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Erdal Safak

Publications and source records attributed to Erdal Safak.

16 recordsLinked to original sources
USGS2007

Rotational Seismology Workshop of February 2006

Introduction A successful workshop titled 'Measuring the Rotation Effects of Strong Ground Motion' was held simultaneously in Menlo Park and Pasadena via video conference on 16 February 2006. The purpose of the Workshop and this Report are to summarize existing data and theory and to explore future challenges for rotational seismology, including free-field strong motion, structural strong motion, and teleseismic motions. We also forged a consensus on the plan of work to be pursued by this international group in the near term. At this first workshop were 16 participants in Menlo Park, 13 in Pasadena, and a few on the telephone. It was organized by William H. K. Lee and John R. Evans and chaired by William U. Savage in Menlo Park and by Kenneth W. Hudnut in Pasadena. Its agenda is given in the Appendix. This workshop and efforts in Europe led to the creation of the International Working Group on Rotational Seismology (IWGoRS), an international volunteer group providing forums for exchange of ideas and data as well as hosting a series of Workshops and Special Sessions. IWGoRS created a Web site, backed by an FTP site, for distribution of materials related to rotational seismology. At present, the FTP site contains the 2006 Workshop agenda (also given in the Appendix below) and its PowerPoint presentations, as well as many papers (reasonable-only basis with permission of their authors), a comprehensive citations list, and related information. Eventually, the Web site will become the sole authoritative source for IWGoRS and shared information: http://www.rotational-seismology.org ftp://ehzftp.wr.usgs.gov/jrevans/IWGoRS_FTPsite/ With contributions from various authors during and after the 2006 Workshop, this Report proceeds from the theoretical bases for making rotational measurements (Graizer, Safak, Trifunac) through the available observations (Huang, Lee, Liu, Nigbor), proposed suites of measurements (Hudnut), a discussion of broadband teleseismic rotational seismology (Cochard, Igel, Schreiber, Teisseyre, Wassermann, Majewski), sensor-calibration issues (Evans, Hutt), and finally the summary and conclusions (Savage). As a direct result of the 2006 Workshop and the formation of IWGoRS, we held a special session at the Fall 2006 AGU meeting (convened by H. Igel, W.H.K. Lee, and M.I. Todorovska). Currently, the first formal Workshop of the IWGoRS is being organized by W.H.K. Lee, M. Celebi, and M. I. Todorovska with sponsorship by the USGS and assistance from many others; this First International Workshop on Rotational Seismology and Engineering Applications will be held in September 2007 at Menlo Park, California (http://pubs.usgs.gov/of/2007/1144/). The following summarizes presentations and discussions during and shortly after the informal Workshop of February 2006.

Open-File Report↗
USGS2006

A simple model for strong ground motions and response spectra

A simple model for the description of strong ground motions is introduced. The model shows that response spectra can be estimated by using only four parameters of the ground motion, the RMS acceleration, effective duration and two corner frequencies that characterize the effective frequency band of the motion. The model is windowed band-limited white noise, and is developed by studying the properties of two functions, cumulative squared acceleration in the time domain, and cumulative squared amplitude spectrum in the frequency domain. Applying the methods of random vibration theory, the model leads to a simple analytical expression for the response spectra. The accuracy of the model is checked by using the ground motion recordings from the aftershock sequences of two different earthquakes and simulated accelerograms. The results show that the model gives a satisfactory estimate of the response spectra.

Earthquake Engineering and Structural Dynamics↗
USGS2006

On low-frequency errors of uniformly modulated filtered white-noise models for ground motions

Low-frequency errors of a commonly used non-stationary stochastic model (uniformly modulated filtered white-noise model) for earthquake ground motions are investigated. It is shown both analytically and by numerical simulation that uniformly modulated filter white-noise-type models systematically overestimate the spectral response for periods longer than the effective duration of the earthquake, because of the built-in low-frequency errors in the model. The errors, which are significant for low-magnitude short-duration earthquakes, can be eliminated by using the filtered shot-noise-type models (i. e. white noise, modulated by the envelope first, and then filtered).

Earthquake Engineering and Structural Dynamics↗
USGS1994

Prediction of structural response to large earthquakes by using recordings from smaller earthquakes

The feasibility of predicting structural response to large earthquakes by using recorded responses from collocated smaller earthquakes is investigated. Records from large earthquakes can be approximated as linear combinations of records from smaller earthquakes. Two methods are introduced to predict structural response to a large earthquake by using the recorded response to a smaller earthquake. The accuracy of the methods are tested by applying them to data from a highway overpass.

Conference Paper↗
USGS1990

Method to estimate center of rigidity using vibration recordings

A method to estimate the center of rigidity of buildings by using vibration recordings is presented. The method is based on the criterion that the coherence of translational motions with the rotational motion is minimum at the center of rigidity. Since the coherence is a function of frequency, a gross but frequency-independent measure of the coherency is defined as the integral of the coherence function over the frequency. The center of rigidity is determined by minimizing this integral. The formulation is given for two-dimensional motions. Two examples are presented for the method; a rectangular building with ambient-vibration recordings, and a triangular building with earthquake-vibration recordings. Although the examples given are for buildings, the method can be applied to any structure with two-dimensional motions.

Journal of Structural Engineering↗
USGS1989

Seismic response of a large-span roof diaphragm

Records obtained from the West Valley College Gymnasium in Saratoga, California during the 1984 Morgan Hill earthquake are used to study the dynamic behavior of the overall gymnasium as well as its flexible disaphragm. The ground-level motions recorded in the two orthogonal axes of the structure differ considerably in peak acceleration and amplify by approximately 1.5 times at the roof edges and by 4-5 times at the center of the diaphragm. The diaphragm responds with a frequency of approximately 4 Hz in both orthogonal axes. A simple finite-element model is used to match the fundamental frequency of the diaphragm with that from the records. Using this model and the ground-level motions as input, the diaphragm center displacements are calculated by varying the structural damping. Best comparisons are obtained for 5% damping. These results are discussed in terms of the code provisions.

Earthquake Spectra↗
USGS1989

Optimal-adaptive filters for modelling spectral shape, site amplification, and source scaling

Optimal filtering techniques have been used successfully in various areas in science and engineering. They are based on statistical properties of the signal and the noise, and stochastic approximation theory. In addition to filtering, optimal filters can also be used for smoothing, prediction, and system identification. This paper introduces some applications of optimal filtering techniques to earthquake engineering by using the so-called ARMAX models. Three applications are presented: (a) spectral modelling of ground accelerations, (b) site amplification (i.e., the relationship between two records obtained at different sites during an earthquake), and (c) source scaling (i.e., the relationship between two records obtained at a site during two different earthquakes). A numerical example for each application is presented by using recorded ground motions. The results show that the optimal filtering techniques provide elegant solutions to above problems, and can be a useful tool in earthquake engineering.

Soil Dynamics and Earthquake Engineering↗
USGS1989

Adaptive modeling, identification, and control of dynamic structural systems. I. Theory

A concise review of the fheory of adaptive modeling, identification, and control of dynamic structural systems based on discrete‐time recordings is presented. Adaptive methods have four major advantages over the classical methods: (1) Removal of the noise from the signal is done over the whole frequency band; (2) time‐varying characteristics of systems can be tracked; (3) systems with unknown characteristics can be controlled; and (4) a small segment of the data is needed during the computations. Included in the paper are the discrete‐time representation of single‐input single‐output (SISO) systems, models for SISO systems with noise, the concept of stochastic approximation, recursive prediction error method (RPEM) for system identification, and the adaptive control. Guidelines for model selection and model validation and the computational aspects of the method are also discussed in the paper. The present paper is the first of two companion papers. The theory given in the paper is limited to that which is necessary to follow the examples for applications in structural dynamics presented in the second paper.

Journal of Engineering Mechanics↗
USGS1988

Stochastic system identification in structural dynamics

Recently, new identification methods have been developed by using the concept of optimal-recursive filtering and stochastic approximation. These methods, known as stochastic identification, are based on the statistical properties of the signal and noise, and do not require the assumptions of current methods. The criterion for stochastic system identification is that the difference between the recorded output and the output from the identified system (i.e., the residual of the identification) should be equal to white noise. In this paper, first a brief review of the theory is given. Then, an application of the method is presented by using ambient vibration data from a nine-story building.

Conference Paper↗
USGS1985

SENSITIVITY OF STRUCTURAL RESPONSE TO GROUND MOTION SOURCE AND SITE PARAMETERS.

Designing structures to withstand earthquakes requires an accurate estimation of the expected ground motion. While engineers use the peak ground acceleration (PGA) to model the strong ground motion, seismologists use physical characteristics of the source and the rupture mechanism, such as fault length, stress drop, shear wave velocity, seismic moment, distance, and attenuation. This study presents a method for calculating response spectra from seismological models using random vibration theory. It then investigates the effect of various source and site parameters on peak response. Calculations are based on a nonstationary stochastic ground motion model, which can incorporate all the parameters both in frequency and time domains. The estimation of the peak response accounts for the effects of the non-stationarity, bandwidth and peak correlations of the response.

Conference Paper↗