Directivity in NGA Earthquake Ground Motions: Analysis Using Isochrone Theory

Spudich, Paul; Chiou, Brian

doi:10.1193/1.2928225

Cited by 152 publications

(142 citation statements)

References 14 publications

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“…The large variability, which we obtained at a short distance for unilateral ruptures, may, however, be strongly reduced if azimuth is considered as a predictor. This could be quantified by computing median ground motion from prediction models that account for directivity effects (e.g., Somerville et al, 1997;Spudich and Chiou, 2008) or simply by assessing the variability in various azimuth ranges.…”

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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show abstract

“…The directivity of the earthquake rupture propagation gives rise to a large variability of the ground motions recorded at a given distance from the source over various source-receiver azimuths (e.g., Somerville et al, 1997;Spudich and Chiou, 2008). In particular, the energy of the seismic waves successively released from the fault constructively interferes in the forward direction of the rupture, which makes the amplitude of the ground shaking large, especially when the rupture speed approaches the shear-wavespeed.…”

Section: Introductionmentioning

confidence: 99%

Spatial Variability of the Directivity Pulse Periods Observed during an Earthquake

Fayjaloun¹,

Causse²,

Cornou³

et al. 2016

Bulletin of the Seismological Society of America

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The ground velocity pulses generated by rupture directivity effects in the near-fault region can cause a large amount of damage to structures. Proper estimation of the period of such velocity pulses is of particular importance in characterizing near-fault seismic hazard and mitigating potential damage. We propose a simple equation to determine the pulse period as a function of the site location with respect to the fault rupture (defined by the hypocentral distance hypD, the closest distance to the rupture area clsD, and the length of the rupture area that breaks toward the site D) and some basic rupture properties (average rupture speed and average rise time). Our equation is first validated from a dataset of synthetic velocity time histories, deploying simulations of various strike-slip extended ruptures in a homogeneous medium. The analysis of the synthetic dataset confirms that the pulse period does not depend on the whole rupture area, but only on the parameter D. It also reveals that the pulse period is not sensitive to the level of slip heterogeneity on the fault plane. Our model is tested next on a real dataset build from the Next Generation Attenuation-West2 Project database, compiling 110 observations of velocity pulse periods from 10 strike-slip events and 6 non-strike-slip events. The standard deviation of the natural logarithm residuals between observations and predictions is ∼0:5. Furthermore, the correlation coefficient between observations and predictions equals ∼0:8, indicating that despite its simplicity, our model explains fairly well the spatial variability of the pulse periods.

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“…As unilateral rupture occurs, seismic waves radiated in the direction of rupture could be greatly amplified, and even moderate magnitude earthquakes can sometimes cause serious damage (Huang et al 2011;Kanamori et al 2016). Knowing the directivity of earthquakes is therefore important for ground shaking prediction and in turn helps with hazard mitigation (Somerville et al 1997;Spudich & Chiou 2008;Kurzon et al 2014). Moreover, directivity can also be used to discriminate which nodal plane corresponds to the actual fault plane (Mori & Hartzell 1990;Warren & Shearer 2006;Frez et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Toward automated directivity estimates in earthquake moment tensor inversion

Huang

Aso

Tsai

2017

Geophysical Journal International

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S U M M A R YRapid estimates of earthquake rupture properties are useful for both scientific characterization of earthquakes and emergency response to earthquake hazards. Rupture directivity is a particularly important property to constrain since seismic waves radiated in the direction of rupture can be greatly amplified, and even moderate magnitude earthquakes can sometimes cause serious damage. Knowing the directivity of earthquakes is important for ground shaking prediction and hazard mitigation, and is also useful for discriminating which nodal plane corresponds to the actual fault plane particularly when the event lacks aftershocks or outcropped fault traces. Here, we propose a 3-D multiple-time-window directivity inversion method through direct waveform fitting, with source time functions stretched for each station according to a given directivity. By grid searching for the directivity vector in 3-D space, this method determines not only horizontal but vertical directivity components, provides uncertainty estimates, and has the potential to be automated in real time. Synthetic tests show that the method is stable with respect to noise, picking errors, and site amplification, and is less sensitive to station coverage than other methods. Horizontal directivity can be properly recovered with a minimum azimuthal station coverage of 180 • , whereas vertical directivity requires better coverage to resolve. We apply the new method to the M w 6.0 Nantou, Taiwan earthquake, M w 7.0 Kumamoto, Japan earthquake, and M w 4.7 San Jacinto fault trifurcation (SJFT) earthquake in southern California. For the Nantou earthquake, we corroborate previous findings that the earthquake occurred on a shallow east-dipping fault plane rather than a west-dipping one. For the Kumamoto and SJFT earthquakes, the directivity results show good agreement with previous studies and demonstrate that the method captures the general rupture characteristics of large earthquakes involving multiple fault ruptures and applies to earthquakes with magnitudes as small as M w 4.7.

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Directivity in NGA Earthquake Ground Motions: Analysis Using Isochrone Theory

Cited by 152 publications

References 14 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

Spatial Variability of the Directivity Pulse Periods Observed during an Earthquake

Toward automated directivity estimates in earthquake moment tensor inversion

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