Earthquake activity continues with large quakes in southern California
My column last week focused on earthquake activity over the last month. Although, the overall number of earthquakes since the beginning of this year seems to fall within “normal” ranges, the activity over the last 3 weeks or so has gained a lot of attention, especially with recent events.
On Independence Day last Thursday, a 6.4 magnitude earthquake hit Southern California, near the city of Ridgecrest. After that strong earthquake, a magnitude 7.1 hit the region Friday, which was about 11 times stronger than the one on Thursday. According to the United States Geological Survey, there have been close to 5,000 aftershocks in the Southern California area since Thursday.
Based on the USGS data, after the 6.4 quake last Thursday, there was a magnitude 5.4 that occurred a day later. Then, came the 7.1 earthquake that rocked the region Friday night. Since that large quake, there were three additional earthquakes in the same region that measured 5.4, 5.5 and 5.4.
The chances of another magnitude 7 earthquake striking the same area within the next several weeks are extremely small. However, there is about a 25 percent chance of a magnitude 6 hitting that area through the middle of the month.
As I mentioned last week, according to the Southern California Seismic Network, there was a swam of over 1,060 small earthquakes from May 25 through June 19 that hit the Riverside to Chino areas of Southern California. Most were so small that residents did not feel them. The largest, however, was a 3.2 magnitude on June 2. There was also another period of earthquake swarms within the same region back in February and March of this year.
Whether or not those swam of earthquakes were a precursor to the big earthquakes in Southern California is still uncertain. However, there may be some kind of connection between these two events that will likely lead to more studies in the future.
Despite the big 7.1 earthquake in Southern California, this was likely not the “big one” that many seismologists have been forecasting. California has many fault systems, including the notorious San Andreas Fault. The earthquakes that occurred near Ridgecrest did not occur along the San Andreas Fault. Instead, they happened on smaller faults in Kern County.
A fault is a crack in the Earth’s surface. When the rocks on either side slip with respect to the other, the ground will vibrate. The San Andreas Fault runs from the California coast near San Francisco and goes down the state to just east of Los Angeles. One of the most famous major earthquakes along the fault system occurred in San Francisco on April 18, 1906. By the way, scientists say there is about a 70 percent chance of another large earthquake in the San Francisco Bay area by 2030.
With the recent activity in Southern California, some people are wondering on whether this will lead to a major earthquake in the Pacific Northwest. The events may be unrelated, but on Wednesday, July 3, a 6.2 magnitude quake was measured near Bella Bella, Canada, near the central coast region of British Columbia. The following day, there were four aftershocks that measured between 4.5 and 5.6 in the same region.
Although major earthquakes in the Pacific Northwest are not very common, scientists are concerned about a potential large event along the west coast of Washington. Based on historical evidence, there was a huge megathrust earthquake on Jan. 26, 1700, that was known as the Cascadia earthquake. It happened across a 620-mile area along the Cascadia subduction zone from the middle of Vancouver Island in British Columbia, Canada southward along the Pacific Northwest coast down into northern California. The magnitude was estimated between 8.7 and 9.2. The devastating Alaskan earthquake in 1964, the second largest recorded in history, was a 9.2.
The big quake in 1700 was believed to have generated a large tsunami that hit the coast of Japan. It may also have been linked to the Bonneville Slide. This was a major landslide that dammed the Columbia River near Cascade Locks in Oregon. The Native Americans referred to this as the “Bridge of the Gods.” However, other investigations state that the landslide occurred around 1450 based on radiocarbon dating and dendrochronology (tree rings).
In terms of our local weather, readings will be warm over at least the next 10 days as highs should be well into 80s in the Coeur d’Alene area later in the week. Cliff and I wouldn’t be surprised to see a few 90-degree afternoons toward the middle of the month.
The rest of the summer season still looks a bit drier than normal, but not as dry as the summers of 2017 and 2018. In July of 2018, only 0.04 inches of rain fell. So far, Cliff has measured .17 inches this month.
In 2018, Aug. was very dry until we received a half-inch of rain on August 27. With little moisture and hot temperatures, North Idaho, as well as much of the western U.S., suffered through one of the worst fire seasons in history. Let’s hope this year will be different.
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Contact Randy Mann at randy@longrangeweather.com