Complete synthetic seismograms for a spherically symmetric earth by a numerical computation of the Green's function in the frequency domain

Friederich, Wolfgang; Dalkolmo, Jörg

doi:10.1111/j.1365-246x.1995.tb07012.x

Cited by 117 publications

(112 citation statements)

References 22 publications

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“…An isotropic PREM was used as the spherically-symmetric reference Earth structure (21). Implementation of the direct Green's function method (22,23) involved all spherical harmonic degrees from 0-3000, and discretization of the finite fault plane into approximately 35 km 2 patches sufficient to sample the wavefield with at least 10 points per wavelength. We use 6 × 6 km grid spacing, low-pass filtered with a corner period of 10 s, and calculate the stress at 10 km depth (for comparison, the depth of post-mainshock rift events is 13 AE 7 km).…”

Section: Dynamic Stressmentioning

confidence: 99%

Stress imparted by the great 2004 Sumatra earthquake shut down transforms and activated rifts up to 400 km away in the Andaman Sea

Sevilgen¹,

Stein

Pollitz

2012

Proc. Natl. Acad. Sci. U.S.A.

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The origin and prevalence of triggered seismicity and remote aftershocks are under debate. As a result, they have been excluded from probabilistic seismic hazard assessment and aftershock hazard notices. The 2004 M ¼ 9.2 Sumatra earthquake altered seismicity in the Andaman backarc rift-transform system. Here we show that over a 300-km-long largely transform section of the backarc, M ≥ 4.5 earthquakes stopped for five years, and over a 750-kmlong backarc section, the rate of transform events dropped by twothirds, while the rate of rift events increased eightfold. We compute the propagating dynamic stress wavefield and find the peak dynamic Coulomb stress is similar on the rifts and transforms. Longperiod dynamic stress amplitudes, which are thought to promote dynamic failure, are higher on the transforms than on the rifts, opposite to the observations. In contrast to the dynamic stress, we calculate that the mainshock brought the transform segments approximately 0.2 bar (0.02 MPa) farther from static Coulomb failure and the rift segments approximately 0.2 bar closer to static failure, consistent with the seismic observations. This accord means that changes in seismicity rate are sufficiently predictable to be included in post-mainshock hazard evaluations.Coulomb stress transfer | great earthquakes | seismicity rate changes

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Section: Dynamic Stressmentioning

confidence: 99%

Stress imparted by the great 2004 Sumatra earthquake shut down transforms and activated rifts up to 400 km away in the Andaman Sea

Sevilgen¹,

Stein

Pollitz

2012

Proc. Natl. Acad. Sci. U.S.A.

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“…The test which is performed with the use of FLSPHER package (Friederich and Dalkolmo 1995) is aimed to see how well the velocities in different depth intervals are constrained by observed modes.…”

Section: Sensitivity Analysismentioning

confidence: 99%

Inversion of Scholte wave dispersion and waveform modeling for shallow structure of the Ninetyeast Ridge

2008

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The construction of S-wave velocity models of marine sediments down to hundreds of meters below the seafloor is important in a number of disciplines. One of the most significant trends in marine geophysics is to use interface waves to estimate shallow shear velocities which play an important role in determining the shallow crustal structure. In marine settings, the waves trapped near the fluid-solid interface are called Scholte waves, and this is the subject of the study. In 1998, there were experiments on the Ninetyeast Ridge (Central Indian Ocean) to study the shallow seismic structure at the drilled site. The data were acquired by both ocean bottom seismometer and ocean bottom hydrophone. A new type of seafloor implosion sources has been used in this experiment, which successfully excited fast and high frequency (>500 Hz) body waves and slow, intermediate frequency (<20 Hz) Scholte waves. The fundamental and first higher mode Scholte waves have both been excited by the implosion source. Here, the Scholte waves are investigated with a full waveform modeling and a group velocity inversion approach. Shear wave velocities for the uppermost layers of the region are inferred and results from the different methods are compared. We find that the full waveform modeling is important to understand the intrinsic attenuation of the Scholte waves between 1 and 20 Hz. The modeling shows that the S-wave velocity varies from 195 to 350 m/s in the first 16 m of the uppermost layer. Depths levels of high S-wave impedance contrasts compare well to the layer depth derived from a P-wave analysis as well as from drilling data. As expected, the P-to S-wave velocity ratio is very high in the uppermost 16 m of the seafloor and the Poisson ratio is nearly 0.5. Depth levels of high S-wave impedance contrasts are comparable to the layer depth derived from drilling data.

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“…For benchmarking we thus have to revert to spherically symmetric models, but as the code is written in cylindrical coordinates, even transversely isotropic media lead to a stiffness tensor that is fully populated (those elements that are nonzero in the effective stiffness tensor, see above) and the full stiffness matrix is tested. As a reference, we use Yspec by Al-Attar & Woodhouse (2008), which is a generalization of the direct radial integration method (Friederich & Dalkolmo 1995) including self-gravitation (switched off for the benchmark).…”

Section: B E N C H M a R K Smentioning

confidence: 99%

Seismic wave propagation in fully anisotropic axisymmetric media

Driel

Nissen‐Meyer

2014

Geophysical Journal International

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S U M M A R YWe present a numerical method to compute 3-D elastic waves in fully anisotropic axisymmetric media. This method is based on a decomposition of the wave equation into a series of uncoupled 2-D equations for which the dependence of the wavefield on the azimuth can be solved analytically. Four independent equations up to quadrupole order appear as solutions for moment-tensor sources located on the symmetry axis while single forces can be accommodated by two separate solutions up to dipole order. This decomposition gives rise to an efficient solution of the 3-D wave equation in a 2-D axisymmetric medium. First, we prove the validity of the decomposition of the wavefield in the presence of general anisotropy. Then we use it to derive the reduced 2-D equations of motions and discretize them using the spectral element method. Finally, we benchmark the numerical implementation for global wave propagation at 1 Hz and consider inner core anisotropy as an application for high-frequency wave propagation in anisotropic media at frequencies up to 2 Hz.

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Complete synthetic seismograms for a spherically symmetric earth by a numerical computation of the Green's function in the frequency domain

Cited by 117 publications

References 22 publications

Stress imparted by the great 2004 Sumatra earthquake shut down transforms and activated rifts up to 400 km away in the Andaman Sea

Stress imparted by the great 2004 Sumatra earthquake shut down transforms and activated rifts up to 400 km away in the Andaman Sea

Inversion of Scholte wave dispersion and waveform modeling for shallow structure of the Ninetyeast Ridge

Seismic wave propagation in fully anisotropic axisymmetric media

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