Processing of the Upper Left Abutment Record from Pacoima Dam for the Northridge Earthquake

The Pacoima Dam was strongly shaken during the Northridge earthquake. Analysis of the record from the upper left abutment site indicates that the site tilted about 3° to the northeast (downslope) during the earthquake. This is obtained by subtracting a simple tilting function determined from the record. The 3° is independently confirmed by level measurements at the site. The concrete pier to which the instrument is bolted appears to be well connected to the rock ridge, and there is no relative displacement apparent between the pier and the rock. In contrast, the gunite and thin concrete on the rock is badly broken up and shifted.