Frequency and distance changes in the apparent<i>P</i>-wave radiation pattern: effects of seismic wave scattering in the crust inferred from dense seismic observations and numerical simulations

Kobayashi, Manabu; Takemura, Shunsuke; Yoshimoto, Keitaro

doi:10.1093/gji/ggv263

Cited by 30 publications

(28 citation statements)

References 40 publications

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“…However, Sawazaki et al (2011) pointed out that spatial distribution of maximum amplitudes and energy partitioning in each component show different frequency-dependent properties. Therefore, on the basis of the method by Kobayashi et al (2015), we measured codanormalized maximum P-and S-wave amplitudes (hereafter, these are referred to as the "P-wave amplitude" and "S-wave amplitude, " respectively) from three-component root-mean-square (RMS) envelopes for the following different frequency bands: 0.5-1, 1-2, 2-4, 4-8, and 8-16 Hz.…”

Section: Apparent Radiation Pattern For Crustal Earthquakesmentioning

confidence: 99%

“…Considering typical correlation length a of crustal heterogeneities (e.g., Takemura et al 2009;Kobayashi et al 2015), this feature appears in the strong scattering domain of ka-kL diagram ( Fig. 13.11 of Aki and Richards 1980), in where conventional ray theory does not stand.…”

Section: Frequency and Distance Dependences In The Apparent Radiationmentioning

confidence: 99%

“…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%

“…Takemura et al (2009Takemura et al ( , 2015 and Kobayashi et al (2015) reported that the apparent P-and S-wave radiation patterns are distorted with increasing distance but still preserving the original four-lobe pattern at hypocentral distances less than 40 km even for high frequencies. In this study, we firstly investigated the frequency-and distance-dependent characteristics of the apparent P-and S-wave radiation patterns using dense and large number seismograms.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Apparent Radiation Pattern For Crustal Earthquakesmentioning

confidence: 99%

Section: Frequency and Distance Dependences In The Apparent Radiationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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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“…The alternative interpretation is that distortion of radiation patterns in the long-period band reduces maximum source amplitude ratios and affects CMT estimates. Such distortion is known in high-frequency bands of around several hertz and has been explained by the path effect caused by scattering of seismic waves (e.g., Liu and Helmberger 1985;Takemura et al 2009Takemura et al , 2015Kumagai et al 2010Kumagai et al , 2011Kobayashi et al 2015). Because such scattering effects may not be dominant in the Normalized frequency distributions of observed amplitude ratios estimated for all events and for thrust, strike-slip, and odd mechanism events for a the Philippines network (Fig.…”

Section: Discussionmentioning

confidence: 98%

Discriminating non-seismic long-period pulses and noise to improve earthquake source inversion

et al. 2016

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Broadband seismometers produce artifacts resembling long-period pulses (non-seismic pulses) that degrade centroid moment tensor (CMT) estimations based on waveform inversion of broadband seismic records in long-period bands (50-200 s). We propose a method to discriminate non-seismic pulses and long-period noise from seismic signals, which can be applied to automatic CMT inversion analysis. In this method, we calculate source amplitudes as peakto-peak displacement amplitudes in individual long-period seismic records after each event has been corrected for medium attenuation and geometric spreading and then estimate the ratios of individual source amplitudes to the minimum source amplitude. Because source amplitude ratios for non-seismic pulses tend to be greater than those of the seismic signals, we use seismic records in CMT estimations only if their source amplitude ratios are lower than a threshold value (R). We tested this method using broadband seismic data from the Philippines and found that reprocessed inversion solutions using this method showed a clear improvement when using R = 11, although focal mechanism estimations were not entirely stable. To investigate the general applicability of this method, we analyzed broadband seismic data from F-net in Japan. Our analysis indicated that source amplitude ratios in F-net data ranged up to about 20, indicating that the threshold value may be dependent on station density. Given that F-net is one of the highest density networks in the world, we may assume that a threshold value between 10 and 20 is appropriate for application of our method for most regional broadband networks. Our synthetic tests indicated that source amplitude ratios can be as high as 10 3 , although observed ratios are only within the range 10-20. This suggests that we happened to observe only events having focal mechanisms with source amplitude ratios of 10-20. Alternatively, these high source amplitude ratios can be explained by distortion of radiation patterns in the long-period band, which reduces maximum source amplitude ratios and affects CMT estimates.

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Diminishing high‐frequency directivity due to a source effect: Empirical evidence from small earthquakes in the Abruzzo region, Italy

Pacor

Gallovič

Puglia

et al. 2016

Geophysical Research Letters

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The aim of this study is to investigate the directivity effects of ~250 aftershocks (magnitudes 3–5.5) of the Mw 6.1 2009 L'Aquila earthquake (central Italy). To this end, we estimate the apparent source spectra at each station removing path and site effects inferred by standard Generalized Inversion Technique. Then, we evaluate the residuals between the apparent source spectra and the event mean source spectrum at selected frequencies. We investigate azimuthal and frequency dependence of the residuals for 40 events with the best station coverage. For most of events with the strongest directivity effect (Mw 3.4–4.0), we observe a remarkable decrease of the directivity amplification at high frequencies, which has not yet been documented for such relatively small‐magnitude events. Since there is negligible distance dependence, we ascribe this observation to a source phenomenon such as significant small‐scale rupture propagation complexity.

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Frequency and distance changes in the apparentP-wave radiation pattern: effects of seismic wave scattering in the crust inferred from dense seismic observations and numerical simulations

Cited by 30 publications

References 40 publications

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

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

Discriminating non-seismic long-period pulses and noise to improve earthquake source inversion

Diminishing high‐frequency directivity due to a source effect: Empirical evidence from small earthquakes in the Abruzzo region, Italy

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