Símon Ólafsson

A Fast and Efficient Simulation of the Far-Fault and Near-Fault Earthquake Ground Motions Associated with the June 17 and 21, 2000, Earthquakes in South Iceland

The two Mw 6.5 earthquakes on June 17 and 21, 2000, respectively, in the populated South Iceland Seismic Zone (SISZ) significantly augmented the Icelandic database of strong ground motions, and several strong velocity pulses were recorded at near-fault sites. The strong motions are interpreted via the Specific Barrier Model (SBM) and a mathematical model of near-fault velocity pulses. The data indicates self-similar source scaling and significantly greater attenuation of seismic waves than in other interplate regions. Through inversion of the data a new attenuation function for the SISZ has been adopted, which results in unbiased simulations. For the first time, the characteristics of the recorded near-fault pulses have been identified and compared to the worldwide database of such records. The SBM and the near-fault pulse model combine naturally in a fast and efficient synthesis of realistic, broad-band strong ground motions in the far-fault and near-fault region. Such simulations are showcased for the June 2000 earthquakes and indicate that the modeling approach adopted in this study is an effective tool for the estimation of realistic earthquake ground motions in the SISZ.

A THEORETICAL ATTENUATION MODEL FOR EARTHQUAKE-INDUCED GROUND MOTION

A theoretical attenuation model of earthquake-induced ground motion is presented and discussed. This model is related directly to physical quantities such as source and wave motion parameters. An attenuation formula for rms acceleration of ground motion is derived and verified using acceleration data from moderate-sized earthquakes recorded in Iceland from 1986 to 1997. The source parameters and the crustal attenuation are computed uniformly for the applied earthquake data. Furthermore, attenuation formulas for peak ground acceleration are put forward.

Digital Filters for Simulation of Seismic Ground Motion and Structural Response

Discrete time series representations for some commonly used relations in earthquake engineering and engineering seismology are presented and the advantages, compared with their continuous time counterparts, are discussed. Seismic source models derived by Brune are presented in discrete time form, as well as a model by Savage, which includes directivity. The discrete time series models are presented as recursive filters (ARMA models) that simplify the simulation process and do not involve the numerical Fourier transform. Furthermore, a demonstration is made of the use of discrete time representations for a SDOF system and their use for the computation of earthquake response spectra.

MODELING THE MECHANICAL RESPONSE OF A LEAD-CORE BEARING DEVICE: DAMAGE MECHANICS APPROACH

Abstract. This paper presents the results of a numerical study aimed at developing a rational approach to assess the degradation of mechanical properties of lead-core bearing devices used for passive seismic isolation. The lead-core rubber bearing is modeled as a multiple-component system. Appropriate constitutive laws and failure criteria are defined for each component of the system. Two alternative constitutive relations are defined for the lead core: bilinear material model by assuming isotropic hardening after yielding, and a model formulated in the framework of continuum damage mechanics. The numerical procedure used to simulate the mechanical response of the device allows the monitoring of accumulated mechanical damage throughout the loading history. Preliminary simulation results obtained by finite element analysis are reported. Specifically, these are shear force-displacement hysteresis loops under various loading conditions in a typical characterization test.

Earthquake Engineering and Structural Dynamics in Memory of Ragnar Sigbjörnsson

Structural engineering for earthquake resistance is undergoing a major revision in its approach toward the fulfillment of seismic safety and utilitarian serviceability in design. Rather than sticking to the established precepts of prescriptive design rules, design has turned toward the achievement of specific results through procedures that are tailored for different buildings and uses. These procedures represent notable research contributions, but they are complicated conceptually for implementation in structural engineering practice, and nonlinear building response estimates, frequently assumed to be performance, can vary within broad limits even for simple applications. In this text we relate the history of code developments. We focus on the two main requirements of earthquake-resistant design of building structures: (1) Life Safety and (2) Protection of the Investment and relate the two demands to current concepts of Performance-Based Building Design. While we provide a personalized vision for the way in which the PBSD framework developed and matured during the last half century, a thorough historiography is not within the scope of the text. We nominate drift to serve as the prime metric for performance judgment.

A Study of Rigid Blocks Rocking Against Rigid Walls

The safety of typical bookshelf is investigated using an inverted pendulum approach. A general bookcase is modelled as a rocking block and its response to damped harmonic excitation is simulated. The rocking of the block is considered as one sided since these household items generally stand parallel to a wall. This approach adds restraints to the rocking behaviour. The overturning spectra for the bookcase is presented for one-sided and two-sided rocking for a range of damped harmonic excitations, demonstrating the chaotic behaviour of the inverted pendulum model. Furthermore, results indicate one-sided rocking to be more prone to overturning, making it a more unstable system than its two-sided counterpart.

Determination of Parameters for Stochastic Strong Motion Models Representing Earthquakes in the South Iceland Seismic Zone

The parameters for a point source model are estimated using strong ground motion recorded in the largest earthquakes in south Iceland since a strong motion network established (from 1986 to 2008). The model is found to provide a good fit to the ground motion records. Parameters were estimated for the earthquakes of 17th June 2000 Mw 6.5, 21st June 2000 Mw 6.4, 29 May 2008 Mw 6.3 and 25 May 1987 Mw 5.8. Great variability in parameters was observed. A mean kappa, κ = 0.04 s, was observed. The stress drop for the three larger events had an estimated average value of 80 × 10 5 Pa and an average dislocation of 90 cm. Closed form relations for root-mean-squared (rms) acceleration are presented for the ground motion in the near and far field. A peak factor is then applied to rms acceleration in order to obtain peak ground acceleration. The model can be applied instead of empirical ground motion prediction equations to estimate ground motion and potential seismic hazard in Iceland. Its estimated parameters can be used in the framework of stochastic modelling to simulate artificial ground acceleration for the dynamic analysis of structures.