The West Coast has been recently experiencing more earthquakes

According to the U.S. Geological Survey, a 3.7 magnitude earthquake was reported near Vancouver, Canada, last Friday morning. The website, earthquaketrack.com, indicates that the Pacific Northwest has experienced over 90 small earthquakes within the past month alone. Over the previous 365 days, there have been over 800 tremors.

Within the last week, there were several earthquakes that registered at least a 4.0 in magnitude off the Oregon coast and near Vancouver, Canada. Data from the USGS shows that Sept. 29, there was a 2.1 magnitude tremor north of Kellogg and Sept. 30, there was a 2.7 magnitude earthquake nearly 12 miles north-northeast of Kootenai, Idaho.

As of the weekend, more small earthquakes were reported in Washington. However, the Pacific Northwest has not been the only region to experience numerous earthquakes. The USGS reports that Southern California has broken the record for the most magnitude 4 or higher quakes in a single year. As of early October, there have been 14, which breaks the previous record of 13. One of the highest magnitudes occurred Aug. 6 with a 5.3 near Bakersfield and a 4.7 magnitude that hit Malibu on Sept. 12. Since that date, there have been 73 earthquakes, mostly very small, within the last 30 days. By the way, the average number of tremors in this region is over 900 per year.

With its many fault systems, California has been known as “earthquake country.” The most famous fault is the notorious San Andreas Fault which runs for approximately 1,200 miles through Southern California and the coastal regions of the northern and central parts of the state. This fault also is the major tectonic boundary between the Pacific Plate and the North American Plate. They are moving about an inch per year and the two plates are slipping past one another around the central portions of the fault due to softer rocks. However, the northern and southern portions of the plates are “locked” together, which creates high stress for the fault.

The last major San Andreas Fault earthquake in Southern California occurred in 1857. Geologic evidence suggests that the earthquake-recurrence interval in this region is approximately 140 to 160 years. Therefore, many scientists claim that this part of the fault is “overdue.” The last major earthquake in the northern part of the fault (7.0 or higher) was the infamous 1906 San Francisco earthquake with an estimated 7.9 magnitude.

The Pacific Northwest will eventually see another major earthquake along a different region called the Cascadia Subduction Zone. Scientists say that the recent activity does not necessarily indicate that the Northwest will experience “a more severe earthquake” in the near future, but they do indicate that the region may also be overdue for a strong event. They estimate that the region has about a 37% chance of at least a 7.1 event within the next 50 years.

Based on historical evidence, there was a huge megathrust earthquake 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 that resulted in catastrophic damage to Anchorage was the second largest in recorded history and had a magnitude of 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, it continues to be much drier than normal in Coeur d’Alene and the rest of the Inland Empire. Since Jan. 1, we’ve only had 15.15 inches of rain and melted snow in Coeur d’Alene, compared to the normal of close to 18 inches. The latest U.S. Drought Monitor has the Spokane and Coeur d’Alene region experiencing moderate to severe drought conditions. For September, Coeur d'Alene picked up 0.88 inches of rain, but at the Spokane International Airport, only 0.04 inches fell for the entire month.

With the strong high-pressure system that is dominating our region, the dry weather pattern is expected to hold on for the next week to 10 days. However, there may be several storm systems that will bring us a chance of some showers. The long-range computer models are pointing to a breakdown of the high-pressure ridge, perhaps around the middle to the end of the month. Even if the ridge holds on beyond the middle of October, weather patterns are still expected to be wetter across our region either late this month or November.

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Contact Randy Mann at randy@longrangeweather.com.