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Did You Feel Those Earthquakes?

The Puget Sound was rocked early Friday morning. Quite literally, the ground shook when two earthquakes hit the Monroe region in quick succession. The first was a 4.6 magnitude earthquake “0km SSW of Three Lakes, WA” at 2:51 am. Two minutes later a 3.5 magnitude earthquake was registered by USGS “4km W of Monroe, WA” at 2:53 am.

What the USGS Tells Us

According to the USGS website, five people in Auburn registered they felt the Three Lakes earthquake. The responses on the map indicate it was felt as far north as Sechelt British Columbia (above Vancouver) and potentially as far south as the Portland area. Olympia had many responses (40), indicating they felt the earthquake. Some indicated they felt it in Spokane, but it was felt strongest in the Kennewick area.

The second earthquake, centered closer to Monroe, was not as strong. While people in Maple Valley and Kent reported feeling the Monroe earthquake, none from Auburn recorded feeling it with the USGS. Vancouver was the farthest north this earthquake was felt, and though one of two in Portland indicated feeling it the most concentrated numbers remained around the Puyallup/Tacoma area. Only a handful of people east of Goldbar reported feeling the Monroe earthquake.

We caught up with Brian Terbush, the Earthquake/Volcano Program Coordinator at Washington State Emergency Management Division, to find out more about Friday’s earthquakes and what they might mean. “The Earthquakes [Friday] were relatively large for Earthquakes in Washington,” said Terbush, “but as we like to keep reminding people, Washington State has the second-highest seismic risk in the country (just behind California). So Earthquakes are not unusual, and you should expect that they occur once in a while.”

Terbush went on to remind that “there is not any strong link between earthquakes on individual faults and earthquakes on other faults. In 2009, the Kingston Earthquake M4.5 was a very similar size earthquake that did not lead to any other earthquakes in the area. Neither did Nisqually in 2001, or the 1999 Satsop Earthquake, which were both much stronger. These other examples of also didn’t contribute to any Volcanoes erupting, so that shouldn’t be something people worry about.”

As we learned when we spoke to Terbush and USGS Scientists earlier this year, earthquakes are not something that can be predicted. “USGS has provided aftershock forecasts following this earthquake, saying that there is a 4% chance there will be a larger earthquake on this fault within the next week,” explained Terbush.

USGS provides “Aftershock forecasts” for earthquakes now. “Which are exactly what they sound like,” said Terbush. “This aftershock sequence has fallen within reason based on the forecast they provided.”

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Earthquakes mapped out by USGS

Over this past weekend, small earthquakes did continue, as the USGS predicted.

1.7 4km W of Monroe, WA – 07-12-2019, 2:56 am
1.6 4km E of Cathcart, WA – 07-12-2019, 3:28am
1.5 4km W of Monroe, WA – 07-12-2019, 3:50 am
1.6 4km W of Monroe, WA – 07-12-2019, 7:12 am
1.8 4km W of Monroe, WA – 07-12-2019, 12:04 pm
2.0 4km E of Cathcart, WA – 07-12-2019, 2:31pm
2.3 4km ENE of Cathcart, WA – 7-13-2019, 08:04 pm
1.6 4km ENE of Cathcart, WA – 7-14-2019, 07:18 pm
2.5 4km W of Monroe, WA – 07-14-2019, 10:44 am
1.9 3km ENE of Cathcart, WA – 7-14-2019, 07:30 pm

Here’s the aftershock forecast for the Three Lakes earthquake. 

“All of these other smaller quakes have been aftershocks,” confirmed Terbush. “If there is a larger one on that fault (4% chance it’ll happen before Friday, based on their models and predictions), the Friday earthquake, and all of the subsequent aftershocks would be considered “foreshocks,” and the larger one will be the new “main shock.” And USGS would come up with a new aftershock forecast for that new earthquake based on the data that comes in.”

What About California?

Speaking to the recent earthquakes in California, Terbush assured that while “the Earthquakes in California were certainly very strong, and [they] were unusual, because the first large earthquake turned out to not be the strongest. This is something you can only tell after the sequence has completed, but the initial aftershock forecast that came out from USGS predicted about a 1 in 10 chance that a larger earthquake could occur after the initial one.”

“Whereas again,” Terbush continued “the chance of that is only 4% or 1 in 25 of that here. Just looking at the Ridgecrest Earthquake in comparison to ours in Snohomish County, there have been significantly more aftershocks in California.”

Terbush also reminded that “there is not any strong link between earthquakes on individual faults and earthquakes on other faults. In 2009, the Kingston Earthquake M4.5 was a very similar size earthquake that did not lead to any other earthquakes in the area. Neither did Nisqually in 2001, or the 1999 Satsop Earthquake, which were both much stronger. These other examples of also didn’t contribute to any Volcanoes erupting, so that shouldn’t be something people worry about.”

How Will This Impact Local Volcanic Activity?

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Mt. Rainier from Auburn | Photo by Jessica LaVoie

Recent reports have indicated Mt. Hood is more active recently. “Mt. Hood is having a seismic swarm which is considered very normal behavior for Mt. Hood,” said Terbush. “Based on the types of activity, the earthquakes are located on a fault, and unrelated to magma movement. Mt. Hood, like Mt. Rainier and Mt. St. Helens, is highly monitored by the Pacific Northwest Seismic Network, as well as additional monitoring using GPS from the USGS Cascades Volcano Observatory. Large amounts of seismic activity without any significant uplift on the volcano means that there isn’t magma entering the volcano, so that’s a good sign there isn’t an impending eruption.”

Terbush went on to say that, “when looking at the location and depth of the earthquakes over time, and they aren’t becoming any shallower or showing other signs of moving fluids, there is a pretty low chance that it is leading toward an eruption.”

Are You Prepared?

These recent earthquakes, and Mt. Hood’s activity (albeit typical) are great reminders to ensure you and your household are prepared for any emergency.

“This earthquake serves as a friendly reminder that we have earthquakes here, and should be a good reminder to everyone to refresh their memories on what to do when the ground starts shaking,” said Terbush. “For example, if they stayed in bed since it happened at 2:50 in the morning, that was the safest action. [That is], provided they don’t keep a collection of heavy picture frames and other objects on shelves over their bed – not a good idea in Earthquake Country, and probably a good reminder that it’s time to find a better place for those things.”

If there is rain in the forecast, you dress accordingly, right? With earthquakes and volcanic eruptions in Auburn’s forecast, ensure your home is prepared! For tips on preparedness, contact City of Auburn Emergency Management Department or go to mil.wa.gov/preparedness for general tips in the State.

https://www.youtube.com/watch?v=xlWgxSnVcwU&t=

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