Consider this: in the time that it takes you to read this sentence, at least one earthquake has been recorded somewhere in the world. In fact, there have probably been a hundred or more earthquakes today, most of which were too small to be recorded. Earthquakes are a common natural phenomena, with some 30,000 earthquakes recorded every year. That means there’s at least 50 earthquakes a day around the world.
Living on shaky ground
Oregon is on the cusp of experiencing a major earthquake in the near future. Lying off the coast of Oregon is a massive fault called the Cascadia Subduction Zone. This is the site where one tectonic plate overlaps another. Currently, scientists are predicting that there is a one in three chance of a magnitude-eight earthquake in Cascadia over the next 50 years.
According to Bruce Johnson, state bridge engineer with the ODOT, most of Portland’s bridges would be damaged and could even face collapse in a the event of a major earthquake.
Our region has not produced an earthquake since 1700 and is building up pressure where the Juan de Fuca Plate is subsiding underneath the North American plate.
Portland is just one city within this zone that stands to suffer significant damage as the result of a devastating earthquake. Reports by the Oregon Department of Transportation (ODOT) show that the city’s infrastructure is extremely vulnerable, and a sizeable earthquake could sever many of the major transport routes throughout the city.
More than half of Oregon’s 2,800 state bridges were built before 1970 and as such have no seismic design of any kind, putting them at risk of damage in a quake or other natural disaster. Data collected by the ODOT shows that of the 1,232 lifeline structures identified in Portland, 713 bridges are considered seismically vulnerable or potentially seismically vulnerable. That means that nearly 60 percent of state-identified lifeline bridges could face collapse or be potentially taken out of use after a quake.
Which bridges will be the worst hit?
The Interstate Bridge is a critical connection between Oregon and Washington, carrying some 130,000 cars and trucks daily over the Columbia River along Interstate 5. In a magnitude 8 or 9 Cascadia Subduction Zone quake, this connection is likely to be taken out. The drawbridge towers are likely to collapse, sending giant concrete blocks smashing through the bridge deck, and middle sections of the bridge will crumble into the river, meaning that the bridge will be impassable to traffic. This will also block ships from travelling along the river.
Government records indicate the Ross Island, Hawthorne, Steel and Broadway Bridges are also likely to collapse during a major earthquake. The Morrison and Burnside bridges could remain standing, but with extensive damage. The Marquam and Freemont bridges would survive but would be out of use. Their middle spans would remain but the approaches would collapse, rendering the bridges inaccessible.
Map Credit: Kyle Iboshi,KGQ Portland
Will any bridges be spared?
The recently rebuilt Sellwood Bridge is now Portland’s most earthquake-resilient bridge for car and truck traffic. It has been designed to flex and bend, allowing the bridge to absorb some of the energy created by an earthquake, and preventing it from cracking and falling apart. This new bridge is built into solid bedrock foundation which makes it a lot sturdier than the previous bridge, which lay in soft foundations.
Hope for the best, prepare for the worst
The vulnerability of Portland’s infrastructure is a timely reminder of how our next major earthquake will have devastating consequences for both the city itself, and its inhabitants.
Earthquakes can strike without warning, so it is essential to have a plan in place and be as prepared as possible in the event that one does occur. Preparing the basics for survival and making a plan can minimize the effects of a disaster on you and your loved ones.
As the ODOT reports have shown, Portland’s major transport routes are very likely to be disrupted or destroyed following a major earthquake or natural disaster. This means that movement around the city will be limited, so it is important to be self-reliant in the event that you may not be able to leave your house or access goods and services. The most important thing that our community can do is have an emergency kit in your home. Make sure you have enough supplies (food, water, first aid) to ensure that you and your family can survive at home for three days to a week following a disaster.
There’s no denying that our planet is a very active, and earthquakes are a constant reminder of our vulnerability. So by preparing for the worst, you and your family stand a good chance of getting through.