In January 2010 collapse Northern Pakistan has blocked one of the rivers. If this natural dam breaks, the water of the lake temporary bridge will be demolished and the flood of people downstream. (Image of Jesse Allen, Robert Simmon / NASA Earth Observatory.)
March 22, 2013. Large landslides have a characteristic seismic handwriting, enabling engineers to evaluate their size, duration and even the distance traveled by them, says a new study.
This conclusion is particularly valuable in the detection and description of landslides that occur on steep slopes in maloobitaemyh areas because landslides can dam the river, and thereby create a large lake. Breaking such a dam flooded populous areas downstream.
Seismometers and similar equipment recorded the movement of the earth at all frequencies, but seismologists usually pay attention only to those who point to the earthquake. The waves produced by a push or explosion (during mining or underground nuclear tests), seen very well, says seismologist Goran Ekstrom from Terrestrial Observatory Lamont — Doherty (USA). A low-frequency waves generated by large landslides, sometimes hard to see the confusion of the seismic terrestrial cortex.
27 of the 29 largest in the world landslides from 1980 to 2012 (including the strongest — collapse, caused eruption of Mount St. Helens in May 1980) were registered seismometric equipment, part of a worldwide network. Seismic vibrations produced by the other two, clearly visible in the data collected by the regional networks, said Mr. Ekstrom.
When he and his colleague Colin Stark analyzed information about all of these landslides, it was evident that certain characteristics of landslides can be drawn from the information on the movement of soil, that is, in the same way that experts estimate the strength of earthquakes and the direction in which the sides of the fault zone slid relative to each other. For example, when a stone falling from the slope of the mountain, the peak becomes easier, that is, in accordance with Newton's laws of motion, as if the mountain jumps and pulls away from the rockfall, producing such fluctuations in the earth's crust, by which to judge the size of the collapse and its direction, explains Mr. Ekstrom.
See also: Landslide lake in Pakistan. Photo
Subsequent tremors reveal new aspects of the landslide: how long it lasted, how far was and what type of terrain. Mr. Ekstrom gives the following example: In some cases, land and stones fall on glaciers, and almost without experiencing friction, slip a few kilometers across the ice. Because of this, the seismic vibrations are almost not made until the material runs into the opposite slope of the valley.
Thus, researchers can finally reconstruct strong landslides that still seemed impossible. Thus, the analysis and Stark Ekström showed that landslide near the glacier Siachen on the border of India and Pakistan in September 2010, he was a seven landslides that occurred during the four days. A geologist, later revealed to be in the wrong place, would have considered it a landslide (maximum — two), said Mr. Ekstrom.