This Monday, September 19, Mexico was hit by a new and powerful earthquake, which notably caused a seismic crisis further north, in California. The effects of this earthquake were also seen right in the middle of the Death Valley desert region, generating a tsunami in a flooded cave.
On Monday, September 19, Mexico was shaken by a violent earthquake of magnitude 7.6. this event is it happened on the same date than two previous earthquakes, which killed many people in 1985 and more recently in 2017.
For three days, several aftershocks have been felt in Mexico City, including a particularly strong one on Thursday, with a magnitude of 6.9. But this seismic activity has also spread further north, especially in California. The coast and also the interior have been seized by tremors in recent days. Twenty-five earthquakes struck the Sacramento area in 24 hours. However, the power of this seismic swarm remains low, with no impact on the population.
A region under strong tectonic constraints
The occurrence of such tremors is not surprising for the region of the west coast of the North American continent, which is located at the interface between various tectonic plates. The west coast of Mexico is, in effect, the scene of the confrontation between three different plates: the Cocos and Rivera plates, which both pass under subduction under the North American plate. Diving under the North American continent at the level of Mexico, the two small plates they generate enormous compressive stresses that are periodically released in the form of earthquakes, sometimes very violent and capable of producing tsunamis. This Monday, September 19, it is this mechanism that caused the earthquake that was felt in Mexico City.
To the north, we switch to a confrontation between the North American and Pacific plates. Here, there is no subduction, but a long shear zone. This is the well-known San Andreas Fault. The two tectonic blocks move on either side of this plate boundary on the order of 4 cm/year, again causing large earthquakes.
The shadow of the Big One hangs ever
With the entire region under enormous tectonic stress, an earthquake in Mexico could very well cause destabilization further north. And this new seismic crisis that is hitting California undoubtedly arouses fear of the Big One, this terrible earthquake that the population is preparing to experience from one day to the next.
But the earthquake in Mexico had another surprising effect. When the ground began to shake in Mexico City, officials from the Death Valley National Park noticed a strange phenomenon, about 3,000 kilometers from the epicenterin the heart of this desert region of California.
A tsunami in the desert, 3,000 kilometers from the epicenter
While investigating a water-filled cave called Devils Hole, they witnessed an abnormal movement of water, which quickly turned into large waves hitting the edges of the abyss. This effect, called “seiche”, is directly related to the earthquake in Mexico and can be compared to a true “tsunami in the desert”, according to a park employee.
The Mexico earthquake has caused waves in California’s Death Valley. © BNO News, YouTube
This is not the first time the phenomenon has been observed in Devils Hole. Previous very powerful earthquakes that have occurred in Japan, Indonesia and Chile have each time caused movements, more or less marked, of the water surface, while observers do not feel any tremor. This cave seems to be a real indicator of the earthquakes that are taking place in the world.
The seiche phenomenon is usually observed in closed basins and is defined by the generation of standing waves under the effect of seismic tremors, wind or variations in atmospheric pressure. This type of oscillation produced by the imbalance of the water mass can last a long time, sometimes several hours, after the cessation of the disturbance.