2023-06-10 11:46:29
IFor example, it is possible that the prolonged drought in southern California will also cause severe earthquake in the golden state has dried up? A research group from San Diego now suspects this after examining the southernmost foothills of the famous San Andreas Fault. The researchers found that severe earthquakes always occurred there when the Salton Sea and its geological predecessor experienced intense flooding.
The San Andreas Fault is a nearly 1,300-kilometer long geological demarcation that extends from the extreme north California’s to the Imperial Valley just before the Mexican border. Several catastrophic earthquakes have occurred along the northern and central portions of this fault over the past 170 years, including San Francisco in 1906.
In contrast, in the southern section, which extends from the level of Los Angeles to almost the state border, it has been remarkably seismically quiet over the past 300 years. And from the last known strong earthquake, which took place there in about 1726, only a few historical records survive.
Like patterns on wallpaper
The research group led by Ryley Hill from the University of California in San Diego has now investigated why there has been no significant earthquake in the southern section of the fault for so long. Among other things, they evaluated the results of trenches that geologists had dug in several places across the earthquake fault.
The ground movements triggered by previous earthquakes can often be read off the walls of such narrow ditches like a pattern on wallpaper. According to these analyses, there have been at least five major earthquakes in this area of Southern California in the past 1000 years.
At the same time, the researchers used other measurement data showing the historical water levels of the Salton Sea and its predecessor, Lake Cahuilla. Although the Imperial Valley landscape has a desert climate, there is always a large lake there. It was created in geological time because the Colorado, which normally flows further east, flooded the area again and again in its meanders.
The current Salton Sea was formed there about 100 years ago when one of the dikes of an irrigation canal broke and the water spilled into the Imperial Valley for more than two years.
High water levels correlate with earthquakes
When comparing the two sets of data, it turned out that the severe earthquakes always occurred when the lake had the highest water levels for several years. However, in the almost 300 years that have passed since the last tremor, the water level has always been low and there have been no earthquakes worth mentioning.
In fact, there can be a physical relationship between water levels and geological conditions in an earthquake fault. If the water level is high, the associated increased hydrostatic pressure in the groundwater counteracts the frictional force that holds the two flanks of a fault together.
If the mechanical stress accumulated in the fault is still large enough, it can be discharged in an earthquake due to the reduced friction. On the other hand, when the water level is low and the hydrostatic pressure is lower, a greater force is required to trigger an earthquake.
The researchers now want to investigate whether there are similar connections between low water and the reduced occurrence of earthquakes at other earthquake faults around the world.
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