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LOCAL NEWS

Earthquake

Oregon had six earthquakes off the coast Thursday morning


Story by Lloyd Gufferson - The Oregon Herald
Published on September 14, 2021 10:07 AM
 
 
Experts say “the big one” is coming — as an early warning system launched Thursday, the 10th anniversary of a devastating quake and tsunami in Japan. Earthquakes in the Cascadia subduction zone, which extends from the ocean off Northern California to Canada’s Vancouver Island, have an average magnitude of around 9, making them among the world’s biggest.
 
PORTLAND, Oregon. — At least six earthquakes were felt more than 100 miles off the Oregon coast Thursday morning;. The quAke events followed an earthquake in the same location Wednesday afternoon. The U.S. National Tsunami Warning Center said there was no tsunami threat from any of the earthquakes.

On Wednesday, a 4.4 magnitude earthquake occurred at 2:36 p.m. about 182 miles northwest of Bandon and had a depth more than 6 miles.

All six quakes on Thursday morning earthquakes were felt within 50 miles of each other. The first quake on Thursday morning, a 4.3 magnitude quake, hit at 3:25 a.m., followed by a 5.4 earthquake at 3:30 a.m., a 5.2 earthquake at 3:35 a.m., a 5.3 earthquake at 3:58 a.m., a 4.1 earthquake at 6:25 a.m. and a 3.8 earthquake at 6:33 a.m.

BACKGROUND

Oregon Earthquakes

The 1993 Scotts Mills earthquake, also known as the 'Spring break quake', occurred in the U.S. state of Oregon on March 25 at 5:34 AM Pacific Standard Time. With a moment magnitude of 5.6 and a maximum perceived intensity of VII on the Mercalli intensity scale, it was the largest earthquake in the Pacific Northwest since the Elk Lake and Goat Rocks earthquakes of 1981. Ground motion was widely felt in Oregon's Willamette Valley, the Portland metropolitan area, and as far north as the Puget Sound area near Seattle, Washington.The Scotts Mills mainshock epicenter was located about 5 kilometers east of the town of Scotts Mills in Marion County, and about 54 kilometers south of Portland. The United States Geological Survey reported that strong motion instruments recorded peak ground accelerations of 0.06 g at Detroit Dam, 44 kilometers to the southeast, and also give an extensive review of damage reports and ground motion intensities.

Reports of the earthquake came from as far as Roseburg in southern Oregon, 165 miles south of the epicenter, to the coastal town of Lincoln City, east to Bend, and north to Seattle. The seismology lab from the University of Washington in Seattle reported the Richter magnitude to be 5.4, but stated that the initial figure could change. An aftershock measuring 3.2 happened within the first hour of the main shock.

Damage Most structural damage consisted of toppled chimneys and failure of walls of unreinforced masonry. Buildings with damage include Molalla High School, the State Capitol in Salem, and the St. Paul Church in Saint Paul. The damage at the capitol occurred in the old wing and that section of the facility was closed after the morning earthquake, and two walls at the high school were partially collapsed. Additional damage to some homes occurred in Molalla in the form of broken windows and brick planters at some homes there. No damage was reported in Portland, but residents did see books knocked off shelves and some car alarms were set off. Several people were treated at the Salem Hospital for injuries related to falling glass.

Oregon may be overdue for a massive earthquake. A resulting tsunami could kill 10,000 people.

We don't know when the Big One will hit but many small quakes have been attempting to get our attention even during a pandemic. Oregonians are used to hearing of little quakes but most of them originate deep in the Pacific Ocean.

Here's a rundown of the biggest earthquakes to hit Oregon in the last few years, using data from the U.S. Geological Survey.

All but two of the 250 strongest quakes were under the ocean, so we made two lists of Oregon quakes: one for the five strongest overall, and one for the five strongest to hit land.

Don't be alarmed when you see the date on the strongest Oregon quake since 2009.

For context, we've also provided a list of the five strongest earthquakes since then anywhere in the world.

For an up-to-date list of earthquakes in the last 30 days, check out our interactive map. To learn how to prepare for the big earthquake scientists say is coming, check out our step-by-step guide.

An earthquake is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to propel objects and people into the air, and wreak destruction across entire cities. The seismicity, or seismic activity, of an area is the frequency, type, and size of earthquakes experienced over a period of time. The word tremor is also used for non-earthquake seismic rumbling.

At the Earth's surface, earthquakes manifest themselves by shaking and displacing or disrupting the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides and occasionally, volcanic activity.

In its most general sense, the word earthquake is used to describe any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's point of initial rupture is called its hypocenter or focus. The epicenter is the point at ground level directly above the hypocenter.

Frequency of occurrence

It is estimated that around 500,000 earthquakes occur each year, detectable with current instrumentation. About 100,000 of these can be felt. Minor earthquakes occur nearly constantly around the world in places like California and Alaska in the U.S., as well as in El Salvador, Mexico, Guatemala, Chile, Peru, Indonesia, the Philippines, Iran, Pakistan, the Azores in Portugal, Turkey, New Zealand, Greece, Italy, India, Nepal and Japan. Larger earthquakes occur less frequently, the relationship being exponential; for example, roughly ten times as many earthquakes larger than magnitude 4 occur in a particular time period than earthquakes larger than magnitude 5. In the United Kingdom, for example, it has been calculated that the average recurrences are: an earthquake of 3.7–4.6 every year, an earthquake of 4.7–5.5 every 10 years, and an earthquake of 5.6 or larger every 100 years. This is an example of the Gutenberg–Richter law.

The number of seismic stations has increased from about 350 in 1931 to many thousands today. As a result, many more earthquakes are reported than in the past, but this is because of the vast improvement in instrumentation, rather than an increase in the number of earthquakes. The United States Geological Survey estimates that, since 1900, there have been an average of 18 major earthquakes and one great earthquake per year, and that this average has been relatively stable. In recent years, the number of major earthquakes per year has decreased, though this is probably a statistical fluctuation rather than a systematic trend. More detailed statistics on the size and frequency of earthquakes is available from the United States Geological Survey . A recent increase in the number of major earthquakes has been noted, which could be explained by a cyclical pattern of periods of intense tectonic activity, interspersed with longer periods of low intensity. However, accurate recordings of earthquakes only began in the early 1900s, so it is too early to categorically state that this is the case.

Most of the world's earthquakes take place in the 40,000-kilometre-long , horseshoe-shaped zone called the circum-Pacific seismic belt, known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate. Massive earthquakes tend to occur along other plate boundaries too, such as along the Himalayan Mountains.

With the rapid growth of mega-cities such as Mexico City, Tokyo and Tehran in areas of high seismic risk, some seismologists are warning that a single quake may claim the lives of up to three million people.

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