scholarly journals Variation in earthquake ground motion on the Fraser delta from strong-motion seismograph records

1998 ◽  
Author(s):  
G C Rogers ◽  
J F Cassidy ◽  
D H Weichert
Keyword(s):  
Ground Motion ◽  
Strong Motion ◽  
Earthquake Ground Motion

Seismic response and retrofit of industrial brick masonry chimneys

1992 ◽  
Vol 19 (1) ◽  
pp. 117-128 ◽  
Author(s):  
A. Ghobarah ◽  
T. Baumber
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Strong Motion ◽  
Brick Masonry ◽  
Wind Loading ◽  
Earthquake Ground Motion ◽  
Lumped Mass ◽  
Mass System ◽  
Higher Modes ◽  
Recent Earthquakes

During recent earthquakes, the documented cases of collapsed unreinforced brick masonry industrial chimneys are numerous. Observed modes of structural failure are either total collapse or sometimes collapse or damage of the top third of the structure. The objective of this study is to analyze and explain the modes of observed failure of masonry chimneys during earthquake events, and to evaluate two retrofit systems for existing chimneys in areas of high seismicity. The behaviour of the masonry chimney, when subjected to earthquake ground motion, was modelled using a lumped mass system. Several actual strong motion records were used as input to the model. The shear, moment, and displacement responses to the earthquake ground motion were evaluated for various chimney configurations. It was found that the failure of the chimney at its base is the result of the fundamental mode of vibration. Failure at the top third of the structure due to the higher modes of vibration is possible when the chimney is subjected to high frequency content earthquakes. Higher modes, which are normally not of concern under wind loading, were shown to be critical in seismic design. Post-tensioning and the reinforcing steel cage were found to be effective retrofit systems. Key words: masonry, chimneys, behaviour, analysis, design, retrofit, dynamic, earthquakes, seismic response.

Improvement of the objective function in the velocity structure inversion based on horizontal-to-vertical spectral ratio of earthquake ground motions

2020 ◽  
Vol 224 (1) ◽  
pp. 1-16
Author(s):  
Mianshui Rong ◽  
Xiaojun Li ◽  
Lei Fu
Keyword(s):  
Objective Function ◽  
Ground Motion ◽  
Velocity Structure ◽  
Strong Motion ◽  
Earthquake Ground Motion ◽  
Inversion Method ◽  
Observation Data ◽  
S Wave ◽  
Inversion Methods ◽  
Underground Velocity Structures

SUMMARY Given the improvements that have been made in the forward calculations of seismic noise horizontal-to-vertical spectral ratios (NHVSRs) or earthquake ground motion HVSRs (EHVSRs), a number of HVSR inversion methods have been proposed to identify underground velocity structures. Compared with the studies on NHVSR inversion, the research on the EHVSR-based inversion methods is relatively rare. In this paper, to make full use of the widely available and constantly accumulating strong-motion observation data, we propose an S-wave HVSR inversion method based on diffuse-field approximation. Herein, the S-wave components of earthquake ground motion recordings are considered as data source. Improvements to the objective function has been achieved in this work. An objective function with the slope term is introduced. The new objective function can mitigate the multisolution phenomenon encountered when working with HVSR curves with multipeaks. Then, a synthetic case is used to show the verification of the proposed method and this method has been applied to invert underground velocity structures for six KiK-net stations based on earthquake observations. The results show that the proposed S-wave EHVSR inversion method is effective for identifying underground velocity structures.

Book Review of “On Strong Motion Seismology” (in Japanese) written and edited by Hiroaki Yamanaka, published by University of Tokyo Press

2006 ◽  
Vol 1 (3) ◽  
pp. 449-451
Author(s):  
Editorial Office
Keyword(s):  
Ground Motion ◽  
Strong Motion ◽  
Earthquake Ground Motion ◽  
Large Fires ◽  
Hyogo Prefecture ◽  
Narrow Belt ◽  
Oil Tanks ◽  
Second Period ◽  
Collapsed Building

This book is a work for general readers, straight-forwardly treating the theme of "strong earthquake ground motion" directly causing disaster and explaining how to cope. Eartquake ground motion is generally said to cause earthquake disasters and the degree of ground motion is determined both by the magnitude of the earthquake and the distance from its epicenter. In reality, however, things are not so simple. In the 2003 Tokachi Offshore Earthquake, for example, shaking at a relatively long 10-second period resonated at the characteristic frequency of oil tanks, triggering sloshing and causing large fires. In the 1995 Southern Hyogo Prefecture Earthquake (the Great Hanshin-Awaji Earthquake Disaster), for another example, a long narrow belt of disaster confirmed where damage to collapsed building was especially significant because only ground within this belt quaked more intensely than elsewhere.

scholarly journals Variation Evaluation of Path Characteristic and Site Amplification Factor of Earthquake Ground Motion at Four Sites in Central Japan

2021 ◽  
Vol 11 (5) ◽  
pp. 7658-7664
Author(s):  
T. Nagao
Keyword(s):  
Ground Motion ◽  
Amplification Factor ◽  
Hazard Analysis ◽  
Strong Motion ◽  
Site Amplification ◽  
Earthquake Ground Motion ◽  
Constraint Condition ◽  
Central Japan ◽  
Source Characteristic ◽  
Site Amplification Factor

The considered parameters in seismic design vary, with the Earthquake Ground Motion (EGM) having the largest variation. Since source characteristic, path characteristic, and Site Amplification Factor (SAF) influence the EGM, it is crucial to appropriately consider their variations. Source characteristic variations are mainly considered in a seismic hazard analysis, which is commonly used to evaluate variations in EGM. However, it is also important to evaluate variations in path characteristic and SAF with only a few studies having individually and quantitatively examined the variations of these two characteristics. In this study, based on strong-motion observation records obtained from four sites in central Japan, the three characteristics were extracted from seismograms using the concept of spectral inversion. After removing the source characteristic, the path characteristic and SAF were separated, and the variations in these two characteristics were quantified. To separate and obtain each characteristic from the observed record, one constraint condition must be imposed, whereas the variations in the constraint condition must be ignored. In that case, the variations in the constraint condition are included in the variations of the separated characteristics. In this study, this problem was solved by evaluating the variation in the constraint condition, which is the SAF at a hard rock site, by the use of the vertical array observation record at the site.

The Loma Prieta earthquake, ground motion, and damage in Oakland, Treasure Island, and San Francisco

1991 ◽  
Vol 81 (5) ◽  
pp. 2019-2047
Author(s):  
Thomas C. Hanks ◽  
A. Gerald Brady
Keyword(s):  
Ground Motion ◽  
San Francisco ◽  
Strong Ground Motion ◽  
Strong Motion ◽  
Earthquake Ground Motion ◽  
Transverse Motion ◽  
Loma Prieta Earthquake ◽  
Loma Prieta ◽  
Treasure Island ◽  
Strong Ground

Abstract The basis of this study is the acceleration, velocity, and displacement wave-forms of the Loma Prieta earthquake (18 October 1989; M = 7.0) at two rock sites in San Francisco, a rock site on Yerba Buena Island, an artificial-fill site on Treasure Island, and three sites in Oakland underlain by thick sections of poorly consolidated Pleistocene sediments. The waveforms at the three rock sites display a strong coherence, as do the three sedimentary sites in Oakland. The duration of strong motion at the rock sites is very brief, suggestive of an unusually short source duration for an earthquake of this size, while the records in Oakland show strong amplification effects due to site geology. The S-wave group at Treasure Island is phase coherent with the Oakland records, but at somewhat diminished amplitudes, until the steps in acceleration at approximately 15 sec, apparently signaling the onset of liquefaction. All seven records clearly show shear-wave first motion opposite to that expected for the mainshock radiation pattern and peak amplitudes greater than expected for sites at these distances (95 ± 3 km) from an earthquake of this magnitude. While the association between these ground motion records and related damage patterns in nearby areas has been easily and eagerly accepted by seismological and engineering observers of them, we have had some difficulty in making such relationships quantitative or even just clear. The three Oakland records, from sites that form a nearly equilateral triangle about the Cypress Street viaduct collapse, are dominated by a long-period resonance (≃ 1 1/2-sec period) far removed from the natural frequency of the structure to transverse motion (2.5 Hz) or from high-frequency amplification bands observed in aftershock studies. A spectral ratio arbiter of this discrepancy confuses it further. The failure of the East Bay crossing of the San Francisco-Oakland Bay Bridge cannot be attributed to relative displacements of the abutments in Oakland and Yerba Buena Island, but the motions of the Bay Bridge causing failure remain unknown. The steps in acceleration at Treasure Island present unusual strong-motion accelerogram processing problems, and modeling suggests that the velocity and displacement waveforms are contaminated by a spurious response of the filtering operations to the acceleration steps. A variety of coincidences suggests that the Treasure island accelerogram is the most likely strong-motion surrogate for the filled areas of the Marina District, for which no mainshock records are available, but the relative contributions of bad ground, poor construction and truly strong ground motion to damage in the Marina District will never by known in any quantitative way. The principal lesson of all of this is that until a concerted effort is mounted to instrument ground and structures that are likely to fail during earthquakes, our understanding of the very complex relationships between strong ground motion and earthquake damage will, in general, remain rudimentary, imprecise, and vague.

scholarly journals Spectrum analysis of strong-motion earthquakes*

1953 ◽  
Vol 43 (2) ◽  
pp. 97-119
Author(s):  
G. W. Housner ◽  
R. R. Martel ◽  
J. L. Alford
Keyword(s):  
Dynamic Response ◽  
Ground Motion ◽  
Spectrum Analysis ◽  
Structural Response ◽  
Strong Motion ◽  
Quantitative Measure ◽  
Analog Computer ◽  
Earthquake Ground Motion ◽  
Earthquake Intensity ◽  
Electric Analog

Abstract The problem of the dynamic response of a structure to earthquake ground motion has been formulated in a manner which permits separation of the characteristics of particular structures from the characteristics of the earthquake. The expression involving the characteristics of the earthquake is defined as the “spectrum” of the earthquake and it is shown that the spectrum is a plot of the maximum response of a simple oscillator versus the period of the oscillator. Eighty-eight such spectra were computed by means of an electric analog computer and are presented in this paper. It is found that damping is a very important parameter in the over-all problem; relatively small amounts of damping reduce the structural response sharply. Further research on damping in buildings is recommended, and it is also proposed that the spectrum be used as a quantitative measure of earthquake intensity.

Stress estimates for the San Fernando, California, earthquake of February 9, 1971: Main event and thirteen aftershocks

1972 ◽  
Vol 62 (3) ◽  
pp. 721-750 ◽  
Author(s):  
M. D. Trifunac
Keyword(s):  
Ground Motion ◽  
Near Field ◽  
Strong Motion ◽  
Earthquake Ground Motion ◽  
The North ◽  
Field Evidence ◽  
North Eastern ◽  
San Fernando ◽  
And Migration ◽  
Stress Drops

Abstract The strong earthquake ground motion recorded in the center of and above the fault plane is combined with field evidence of faulting and instrumental studies of aftershocks to deduce stresses during and after the San Fernando earthquake of February 9, 1971. Stress computations based on Brune's near-field, shear-wave spectra, peak velocity of ground motion, energy calculated from the strong-motion record, and a model of circular dislocation give mutually consistent stress estimates, which suggest that the effective stress operating during the earthquake was approximately 100 bars, while during the earthquake it dropped several tens of bars. The energy of the main event is estimated to be 1022 dyne cm. Thirteen aftershocks, recorded during the first 6 min, were associated with stress drops ranging from 10 to 500 bars, these events clustering along the north-eastern end of the dislocation surface. The strong-motion accelerograms provide invaluable data for detailed investigations of the pattern of earthquake energy release during and immediately after an earthquake. Used for the first time in this study, strong-motion accelerograms gave an excellent picture of stress history and migration of seismic activity during the first 6 min.

Network analysis of earthquake ground motion spatial correlation: A case study with the san jacinto seismic nodal array

2021 ◽  
Author(s):  
Yixiao Sheng ◽  
Qingkai Kong ◽  
Gregory C Beroza
Keyword(s):  
Spatial Correlation ◽  
Ground Motion ◽  
Strong Motion ◽  
Earthquake Ground Motion ◽  
Graph Analytics ◽  
Motion Data ◽  
Large N ◽  
Aftershock Sequences ◽  
Weak Constraints

Summary The spatial correlation of earthquake ground motion intensity can be measured from strong motion data; however, the data used in past studies is sparsely sampled in space, and only the inter-station distance was considered as a correlation variable. These limitations mean that we have only weak constraints on the true correlation structure of ground motion and that potentially important aspects of spatial correlation are unconstrained. In this study, we combine a large-N seismic array and graph analytics to explore this issue at a local scale using small local and regional earthquakes. Our result suggests site conditions, and how they interact with the incident seismic wavefield, strongly condition the spatial correlation of ground motion. Future progress in characterizing ground motion spatial variability will require dense wavefield measurements, either through nodal deployments, or perhaps distributed acoustic sensing (DAS) measurements, of seismic wavefields. Aftershock sequences of major earthquakes would provide particularly data-rich targets of opportunity.

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