scholarly journals Shallow P- and S- wave velocities at eleven aftershock recording stations of the Northridge earthquake, San Fernando Valley, California

1996 ◽  
Author(s):  
R.A. Williams ◽  
W.J. Stephenson ◽  
J.K. Odum ◽  
D.M. Worley
Keyword(s):  
Northridge Earthquake ◽  
S Wave ◽  
Wave Velocities ◽  
San Fernando ◽  
San Fernando Valley

Interpretation of significant ground-response and structure strong motions recorded during the 1994 Northridge earthquake

1996 ◽  
Vol 86 (1B) ◽  
pp. S231-S246 ◽  
Author(s):  
A. F. Shakal ◽  
M. J. Huang ◽  
R. B. Darragh
Keyword(s):  
Flexible Structures ◽  
Northridge Earthquake ◽  
Moment Frame ◽  
Ground Response ◽  
Short Period ◽  
Frame Buildings ◽  
Story Drift ◽  
San Fernando ◽  
San Fernando Valley ◽  
The Moment

Abstract Some of the largest accelerations and velocities ever recorded at ground-response and structural sites occurred during the Northridge earthquake. These motions are greater than most existing attenuation models would have predicted. Although the motions are large, the correspondence between measured acceleration and damage requires further study, since some sites with high acceleration experienced only moderate damage. Also, some peak vertical accelerations were larger than the horizontal, but in general, they are smaller and fit the pattern observed in previous earthquakes. Strong-motion records processed to date show significant differences in acceleration and velocity waveforms and amplitudes across the San Fernando Valley. Analysis of processed data from several buildings in the San Fernando Valley indicates that short-period buildings such as shear-wall buildings experienced large forces and relatively low inter-story drift during the Northridge earthquake. However, long-period (1 to 5 sec) steel or concrete moment-frame buildings experienced large inter-story drift. For this earthquake, accelerations did not always amplify from base to roof for flexible structures like the moment-frame buildings, but the displacements were always larger at the roof. The drifts at many of the moment-frame buildings were larger than the drift limit for working stress design in the building code. The records from a base-isolated building indicate that high-frequency motion was reduced significantly by the isolators. The isolators deformed about 3.5 cm, which is much less than the design displacement. The records from a parking structure show important features of the seismic response of this class of structure.

Seismology

1995 ◽  
Vol 11 (2_suppl) ◽  
pp. 1-12
Keyword(s):  
Los Angeles ◽  
Seismic Hazard ◽  
Focal Depth ◽  
High Rate ◽  
Northridge Earthquake ◽  
Los Angeles Basin ◽  
San Fernando ◽  
Northern Edge ◽  
San Fernando Valley ◽  
The Moment

The Northridge earthquake occurred on January 17, 1994, at 4:31 a.m. Pacific Standard Time. The hypocenter was about 32 km west-northwest of Los Angeles in the San Fernando Valley at a relatively deep focal depth of 19 km. The moment magnitude for the earthquake is Mw6.7. The earthquake occurred on a south-southwest dipping thrust ramp beneath the San Fernando Valley and, thus, reemphasized the seismic hazard of concealed faults in the greater Los Angeles region. The Northridge earthquake also indicates a continuing high rate of seismicity along the northern edge of the Los Angeles basin.

Fire-Related Aspects

1995 ◽  
Vol 11 (2_suppl) ◽  
pp. 419-435 ◽  
Keyword(s):  
Los Angeles ◽  
Fire Department ◽  
Northridge Earthquake ◽  
Mutual Aid ◽  
Fire Departments ◽  
Santa Monica ◽  
San Fernando ◽  
Wide Scale ◽  
San Fernando Valley ◽  
Alternative Water

The Northridge earthquake caused high shaking intensities for several million persons in the northern Los Angeles region, centered in the San Fernando Valley. Fire protection for the heavily damaged area is furnished primarily by Los Angeles City Fire Department and, to a lesser extent, Los Angeles County, Santa Monica, and other departments. The earthquake resulted in about 110 fires, about 80% of which were structure fires. Of these, most were in single-or multi-family dwellings. All of the initial fires were out before noon despite impaired communications, wide-scale failure of firefighting water supply in large parts of the San Fernando Valley, and other problems. Alternative water supplies, such as backyard swimming pools, were employed in some cases. Mutual aid was requested by fire departments in the affected area, but resources from outside the Los Angeles metropolitan area were not required.

An autoethnographic account of urban restructuring and neighborhood change in Los Angeles’ San Fernando Valley

2019 ◽  
Vol 27 (3) ◽  
pp. 379-394 ◽  
Author(s):  
Stefano Bloch
Keyword(s):  
Los Angeles ◽  
Cultural Landscape ◽  
Neighborhood Change ◽  
General Motors ◽  
Northridge Earthquake ◽  
Urban Restructuring ◽  
Time Period ◽  
San Fernando ◽  
San Fernando Valley ◽  
Children Welfare

Suburbs have long been glossed over by critical urbanists for being culturally, even if not spatially, less than urban. In Los Angeles, it is the San Fernando Valley that has received such treatment as scholars have tended toward the metropolitan basin. In this article, I aim to help re-center the San Fernando Valley as a complex and conflictual cultural landscape through an autoethnographic exploration of four moments of urban restructuring in the Panorama City neighborhood. I provide a personal account of how a succession of events – the 1992 LA Riot, 1993 General Motors Plant closure, 1994 Northridge earthquake, and 1996 dismantling of the Aid for Families with Dependent Children welfare program – led to the disruption and partial destruction of a neighborhood. I situate these moments of crisis within the context of a civil gang injunction and outbreak of abject violence during this time period, which further destabilized the neighborhood and informed my own decision to pick up a gun.

The relation between seismic P‐ and S‐wave velocity dispersion in saturated rocks

Geophysics ◽  
1994 ◽  
Vol 59 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Gary Mavko ◽  
Diane Jizba
Keyword(s):  
Wave Velocity ◽  
Large Scale ◽  
Velocity Dispersion ◽  
Seismic Velocity ◽  
Ultrasonic Velocities ◽  
S Wave ◽  
Local Flow ◽  
Wave Velocities ◽  
Shear Compliance

Seismic velocity dispersionin fluid-saturated rocks appears to be dominated by tow mecahnisms: the large scale mechanism modeled by Biot, and the local flow or squirt mecahnism. The tow mechanisms can be distuinguished by the ratio of P-to S-wave dispersions, or more conbeniently, by the ratio of dynamic bulk to shear compliance dispersions derived from the wave velocities. Our formulation suggests that when local flow denominates, the dispersion of the shear compliance will be approximately 4/15 the dispersion of the compressibility. When the Biot mechanism dominates, the constant of proportionality is much smaller. Our examination of ultrasonic velocities from 40 sandstones and granites shows that most, but not all, of the samples were dominated by local flow dispersion, particularly at effective pressures below 40 MPa.

Nonlinear behavior of soil sediments identified by using borehole records observed at the Ashigra Valley, Japan

1995 ◽  
Vol 85 (6) ◽  
pp. 1821-1834
Author(s):  
Toshimi Satoh ◽  
Toshiaki Sato ◽  
Hiroshi Kawase
Keyword(s):  
Shear Strain ◽  
Main Part ◽  
Nonlinear Behavior ◽  
Strong Motion ◽  
S Wave ◽  
Ground Shaking ◽  
Wave Velocities ◽  
The One ◽  
Soil Sediments ◽  
Strong Ground

Abstract We evaluate the nonlinear behavior of soil sediments during strong ground shaking based on the identification of their S-wave velocities and damping factors for both the weak and strong motions observed on the surface and in a borehole at Kuno in the Ashigara Valley, Japan. First we calculate spectral ratios between the surface station KS2 and the borehole station KD2 at 97.6 m below the surface for the main part of weak and strong motions. The predominant period for the strong motion is apparently longer than those for the weak motions. This fact suggests the nonlinearity of soil during the strong ground shaking. To quantify the nonlinear behavior of soil sediments, we identify their S-wave velocities and damping factors by minimizing the residual between the observed spectral ratio and the theoretical amplification factor calculated from the one-dimensional wave propagation theory. The S-wave velocity and the damping factor h (≈(2Q)−1) of the surface alluvial layer identified from the main part of the strong motion are about 10% smaller and 50% greater, respectively, than those identified from weak motions. The relationships between the effective shear strain (=65% of the maximum shear strain) calculated from the one-dimensional wave propagation theory and the shear modulus reduction ratios or the damping factors estimated by the identification method agree well with the laboratory test results. We also confirm that the soil model identified from a weak motion overestimates the observed strong motion at KS2, while that identified from the strong motion reproduces the observed. Thus, we conclude that the main part of the strong motion, whose maximum acceleration at KS2 is 220 cm/sec2 and whose duration is 3 sec, has the potential of making the surface soil nonlinear at an effective shear strain on the order of 0.1%. The S-wave velocity in the surface alluvial layer identified from the part just after the main part of the strong motion is close to that identified from weak motions. This result suggests that the shear modulus recovers quickly as the shear strain level decreases.

Jacobian matrix for the inversion of P- and S-wave velocities and its accurate computation method

2010 ◽  
Vol 54 (5) ◽  
pp. 647-654 ◽  
Author(s):  
FuPing Liu ◽  
XianJun Meng ◽  
YuMei Wang ◽  
GuoQiang Shen ◽  
ChangChun Yang
Keyword(s):  
Jacobian Matrix ◽  
Computation Method ◽  
S Wave ◽  
Wave Velocities ◽  
Accurate Computation
Sign in / Sign up

Export Citation Format

Share Document