Impact of the Hypocenter Location of a Mw7.0 Scenario Earthquake on the Hayward Fault on the Seismic Response of Tall Buildings in San Francisco

Abstract

A regional seismic risk assessment of the tallest 150 buildings in the Financial District of the city of San Francisco, California is conducted when subjected to three hypothetical M_w7.0 earthquakes on the Hayward Fault with different hypocenters, but rupturing the same area, situated to the north, east, and south of the Financial District. The analyses are conducted using a probabilistic Monte Carlo-based framework previously proposed by the authors, which uses reduced-order models with linear-elastic analyses to perform simplified site-response analyses at each site and compute responses of each building in both principal orientations. The combined effect of the hypocenter location and building orientation on the hazard and building responses is carefully analyzed. Results indicate that peak building inter-story drift ratios may change by as much as 20% with a change in the hypocenter location along the Hayward Fault, suggesting that regional seismic risk assessments for a scenario earthquake should consider multiple hypocenter locations for a given rupture area. Furthermore, peak building inter-story drift ratios can change by as much as 34% with a change in both the hypocenter location along the Hayward Fault and the building principal orientation. Building inter-story drift ratios at different building heights (i.e., not just where inter-story drift ratios are maximum) can also change by much more than 34% with a change in the hypocenter location. This study also compares the hazard and building responses computed with the proposed framework to those computed with a commonly used Ground Motion Model (GMM). Results show that current GMMs overestimate response spectral ordinates for longer periods of vibration at shallow, soft-soil sites, consequently leading to overestimations in displacement-based responses of tall buildings.