Earthquake Motions
Recorded on a 5000-Node Seismic Network
in Long Beach, California

Robert W. Clayton, Caltech
Dan Hollis, NodalSeismic Inc.
Magali Barba, UC Berkeley

Data Provided Courtesy of NodalSeismic Inc. and Signal Hill Petroleum

The movies of earthquake motion have been constructed from a 5000 node array run by NodalSeismic Inc. for Signal Petroleum. The network was deployed for approximately 6 months during the first half of 2011, and was designed to provide high resolution images of the Long Beach Oil Field. The survey had an active component that ran 9am-4pm weekdays. The sensors are autonomous units that run 24 hoirs a day. They have a standard velocity sensor with a lower roll-off at 3 Hz.

Standard Industry Source (Vibrators)

The active source component of the survey consisted of Vibrator sources runing either as a single unit or in a group of four. Each vibrator can exert a force of 30 tons, but in normal operation the force is dialed back to 20-30% of that because of the close proximity of buildings. They sweep 10-80 Hz in a chirp that lasts 20 seconds. The crosscorrelation of the the chirp signal with the data recorded by the seismic network, simulated an impulsive source.

Earthquake Sources

Earthquake Movies
Earthquake Movie (click to run) Notes
Mb 2.5
distance 5 km
 Notes:  The amplitudes of the shaking at each station
are displayed on a color scale with blue for negative
values and red for postive values. In the first movie
only negative values are shown.  In the second movie,
only positive values are shown. For the first two movies
the filter is set from 1-50 Hz which shows both P and
S waves.  In the third movie, the filter is 1-14 Hz,
which emphasizes the S-wave.
Mb 2.9
distance 35 km
Mb 3.4
distance 20 km
Channel Island
Mb 3.7
distance 75 km
San Bernardino
Mb 2.9
distance 75 km
distance > 90.0
The energy in the Japan Earthquake is very small and is
below the frequency  range of the sensors, which have a
response band of 3 Hz and above. The energy also arrives
at Long Beach nearly vertically. Nevertheless, the waves
arriving from Japan can be seen at low frequency waves
that span a large part of the apperature of the network

Wave Focusing - Carson Earthquake

Three successive frames of the Carson earthquake show how the focussing of energy changes as the earthquake passes.

Maximium Ground Acceleration

The maximum at each station is displayed for three earthquakes. The red values ate the maximum intensity and for the carson event represent an acceleration of about 5 cm/sec**2.
Covina Carson Compton

Backprojection Movies


SubArray Movies