Directional topographic site response at Tarzana observed in aftershocks of the 1994 Northridge, California, earthquake: Implications for mainshock motions

1996 ◽  
Vol 86 (1B) ◽  
pp. S193-S208 ◽  
Author(s):  
Paul Spudich ◽  
Margaret Hellweg ◽  
W. H. K. Lee
Keyword(s):  
Site Response ◽  
Aftershock Sequence ◽  
Northridge Earthquake ◽  
Factors Affecting ◽  
Soil Response ◽  
Amplification Ratio ◽  
East End ◽  
A Site ◽  
The Hill ◽  
East West

Abstract The Northridge earthquake caused 1.78 g acceleration in the east-west direction at a site in Tarzana, California, located about 6 km south of the mainshock epicenter. The accelerograph was located atop a hill about 15-m high, 500-m long, and 130-m wide, striking about N78°E. During the aftershock sequence, a temporary array of 21 three-component geophones was deployed in six radial lines centered on the accelerograph, with an average sensor spacing of 35 m. Station C00 was located about 2 m from the accelerograph. We inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion. We identified a 3.2-Hz resonance that is a transverse oscillation of the hill (a directional topographic effect). The top/base amplification ratio at 3.2 Hz is about 4.5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill. This resonance is seen most strongly within 50 m of C00. Other resonant frequencies were also observed. A strong lateral variation in attenuation, probably associated with a fault, caused substantially lower motion at frequencies above 6 Hz at the east end of the hill. There may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill, causing particle motions (not spectral ratios) at the top of the hill to be rotated about 20° away from the direction transverse to the hill. The resonant frequency, but not the amplitude, of our observed topographic resonance agrees well with theory, even for such a low hill. Comparisons of our observations with theoretical results indicate that the 3D shape of the hill and its internal structure are important factors affecting its response. The strong transverse resonance of the hill does not account for the large east-west mainshock motions. Assuming linear soil response, mainshock east-west motions at the Tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill. Probable variations in surficial shear-wave velocity do not account for the observed differences among mainshock acceleration observed at Tarzana and at two different sites within 2 km of Tarzana.

An Iron Age A site on the Chilterns

1951 ◽  
Vol 31 (3-4) ◽  
pp. 132-148 ◽  
Author(s):  
K. M. Richardson ◽  
Alison Young
Keyword(s):  
Water Supply ◽  
Iron Age ◽  
The West ◽  
North West ◽  
The North ◽  
Roman Villa ◽  
Adjoining Area ◽  
Cursory Examination ◽  
A Site ◽  
The Hill

In 1946 a visit to the barrow, which lies on the edge of the western scarp of Chinnor Common, and a cursory examination of the adjoining area, cultivated during the war, resulted in finds of pottery and other objects indicating Iron Age occupation. The site lies on the saddleback of a Chiltern headland, at a height of about 800 ft. O.D. Two hollow ways traverse the western scarp, giving access to the area from the Upper Icknield Way, which contours the foot of the hill, then drops to cross the valley, passing some 600 yards to the north of the Iron Age site of Lodge Hill, Bledlow, and rising again continues northwards under Pulpit Hill camp and the Ellesborough Iron Age pits below Coombe Hill. The outlook across the Oxford plain to the west is extensive, embracing the hill-fort of Sinodun, clearly visible some fourteen miles distant on the farther bank of the Thames. The hollow way at the north-west end of the site leads down to a group of ‘rises’ hard by the remains of a Roman villa, and these springs are, at the present day, the nearest water-supply to the site.

The accuracy of soil response estimates using soil-to-rock spectral ratios

1996 ◽  
Vol 86 (2) ◽  
pp. 519-523
Author(s):  
Igor A. Beresnev ◽  
Kuo-Liang Wen
Keyword(s):  
Site Response ◽  
Soft Soil ◽  
Strong Motion ◽  
Finite Depth ◽  
Spectral Ratios ◽  
Site Specific ◽  
Soil Response ◽  
Strong Motion Records ◽  
The Real ◽  
Specific Amplification

Abstract Spectral ratios between soft soil and reference rock sites are often used to predict the sedimentary site response to earthquakes. However, their relationship with the genuine site-specific amplification function is often unclear. We compare the soil-to-rock spectral ratios between the stations that are 3.3 km apart with the “genuine” response given by the ratios between the surface and 17 and 47 m downhole. Data from the SMART1 array in Taiwan are used. The “weak” and “strong” motion records are addressed separately to allow for nonlinear soil response. The soil-to-rock spectral ratios are nearly identical to the “true” amplification at the frequencies from 1 to 10 Hz, if the finite depth of the borehole is taken into account. They correctly capture the strong-motion deamplification effect. However, the soil-to-rock spectral ratios are roughly 1.4 times more uncertain than surface-to-47-m ratios. In summary, the soil-to-rock spectral ratios can be considered as the reliable estimates of the real site response.

Taiwan-Specific Model for VS30 Prediction Considering Between-Proxy Correlations

2018 ◽  
Vol 34 (4) ◽  
pp. 1973-1993 ◽  
Author(s):  
On Lei Annie Kwok ◽  
Jonathan P. Stewart ◽  
Dong Youp Kwak ◽  
Pang-Li Sun
Keyword(s):  
Ground Motion ◽  
Prediction Models ◽  
Site Response ◽  
Specific Model ◽  
Weighted Mean ◽  
Response Models ◽  
Database File ◽  
A Site ◽  
Gradient Effects ◽  
Model Weighting

Ergodic site response models are generally conditional on the time-averaged shear wave velocity in the upper 30 m ( V S30). Ground motion databases contain many recordings from Taiwan, and because of site characterization efforts, 56% of recording sites have V S30 derived from measurements. We develop proxy-based V S30 prediction models, one application of which is for the remaining 44% of Taiwan sites. Our approach, which can be suitable for other regions, differs from previous studies in which proxies are based on detailed geologic categories and possible within-category topographic gradient effects. Instead, we use three broad, age-based geologic categories, and for the youngest category of Holocene and Quaternary undivided sediments, we propose models conditioned on gradient and elevation. We also adapt a geomorphic terrain-based method, thus providing two V S30-prediction models. We describe a model weighting scheme that combines the models in consideration of their relative dispersions and correlation, producing a weighted mean and standard deviation natural-log V S30. Included as an electronic supplement is a profile database file and a site database with site parameters for Taiwan ground motion stations.

scholarly journals Annual variations of soil erodibility of silt loam developed from loess based on 10-years runoff plot studies

2008 ◽  
Vol 39 (1) ◽  
pp. 77-83 ◽  
Author(s):  
Jerzy Rejman ◽  
Ryszard Brodowski ◽  
Iwona Iglik
Keyword(s):  
Climatic Conditions ◽  
Soil Erodibility ◽  
Silt Loam ◽  
Factors Affecting ◽  
Erosion Risk ◽  
Annual Variations ◽  
Erosion Prediction ◽  
K Factor ◽  
A Site ◽  
Runoff Plot

Annual variations of soil erodibility of silt loam developed from loess based on 10-years runoff plot studies Results of 10-years runoff plot experiments carried out on two sites of the Lublin Upland were presented. Despite similar soils and climatic conditions, studies showed large differences in annual soil erodibility (K factor of the USLE) between both sites. Experimentally derived values of the factor were dependent on tillage direction and time of maintaining runoff-plots in fallow conditions. On a site cultivated in contour direction, 4-year period was insufficient to achieve K values similar to the predicted values from the USLE. In contrast to this, on a site cultivated up-down slope, similar experimental and predicted K values were obtained after 2 years and remained at the same level during next 4 years. Results enabled to identify limitations of the USLE application for erosion prediction in Poland. Studies proved that soil erodibility could be used for prediction of erosion risk for silt loam developed from loess. However, application of soil erodibility approach to the event-base models is questionable for variation of K factor in the initial years. As far, the factors affecting soil erodibility changes are not recognized and need further research.

scholarly journals Exploiting structural and conformational effects for a site-selective lithiation of azetidines

2016 ◽  
Vol 88 (7) ◽  
pp. 631-648 ◽  
Author(s):  
Giovanna Parisi ◽  
Marina Zenzola ◽  
Emanuela Capitanelli ◽  
Claudia Carlucci ◽  
Giuseppe Romanazzi ◽  
...  
Keyword(s):  
Chemical Space ◽  
Molecular Structures ◽  
Structural Factors ◽  
Factors Affecting ◽  
Selective Functionalization ◽  
Conformational Effects ◽  
Conformational Preferences ◽  
A Site ◽  
Site Selective

AbstractInterest in molecular structures bearing four-membered heterocycles (FMHs) is growing due to the possibility to explore new regions of the chemical space and get new lead molecules. Our interest in the development of divergent synthesis of functionalized FMHs, prompted us to disclose factors affecting the reactivity of nitrogen-bearing FMHs towards metalating agents. Our investigations demonstrated that structural factors and conformational preferences need to be considered in planning a site-selective functionalization of azetidines. It will be showed how such factors could have pivotal importance in the reactivity of FMHs.

Preferred Direction of Damage to Concrete Block Fences in the M6.7 Northridge Earthquake of 17 January 1994

2002 ◽  
Vol 18 (2) ◽  
pp. 369-379 ◽  
Author(s):  
David L. Snyder ◽  
Glenn Borchardt
Keyword(s):  
Failure Rate ◽  
Concrete Block ◽  
Insurance Companies ◽  
Northridge Earthquake ◽  
Single Family ◽  
The South ◽  
Preferred Direction ◽  
The North ◽  
Structural Reinforcement ◽  
East West

The Northridge earthquake toppled three times more concrete block fences that were oriented east-west than those oriented north-south. Toppled fences were twice as likely to fall to the north as to the south. This was discovered during damage causation studies for insurance companies in our survey of more than 200 single-family residences within 29 km of the epicenter. Two hundred nineteen fences were built within 11 degrees of either north (55%) or east (45%), providing an opportunity to study the effect of orientation. Of those fences that were completely toppled, 19 were oriented east-west, while only 7 were oriented north-south. This preferred direction of damage for toppled fences was observed in all four quadrants about the epicenter and at distances of up to 17 km. In the NW quadrant, immediately above the aftershock zone, all toppled fences were oriented E-W, none were oriented N-S. The 58 fences oriented within 11 degrees of either NE or SE had no preferred direction of damage. In general, the failure rate for all 297 fences correlated with Modified Mercalli Intensity, location on alluvium as opposed to bedrock, and lack of structural reinforcement.

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.

A Procedure for Predicting Energy From a Tidal Turbine Farm

2007 ◽  
Author(s):  
Ye Li ◽  
Sander M. Calisal
Keyword(s):  
Power Generation ◽  
Tidal Current ◽  
Companion Paper ◽  
Dominant Factor ◽  
Systematic Analysis ◽  
Power Cost ◽  
Factors Affecting ◽  
Tidal Turbine ◽  
Tidal Current Turbine ◽  
A Site

A tidal current turbine is a device for harnessing energy from tidal current. A group of tidal current turbines, distributed schematically at a site, is called a tidal turbine farm. A tidal turbine farm has to be located in a confined channel or a straight where consistent high-velocity tidal current flow is available for the cost-effectiveness concern. This narrow geographical condition poses challenges for turbine farm planners to distribute turbines strategically. Turbines’ distribution in a farm affects power generation efficiency and the resultant tidal unit power cost. In this paper, we propose a procedure for predicting energy generation from a tidal turbine farm by investigating the optimal distribution of turbines at a given site. The objective of optimizing the turbines distribution is to maximize the power output efficiency. To fulfill this, we conducted a systematic analysis on power generation from a tidal turbine farm to identify the key factors affecting the optimal tidal turbines distribution with an emphasis on the turbines’ hydrodynamics analysis and briefed the turbine working principle. As a companion paper to Li and Calisal (2007) which discusses the principle of a stand alone turbine, turbine configuration and interactions (i.e. angle of attack, turbine relative distance and turbine size) are extended here. The main assumption of this discussion is that vortex shedding impact is the dominant factor causing the turbine efficiency loss. Considering the turbine design principle, a simplified relationship between turbines distribution and turbine farm efficiency is formulated. Then, numerical simulation results are presented for a given site in British Columbia together with extended general solution.

INTERPRETATIONS OF THE CARBON DIOXIDE DEPENDENCE OF THE HILL REACTION

1965 ◽  
Vol 43 (1) ◽  
pp. 119-127 ◽  
Author(s):  
Norman E. Good
Keyword(s):  
Carbon Dioxide ◽  
Quantum Theory ◽  
Hill Reaction ◽  
Oxygen Production ◽  
Quantum Mechanism ◽  
Photosynthetic Oxygen ◽  
The One ◽  
A Site ◽  
The Hill ◽  
Isolated Chloroplasts

Heretofore Warburg's one-quantum theory of photosynthesis has seemed inconsistent with the existence of the Hill reaction. The one-quantum theory states that massive oxygen uptake and CO2 release are preconditions of photosynthetic oxygen production, yet isolated chloroplasts produce oxygen at high rates apparently without consuming any oxygen or producing any CO2. Warburg has attempted to resolve the dilemma by pointing out a CO2 dependence of the Hill reaction. On the basis of this observation he proposed a reinterpretation of the Hill reaction which is consistent with the one-quantum theory. The effect of CO2 on isolated chloroplasts has been confirmed and some of the conditions which are necessary for the demonstration of the effect have been defined. It is not clear if CO2 is actually metabolized as Warburg claims. Contrary to Warburg's model, its participation seems to be at a site remote from the photochemical act. A number of other reasons for doubting the reality of the one-quantum mechanism are presented.

Empirical Evidence for Site Coefficients in Building Code Provisions

2002 ◽  
Vol 18 (2) ◽  
pp. 189-217 ◽  
Author(s):  
Roger D. Borcherdt
Keyword(s):  
Confidence Level ◽  
Empirical Data ◽  
Site Response ◽  
Building Code ◽  
Northridge Earthquake ◽  
Empirical Estimates ◽  
Site Coefficients ◽  
Percent Confidence Level ◽  
Lower Confidence Bound ◽  
Code Provisions

Site-response coefficients, Fa and Fv, used in U.S. building code provisions are based on empirical data for motions up to 0.1 g. For larger motions they are based on theoretical and laboratory results. The Northridge earthquake of 17 January 1994 provided a significant new set of empirical data up to 0.5 g. These data together with recent site characterizations based on shear-wave velocity measurements provide empirical estimates of the site coefficients at base accelerations up to 0.5 g for Site Classes C and D. These empirical estimates of Fa and Fv as well as their decrease with increasing base acceleration level are consistent at the 95 percent confidence level with those in present building code provisions, with the exception of estimates for Fa at levels of 0.1 and 0.2 g, which are less than the lower confidence bound by amounts up to 13 percent. The site-coefficient estimates are consistent at the 95 percent confidence level with those of several other investigators for base accelerations greater than 0.3 g. These consistencies and present code procedures indicate that changes in the site coefficients are not warranted. Empirical results for base accelerations greater than 0.2 g confirm the need for both a short- and a mid- or long-period site coefficient to characterize site response for purposes of estimating site-specific design spectra.

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