method has been used to extract impedance and attenuation structures in the vicinity of boreholes (Langston & Ayele, 2016). Furthermore, Porter et al (2016) combined ambient noise tomography with WG to calculate a three‐dimensional S wave velocity structure.…”

Sequence of deep-focus earthquakes beneath the Bonin Islands identified by the NIED nationwide dense seismic networks Hi-net and F-net

“…2, we made snapshots of wave energy propagation using the MS envelopes obtained at each Hi-net station. Spatiotemporal changes in the seismic wavefield are very useful for investigating the seismic wave propagation observed across Japan, or the occurrences of multiple earthquakes (e.g., Hoshiba 2013; Maeda et al 2016). We applied spatial interpolation and extrapolation to the MS amplitudes at each time step, using the gridding algorithm of the Generic Mapping Tools software package (Wessel and Smith 1998).…”