Pseudo-velocity Response Research Articles

SEA96--A New Predictive Relation for Earthquake Ground Motions in Extensional Tectonic Regimes

We present a new predictive relation for horizontal peak ground acceleration and 5% damped pseudo-velocity response spectrum appropriate for predicting earthquake ground motions in extensional tectonic regimes. This new empirical relation, which we denote “Sea96,” was originally derived by Spudich et al. (1996) as part of a project to estimate seismic hazard at the site of a proposed nuclear waste repository at Yucca Mountain, Nevada. Because of the length and relative inaccessibility of that report, we are briefly presenting the Sea96 relation and its derivation here. We developed our relation based on data from extensional regime earthquakes having moment magnitude M > 5.0 recorded at distances less than 105 km. Extensional regions are regions in which the lithosphere is expanding areally. This areal expansion is the result of applied forces that yield a state of stress for which Sv > SHmax > SHmin , where Sv , SHmax , and SHmin represent principal...

Site-dependent attenuation relations of seismic motion parameters at depth using borehole data

Abstract Using more than 500 accelerometric records from three vertical arrays located in Japan, we performed a regression analysis in order to derive attenuation relationships at underground sites with depths ranging from 100 to 950 m. Analyses were conducted on both peak ground acceleration and pseudo-velocity response spectra. Because of a positive correlation between magnitude and distance, a two-step regression technique was employed. Results show that, compared with surface ground motion, peak accelerations at underground sites are lower by a factor ranging from 1.5 to 4 according to the depth. In the case of response spectra, differences between ground surface and underground spectra are dependent on geological conditions. For the three sites considered in the study, underground pseudo-velocity response spectra show amplitudes lower by a factor ranging from 1.5 to 10 according to the depth or the period considered. Ratios between the receiver responses obtained at different depths provided average transfer functions. Those were compared with transfer functions calculated by averaging ratios of observed response spectra between different depths. A good agreement between the two techniques was found. Finally, theoretical transfer functions were estimated using both one-dimensional SH and complete wave modeling. It was shown that the characteristics of the incident wave field can play an important role in the estimation of theoretical transfer functions.

Assessment of potential strong ground motions in the city of Rome

A methodology is used which combines stochastic generation of random series with a finite-difference technique to estimate the expected horizontal ground motion for the city of Rome as induced by a large earthquake in the Central Apennines. In this approach, source properties and long-path propagation are modelled through observed spectra of ground motion in the region, while the effects of the near-surface geology in the city are simulated by means of a finite-difference technique applied to 2-D models including elastic and anelastic properties of geologic materials and topographic variations. The parameters commonly used for earthquake engineering purposes are estimated from the simulated time histories of horizontal ground motion. We focus our attention on peak ground acceleration and velocity, and on the integral of the squared acceleration and velocity (that are proportional to the Arias intensity and seismic energy flux, respectively). Response spectra are analyzed as well. Parameter variations along 2-D profiles visualize the effects of the small-scale geological heterogeneities and topography irregularities on ground motion in the case of a strong earthquake. Interestingly, the largest amplification of peak ground acceleration and Arias intensity does not necessarily occur at the same sites where peak ground velocity and flux of seismic energy reach their highest values, depending on the frequency band of amplification. A magnitude 7 earthquake at a distance of 100 km results in peak ground accelerations ranging from 30 to 70 gals while peak ground velocities are estimated to vary from 5 to 7 cm/s; moreover, simulated time histories of horizontal ground motion yield amplitudes of 5% damped pseudovelocity response spectra as large as 15-20 cm/s for frequencies from 1to 3 Hz. In this frequency band, the mean value is 7 cm/s for firm sites and ranges from 10 to 13 cm/s for soil sites. All these results are in good agreement with predictions based on regressions of Italian and Western North American data.

“Prediction” of strong ground motion for the 1989 Loma Prieta earthquake using empirical Green's functions

Abstract This article examines how the empirical Green9s function seismogram synthesis method might perform as a tool for earthquake hazard analysis by “predicting” strong ground motion from the 18 October 1989 Loma Prieta earthquake. A suite of accelerograms are synthesized for five sites 40 to 80 km from the nearest fault rupture from 25 different source models that might have been considered prior to the occurrence of the Loma Prieta earthquake. Three-component, full wavetrain ground accelerations are synthesized over the frequency range of 0.5 to 25.0 Hz with a sparse distribution of source events for empirical Green9s functions and fairly simple source models. The suite of source models includes a range of rupture histories and geometries, asperity models, and slip models that reflect the uncertainties both in predicting the actual rupture history and in knowledge of modeling rupture processes. The suite of synthesized accelerograms includes a good match to observed time series amplitudes, frequency content, energy distribution, and some waveforms and demonstrates that the character of actual time series can be captured with a range of simple source models. The average levels of peak acceleration, pseudo-velocity response, and Fourier amplitude spectra provide a good prediction to the observed values at four of the five sites. The log-normal standard deviations provide bounds on the predictions that are specific to the source and recording site.

Earthquakes, quaternary faults, and seismic hazard in California

Data describing the locations, slip rates, and lengths of Quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in California. The expected seismic moment M0e and the strength of ground shaking resulting from the entire rupture of each mapped fault (or fault segment) are estimated using empirical relations between seismic moment M0, rupture length, source to site distance, and strong ground motions. Assuming a fault model whereby the repeat time T of earthquakes on each fault equals M0e/M0g (where the moment rate M0g is proportional to fault slip rate), it is observed that the moment‐frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150‐year historical record. The agreement is consistent with the argument that the geologic record of Quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in California. The estimates of T for each fault are the foundation for constructing maps that depict the average return period of ≳ 0.1g peak horizontal ground accelerations, and the horizontal components of peak acceleration, peak velocity, and the pseudovelocity response (at 1‐period and 5% damping) expected to occur at the level of 0.1 probability during a 50‐year period of time. A map is also formulated to show the probability that ≳ 0.1g horizontal ground accelerations will occur during the next 50 years. The maps serve to illustrate the potential value of Quaternary fault studies for assessing seismic hazard. Interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the San Andreas, San Jacinto, Calaveras, Hayward, and Ventura Basin fault zones. Other regions of similarly high hazard may yet remain unrecognized. This inadequacy results primarily from an incomplete data set. Numerous faults, for example, are mapped along the coastal region of northern California and within the Modoc Plateau, but relatively few studies relating to fault slip rate are reported. A similar problem exists for other stretches of coastal California where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate. Geological and geophysical field studies can work to remove these deficiencies. A concerted effort to locate and define rates of activity on all faults in California is the most promising means to further quantify present levels of seismic hazard in California.

Seismic design response by an alternative SRSS rule

AbstractThe square root of the sum of the squares (SRSS) procedure and its modified forms are often used to obtain seismic design response. The design inputs for such procedures are usually defined in terms of pseudo velocity or acceleration response spectra. Erroneous results have been obtained with these existing SRSS procedures, especially in the calculation of responses where high frequency effects dominate. Here an alternative SRSS procedure is developed using the so‐called mode acceleration approach of structural dynamics. The design input in this procedure is defined in terms of relative acceleration and relative velocity spectra. The relative spectra can be related to pseudo spectra. For a given number of modes to be included in the analysis the new SRSS rule proposed here will reduce the error due to the so‐called ‘missing mass’ effect and predict a more accurate response value than the rules which use pseudo spectra as input, for systems either with or without dominant high frequency mode effects.

Earthquake Design of Buildings:Damping

A Fourier spectra analysis of the recorded February 9, 1971, San Fernando earthquake response of 12 southern California high-rise buildings was conducted and damping in building normal modes of vibration was estimated. Obtained damping values were correlated with building basement 0% damped pseudovelocity response spectrum and empirical equations were derived for damping estimation. A procedure utilizing these equations was developed for the selection of damping values for use in building design.

Relations between response and Fourier spectra of shock functions

Using the running Fourier transform technique for solving the equation of motion it is found that velocity and pseudo-velocity response spectra of shock functions are bounded above and below by the amplitude and Fourier spectra respectively. The gap between bounds and spectra is assessed in a numerical example.

Effect of Site Conditions on Earthquake Intensity

A study is reported of over 100 strong motion earthquake accelerograms at seven sites based on interpretation of integrated and balanced strong motion acceleration records and 5% damped pseudo-velocity response spectra from these records; pertinent site properties computed from reported relationships; epicentral distances and earthquake magnitudes; and wave theory applied to bounded elastic media having constant or linearly variant properties. It is concluded that no strong preferential site period was amplified on a maximum pseudo-velocity response spectrum during strong motion earthquake; spectra velocities at soft layer sites average twice the base spectrum values; normal amplification near the earthquake mechanism period is approximately 3.2 times that of the base spectrum; an equation for the maximum velocity of the Helena earthquake is not recommended for design use because of the large number of unknowns. Further study is recommended into the influence of foundation rigidity and structural mass and stiffness related to base motion of the structures and the effective depth of impedence measurement; correlation, from standard soil mechanics methods, of shear strength to shear impedences; and transient random disturbances propagating up through energy absorbent elastic materials.