Preliminary analysis of long-period basin response in the Los Angeles Region from the 1994 Northridge Earthquake

1995 ◽  
Vol 22 (2) ◽  
pp. 101-104 ◽  
Author(s):  
Robert W. Graves
Keyword(s):  
Los Angeles ◽  
Preliminary Analysis ◽  
Northridge Earthquake ◽  
Long Period ◽  
Basin Response ◽  
1994 Northridge Earthquake

scholarly journals Continuous monitoring of seismic energy release associated with the 1994 Northridge earthquake and the 1992 Landers earthquake

1996 ◽  
Vol 86 (1A) ◽  
pp. 255-258 ◽  
Author(s):  
Sharon Kedar ◽  
Hiroo Kanamori
Keyword(s):  
Frequency Band ◽  
Southern California ◽  
Seismic Energy ◽  
Northridge Earthquake ◽  
Time Frequency ◽  
Landers Earthquake ◽  
Long Period ◽  
1992 Landers Earthquake ◽  
Large Earthquakes ◽  
1994 Northridge Earthquake

Abstract We have developed a method to detect long-period precursors for large earthquakes observed in southern California, if they occur. The method allows us to continuously monitor seismic energy radiation over a wide frequency band to investigate slow deformation in the crust (e.g., slow earthquakes), especially before large earthquakes. We used the long-period records (1 sample/sec) from TERRAscope, a broadband seismic network in southern California. The method consists of dividing the record into a series of overlapping 30-min-long windows, computing the spectra over a frequency band of 0.00055 to 0.1 Hz, and plotting them in the form of a time-frequency diagram called spectrogram. This procedure is repeated daily over a day-long record. We have analyzed the 17 January 1994 Northridge earthquake (Mw = 6.7), and the 28 June 1992 Landers earthquake (Mw = 7.3). No slow precursor with spectral amplitude measured over a duration of 30 min larger than that of a magnitude 3.7 was detected prior to either event. In other words, there was no precursor whose moment was larger than ∼0.003% of the mainshock.

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.

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.

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.

Nonlinear ground-motion amplification by sediments during the 1994 Northridge earthquake

Nature ◽  
10.1038/37586 ◽  
1997 ◽  
Vol 390 (6660) ◽  
pp. 599-602 ◽  
Author(s):  
Edward H. Field ◽  
Paul A. Johnson ◽  
Igor A. Beresnev ◽  
Yuehua Zeng
Keyword(s):  
Ground Motion ◽  
Northridge Earthquake ◽  
Ground Motion Amplification ◽  
1994 Northridge Earthquake
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