A formulation of directivity for earthquake sources using isochrone theory

Spudich, Paul; Chiou, Brian; Collins, Nancy; Somerville, Paul

doi:10.3133/ofr20041268

Cited by 27 publications

(28 citation statements)

References 3 publications

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“…Somerville (2000) proposed the ratio of the length of fault between site and hypocenter and the site azimuth as a measure of directivity. Spudich et al (2004) showed that the isochrone velocity ratio (i.e., average isochrone velocity normalized by shear wave velocity) behaves similarly to the directivity parameters of Somerville (2000). Isochrone velocity ratioc was computed for most of the stations used in this study.…”

Section: Directivity Predictormentioning

confidence: 74%

“…The length of fault between station and hypocenter (s) and the width of fault between station and hypocenter (d) are also presented. In addition, isochrone velocity ratio as defined by Spudich et al (2004) is listed for records where it could be computed. Average shear wave velocity in the upper 30 m of the crust v s,30 is also provided.…”

Section: Description Of Metadatamentioning

confidence: 99%

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Quantification of ground-motion parameters and response spectra in the near-fault region

Rupakhety

Sigurdsson

Παπαγεωργιου

et al. 2011

Bull Earthquake Eng

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This study focuses on the characteristics of near-fault ground motions in the forward-direction and structural response associated with them. These ground motions are narrow-banded in nature and are characterized by a predominant period at which structures excited by them are severely affected. In this work, predominant period is defined as the undamped natural period of a single-degree-of-freedom (SDOF) oscillator at which its 5% damped linear elastic pseudo-spectral velocity (PSV) contains a clear and dominant peak. It is found that a linear relationship exists between predominant period and seismic moment. An empirical equation describing this relationship is presented by using a large set of accelerograms. Attenuation equations are developed to estimate peak ground velocity (PGV) as a function of earthquake magnitude and source-to-site distance. In addition, a predictive equation for spectral shapes of PSV (i.e., PSV normalized by PGV) is presented as a continuous function of the undamped natural period of SDOF oscillators. The model is independent of PGV, and can be used in conjunction with any available PGV attenuation relation applicable to near-fault ground motion exhibiting forward-directivity effects. Furthermore, viscous damping of the SDOF is included in the model as a continuous parameter, eliminating the use of so-called damping correction factors. Finally, simple equations relating force reduction factors and displacement ductility of elasto-plastic SDOF systems are presented.

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Section: Directivity Predictormentioning

confidence: 74%

Section: Description Of Metadatamentioning

confidence: 99%

Quantification of ground-motion parameters and response spectra in the near-fault region

Rupakhety

Sigurdsson

Παπαγεωργιου

et al. 2011

Bull Earthquake Eng

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“…This might be an important consideration close to faults, where rupture directivity and radiation pattern can produce strongly correlated motions, in particular at periods of 1 sec or longer (Spudich et al, 2004). Because obtaining a response spectrum is not a linear operation on a time series (the response spectrum of the sum of two time series is not equal to the sum of the response spectra for each time series), the sensitivity to sensor orientation is also shared by almost all other measures of ground-motion intensity.…”

Section: Introductionmentioning

confidence: 99%

Orientation-Independent Measures of Ground Motion

Boore¹

2006

Bulletin of the Seismological Society of America

387

235

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The geometric mean of the response spectra for two orthogonal horizontal components of motion, commonly used as the response variable in predictions of strong ground motion, depends on the orientation of the sensors as installed in the field. This means that the measure of ground-motion intensity could differ for the same actual ground motion. This dependence on sensor orientation is most pronounced for strongly correlated motion (the extreme example being linearly polarized motion), such as often occurs at periods of 1 sec or longer. We propose two new measures of the geometric mean, GMRotDpp, and GMRotIpp, that are independent of the sensor orientations. Both are based on a set of geometric means computed from the as-recorded orthogonal horizontal motions rotated through all possible nonredundant rotation angles. GMRotDpp is determined as the ppth percentile of the set of geometric means for a given oscillator period. For example, GMRotD00, GMRotD50, and GMRotD100 correspond to the minimum, median, and maximum values, respectively. The rotations that lead to GMRotDpp depend on period, whereas a single-period-independent rotation is used for GMRotIpp, the angle being chosen to minimize the spread of the rotation-dependent geometric mean (normalized by GMRotDpp) over the usable range of oscillator periods. GMRotI50 is the groundmotion intensity measure being used in the development of new ground-motion prediction equations by the Pacific Earthquake Engineering Center Next Generation Attenuation project.Comparisons with as-recorded geometric means for a large dataset show that the new measures are systematically larger than the geometric-mean response spectra using the as-recorded values of ground acceleration, but only by a small amount (less than 3%). The theoretical advantage of the new measures is that they remove sensor orientation as a contributor to aleatory uncertainty. Whether the reduction is of practical significance awaits detailed studies of large datasets. A preliminary analysis contained in a companion article by Beyer and Bommer finds that the reduction is small-to-nonexistent for equations based on a wide range of magnitudes and distances. The results of Beyer and Bommer do suggest, however, that there is an increasing reduction as period increases. Whether the reduction increases with other subdivisions of the dataset for which strongly correlated motions might be expected (e.g., pulselike motions close to faults) awaits further analysis.

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“…Parameters believed to affect the amplitude of the pulse are related to the aforementioned rupture-to-site geometry, while empirical models positively correlating the earthquake's magnitude to the period of the pulse (T p ) have been proposed (e.g., Somerville [2003]); global geophysics-based directivity predictors are also available (e.g., Spudich et al [2004]). …”

Section: Introductionmentioning

confidence: 99%

Probability of Occurrence of Velocity Pulses in Near-Source Ground Motions

Iervolino¹,

Cornell²

2008

Bulletin of the Seismological Society of America

107

102

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Near-source ground-motion records affected by directivity may show unusual features in the signal resulting in low-frequency cycle pulses in the velocity time history, especially in the fault-normal component. Such an effect causes the seismic demand for structures to deviate from that of so-called ordinary records. This circumstance may be particularly hazardous for structural engineering applications if it is not properly accounted for. In fact, current attenuation laws are not able to capture such effects well, if at all, and therefore current probabilistic seismic hazard analysis (PSHA) is not able to predict this peculiar spectral shape. This failure may possibly lead to an underestimation of, in particular, the nonlinear demand. Accounting for pulse-type records in earthquake engineering practice should be reflected both in the PSHA and in the record selection for seismic assessment of structures. These applications require a model for the probability of occurrence of pulselike records. Herein such a model is proposed on an empirical basis. A set of pulselike fault-normal ground motions from the Next Generation Attenuation of Ground Motions (NGA) Project dataset, as systematically identified by Baker (2007), is used. The independent variables studied are chosen from those considered by seismologists to affect the amplitude of directivity pulses. Issues related to the dataset and the explanatory power of the proposed models are also discussed.

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A formulation of directivity for earthquake sources using isochrone theory

Cited by 27 publications

References 3 publications

Quantification of ground-motion parameters and response spectra in the near-fault region

Quantification of ground-motion parameters and response spectra in the near-fault region

Orientation-Independent Measures of Ground Motion

Probability of Occurrence of Velocity Pulses in Near-Source Ground Motions

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