Hollister Digital Array

Overview

Agbabian Associates installed the Hollister Earthquake Observatory (HEO) in 1991 with funding from the Kajima Engineering and Construction Corp. Kajima Corp donated this array to the University of California, Santa Barbara in January 1998. The site is located in the Salinas Valley about 10 kilometers from the San Andreas fault near the cities of Hollister and Salinas in central California. The ground motion array consists of a vertical array of six accelerometers in Quaternary alluvium and bedrock, and three accelerometers installed at a remote rock station, 3 km to the Northeast. The location of HEO along the San Andreas Fault in Central/Northern California increases our chances of recording a moderate to large earthquake.

Tabs

Geological/Geotechnical Information

At the main station the interface between alluvium and bedrock is reached at 192 meters. At the remote rock site alluvium overlies Tertiary sandstone overlying granitic basement.

On 12 August 1998, an Mw 5.1 earthquake occurred 13 km almost due east of HEO. All accelerometers recorded the event. In addition to the mainshock, the array recorded one foreshock and at least three aftershocks. Although the GL-53 and GL-192 recordings are 3km apart, an order of magnitude further than the Tertiary and granite recordings at the remote site, the mainshock acceleration time histories at these locations are more similar because they are both in granite bedrock. The difference between the two outcrop (Tertiary and granite) observations at the remote site emphasizes the importance of vertical array data.

Instrumentation

At the HEO main soil station accelerometers are located at 192, 110, 50, 20, 10, and 0 meters depth, going from crystalline rock at the bottom, up through consolidated and unconsolidated alluvium to the surface. Three sensor locations, surface Sandstone, surface Granite, and GL-53 meter borehole Granite are instrumented at the remote rock station

Data Channels - a list of active sensors, depths and assigned location codes at the site.

Cross-Section - a diagram showing the relative depths of sensors at the site

Surface Layout (Remote) - a diagram showing the relative positions of sensors at the site

Surface Layout (Main Station) - a diagram showing the relative positions of sensors at the Main Station

Images

NEES@UCSB

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