Earthquake counts and RMS amplitude (proportional to average ground motion amplitude - see explanation below) of earthquakes at selected stations during the last 2 weeks. Earthquakes counts are determined using an automatic algorithm that detects signal increase in continuously recorded digital data. RMS amplitude is the signal strength of each trigger, which is proportional to the energy in the earthquake (see explanation below). Automatic processes may misinterpret signals. A Station Map of seismographs is available.

The level of ground shaking rises and falls in response to the frequency and sizes of earthquakes that occur.

Time on the plots is given as date in Universal time (UT = PST + 8 hours).

The ground motion displayed on the figures is the RMS amplitude in raw counts as recorded on the computer. That is, the square root of the average ground motion squared. The averages are computed from ground motion data sampled 100 times per second.

The amplitudes can be converted to ground velocity or ground displacement if one accounts for the sensitivity of the seismograph station (varies for each station and varies also with the frequency of ground motion in Hz). For example at station JUN the sensitivity to ground velocity is 4.9 millimicrons/sec/count at 3 Hz. The sensitivity to ground displacement is 0.26 millimicrons/count at 3 Hz. Note 1,000,000 millimicrons= 1 millimeter.

As an example, if the plot shows an RMS amplitude of 100 counts at station JUN and if we assume the vibrations have a frequency of about 3 Hz, then the true RMS amplitude of ground motion at JUN, 6 km south of the source of the vibrations, is (100 counts)x( 0.26 millimicrons/count) = 26 millimicrons.