On April 18, 1906, the seismographic station at the University of California's Lick Observatory on Mt. Hamilton obtained the only good record of local strong ground motion from the great earthquake that devastated San Francisco that day.
Astronomers at Lick Observatory recently discovered what appears to be the original tracing of the 1906 earthquake from the Mt. Hamilton seismograph. The Mt. Hamilton tracing provided the most scientifically useful local record of the event and was reproduced in the official state report on the earthquake (known as the Lawson Report). The original has now been archivally mounted and is being put on display in the main building at Lick Observatory.
"It is a tangible link to April 18, 1906, and has the fascination of an artifact that connects us across many years to an important event," said Tony Misch, support astronomer at Lick Observatory, who found the tracing in the "plate vault" where old photographic plates from astronomical observations are stored.
"It is actually quite a beautiful artifact," added Remington Stone, recently retired operations manager at Lick Observatory, who initiated the search for the observatory's seismographic records from 1906.
The instrument at Mt. Hamilton that recorded the earthquake was a Ewing three-component seismograph, which made tracings on smoked glass plates. A permanent photographic record was then obtained, probably by placing the glass plate on photosensitive paper and exposing it to light, according to seismologist Robert Uhrhammer of the Berkeley Seismological Laboratory.
The smoked glass recording plates were routinely wiped clean, resmoked, and reused, Uhrhammer said. The tracing now on display shows wavy blue background lines in a pattern typically seen on photographic copies of smoked-glass seismograms. The darker seismic traces were also originally light blue and were traced in ink during the annotation process, he said.
"All the evidence indicates that it is indeed the original tracing of the Mt. Hamilton Ewing three-component seismogram record of the 1906 earthquake," Uhrhammer said.
The seismographic station at Mt. Hamilton was established in 1887 by the first director of Lick Observatory, Edward S. Holden, who also established a similar seismographic station at UC Berkeley.
Founded in 1888, Lick Observatory remains among the most productive research observatories in the world. It is located on the summit of Mt. Hamilton in the Diablo Range east of San Jose. Driving time from San Jose is about one hour via Mt. Hamilton Road (Route 130). The observatory is open to daytime visitors nearly every day of the year and is closed to the public at night after 5 p.m.
Additional information about the Lick Observatory is available on the web at http://www.ucolick.org/public/visitors.html.
