It’s our fault

By Andrew Lohafer

Bellingham is situated on an enormous fault. The Horizon turned to geology teacher Doug McKeever to answer some of our pressing questions about earthquakes.

 

   What causes earthquakes?

The basic cause of nearly all earthquakes is due to strain (caused by stress) that has accumulated to the breaking point of rock.  The energy released travels through earth materials as seismic waves, which can often be felt by humans, recorded by seismographs, and can cause catastrophic damage, depending on factors such as distance from focus (starting point of earthquake), type of earth material (bedrock vs. saturated soft sediment or landfill), type of construction and building materials, population density, even time of day or season.

 

     What is the likelihood of us having a major earthquake here in the Northwest?

  The likelihood of having a “major” (magnitude 7 or more) earthquake in the region is 100 percent.  “Where” is not the problem….. “When” and “how big” and “with what consequences” are the issues. Earthquakes have proven to be essentially unpredictable in the short term. That’s why in my opinion an Italian court was outrageously misguided in sentencing 6 Italian seismologists with manslaughter for not “predicting the unpredictable” (the L’Aquila 2004 Italian earthquake that killed 309).

 

    What is the fault line?

  There are numerous faults in the area. The most significant is the Cascadia fault, the tectonic plate boundary between the oceanic Juan de Fuca plate to the west, which is sliding (sub ducting) under the continental North American plate where we live. Other faults include the Boulder Creek fault near Kendall, the Seattle fault, the South Whidbey fault, and the Devils Mountain fault near Mt. Vernon, any one of which is likely capable of rupturing and producing earthquakes. There are also likely to be other faults that haven’t been mapped or haven’t ruptured to produce historic earthquakes. But what we don’t know can hurt us!

 

   Should we worry about other natural disasters around this area?

  As long as one stays off river floodplains, avoids steep slopes capable of landslides, doesn’t live on a low-lying coastal area with limited rapid escape options, and removes hazardous trees near one’s home, we live in one of the safer areas in the United States.

 

What should we do to prepare for an earthquake?

Preparation includes becoming aware by taking a WCC class such Natural Disasters (Geology 140) or Environmental Geology, Geology 110). Other aspects of preparation include having a plan in event of a natural disaster and having a “72 hour kit,” which involves being independent of outside help for a minimum of three days. This includes but is not limited to having non-perishable food, water, flashlights, battery radio, prescription medicines, and first aid supplies, and first aid training.”

 

   When was the last time the Northwest had a severe earthquake?

Perhaps the largest historic earthquake in the Pacific Northwest since 1700 occurred in 1872 with an epicenter near Chelan. Since 1900 there have been six earthquakes of magnitude 6 or more, with an average interval of 18.4 years but with as little as three years and as much as 36 years separating them (so much for the average!).  On February 28, 2001, there was an earthquake of magnitude 6.8 centered near Anderson Island in south Puget Sound (the “Nisqually earthquake”).

The most recent great earthquake (M=8 or above) was one occurring on the Cascadia fault on January 26, 1700, at about 9 p.m. local time. It had an approximate magnitude of 9, equivalent to the M=9 earthquake near Sumatra in 2004 that led to the catastrophic Indian Ocean tsunami or the March 11, 2011 earthquake near Japan.  A repeat of the 1700 quake is likely, since the shallow part of the fault is locked and accumulating strain energy.  As stated earlier, “when” and “how big” are the questions.”


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