A recently identified fault line, spanning about 45 miles, poses a tsunami risk to over a million northeastern US residents. Situated in British Columbia, Canada, the fault's unnoticed existence for millennia raises concerns about a potential large earthquake and subsequent tsunami affecting the Georgia Basin, including parts of Washington and British Columbia.
The discovery reported in the paper, titled "Discovery of an Active Forearc Fault in an Urban Region: Holocene Rupture on the XEOLXELEK-Elk Lake Fault, Victoria, British Columbia, Canada" published in the journal Tectonics, involved researchers such as Nick Harrichhausen from the Université Grenoble Alpes in France.
A picture taken in Chipiona, southern Spain, on November 6, 2023 shows a sign in the street showing the direction to go in case of a tsunami during an annual tsunami drill.
XELF Fault: Past Earthquake Points to Possible Tsunami Threat in the Pacific Northwest
Harrichhausen and his team uncovered evidence of a significant earthquake originating from the XEOLXELEK-Elk Lake Fault (XELF) thousands of years ago, suggesting the potential for a recurrence. The XELF, categorized as a 'dip-slip' fault, raises concerns about the possibility of a local tsunami in the Georgia Basin, impacting cities in both the United States and Canada.
Given its history, indicating seismic activity between 4,700 and 2,300 years ago, predicting the timeline for the next event is challenging and necessitates an understanding of past earthquake recurrence intervals. Harrichhausen advocates for preparedness in the face of the Pacific Northwest's extensive fault lines, emphasizing the importance of having essential supplies readily available.
Named XELF, the fault traverses the Saanich Peninsula diagonally and holds the potential to extend its impact to the United States, particularly affecting the northern Puget Sound area. The study's limitations, driven by the requirement for two separate earthquakes to estimate intervals, underscore the ongoing need for research to comprehend the hazard posed by the fault.
By delving into the fault through trench excavation, Harrichhausen and his team utilized changes in magnetic fields to identify signs of past earthquakes. The slip-dip fault altered the landscape within the last 12,000 years, with a likely timeframe between 4,700 and 2,300 years ago.
The 'dip-slip' nature of the XELF, involving vertical movement of rock blocks, raises the risk of damaging earthquakes and potential tsunamis in urban areas. This highlights the importance of understanding and preparing for the geological threat posed by the XEOLXELEK-Elk Lake Fault.
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How Do Some Earthquakes Lead to Tsunamis?
The most devastating tsunamis typically result from large, shallow earthquakes situated near or on the ocean floor, particularly in regions marked by tectonic subduction along plate boundaries. These areas experience heightened seismic activity due to the collision of tectonic plates.
As these plates shift against each other, significant earthquakes occur, causing substantial displacement of the ocean floor, ranging from a few kilometers to over 1,000 km. The abrupt vertical movements disturb the ocean's surface, displacing water and creating destructive tsunami waves.
These waves can traverse extensive distances, causing havoc along their path. For instance, the 1960 Chilean tsunami, generated by a magnitude 9.5 earthquake with a rupture zone exceeding 1,000 km, inflicted damage not only in Chile but also reached Hawaii, Japan, and other Pacific regions.
It's important to note that not all earthquakes trigger tsunamis, typically requiring a Richter magnitude surpassing 7.5 for significant tsunami generation. The majority of tsunamis, over 80%, occur in the Pacific along its Ring of Fire subduction zones, where great earthquakes with vertical slip disturbances can generate tsunamis that propagate in all directions.
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