A composite source model of the 1994 Northridge earthquake using genetic algorithms

1996 ◽  
Vol 86 (1B) ◽  
pp. S71-S83 ◽  
Author(s):  
Yuehua Zeng ◽  
John G. Anderson
Keyword(s):  
Genetic Algorithms ◽  
Los Angeles ◽  
Strong Motion ◽  
Computation Time ◽  
Source Model ◽  
Northridge Earthquake ◽  
Good Convergence ◽  
Strong Ground Motion Prediction ◽  
Composite Source Model ◽  
1994 Northridge Earthquake

Abstract The 17 January 1994 Northridge earthquake (Mw 6.7) occurred on a buried thrust fault in the northwest Los Angeles metropolitan area. We investigate the source process of this earthquake using the CSMIP strong motion records and a composite source model developed by Zeng et al. (1994a) for realistic earthquake strong ground motion prediction. Our previous studies demonstrated the realism of the synthetic strong motions generated from the composite source model by comparing them with observed records from earthquakes in many areas of the world. This article addresses an inverse study of the problem to find a specific composite source model for the Northridge earthquake. This is done by adjusting the location of a suite of composite subevents, using genetic algorithms (Holland, 1975), to best match the observed waveforms. A test run of the genetic algorithm on synthetic data sets finds a very good convergence of the approach. We reduce largely the intensive computation time by identifying subevents with major contribution to the waveform fit. Our result for the 1994 Northridge earthquake indicates a complex earthquake rupture process with three large slip zones: one at the hypocenter and the other two to the west of the hypocenter. We then use this model to compute the high-frequency strong-motion velocity and acceleration. The results show that the composite source model provides a very realistic broadband source description for the Northridge earthquake.

Engineering observations on ground motion at the Van Norman Complex after the 1994 Northridge earthquake

1996 ◽  
Vol 86 (1B) ◽  
pp. S333-S349 ◽  
Author(s):  
J. P. Bardet ◽  
C. Davis
Keyword(s):  
Ground Motion ◽  
Earthquake Engineering ◽  
Low Frequency ◽  
Strong Motion ◽  
Response Spectra ◽  
Vertical Acceleration ◽  
Northridge Earthquake ◽  
Peak Acceleration ◽  
Geotechnical Earthquake Engineering ◽  
1994 Northridge Earthquake

Abstract During the 1994 Northridge earthquake, the Van Norman Complex yielded an unprecedented number of recordings with high acceleration, in the close proximity of the fault rupture. These strong-motion recordings exhibited the pulses of the main event. One station recorded the largest velocity ever instrumentally recorded (177 cm/sec), resulting from a 0.86 g peak acceleration with a low frequency. Throughout the complex, the horizontal accelerations reached peak values ranging from 0.56 to 1.0 g, except for the complex center, where the peak acceleration did not exceed 0.43 g. The vertical acceleration reached maximum peak values comparable with those of the horizontal acceleration. The acceleration response spectra in the longitudinal and transverse directions were significantly different. Such a difference, which is not yet well documented in the field of geotechnical earthquake engineering, indicates that the amplitude and frequency content of the ground motion was directionally dependent in the Van Norman Complex.

Using safety inspection data to estimate shaking intensity for the 1994 Northridge earthquake

1998 ◽  
Vol 88 (5) ◽  
pp. 1243-1253
Author(s):  
Katharina Thywissen ◽  
John Boatwright
Keyword(s):  
Los Angeles ◽  
Census Tract ◽  
Residential Buildings ◽  
Intensity Level ◽  
Northridge Earthquake ◽  
Single Family ◽  
Census Tracts ◽  
Wood Frame ◽  
Inspection Data ◽  
1994 Northridge Earthquake

Abstract We map the shaking intensity suffered in Los Angeles County during the 17 January 1994, Northridge earthquake using municipal safety inspection data. The intensity is estimated from the number of buildings given red, yellow, or green tags, aggregated by census tract. Census tracts contain from 200 to 4000 residential buildings and have an average area of 6 km2 but are as small as 2 and 1 km2 in the most densely populated areas of the San Fernando Valley and downtown Los Angeles, respectively. In comparison, the zip code areas on which standard MMI intensity estimates are based are six times larger, on average, than the census tracts. We group the buildings by age (before and after 1940 and 1976), by number of housing units (one, two to four, and five or more), and by construction type, and we normalize the tags by the total number of similar buildings in each census tract. We analyze the seven most abundant building categories. The fragilities (the fraction of buildings in each category tagged within each intensity level) for these seven building categories are adjusted so that the intensity estimates agree. We calibrate the shaking intensity to correspond with the modified Mercalli intensities (MMI) estimated and compiled by Dewey et al. (1995); the shapes of the resulting isoseismals are similar, although we underestimate the extent of the MMI = 6 and 7 areas. The fragility varies significantly between different building categories (by factors of 10 to 20) and building ages (by factors of 2 to 6). The post-1940 wood-frame multi-family (≧5 units) dwellings make up the most fragile building category, and the post-1940 woodframe single-family dwellings make up the most resistant building category.

A Multidimension Source Model for Generating Broadband Ground Motions with Deterministic 3D Numerical Simulations

2021 ◽  
Author(s):  
Xiang-Chao Wang ◽  
Jin-Ting Wang ◽  
Lei Zhang ◽  
Shuai Li ◽  
Chu-Han Zhang
Keyword(s):  
Numerical Simulations ◽  
Ground Motions ◽  
Source Parameters ◽  
Spectral Characteristics ◽  
Source Model ◽  
Rupture Process ◽  
Northridge Earthquake ◽  
Scenario Earthquake ◽  
Source Models ◽  
1994 Northridge Earthquake

ABSTRACT A multidimension source model for generating broadband ground motions with deterministic 3D numerical simulations is proposed in this article. In this model, the source is composed of several superimposed layers, and the total seismic moment is assigned to these layers in different proportions. Each layer exactly fills up the seismic fault and is uniformly divided into subsources with size decreased progressively to reflect different levels of rupture details. Hence, the proposed multidimension source model may consider the realistic rupture process of an earthquake, that is, the spatial and temporal heterogeneity of source parameters, and generate broadband ground motions. To verify this source model, the 1994 Northridge earthquake is simulated with four multidimension source models, based on different source inversion results. The amplitudes, durations, and spectral characteristics of the observed ground motions of the 1994 Northridge earthquake are respectably reproduced in a range of frequencies up to 5 Hz. In addition, a scenario earthquake is also simulated with four multidimension source models, with different synthetic rupture process. The simulated ground motions of the scenario earthquake are generally in good agreement with the Next Generation Attenuation-West 2 ground-motion prediction equations. This demonstrates that it is promising to simulate realistic broadband ground motions of strong earthquakes with a proper source description and realistic Earth models.

scholarly journals The city of Los Angeles experience during the 1994 Northridge earthquake

1997 ◽  
Vol 30 (1) ◽  
pp. 2-13
Author(s):  
N. Delli Quadri
Keyword(s):  
Los Angeles ◽  
Disaster Response ◽  
The Other ◽  
Northridge Earthquake ◽  
Emergency Situations ◽  
The World ◽  
Surrounding Areas ◽  
The City ◽  
1994 Northridge Earthquake

A successful disaster response depends greatly on how well and how quickly resources can be mobilized and allocated. To do this effectively, there must be a system in place that can collect, prepare and send the resources; and a system at the other end that can effectively receive and deploy them. The information gained from the Northridge Earthquake and the lesson learned by the City of Los Angeles and its surrounding areas can be of great value to jurisdictions around the world in planning and preparing for future disaster and emergency situations.

The Rinaldi Strong Motion Accelerogram of the Northridge, California Earthquake of 17 January 1994

1998 ◽  
Vol 14 (1) ◽  
pp. 225-239 ◽  
Author(s):  
Mihailo D. Trifunac ◽  
Maria I. Todorovska ◽  
Vincent W. Lee
Keyword(s):  
Los Angeles ◽  
Earthquake Engineering ◽  
High Frequency ◽  
Response Spectrum ◽  
Strong Motion ◽  
Western United States ◽  
Peak Ground Velocity ◽  
Northridge Earthquake ◽  
The Difference ◽  
Different Time Scales

The Rinaldi record of the 1994 Northridge earthquake is one of the most important strong motion records in earthquake engineering (largest recorded horizontal peak ground velocity in the western United States, ∼170 cm/s). Digitization of this record was not straightforward because of numerous stalls and malfunction of the half-second pulse relays. It was digitized and processed for the Los Angeles Department of Water and Power soon after the earthquake, and was recently redigitized and reprocessed. This paper presents the results of the recent digitization and processing and a comparison of the two digital versions of the record. The “new” version differs from the “old” version in the number of stalls corrected for (17 versus one stall), total length of digitized traces (∼20 s versus ∼15 s), and amplitudes of some high frequency acceleration peaks (in the “old” version, some high frequency peaks have been underestimated). The peak amplitudes of corrected acceleration, velocity and displacement, and the linear response spectrum amplitudes are not significantly different. However, the two digital interpretations have different time scales, because of the difference in the number of stalls accounted for.

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