Scientists have gone through seismic data for Southern California, and by looking intensely at the data, they have discovered two million previously unidentified tiny earthquakes in Southern California that happened between 2008 and 2017. Caltech seismologists performed a detailed study of seismic data.
The researchers’ efforts expanded the earthquake catalog in the region and period of time by a factor of ten pushing the catalog from about 180,000 quakes to 1.81 million. The data shows that there are about 495 daily earthquakes across southern California that happen at a timespan of about three minutes apart.
The data previously in the earthquake catalog suggested that earthquakes in the region were about 30 minutes apart. The new data research adds quakes to the catalog that are between negative magnitude 2.0 and 1.7. The team added all the quakes by utilizing a labor-intensive identification technique that usually is only employed on small scales.
Quakes this tiny are difficult for scientists to identify because they are hidden in the background noise of events like vehicle traffic or building construction. The team says that it’s not that scientists didn’t know these small quakes were occurring, it’s just hard to separate them from all the background noise. To separate quakes from the background noise, the team used a technique caleld “template matching.”
That technique uses more significant and more easily identifiable quakes as templates to show what an earthquake signal at a location should look like in general. Then when a tremor with a matching waveform is identified the researchers use scanned records from nearby seismometers to see if the quake signal was recorded elsewhere and could be verified. The technique works in areas with closely space seismometers.