Unexpected Directionality of Failures in the 1906 San Francisco Earthquake near Point Reyes Station

This study investigates the directions of structural failures and toppling near Point Reyes Station during the 1906 San Francisco earthquake (M-w 7.9). We examined archives of the Jack Mason Museum of West Marin History and other historical sources for photographs and other evidence relevant to the dynamics of the 1906 rupture in this area. Using historical maps, site investigations, and previously unpublished photographs, we determined the precise locations and orientations of several structures, including a correction to the orientation of the train that was the subject of previous studies. Based on the photographic evidence and written accounts, we estimate the direction of toppling or collapse of each structure. Nearly all objects found were thrown in a direction approximately parallel to the right-lateral San Andreas fault, and in the same direction as the static ground displacement. This suggests that fault-parallel accelerations may have been stronger than fault-normal accelerations, and that the slip on the fault may have begun slowly and stopped more suddenly.

Automated summary

This study investigates the directions of structural failures and toppling near Point Reyes Station during the 1906 San Francisco earthquake, and suggests that fault-parallel accelerations may have been stronger, leading to a more sudden slip on the fault.