A 7.0 magnitude earthquake struck Northern California, raising initial concerns about a possible tsunami along the coasts of the State and Oregon.
The quake, classified as shallow, occurred along the Mendocino fault zone, characterized by horizontal rather than vertical movements, as explained by geologist Pat Abbott from San Diego State University.
This type of movement makes the generation of large waves less likely, but the earthquake’s magnitude was sufficient to justify the immediate issuance of a warning.
The dynamics of the Mendocino fault zone
The affected region is known for its transform faults, where tectonic plates move laterally relative to each other.
Such faults, although active, are less prone to producing significant vertical displacements of the seabed, which are the main cause of devastating tsunamis.
However, the Mendocino fault zone is historically active: in the past hundred years, the USGS (United States Geological Survey) has recorded at least 40 earthquakes of magnitude 6.0 or higher in the same area.
Despite the limited risk, the quake generated a small tsunami with a maximum height of just 2 inches, insufficient to cause significant damage.
This episode stands in stark contrast to the more severe tsunami caused by the volcanic eruption in Tonga in 2022, when waves several meters high reached the coast of California, causing significant damage.
Tsunami warning: an essential measure
The tsunami warning issued immediately after the earthquake was based on the magnitude and location of the quake, near the coast. Authorities could not rule out a significant risk in the minutes immediately following the event.
Once the absence of a serious threat was confirmed, the warning was lifted.
The decision to activate the warning promptly highlights the importance of rapid assessment of seismic data.
In events like the one in Northern California, the time available to react is minimal: waves from a potential tsunami generated a few miles from the coast could impact inhabited areas within minutes, leaving little room for preventive evacuations.
The danger of the Cascadia subduction zone
Compared to the Mendocino fault zone, the Cascadia Subduction Zone represents a much higher danger.
This geological system, which extends from Northern California to British Columbia, is known for its ability to produce catastrophic earthquakes.
Here, one tectonic plate is pushed under another, generating powerful vertical displacements of the seabed. A similar event occurred in 1700, with an estimated magnitude of 9.0, triggering a devastating tsunami that hit both the west coast of the United States and Japan.
If an earthquake of this magnitude were to occur today, the impact would be devastating, with potential waves several meters high that could hit the coasts of California, Oregon, and Washington in a short time.
Such events highlight the need for advanced warning systems and adequate preparation by authorities and coastal populations.
The warning from past events
Thursday’s episode provided an opportunity to test the effectiveness of emergency protocols and warning systems.
Although the event did not cause damage, it serves as a reminder of the vulnerability of coastal regions to seismic events and tsunamis.
Situations like the Sendai earthquake in 2011, which devastated Japan, and the eruption in Tonga in 2022, demonstrate how a rapid response can make a difference. In the case of the earthquake in California, the close proximity of the quake to the coast would have reduced the arrival time of a hypothetical tsunami to a few minutes, an extremely short window compared to major events in the Pacific, which can take 8 to 12 hours to reach the mainland.
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