Earthquakes increasing; 'big one' coming soon?

Within the last two weeks, there have been three major earthquakes, one in the San Francisco Bay Area, another off the South American coastline near Peru and a third near Chile. For August, there were a total of five quakes measuring 6.0 or higher. The other two locations included Wenping, China and the Federates States of Micronesia.

The one in California was centered about 6 miles outside the city of Napa, which is east of San Francisco. It struck very early Sunday morning, Aug. 24, and had a magnitude of 6.0. California has many fault systems and this particular quake did not occur along the infamous San Andreas Fault.

The last major earthquake in the U.S. was the Loma Prieta earthquake in northern California on Oct. 17, 1989. It measured 6.9 on the Moment Magnitude Scale. The Moment Magnitude Scale is the measurement system for earthquakes rather than the famous Richter Scale. Both scales are similar, but the Moment Magnitude Scale was developed in the 1970s and is more effective for characterizing some classes of moderate to major earthquakes.

Many are wondering if we're seeing an increase in earthquake activity. According to the U.S. Geological Survey, the first quarter of 2014 has had more than double the rate of major earthquakes higher than a 7.0 when compared with the average since 1979. However, a sampling since 1979 may not be large enough to make this type of comparison, but it does make many scientists wonder when the next big one will strike.

The largest earthquake to ever occur in the U.S. happened on March 28, 1964, at Prince William Sound in Alaska. Anchorage was completely devastated as it had the second highest ever worldwide recording of 9.2. The highest occurred in Chile in 1960 with a magnitude of 9.5. The most famous U.S. earthquake rocked San Francisco on April 18, 1906. The magnitude 7.8 resulted in property damage of $524 million (1906 dollars).

Earlier this summer, the U.S. Geological Survey updated their national seismic hazard map from 2008. The coastline from northern California northward to British Columbia has been listed as a high risk zone for a major earthquake. The shifting of the Earth's crust leads to increasing stress. For the last 300 years, the Juan De Fuca plate off the northwest coast has been colliding with and diving under the huge North American plate. This area of stress along the Pacific coast is called the Cascadia subduction zone. In 1700, an estimated 9.0 mega-thrust earthquake hit the Northwest and created a giant tsunami that hit Japan. Over the years, major earthquakes occur about every 300 to 500 years in this region.

It's not a question of 'if' the next major quake will hit the Northwest coast, but 'when.' The next major event would likely cause extreme and catastrophic damage to the major cities along the northwestern coastline. However, the Cascade Mountains would likely deflect the major earthquake waves to the north and south, so the effects of this future quake would probably not be quite as strong across Inland Empire, including North Idaho.

In the Midwest, there is also a high risk of earthquake activity along the New Madrid Fault which runs 150 miles within Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri and Tennessee. In 1811 and 1812, there were 4 major earthquakes of at least 7.5 magnitudes or higher that rang church bells in Boston. Scientists believe that another major earthquake is due for this region, but they're not certain when that will occur. Some believe that there is a 7-10 percent chance of this event within the next 50 years.

In Oklahoma, there have been a large number of smaller earthquakes. In June, Oklahoma actually reported more temblors than California, which may be the result of fracking in the area.

The most likely place for the next major earthquake would be along the notorious San Andreas Fault.

The southern portion of the fault, located in Southern California, has not reported a major event since 1857. Geologic evidence shows that the southern portion of the San Andreas Fault creates major earthquakes about every 150 years, so this area is overdue. Stay tuned.

NORTH IDAHO WEATHER REVIEW AND LONG-RANGE OUTLOOKS

By Climatologist Cliff Harris

The month of September started off with a 'bang,' literally, as another thunderstorm in a series of summer 'boomers' tore through the area with strong winds and briefly heavy rains. Temperatures fell more than 30 degrees in town in just a few hours, from 78 degrees to 44 degrees and a hint of fall in the air.

Hayden picked up .59 inches of precipitation from the early September storm. Post Falls received .47 inches and we measured .39 inches at my station on Player Drive, which pushed our annual 2014 rainfall total to more than seven inches above normal by Sept. 4, the day of this writing. Oddly enough, Spokane's precipitation was barely normal for the year at 10.22 inches compared to the usual 10.17 inches to date. Our 2014 rainfall in Coeur d'Alene reached a healthy 23.45 inches thanks to numerous summer thunderstorms following frequent periods of 90-degree plus temperatures.

Longer-term weatherwise, we're expecting that areas from Spokane westward to the eastern slopes of the Cascade Mountains will be a bit drier and warmer than usual during the rest of September and probably well into the month of October before the annual rainy season kicks in.

However, from Sandpoint, Rathdrum and Coeur d'Alene in North Idaho eastward through Whitefish, Kalispell and Missoula, Montana, we probably will be slightly wetter than usual with a tad cooler than normal temperatures that will likely produce scattered areas of frost this September and widespread hard freezes in October.

The type of winter weather that we will endure locally in the Inland Empire will at least partially depend upon what happens with the current rather 'weak' El Nino in the tepid waters of the eastern Pacific Ocean. Stay tuned.

SPECIAL NOTE: Thanks to Meteorologist Randy Mann for filling in for me while I was on a brief vacation celebrating my mother's 98th birthday. Randy wrote this week's earthquake article.

Cliff Harris is a climatologist who writes a weekly column for The Press. His opinions are his own. Email sfharris@roadrunner.com