Is there earthquake weather?
In more recent times, people have thought, for example, that earthquakes are more likely when it is hot and dry due to the seemingly frequent co-occurrence of such conditions, particularly in California, Hough says. For the most part, these studies have not held up under scientific scrutiny, and earthquake researchers have set them aside as intriguing but unfounded ideas.
But in the last decade, new efforts to identify effects of weather-related, or in some cases climate-related, processes on seismicity have drawn new interest.
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And then there are the two most recent contributions looking at links with the South Asian monsoon and wet tropical cyclones. Each of these modern efforts has made use of increasingly sensitive instrumentation capable of recording subtle seismic signals and crustal movements that were once beyond detection. Monsoon Triggering in the Himalayas One location where researchers have compiled a record of seismicity and ground motion in the last couple of decades is northern India and Nepal.
Where the northward-bound Indian Plate collides with and subducts below the Eurasian Plate at a rate of about 20 millimeters per year, roughly 2, earthquakes occur annually along the Main Himalayan Thrust MHT Fault.
Thanks to the Himalayas, much of the Indian subcontinent is also deluged under a meter or more of rain each year during the annual summer monsoon. The mountains deflect moisture-laden air coming ashore from the Indian Ocean upward into the atmosphere, causing water vapor to cool, condense and precipitate.
The seismicity and monsoonal trends also coincide with small but significant north-south ground motions, which the group has measured using GPS instruments installed above the MHT in Nepal. Their hypothesis is that the tremendous excess of monsoonal rainwater that collects on the Indian Plate — which has been measured by the Gravity Recovery and Climate Experiment GRACE spacecraft — weighs it down enough to pull it away from the Eurasian Plate slightly, temporarily relieving a small portion of the stress mounting on the MHT.
Is there earthquake weather?
As the rainwater drains away and evaporates in the dry winter season, the plate rebounds and tension on the fault is increased, triggering more earthquakes. So far, the group has found no other explanation for the observed seismicity patterns. The monsoon and the tides both place periodic loads on the MHT, adding a roughly fixed amount of stress at regular intervals.
But whereas changes in earthquake frequency correspond with the monsoon, which lasts several months and occurs annually, there is no such correlation in their data with Earth tides, which oscillate back-and-forth twice a day. The apparent dependence of seismicity along the MHT on the duration of loading is one among a number of complexities that Ader and his collaborators are attempting to simulate with computer models in an effort to improve the understanding of earthquake physics.
They found that during the last 35 years, erosion rates were about 6 millimeters per year — far surpassing longer historical averages and possibly due to the rampant deforestation of the mountains. Much of this resulting sediment accumulated over time in the nearby Momance River Delta.
The heavy rains ofthey suggested, caused myriad landslides and even more rapid erosion — between 20 and 25 millimeters per year — and were strong enough to transport much of the accumulated sediment offshore and out of the delta.
Although the pieces fit together, it was only one example of a multistep process involving heavy rains leading to landslides, erosion and mass transport and, eventually, removal of enough stress off a fault to trigger it to rupture.
They found those ingredients in Taiwan. In the paper, Liu and his colleagues provided convincing evidence for a link between typhoons barrelling across Taiwan and the timing of small earthquakes beneath the island. Their take on the connection is that the reduced atmospheric pressure that characterises these powerful Pacific equivalents of hurricanes is sufficient to allow earthquake faults deep within the crust to move more easily and release accumulated strain.
Perhaps even more astonishingly, Liu and his team proposed that storms might act as safety valves, repeatedly short-circuiting the buildup of dangerous levels of strain that otherwise could eventually instigate large, destructive earthquakes.
This might explain, the researchers say, why the contact between the Eurasian and Philippine Sea tectonic plates, in the vicinity of Taiwan, has far less in the way of major quakes than further north where the plate boundary swings past Japan.
In a similar vein, it seems that the huge volume of rain dumped by tropical cyclones, leading to severe flooding, may also be linked to earthquakes.Secrets Of The Earth: Hoover Dam Causes Quakes
It is possible that floodwaters are lubricating fault planes, but Wdowinski has another explanation. He thinks that the erosion of landslides caused by the torrential rains acts to reduce the weight on any fault below, allowing it to move more easily.
It has been known for some time that rainfall also influences the pattern of earthquake activity in the Himalayas, where the Nepal earthquake took close to 9, lives, and where the threat of future devastating quakes is very high. During the summer monsoon season, prodigious quantities of rain soak into the lowlands of the Indo-Gangetic plain, immediately to the south of the mountain range, which then slowly drains away over the next few months.
This annual rainwater loading and unloading of the crust is mirrored by the level of earthquake activity, which is significantly lower during the summer months than during the winter. Hurricanes, typhoons and cyclones can also affect the timing of earthquakes in mountainous tropical areas, found Shimon Wdowinski, a geophysicist at the University of Miami in Florida who, along with a colleague, analyzed data from the last 50 years of earthquakes in Haiti and Taiwan.
Eighty-five percent of quakes that were magnitude 6 or higher happened within the first four years after excessively wet storms, Wdowinski and a colleague found.
Can severe weather trigger earthquakes?
That rate of trembling is five times higher than what overall trends would predict. For earthquakes that were magnitude 5 or higher, 35 percent of them happened in the first four years after the wettest storms, which was double the expected rate.
In Januaryfor example, a catastrophic earthquake shook Haiti—about 18 months after the island was hit by a severe hurricane season that included two tropical storms and two hurricanes. One large earthquake struck there infor example, three years after a typhoon caused major damage and flooding.
Another quake hit the region inseven months after a cyclone dropped more than inches of rain in just five days.