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Long-standing monster earthquakes off the coast of California, Oregon and Washington have allowed some coastal areas to sink more than six feet, dramatically increasing the risk of flooding and could fundamentally reshape the area without warning.
These are the discoveries of new research examining the impact of a large earthquake in the Cascadia subduction zone, from Northern California to Vancouver Island, Canada.
The study was published Monday in the journal Proceedings of the National Academy of Sciences and concluded that in the highest level of sinking or land sink seismic scenario, the area at risk of flooding would expand 116 square miles, swath, 2.5 times the size of San Francisco.
Such a scenario would more than double “exposure of floods on residents, structures and roads.” Authorities write that the future of “roads, bridges and bridge compromises” should be fought against lifelines and infrastructures that have been flooded or permanently flooded.
In other words, strong earthquakes in this sector will risk “a significant change in coastlines and severely affect coastal populations, infrastructure and ecosystems,” the study said. Unlike relative sea level rises, driven more slowly by climate change, the rise caused by major earthquakes “will occur within minutes and leave no time for adaptation or mitigation.”
According to the US Geological Survey, the last mega-coke in the Cascadia subduction zone occurred in 1700.
From California’s north coast to Washington, scientists say the next major earthquake (below 8 magnitude) could sink 1.6 to 6.6 feet of land.
Currently, more than 8,000 people live in the flood plains along the mouth of the Cascadia coast. However, if there is a high level of subsidence after an earthquake, the figure is nearly tripled and above 22,000, the study is calculated.
The resulting flood plains affected by Quake threatened almost 36,000 structures, up 168% from the current few digits.
Another 777 miles of roads are located in the new flood plain, almost tripling the total risk to a 1,212-mile road.
Flood plains are defined as areas where flooding is at least 1% of the time, according to the Federal Emergency Management Agency. These are areas where there is a possibility of at least a quarter of flooding during a 30-year mortgage. Flood insurance must be purchased by households and business owners in high-risk areas with federal regulations or mortgages from insured lenders.
Radiocarbon dating suggests that over 11 major earthquakes have occurred off the coast of California North Coast, Oregon and Washington over the past six to seven thousand years.
“Routine climate-driven sea level rise is not the only threat of flooding,” the study said. “The next great coastal sinking [Cascadia subduction zone] Earthquakes could “have a sudden, relative sea level rise of more than three feet more than expected.”
When discussing future megakokis in the Cascadia subduction zone, “We hear a lot about tsunamis and shaking, but for decades, subsidences that completely change earthquakes,” he said in an interview with Professor Tina Dura of Earth Sciences at Virginia Tech.
One estimate issued by FEMA is that a magnitude 9 earthquake along the full length of the 800-mile fault zone will kill 5,800 people from the earthquake alone. An additional 8,000 could die from the resulting tsunami, rise up to 80 feet, providing coastal areas along the 10-minute warning. Total economic losses could reach $134 billion.
This map shows the location of the Cascadia subduction zone.
(FEMA)
In 1700 years of Cascadia Megakoki, the oral history explains that its tsunami is sweeping over 50 feet of coastal villages. According to a US Geological Survey, only one of more than 600 survived in Annakura, a village now known as Vancouver Island.
The tsunami was so strong that we uprooted the trees. When it finally retreated, it turns out that Tretops is scattered with garbage and the hands and feet of the victim. The “ghost forest” of decayed trees found in the tidal wetlands and estuaries in the area is evidence that the land had sunk during the earthquake, causing the trees to own death, USGS said.
Scientists say the results of the latest research should be a wake-up call for residents and government officials considering reactive response. Dura already has a part of Route 101, which routinely falls into flooding during the very high king tides.
Scientists say that authorities should consider whether critical infrastructure, such as airports, falls under the earthquake spreading plain.
Authorities may also want to consider considering infrastructure for buildings such as schools, fire departments and wastewater treatment plants that “what we have shown is likely to become flood plains,” Dura said.
Research shows that prominent areas at risk of land sinking following megacaulking along the Cascadia subduction zone include:
The Humboldt Bay area of California, including the surrounding areas of Oregon, Waldport and Bayshore along Alcea Bay. Newport and South Beach along Yaquina Bay. Willapa Bay area, which includes Gearheart and Seaside along the Nekanicum River, including communities in Washington, Long Beach, Ocean Park, Talkland and Raymond. Glaze Harbor area, including Ocean Shore, Westport and Aberdeen.
Traditionally, scientists and government officials have focused on climate-driven sea level rise, calculating the expected increased risk of coastal flooding. However, the study argues that ignoring the role of major earthquakes is myopic.
“Earthquake-driven coastal subsidence after a recent historic earthquake has had serious consequences for the community, leading to permanent land loss, infrastructure damage and forced relocation,” the study states.
One example was the 2011 magnitude 9.1 earthquake off the east coast of Japan, where some land sank up to three feet. News reports show that the sinking land was forced to fight regular flooding.
Another magnitude 9.1 earthquake struck near Sumatra, Indonesia in 2004, causing land subsidence of up to three feet. Areas used for aquaculture suffer from chronic tide flooding, leading to oversulination and land loss, the study says.
The 1964 magnitude 9.2 Alaska earthquake caused more than six feet of land along the coast to sink. In some places, the subsidence was even more severe.
Before the 1964 size 9.2 earthquake in Alaska, the sidewalk in front of the store on the right of this photo in Anchorage was levelled with the one on the left.
And the 1960 Chilean 9.5 earthquake caused up to eight feet of coastal subsidence, “submerging coastal pine forests and farms forever, converting them into intertidal marsh, flooding coastal towns and forcing residents to abandon their homes.
In addition to Dura, the study has 19 other co-authors. University of Oregon; Rowan University; University of North Carolina; Durham University; USGS; Cal Poly Humboldt; Oregon Department of Geology and Mining. University of Hong Kong. Nanyang University of Technology in Singapore.
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