Design ground motions near active faults

2009 ◽  
Vol 42 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Jonathan D. Bray ◽  
Adrian Rodriguez-Marek ◽  
Joanne L. Gillie
Keyword(s):  
Urban Areas ◽  
Site Effects ◽  
Site Response ◽  
Ground Motions ◽  
Soft Soil ◽  
Active Faults ◽  
Peak Ground Velocity ◽  
Near Fault ◽  
Effective Performance ◽  
Lower Magnitude

Forward-Directivity (FD) in the near-fault region can produce intense, pulse-type motions that differ significantly from ordinary ground motions that occur further from the ruptured fault. Near-fault FD motions typically govern the design of structures built close to active faults so the selection of design ground motions is critical for achieving effective performance without costly over-design. Updated empirical relationships are provided for estimating the peak ground velocity (PGV) and period of the velocity pulse (Tv) of near-fault FD motions. PGV varies significantly with magnitude, distance, and site effects. Tv is a function of magnitude and site conditions with most of the energy being concentrated within a narrow-period band centred on the pulse period. Lower magnitude events, which produce lower pulse periods, might produce more damaging ground motions for the stiff structures more common in urban areas. As the number of near-fault recordings is still limited, fully nonlinear bi-directional shaking simulations are employed to gain additional insight. It is shown that site effects generally cause Tv to increase. Although the amplification of PGV at soil sites depends on site properties, amplification is generally observed even for very intense rock motions. At soft soil sites, seismic site response can be limited by the yield strength of the soil, but then seismic instability may be a concern.

Deterministic 3D Ground-Motion Simulations (0–5 Hz) and Surface Topography Effects of the 30 October 2016 Mw 6.5 Norcia, Italy, Earthquake

2021 ◽  
Author(s):  
Arben Pitarka ◽  
Aybige Akinci ◽  
Pasquale De Gori ◽  
Mauro Buttinelli
Keyword(s):  
Surface Topography ◽  
Ground Motion ◽  
Seismic Station ◽  
Ground Motions ◽  
Peak Ground Velocity ◽  
Earth Model ◽  
Rupture Directivity ◽  
Epicentral Area ◽  
Near Fault ◽  
Local Topography

ABSTRACT The Mw 6.5 Norcia, Italy, earthquake occurred on 30 October 2016 and caused extensive damage to buildings in the epicentral area. The earthquake was recorded by a network of strong-motion stations, including 14 stations located within a 5 km distance from the two causative faults. We used a numerical approach for generating seismic waves from two hybrid deterministic and stochastic kinematic fault rupture models propagating through a 3D Earth model derived from seismic tomography and local geology. The broadband simulations were performed in the 0–5 Hz frequency range using a physics-based deterministic approach modeling the earthquake rupture and elastic wave propagation. We used SW4, a finite-difference code that uses a conforming curvilinear mesh, designed to model surface topography with high numerical accuracy. The simulations reproduce the amplitude and duration of observed near-fault ground motions. Our results also suggest that due to the local fault-slip pattern and upward rupture directivity, the spatial pattern of the horizontal near-fault ground motion generated during the earthquake was complex and characterized by several local minima and maxima. Some of these local ground-motion maxima in the near-fault region were not observed because of the sparse station coverage. The simulated peak ground velocity (PGV) is higher than both the recorded PGV and predicted PGV based on empirical models for several areas located above the fault planes. Ground motions calculated with and without surface topography indicate that, on average, the local topography amplifies the ground-motion velocity by 30%. There is correlation between the PGV and local topography, with the PGV being higher at hilltops. In contrast, spatial variations of simulated PGA do not correlate with the surface topography. Simulated ground motions are important for seismic hazard and engineering assessments for areas that lack seismic station coverage and historical recordings from large damaging earthquakes.

Earthquake Proof Efficiency of Sliding Base Isolator With Dog-Bone Type Damping

2005 ◽  
Author(s):  
C. S. Tsai ◽  
Tsu-Cheng Chiang ◽  
Bo-Jen Chen
Keyword(s):  
Ground Motions ◽  
Active Faults ◽  
Friction Behavior ◽  
Near Fault ◽  
The Past ◽  
Numerical Studies ◽  
Dog Bone ◽  
Base Isolator ◽  
Near Fault Earthquakes ◽  
Base Isolators

In recent years, there have been more and more seismic retrofit applications of using base isolators in seismic prone regions. In the past, the focuses of researches on the efficiency of various base isolators have been aimed at their behavior under earthquakes without long predominant periods. The doubts of efficiency of the base isolator nearby active faults or located at a soft deposit soil have been raised by researchers. It is revealed from previous studies that the seismic responses of the base isolated structure are significant due to the influence of resonance. In order to minimize the inherent shortcomings of base isolators, various base isolators with dog bone type of friction behavior have been proposed in this study. In the meanwhile, the exact solutions used to describe the behavior of the proposed isolators have also been derived in this study. The numerical studies show that the displacement responses of proposed isolators under near fault earthquakes and ground motions with long predominant periods are much lower than those of the traditional FPS and VCFPS devices. Hence, the required dimensions of proposed isolators can be smaller than those for the FPS and VCFPS isolators.

Nonlinear site effects on strong ground motion at a reclaimed island

2000 ◽  
Vol 37 (1) ◽  
pp. 26-39 ◽  
Author(s):  
Jun Yang ◽  
Tadanobu Sato ◽  
Xiang-Song Li
Keyword(s):  
Ground Motion ◽  
Site Effects ◽  
Site Response ◽  
Ground Motions ◽  
Soil Liquefaction ◽  
Large Strains ◽  
Stress Strain ◽  
Element Analysis ◽  
Soil Response ◽  
Kobe Earthquake

Recently there has been an increased interest in the study of the nonlinearity in soil response for large strains through in situ earthquake observations. In this paper, the downhole array acceleration data recorded at a reclaimed island, Kobe, during the 1995 Kobe earthquake are used to study nonlinear site effects. Particular attention is given to the liquefaction-induced nonlinear effects on the recorded ground motions. By using the spectral ratio and the spectral-smoothing technique, the characteristics of the ground motions are analyzed. It is shown that the peak frequencies in spectral ratios were shifted to lower frequencies when the strongest motions occurred. The increase in the predominant period was caused primarily by a strong attenuation of low-period waves, rather than by amplification of long-period motions. Based on the spectral analyses, the nonlinearity occurring in the shallow liquefied layer during the shaking event is identified, manifested by a significant reduction of the shear modulus. A fully coupled, inelastic, finite element analysis of the response of the array site is carried out. The stress-strain histories of soils and excess pore-water pressures at different depths are calculated. It is suggested that the stress-strain response and the build up of pore pressure are well correlated to the variation of the characteristics of ground motions during the shaking history.Key words: site response, ground motion, nonlinearity, soil liquefaction, array records, Kobe earthquake.

Pitfalls of Deterministic Application of Nonlinear Site Factors in Probabilistic Assessment of Ground Motions

2009 ◽  
Vol 25 (3) ◽  
pp. 541-555 ◽  
Author(s):  
Christine A. Goulet ◽  
Jonathan P. Stewart
Keyword(s):  
Site Effects ◽  
Site Response ◽  
Ground Motions ◽  
Site Conditions ◽  
Return Periods ◽  
Site Factors ◽  
Intensity Measures ◽  
Site Specific ◽  
Nonlinear Site Response ◽  
Rock And Soil

It is common for ground motions to be estimated using a combination of probabilistic and deterministic procedures. Probabilistic seismic hazard analyses (PSHA) are performed to estimate intensity measures ( IMs) for reference site conditions (usually rock). This is followed by a deterministic modification of the rock IMs to account for site effects, typically using site factors from the literature or seismic codes. We demonstrate for two California sites and three site conditions that the deterministic application of nonlinear site factors underestimates ground motions evaluated probabilistically for return periods of engineering interest. Reasons for this misfit include different standard deviation terms for rock and soil sites, different controlling earthquakes, and overestimation of the nonlinear component of the site response in the deterministic procedure. This problem is solved using site-specific PSHA with appropriate consideration of nonlinear site response, within the hazard integral.

Site Effects for the Sacramento-San Joaquin Delta

2009 ◽  
Vol 25 (2) ◽  
pp. 301-322 ◽  
Author(s):  
Tadahiro Kishida ◽  
Ross W. Boulanger ◽  
Norman A. Abrahamson ◽  
Michael W. Driller ◽  
Timothy M. Wehling
Keyword(s):  
Seismic Wave ◽  
Regression Models ◽  
Site Effects ◽  
Site Response ◽  
Hazard Analysis ◽  
Ground Motions ◽  
Response Spectra ◽  
Organic Soils ◽  
Wave Amplification ◽  
Seismic Wave Amplification

Seismic site response and site effects models are presented for levees in the Sacramento-San Joaquin Delta where the subsurface soils include thick deposits of highly organic soils. Sources of uncertainty that contribute to the variation of seismic wave amplification are investigated, including variations in the input ground motions, soil profiles, and dynamic soil properties through Monte Carlo simulations of equivalent-linear site response analyses. Regression models for seismic wave amplification for levees in the Delta are presented that range from a function of peak outcrop acceleration alone to a vector of response spectra ordinates and soil profile parameters. The site effects models were incorporated into a probabilistic seismic hazard analysis for a representative location, and the relative impacts of the various models on the computed hazard are evaluated.

Identification of Pulse Periods in Near‐Fault Ground Motions Using the HHT Method

2019 ◽  
Vol 109 (6) ◽  
pp. 2384-2398 ◽  
Author(s):  
Xiaoyu Chen ◽  
Dongsheng Wang ◽  
Rui Zhang
Keyword(s):  
Ground Motion ◽  
Time Course ◽  
Ground Motions ◽  
Flexible Structures ◽  
Peak Ground Velocity ◽  
Damage Effect ◽  
Near Fault ◽  
Long Period ◽  
Frequency Components ◽  
Ground Motion Records

Abstract Large‐amplitude and long‐period pulses are observed in velocity time histories of near‐fault ground‐motion records. The pulses in these records have significant damage effect on flexible structures due to their long‐period property; therefore, more attention should be paid to the frequency components in the ground motion. Based on the identification of frequency components in the original record, a new method based on the Hilbert–Huang transform (HHT) is proposed here. A ground‐motion record can be decomposed into several intrinsic mode functions (IMFs) that carry different frequency components by the HHT without contamination from any a prior function. Only two fixed parameters, the peak ground velocity (PGV)/peak ground acceleration (PGA) ratio and the energy change of every IMF, are used to classify pulse‐like ground‐motion records. The inherent pulses of these records can also be extracted, based on the selection of IMFs for which PGV/PGA ratios are larger than 0.12 and energy changes that are greater than 0.1. For multipulse cases, all the pulses can be captured after extracting once, and the time course of inherent pulses can also be obtained. Then, pulse periods are calculated based on the solutions of instantaneous frequency of the peak for the extracted pulses. All the periods obtained using the HHT method can be verified by the results obtained from Baker’s wavelet method. The 24 controversial records that are discussed in previous studies are examined here as well. The HHT method is a complete procedure that includes the classification of pulse‐like ground motions, the extraction of velocity pulses, and the solution of pulse periods. It works well for multipulse records, especially because it can provide the exact timing of all the inherent pulses.

scholarly journals Influence of source and site effects of 2003 Tokachi-oki earthquake on the generation of high PGA in the near-fault zones

2021 ◽  
Author(s):  
Olga V. PAVLENKO
Keyword(s):  
Site Effects ◽  
Seismic Waves ◽  
Soft Soil ◽  
Strong Motion ◽  
Tohoku Earthquake ◽  
Fault Zones ◽  
Soil Behavior ◽  
Near Fault ◽  
Acceleration Time Histories ◽  
Remote Sites

Abstract Source and site effects of 2003 Tokachi-oki earthquake (Japan, Mw~8.3) and their influence on the distribution of peak ground accelerations (PGA) in the near-fault zones are studied. Based on records of KiK-net vertical arrays, models of soil behavior are constructed, i.e. vertical distributions of stresses and strains induced in soil layers by strong motion. The method is used suggested by Pavlenko and Irikura and previously applied for studying soil behavior during 1995 Kobe, 2000 Tottori, and 2011 Tohoku earthquakes. During the Tokachi-oki earthquake, we did not find a widespread nonlinearity of soft soil behavior. Manifestations of soil nonlinearity were observed at sites closest to the source; at remote sites where high PGA were recorded, soil behavior was virtually linear, and shear moduli in soils increased till the moments of the highest intensity of motion, then decreased. The shapes of acceleration time histories at remote sites indicate directivity effects: seismic waves radiated by the crack tip during its propagation along a section of the fault plane came to the stations simultaneously. Soil hardening occurred at these sites that increased amplification and PGA on the surface. Similar effects were observed during 2011 Tohoku earthquake; evidently, they can occur during future strong earthquakes.

Basin and Site Effects in the U.S. Pacific Northwest Estimated from Small-Magnitude Earthquakes

2021 ◽  
Author(s):  
John M. Rekoske ◽  
Morgan P. Moschetti ◽  
Eric M. Thompson
Keyword(s):  
Shear Wave ◽  
Pacific Northwest ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Site Effects ◽  
Site Response ◽  
Ground Motions ◽  
Sedimentary Basins ◽  
Small Magnitude ◽  
The U.S

ABSTRACT Earthquake hazards in the U.S. Pacific Northwest (PNW) are increased by the presence of deep sedimentary basins that amplify and prolong ground shaking. To better understand basin and site effects on ground motions, we compile a database of recordings from crustal and intraslab earthquakes. We process 8028 records with magnitudes from 3.5 to 6.8 and hypocentral depths up to 62 km to compute Fourier amplitude spectra of ground acceleration for frequencies of 0–20 Hz. We compute residuals relative to the Bayless and Abrahamson (2019; hereafter, BA18) ground-motion model and perform a series of linear, crossed, mixed-effects regressions. In addition to estimating the bias, event, and site terms, we incorporate groupings for broad regionalized site response in three different regions (Seattle basin, Puget Lowland, non-Puget Lowland), for effects from seismotectonic regime (crustal and intraslab sources), and for interactions between the regions and seismotectonic regimes. We find that the scaling of site response with respect to VS30 (time-averaged shear-wave velocity from the surface to a depth of 30 m) and to basin depth indicators Z1.0 and Z2.5 (depths to the 1.0 and 2.5 km/s shear-wave velocity horizons) is generally consistent with BA18; however, the region terms display strong spatial amplification patterns. For frequencies less than 5 Hz, the Seattle basin amplifies ground motions up to a factor of four, relative to the non-Puget Lowland, with a maximum amplification around near 0.5 Hz. Sites in the Puget Lowland amplify low frequencies up to a factor of 2.5. At higher frequencies (f>5  Hz), the Puget Lowland and Seattle basin show regional deamplification of ground motions, with the smallest average amplification factor of 0.65 occurring at 10.0 Hz. Although we observe slight differences in the seismotectonic regime terms, we find that the region terms are significantly more important for modeling earthquake hazard in the PNW.

National Mitigation Strategy against Earthquakes in Central Asia

2020 ◽  
Author(s):  
Sung-Woo Moon ◽  
Farkhod Hakimov ◽  
Jong Kim ◽  
Klaus Reicherter ◽  
Hans-Balder Havenith ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Central Asia ◽  
Ground Motion ◽  
Urban Areas ◽  
Site Effects ◽  
Site Response ◽  
Engineering Properties ◽  
Response Analysis ◽  
Earthquake Scenarios ◽  
Geological Conditions

<p>Throughout history, earthquakes have caused extensive damages in urban areas with important infrastructures and high population density. Especially, earthquakes have extensively damaged many regions of Central Asia (e.g., Tashkent in 1966, and Almaty in 1911). Hence, the estimation of the seismic hazard of the urban areas in Central Asia is very important due to the high level of seismicity in Central Asia and the rapid construction of new buildings. The high earthquake-induced damages in the cities often result from the local geological conditions and engineering properties of the soils that can produce significant site effects. Such seismic effects combined with the high vulnerability of buildings can result in extreme disasters during earthquakes. Therefore, geotechnical engineers/seismologists should decide to divide the city into specific microzones depending on their site effects and soil properties. However, conventional approaches in Central Asia have been proposed, based on (1) general engineering geological information; (2) the building code based on the estimates of the ground motions in terms of MSK-64 scale developed in 1978; and (3) the quantitative assessment only mapping and overlaying the data.</p><p>By characterizing the soft layers of their nature, thickness, and structure, and assessing the numerical model developed for the high-seismicity area of Central Asia, we can better assess specific site effects in each region of Central Asia. In addition, to predict the essential consequences of earthquakes, physically-based ground motion simulations should be developed by numerical simulations considering all possible processes of seismic wave propagation. Compared to empirical ground-motion predictions, numerical simulations of earthquake scenarios will provide much more flexible and better-suited solutions for most applications – especially those involving complex city environments. The ground-motion prediction equations or stochastic ground-motion estimates integrate characteristics of the earthquake source, path, attenuation, and site effects via approximate or statistical approaches. This method will provide rapid solutions that may be valid for a well-known context and would also be applied in Central Asia, for comparison with the numerical simulations. Finally, the quantitative approach for microzoning map incorporated with numerical simulation/site response analysis, for infrastructures (e.g., buildings, bridges, and dams) will be significantly useful in the future.</p>

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