It’s typical in South Lake County to feel an earthquake or two each month. They are usually small, in the 3.0 range in magnitude, and over the years, I’ve become quite adept at announcing the quake du jour’s intensity. A recent 4.3-magnitude quake that was fairly shallow caused my eyes to open wide!
The 2021 document entitled Lake Operational Area: Lake County Emergency Operations Plan states, ” The geology of the Northern California Coastal Region is distinct from the rest of California. Geologists and seismologists find the region of special interest because of the San Andreas Fault, which is within 30 miles to the west, the Hayward Fault and Rogers Fault extension into the Mayacamas Fault, which is within 10 miles to the west of Lake County. Throughout Lake County, there are several small active faults, with most centered in the Cobb Mountain area. Minor earthquakes occur almost daily in the south county geothermal fields near the geysers-influenced region.”
The United States Geological Survey (USGS) website entitled, Why are there so many earthquakes in the Geysers area in Northern California? States, “To date, the largest quake recorded at The Geysers is approximately M4.5. It is possible that a magnitude five could occur, but larger earthquakes are thought to be unlikely. In order for a larger earthquake to occur, it is necessary that a large fault exist. For example, the 1906 magnitude (M) 7.8 San Francisco earthquake ruptured nearly 300 miles of the San Andreas Fault. At The Geysers, no such continuous fault is known to exist. Rather, there are numerous small fractures in the rock located near the many steam and injection wells. The activities described above result in local stress changes which, when added to the prevailing regional tectonic stresses, induce the quakes on these small faults.”
Many of us can recall exactly what we were doing when any given shaker of the past occurred. For example, when the 1989 Loma Prieta quake on October 17th struck, which was centered in the San Francisco Bay Area but felt here in Lake County, I was on my way to take an off-campus course through Sonoma State University being held in Ukiah. The seismic activity of the Loma Prieta clocked in at a whopping 6.9, and the car radio explained that ‘this is NOT a test, but an actual report of an earthquake event.’
The main tool utilized to measure an earthquake’s magnitude is a seismometer. The word is derived from the Greek “seismos,” and it was first used by David Milne-Home in 1841. Seismometers measure ground motions and are important tools for both earthquakes and volcanic eruptions. Seismologists generally record magnitude five or larger earthquakes. Those that are smaller than a five are measured by seismological observatories, take their measurements from a scale called ‘the local magnitude scale’, and are measured on a Richter scale. The Richter scale, or ‘Richter Magnitude Scale,’ was designed from a base-10 logarithmic scale and was developed in 1935 by seismologists Charles Francis Richter and Beno Gutenberg, both based at the California Institute of Technology.
Some folks wonder, Is there such a thing as earthquake weather? According to the USGS, the answer is ‘no’. The myth that there is such a thing as earthquake weather has been in circulation since the 4th century B.C. when Aristotle proclaimed that earthquakes derived from the winds that were trapped in caves beneath the Earth. Another belief held that hot weather caused earthquakes, and an even later theory explained that wind and meteors were the causes of quakes. The USGS website on the topic of earthquake weather explained that there is the same chance of an earthquake occurring in any given weather but that enormous typhoons or hurricanes may trigger slow earthquakes in the Earth’s crust.
All of this quake talk leads me to believe that it’s time to check our earthquake kits to be prepared, just in case. If geology-speak is your thing, then visit the following websites for more earthshaking information:
