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LABSHA PROJECT

What would happen to engineered buildings and other structures in the Los Angeles and San Fernando basins if the Nov. 3, 2001 Magnitude 7.9 Denali earthquake were to occur on the San Andreas fault? How severe would the directivity effects be for a N-S rupture? There are many old high-rise buildings in Southern California. The Northridge earthquake exposed the vulnerability of these buildings especially moment frame buildings to connection fracture. Fortunately, the directivity of the Northridge rupture focused the energy away from heavily populated areas. However, the potential for severe earthquakes exists on many major faults in Southern California and the hazard posed by these earthquakes to buildings has not been quantified in a city-wide manner yet. This is the primary objective of the LABSHA project.

We have divided the Southern California area using a grid spaced at approximately 2.5 km in the basins and approximately 5 km elsewhere. Using SPECFEM3D program, developed by Dr. Dimitri Komatitsch and Dr. Jeroen Tromp at Caltech, we are simulating earthquakes on the San Andreas fault (1857 MW = 7.9 event), the Puente Hills fault ( MW = 7.0 event under Los Angeles downtown), the Santa Monica-Hollywood-Raymond fault system, the Newport-Inglewood fault (1933 MW = 6.3 Long Beach event), and the Northridge fault (1994 MW = 6.7 event) for validation of results. We use the computed seismograms to analyze a carefully selected set of tall buildings (the current study is focused on existing and new 20-story steel moment frame buildings) located at each grid location. The nonlinear structural time-history analyses are being performed using the program FRAME3D developed by Dr. Swaminathan Krishnan. These analyses are being executed on two Caltech computer clusters each consisting of 156 processors (733 MHz Linux boxes). The results of this study would be presented in the form of shake maps 9/29/06 the Southern California region. This study will benefit city, state and federal government in laying out emergency response strategies in the event of an earthquake on any of the said faults, in undertaking appropriate retrofit measures for tall buildings, and in formulating zoning regulations for new construction. In addition, the study will provide risk data associated with existing and new construction to insurance companies, real estate developers, and individual owners, so that they can make significant financial decisions.

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