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Mandarin Chinese Language for beginners | Beginner Chinese 2.11: Rivers (2021)-海外双语妈咪

Three Gorges Dam creating triggered earthquake threat

This picture shows the massive Three Gorges Dam in China, which holds back a reservoir on the Yangtze River far larger than any other dam on the planet Earth. The dam was constructed a decade ago and water has sat in the huge reservoir behind the dam for nearly a decade. Newly published science shows that this reservoir triggered an earthquake of magnitude 5 in 2013 on a fault capable of producing still larger quakes.

Water is a key ingredient in faults. Water is incompressible and a fluid, so if water feels pressure on one side, it exerts that pressure in all three directions. If water seeps into a fault that is locked by rocks being squeezed on both sides, the water will push back against the pressure on a fault, reducing the friction on a fault and potentially allowing it to break.

The Three Gorges Dam was constructed in an area of fairly low seismicity. The Yangtze River has slowly carved gorges into the surrounding country, with no major faults crossing the river’s path. Prior to construction of the dam the area was scouted for issues that could prove a seismic hazard to the dam itself, but the area was declared safe due to the lack of activity in the area to be flooded.

As the dam was filled, there were small sequences of earthquakes observed that were likely related to the dam. These quakes shouldn’t be surprising, as putting that much weight on the crust would shift stresses in the entire area and trigger small earthquakes. However, in 2013, a quake with a moment magnitude of 5.1 occurred on a strike slip fault beneath the reservoir. This quake was part of a larger sequence of smaller quakes, which allowed a global team of scientists to map out the extent of the fault by mapping the location of the quakes.

To stress; this fault is unrelated to the systems that caused major, damaging quakes in China over the last decade. There was no link between the Three Gorges Reservoir and quakes like the 2008 Sichuan quake, which killed nearly a hundred thousand people. There was similarly no link between this reservoir and other major quakes since then. However, that this reservoir is unrelated to those quakes does not mean that there is no threat.

This fault is a small but dangerous fault, stretching at least 15 kilometers within a Triassic aged limestone formation. That fault has been inactive in modern times, but it hits the Three Gorges Reservoir and the high water in this reservoir is pushing water into the fault plane. That water was enough to reduce the stress on the fault, and the stress in the crust was enough to cause that magnitude 5 earthquake.

If the full fault ruptured, a fault of that length has the ability to produce magnitude 7+ earthquakes. The scientists cannot assess whether or not this will happen because there is no historic data on this fault, it may never produce anything larger than the 2013 quake. However, the dam itself was built with the ability to withstand the shaking of magnitude 7 earthquakes. A quake that ruptured this full fault could potentially cause enough shaking at the surface to put the dam itself in danger. Tens of millions of people live along the Yangtze River downstream of this dam, including the city of Shanghai.

According to the scientists, this fault was not identified during the survey prior to construction of the dam, highlighting the importance of doing good field geology before major construction projects. At this point, all that can be done is to monitor this fault, to gather more data that will allow better estimates of how it will behave in the future.

-JBB

Image credit: https://commons.wikimedia.org/wiki/File:ThreeGorgesDam-China2009.jpg

Original paper: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL077639

A heat wave from space

This image comes from the Thermal Infrared Sensor instrument on the new Landsat 8 satellite. It shows the city of Shanghai in infrared light. By observing land in these light wavelengths, different temperatures stand out. Brighter yellow colors are hotspots up to 40°C, darker red or maroon colors are cooler but still mostly above 30°C, and the blue dots are clouds. The Yangtze River also stands out.

Just prior to this photo being taken, much of China was gripped by severe heat, including Shanghai itself hitting its all time record high of 40.8° Celsius (105.4°F) on August 7th, 2013. That was the 3rd time during this heat wave that the city set its all-time high temperature.

Also in this image you can recognize the “Urban heat island effect”, where cities tend to be warmer than the surrounding countryside because structures, roofs, and roads tend to absorb sunlight and do not cool off as much during the night as open spaces or vegetated areas. Even individual structures or complexes stand out in heat compared to the areas around them, particularly downtown and near the river.

-JBB

Image credit: NASA Earth Observatory images by Jesse Allen, using Landsat data from the U.S. Geological Survey http://earthobservatory.nasa.gov/IOTD/view.php?id=81870&src=twitter-iotd

Press report on heat wave and bacon-frying http://phys.org/news/2013-08-bacon-fries-pavement-china.html

[DISCUSSION] Growling Tiger, Roaring Dragon 虎啸龙吟, episodes 23-27 (2017-18)

tl; dr Cao Pi died over twenty episodes ago, but it’s all his fault.

Evidently, the second half is proving a lot more consistently engaging than the first—I think it’s clear that this production is a lot better at handling court politics than military tactics. Though this stretch of episodes is technically the “intermediate” between the two main arcs of the second installment (ending Zhuge…

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