The Earth Story

A geophysicist in the 1970s doing a geophysical survey of the border between Finland and Norway discovered that Finland’s highest elevation point was on a slope directly on the border - and the peak of that mountain was actually just a couple meters across the border in Norway. He then proposed the idea of having Norway agree to give Finland this mountain peak as a present, eventually walking across all of Norway to lobby to give them the mountain and settling on 1917, the 100th anniversary of Finland’s founding as a nation. That would give Finland a new highest point and a new mountain. Once the idea was around, they began having to figure out how to actually go about legally making this plan happen - how do you convince a country to give up a mountain?

This is as good of a follow-up to that last article on plumes as I can find. 

Strange Seismic

On Wednesday 12th of August, explosions occurred in Tianjin, China. These explosions were felt several kilometres away; with the first explosion equivalent to detonating 3000Kg of TNT, and the second equivalent to 21,000Kg TNT. What some people are latching onto and considering odd is the fact these explosions were seen on seismographs. The first explosion was 2.3 magnitude and the second 2.9 magnitude (equivalent to 2 minor earthquakes).

The Moment Magnitude scale is usually used to quantify the size of earthquakes, and thus the energy given off by them. Earthquakes produce seismic waves that travel through and around the Earth and are recorded using seismometers. However, it is not just earthquakes that release energy in the form of waves (though these do account for over 90% of seismic events). Seismometers are so sensitive now that they’ll detect energy given off from mining blasts, explosions such as at Tianjin, and even from wind and traffic. The seismic background level of an individual seismometer is shown due to these small occurrences such as weather, ocean waves and traffic. However, to tell a seismic event such as an earthquake (or in this case as an explosion), it must be registered on several different seismometers.

By using more than three seismographic recordings of an event, the location of the seismic event can be triangulated. Using a seismogram, geophysicists can work out how far away the wave had travelled from, and use this information to create a ring around the seismometer of potential start zones of the waves. When this ring is combined with rings around other seismometers of the same one event, they will overlap at one point, which marks the epicentre of the earthquake or seismic event.

~SA Image: http://bit.ly/1IYvAlB Seismic use in tracking explosions: http://bit.ly/1Jc4nuQ

Every geologist, geochemist, and geophysicist will just about agree with this one. Found here.