Near-source effect on radiation pattern of high-frequency S waves: strong SH–SV mixing observed from aftershocks of the 1997 Northwestern Kagoshima, Japan, earthquakes

Takenaka, Hiroshi; Mamada, Yutaka; Futamure, Hayato

doi:10.1016/s0031-9201(03)00006-2

Cited by 35 publications

(22 citation statements)

References 16 publications

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“…Nevertheless the radiation pattern effect, which is clearly observed in our synthetics, might be limited to lower frequency range (<∼1 Hz) in real velocity structures. The theoretical four-lobe S-wave radiation pattern may be limited to low frequencies (< 1 Hz), with an isotropic pattern at high frequency due to the scattering of seismic waves (e.g., Liu and Helmberger, 1985;Takenaka et al, 2003;Takemura et al, 2009). In addition, according to Cho et al (2010), observations suggest that far-field radiation patterns change from a distinct doublecouple pattern, with strong directivity effects at low frequencies (< 1 Hz), to a more isotropic pattern with diminished directivity effects at high frequencies, putting forward the fact that directivity effects are also frequency dependent.…”

Section: Discussionmentioning

confidence: 99%

Is Ground‐Motion Variability Distance Dependent? Insight from Finite‐Source Rupture Simulations

Imtiaz¹,

Causse²,

Chaljub³

et al. 2015

Bulletin of the Seismological Society of America

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The ground-motion variability sigma is a fundamental component in probabilistic seismic-hazard assessment because it controls the hazard level at very low probabilities of exceedance. So far, most of the analyses based on empirical ground-motion prediction equations do not consider any distance dependency of sigma. This study aims to analyze the potential distance dependency of ground-motion variability, especially in the near-field region, where the variability is poorly constrained due to the lack of available records. We, therefore, investigate the distance dependency of sigma by performing numerical simulations of ground motion for some strike-slip events. Synthetic velocity seismograms (up to 3 Hz) have been generated from a suite of finite-source rupture models of past earthquakes. Green's functions were calculated for a 1D velocity structure using a discrete wavenumber technique (Bouchon, 1981). The within-event component of the ground-motion variability was then evaluated from the synthetic data as a function of distance. The simulations reveal that the within-event component of the ground motion shows a distance dependency, subject to the rupture type. For bilateral ruptures, the variability tends to increase with distance. On the contrary, in case of unilateral events, the variability decreases with distance.

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Section: Discussionmentioning

confidence: 99%

Is Ground‐Motion Variability Distance Dependent? Insight from Finite‐Source Rupture Simulations

Imtiaz¹,

Causse²,

Chaljub³

et al. 2015

Bulletin of the Seismological Society of America

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“…Indeed, Takenaka et al (2003) suggested that the frequencydependent distortion of the S-wave radiation pattern might be caused by the mixing and coupling of the horizontal (S H ) and vertical (S V ) S-waves in the heterogeneous structure near the source region. By analyzing dense KiK-net array observations from the Tottori-Ken Seibu earthquake, Mw 6.6, and its aftershocks, Takemura et al (2009) demonstrated the collapse of the S-wave front due to seismic-wave scattering in a heterogeneous structure and showed that the radiation pattern is more isotropic at high frequencies (>2 Hz).…”

Section: Do Source Radiation Patterns Explain the Observed Azimuthal mentioning

confidence: 99%

High-frequency directivity effects: evidence from analysis of the Les Saintes records

et al. 2014

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The main-shock (Mw, 6.3) and the aftershocks of the 'Les Saintes' earthquake sequence (French Indies) were analyzed to quantify highfrequency directivity effects. A correction method was applied to isolate source spectra within a large frequency range (0.5 to 25 Hz). Most of the aftershocks source spectra are fully consistent with a Brune spectrum pointsource shape and do not show any azimuthal dependence. The main-shock (Mw, 6.3) and the two largest aftershocks (Mw, 5.8, 5.3) show, however, a clear azimuthal dependence that indicates significant directivity effect. The discrepancy of the radiated spectral energy and the change in the corner frequencies introduced by directivity effects show that such an effect is significant at high frequency (from 1 to 25 Hz). Our data suggest that the amplitudes in the main-shock Fourier spectrum at directive sites are around a factor of 2.5 higher with respect to anti-directive sites.

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“…It is well known that, as frequency increases over 1 Hz, the spatial distributions of observed maximum P-and S-wave amplitudes during local earthquakes (hereafter, this is called the "apparent radiation pattern") are gradually distorted from the expected four-lobe amplitude pattern of a double-couple point source (e.g., Liu and Helmberger 1985;Satoh 2002a;Takenaka et al 2003;Takemura et al 2009;Sawazaki et al 2011;Kobayashi et al 2015). The frequency-dependent characteristics of the observed apparent radiation patterns have been incorporated into various applications such as the predictions of strong ground motions (e.g., Pitarka et al 2000;Pulido and Kubo 2004), the estimation of high-frequency seismic energy radiation during large earthquakes (e.g., Nakahara 2013), nonvolcanic/volcanic tremors (e.g., Maeda and Obara 2009;Kumagai et al 2010;Cannata et al 2013;, and landslides (e.g., Ogiso and Yomogida 2015), and the earthquake early warning systems (e.g., Okamoto and Tsuno 2015).…”

Section: Introductionmentioning

confidence: 99%

Prediction of maximum P- and S-wave amplitude distributions incorporating frequency- and distance-dependent characteristics of the observed apparent radiation patterns

Takemura

Kobayashi

Yoshimoto

2016

Earth Planets Space

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Frequency-dependent model of the apparent radiation pattern has been extensively incorporated into engineering and scientific applications for high-frequency seismic waves, but distance-dependent properties have not yet been fully taken into account. We investigated the unified characteristics of frequency and distance dependences in both apparent P-and S-wave radiation patterns during local crustal earthquakes. Observed distortions of the apparent Pand S-wave radiation patterns could be simply modeled by using a function of the normalized hypocentral distance, which is a product of the wave number and hypocentral distance. This behavior suggests that major cause of distortion of the apparent radiation pattern is seismic wave scattering and diffraction within the heterogeneous crust. On the basis of observed normalized hypocentral distance dependency, we proposed a method for prediction of spatial distributions of maximum P-and S-wave amplitudes. Our method incorporating normalized hypocentral distance dependence of the apparent radiation pattern reproduced the observed spatial distributions of maximum P-and S-wave amplitudes over a wide frequency and distance ranges successfully.

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Near-source effect on radiation pattern of high-frequency S waves: strong SH–SV mixing observed from aftershocks of the 1997 Northwestern Kagoshima, Japan, earthquakes

Cited by 35 publications

References 16 publications

Is Ground‐Motion Variability Distance Dependent? Insight from Finite‐Source Rupture Simulations

Is Ground‐Motion Variability Distance Dependent? Insight from Finite‐Source Rupture Simulations

High-frequency directivity effects: evidence from analysis of the Les Saintes records

Prediction of maximum P- and S-wave amplitude distributions incorporating frequency- and distance-dependent characteristics of the observed apparent radiation patterns

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