Geoscientists usually work with lines, planes and their angular relationships. Studying these relationships requires some techniques to put real 3D features into simple 2D visualizations. We don’t always need to design super complex 3D models just to figure out the angle between two planes, right?
This is why the Stereographic Projection and the Stereonets became so important to geologists. This projection is fast and efficient when we just want to analyze angular relationships. It does not preserve distances or areas of the features that are projected in it, just angles.
For today’s examples I will assume you already understand how a stereonet works and are familiar with:
- strike and dip / plunge and bearing;
- poles and planes
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The surface of our planet varies greatly in altitude. In fact about ¾ are covered by seawater, whose average level has been conventionally chosen as a reference for the surface elevations. The statistical analysis of the elevations of the earth’s surface shows us something interesting: the highest percentage of the elevations is around two particular values that are the average level of the ocean floor (about -3790) and the average level of the emerged lands (about 840 m).
On the relative graph of the percentage distribution of the areas with respect to the altitudes, called “hypsographic curve”, it can be noted that the portions of surface that reach the minimum altitudes (about -11000 m of the Mariana Trench) and the maximum ones (8850 m of Mount Everest) are a very small fraction of the total.
In a nutshell, the mountain ranges are almost an exception, as are the oceanic trenches, on the surface of the Earth. They appear in so-called belts, which are considerably more developed in one direction than in the other. But what is it that keeps them standing at such exceptional altitudes compared to most of the land above ground?
A bit of a big headline. I’ll explain the earthquakes. Who do I think I am? Well… I’m a geologist. I know the problem. If you want to know about heart attacks, you ask a cardiologist, right? If you lose your tap, you call the plumber, not the cardiologist. Or am I wrong? Geologists know about earthquakes. They have to. It’s a must. Even if they’re not going to deal with earthquakes in their career, they must be familiar with the phenomenon. So, by academic background geologists know very well that earthquakes are an entirely natural phenomenon over which man has no influence. It is due to the fact that the Earth’s lithosphere (the most superficial rocky envelope of the planet) is divided into a series of plates and microplates; most of the earthquakes are distributed along their margins because the plates move one with respect to the other. And huge blocks of rock “rubbing” each other make a big mess. The “mess” are earthquakes: rock breaks, and the energy released at the moment of breaking propagates in all directions in the form of seismic waves, oscillations of the rocky body that also involve the surface on which we live. They are waves completely similar to those generated by a rock thrown into the water (but they are not only those – it’s just to give an idea).
Rome has been hit by earthquakes in the past. There is also evidence on monuments, starting from the Colosseum, as well as evidence of the period. On a general level, I wouldn’t worry much about the “if”. Italy is a seismic zone, nothing much can be done about it. And earthquakes are a natural, inevitable phenomenon. I became a geologist with a thesis on geological structures in the immediate vicinity of Rome. The idea of the supervisor started from morphological features (linear “engravings” visible from satellite – there was no Google Earth to help us) that in the north-south direction seemed to affect the area of Italy’s capital. The question was: do they correspond to seismogenetic structures, i.e. capable of generating earthquakes? So we looked for traces of similar faults on the ground… and found them.
Fifty years after Apollo 11 astronauts deployed the first seismometer on the surface of the Moon, NASA InSight’s seismic experiment transmits data giving researchers the opportunity to compare marsquakes to moon and earthquakes.
Seismologists operating the Marsquake Service at ETH Zurich literally rocked and rolled as they experienced, for the first time, two “marsquakes” in the university’s quake simulator. Researchers uploaded actual data from marsquakes detected on Martian solar day or Sol 128 and 173.The marsquakes were detected by the SEIS seismometer, whose highly sensitive electronics were delivered by the Aerospace Electronics and Instruments laboratory at ETH.