Spectral Comparison of Vertical and Horizontal Seismic Strong Ground Motions in Alluvial Basins

1998 ◽  
Vol 14 (4) ◽  
pp. 573-595 ◽  
Author(s):  
Rouben V. Amirbekian ◽  
Bruce A. Bolt
Keyword(s):  
High Frequency ◽  
Ground Motions ◽  
Frequency Content ◽  
S Waves ◽  
Anelastic Attenuation ◽  
Similar Distance ◽  
Vertical Ground ◽  
Spectral Comparison ◽  
Wave Conversion ◽  
Strong Ground

We analyze observations from the SMART2 array and the 1994 Northridge, California earthquake of spectral differences between vertical and horizontal strong seismic motions in alluvial basins. Our explanation is that the most energetic of such high-frequency vertical ground accelerations are generated by S-to-P seismic wave conversion within the transition zone between the underlying bedrock and the overlying sedimentary layers. The differences in combined scattering and anelastic attenuation for P and S waves lead to the observed spectral differences of the vertical motions between rock and deep alluvium sites. This model also accounts for the frequency content differences between the vertical and horizontal motions at sites in alluvial basins than at rock sites at similar distance ranges. The high-frequency cutoff of the acceleration power spectrum, fmax, is a useful comparison parameter. The results help in computing matched sets of synthetic ground motions above 2 Hz at alluvial sites.

Engineering Analysis of Ground Motion Records from the 2001 Mw 8.4 Southern Peru Earthquake

2010 ◽  
Vol 26 (2) ◽  
pp. 499-524 ◽  
Author(s):  
Adrian Rodriguez-Marek ◽  
James A. Bay ◽  
Kwangsoo Park ◽  
Gonzalo A. Montalva ◽  
Adel Cortez-Flores ◽  
...  
Keyword(s):  
Shear Wave ◽  
High Frequency ◽  
Ground Motions ◽  
Strong Motion ◽  
Frequency Content ◽  
Engineering Analysis ◽  
Data Set ◽  
Strong Motion Records ◽  
Southern Peru ◽  
High Frequency Content

The Mw 8.4 23 June 2001 Southern Peru earthquake generated intense ground motions in a large region encompassing southern Peru and northern Chile. The earthquake was recorded by seven strong motion stations with peak ground accelerations ranging from 0.04 g to 0.34 g for site-to-fault distances ranging from about 70 km to 220 km. At this time, there are no other strong motion records for an earthquake of this magnitude. Hence, the strong motion data set from this earthquake is unique and of particular interest to engineers dealing with seismic design in subduction regions. This paper presents an engineering analysis of the strong motion records. Shear-wave velocity profiles were measured using Spectral Analysis of Surface Waves methods at four stations. Measured shear-wave velocities are high, indicating that all sites classify as stiff soil sites (Site C) according to the International Building Code classification scheme. The strong motion set is characterized by strong high frequency content at large distances from the fault. Site response contributed at least in part to the observed high frequency content in the ground motions. In general, current attenuation relationships for spectral acceleration underpredicted the observed ground motions.

Effects of SSI on EPR™ In-Structure Response for a Rock Site: Coherent and Incoherent High Frequency Ground Motion

2010 ◽  
Author(s):  
James J. Johnson ◽  
Oliver Schneider ◽  
Werner Schuetz ◽  
Philippe Monette ◽  
Alejandro P. Asfura
Keyword(s):  
Ground Motion ◽  
High Frequency ◽  
Ground Motions ◽  
Free Field ◽  
Response Spectra ◽  
Frequency Content ◽  
Structure Response ◽  
Standard Design ◽  
Rock Site ◽  
High Frequency Content

Recently, probabilistic seismic hazard assessments (PSHAs) performed for hard sites world-wide have yielded uniform hazard response spectra (UHRS) with significant high frequency content, i.e., frequency content greater than 10 Hz. This high frequency content is frequently due to near-field relatively low magnitude events. It is well known that these high frequency ground motions are not damaging to ductile structures, systems, and components (SSCs). One method of addressing the effect of these high frequency ground motions on structure response is to take into account the incoherency of ground motion. Over the past 25 years, free-field ground motion has been recorded providing an adequate basis for the development of ground motion coherency functions necessary to assess the effect of incoherence on nuclear power plant structures. The subject of this study was the AREVA NP EPR™ (European Power Reactor) nuclear island (NI) standard design. The effect of incoherency of ground motion on in-structure response spectra (ISRS) was assessed for the NI founded on a stiff rock site and subjected to high frequency enhanced input for hard rock sites. The ISRS at numerous locations and directions in the structures were calculated and compared. SSI is shown to be an important phenomenon for structures founded on stiff sites and subjected to high frequency ground motions.

Simplified R-Factor Relationships for Strong Ground Motions

2003 ◽  
Vol 19 (1) ◽  
pp. 25-45 ◽  
Author(s):  
Isabel Cuesta ◽  
Mark A. Aschheim ◽  
Peter Fajfar
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Structural Systems ◽  
Code Design ◽  
Frequency Content ◽  
Design Spectrum ◽  
Strong Ground Motions ◽  
R Factor ◽  
N2 Method ◽  
Strong Ground

Recent studies have demonstrated the need to consider the ground motion frequency content in the development and use of R−μ−T relationships. Results from two different approaches to determining these relationships are unified in the present paper. Two bilinear R−μ−T/Tg relationships are recommended for most strong ground motions and structural systems. One is more accurate, while the other, more conservative relationship is used in FEMA 273, ATC-32, and the simple version of the N2 method. Both relationships are indexed by the characteristic period of the ground motion, Tg. Simple methods to determine Tg from smoothed design spectra and recorded ground motions are provided. Neither recommended relationships are applicable to the nearly harmonic ground motions that may be generated at sites containing soft lakebed deposits. An example illustrates the application of these relationships to a code design spectrum in both the acceleration-displacement and yield point spectra formats.

Empirical Relationships for Frequency Content Parameters of Earthquake Ground Motions

2004 ◽  
Vol 20 (1) ◽  
pp. 119-144 ◽  
Author(s):  
Ellen M. Rathje ◽  
Fadi Faraj ◽  
Stephanie Russell ◽  
Jonathan D. Bray
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Earthquake Ground Motion ◽  
Rupture Directivity ◽  
Frequency Content ◽  
Deep Soil ◽  
Empirical Relationships ◽  
Strong Ground Motions ◽  
Site Classes ◽  
Strong Ground

The frequency content of an earthquake ground motion is important because it affects the dynamic response of earth and structural systems. Four scalar parameters that characterize the frequency content of strong ground motions are (1) the mean period (Tm), (2) the average spectral period (Tavg), (3) the smoothed spectral predominant period (To), and (4) the predominant spectral period (Tp). Tm and Tavg distinguish the low frequency content of ground motions, while To is affected most by the high frequency content. Tp does not adequately describe the frequency content of a strong ground motion and is not recommended. Empirical relationships are developed that predict three parameters (Tm, Tavg, and To) as a function of earthquake magnitude, site-to-source distance, site conditions, and rupture directivity. The relationships are developed from a large strong-motion database that includes recorded motions from the recent earthquakes in Turkey and Taiwan. The new relationships update those previously developed by the authors and others. The results indicate that three site classes, which distinguish between rock, shallow soil, and deep soil, provide a better prediction of the frequency content parameters and smaller standard error terms than conventional “rock” and “soil” site classes. Forward directivity significantly increases the frequency content parameters, particularly Tm and To, at distances less than 20 km. Each of the frequency content parameters can be predicted with reasonable accuracy, but Tm is the preferred because it best distinguishes the frequency content of strong ground motions.

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