Along the North Pacific, a silence has been stretching for more than three hundred years, hiding an invisible threat under the sea. Nestled between the Juan plaque of Fuca and the North American plate, the Cascadia flaw concentrates colossal energy without ever betraying its presence on the surface. However, scientists fear a brutal awakening, capable of shaking the American West Coast, flooding the plains and sustainably upset landscapes like lifestyles.
On January 26, 1700, an earthquake of an estimated magnitude between magnitude 8.7 and 9.2 shook the whole region. This earthquake generates an “orphan tsunami” detected until Japan. At the time, the event left only geological traces on the North American continent, but today it appears as an essential benchmark in the seismic archives. Since then, the flaw has remained silent, but probabilistic models now estimate at 15% the probability that a new earthquake of magnitude greater than 8 strikes the region in the next fifty years, as explains Iflscience.
This type of fault accumulates pressure without visible sign. When the breakup occurs, the released energy is massive, sudden and difficult to anticipate. It is this scenario that more and more researchers anticipate. A quick event that would upset the entire coast in a few minutes.
Modeled scenarios that worry researchers
Beyond shaking or tsunamis, another phenomenon now attracts the attention of scientists. This is the subsidence, that is to say the sudden lowering of the soil caused by tectonic deformation. This phenomenon could cause a collapse of almost two meters from the level of the ground on large portions of the coast. However, this change of relief occurs in a few moments, leaving a short time to adapt.
A recent study by Tina Dura, a geologist at Virginia Tech, and published in the journal Pnas, offers an unprecedented evaluation of the consequences of this subsidians at the level of the Cascadia flaw. By combining thousands of seismic models with topographic data, the researchers estimated the potential expansion of the flood zone after an earthquake. They identified 24 particularly exposed estuaries, ranging from North California to Washington State. If the earthquake occurred today, approximately 300 additional square kilometers would rock in the area at risk of flood, thus doubling the exposure of roads, homes, schools, hospitals, and even wastewater treatment stations.
This scenario becomes even more worrying when the event is projected by 2100. By then, the elevation of the sea level linked to global warming will considerably amplify the effects of the earthquake. The same study provides that more than 29,000 buildings and 1,600 kilometers of roads would then be exposed to floods. The analysis is based on the projections of the marine level established by the IPCC in its SSP3-7.0 scenario, a frame of reference to model the impacts of high greenhouse gas emissions.
Predict the unpredictable, which local authorities are trying to set up
In recent years, coastal states of Oregon and Washington have been increasing large -scale simulation exercises. Called “Cascadia Rising”, this program mobilizes intervention teams to test the reaction capacity to a major earthquake. The estimates from these scenarios draw up an alarming table. They anticipate up to 30,000 deaths, the destruction of 75% of coastal roads, many schools and more than 2,000 bridges.
However, these projections did not take into account, until recently, the combined effect of the subsidence and the rise of the waters. Today, local authorities acknowledge that updating flooding cards is becoming a priority. However, few municipalities have the resources necessary to initiate a real transformation of their infrastructure. The relocation of certain critical services such as hospitals or power plants promises to be complex and costly.
In some areas, such as the Humboldt bay or the Yaquina region, agricultural land is likely to become unfit for any exploitation. Salt from marine intrusions permanently alters the soils, and repeated floods reduce the quality of groundwater. The natural environment, too, is in danger. Coastal wetlands, real ramparts against storms, could disappear under the combined effects of the earthquake and the elevation of the sea level.
Transformed landscapes and an ecological memory in danger
The consequences of the next earthquake of the Cascadia flaw do not stop at visible damage. By suddenly modifying the altitude of certain areas, it could also erase whole ecosystems. The intertidal marshes, these buffer zones between the sea and the earth play a fundamental role in the filtration of water, the storage of carbon, and the reception of biodiversity. Once flooded permanently, they stop fulfilling these functions.
Research shows that these environments sometimes take centuries to be reconstituted after a sudden submersion. Added to this is the threat of an increase in tidalia, that is to say of the amplitude of the tides. In certain areas of Oregon, the subsidence could vary the tidal levels by more than 10%, which would make the ribs more vulnerable to storms and waves of submersion.
The experience of Japan, Chile or Alaska has shown that these geological transformations spare neither ecosystems nor human societies. The previous earthquakes of magnitude 9 permanently altered the coastlines, resulting in forced trips and a loss of cultural benchmarks. What is played out with the cascadia fault exceeds the simple scale of an earthquake. It is an ecological, human and territorial tilting on the scale of a century.
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
