Geology and Tectonics Geology How do we know the age of the seafloor? Why is the seafloor so recent and the continental crust so old? Where do we find the oldest continental rocks and the oldest seafloor?
What are the different types of rocks? What is a fossil and what are they used for? What are hydrothermal vents, and why do we find them along mid-ocean ridges? Seismology What is a seismic wave? What is the difference between body waves and surface waves, and between P-waves and S-waves?
Why can't S-waves travel through liquids? How far can seismic waves reach? Why do P-waves travel faster than S-waves? Why is the interior of the Earth hot? What is the magnetic field of the Earth? Earthquakes and Faults Why do tectonic plates move? Using satellite observations French researchers led by Anne Socquet from the University of Grenoble arrived at a similar conclusion.
How can this happen? Currently, there are two preliminary explanations. One reason is that the Palu-Koro Fault, which runs north-south through the densely populated city of more than , inhabitants and which ruptured for about miles during the quake, is extremely straight.
It has no bends or small jumps. Hence, like a car can travel much faster on a straight freeway than on a curvy highway in the country, the rupture may picked up its speed along the very straight fault line.
Another possible cause for the high speed quake rupture may have to do with the friction along this straight section of the fault. The friction, or the resistance to rapid movement, seems to have been rather low, hence there was less loss of initial tectonic energy during the rupture propagation. The causal observer may rightly ask, why does it matter how fast earthquake ruptures race through the country side.
Isn't of purely academic interest to determine whether quakes break the speed limit? Well, not really, as the comparison to a real world car crash shows. If a car crashes into a wall at low speed, say ten miles an hour, the vehicle may suffer only superficial damage. Many open cracks in the earth, set off from the main fault, were observed and thought to be the work of a supershear shock wave. Das says that these cracks could be used as a "diagnostic tool" to look for further evidence of supershear earthquakes.
Her analysis is detailed in the Aug. To get a supershear quake you need a very long, straight section of a strike-slip fault one in which the two sides of the fault slide past one another, instead of under or over each other to rupture because, as Das puts it, "earthquakes are like cars.
Seismic waves travel pretty fast. There are three physically different types of waves - P , S , and L. The velocity depends on which type of wave and what part of the earth you are in - crust , mantle , core. The figures and table tell you how long it will take the P-waves from this quake to travel different distances. Note that these are essentially spherical wavefronts, since the waves travel out at constant velocities in all directions.
There is another map on the same page for times around the world, and a table with the same information. We'll have to return to this topic at some point for a larger quake to understand the nature of the shadow zone. Posted by Rob Sternberg at AM. Labels: Lancaster , travel times , velocity. No comments:.
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