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35

Adding a little bit of practical data to the above answer about the Gutenberg-Richter relationship, here is a plot of the per-year cumulative probability of earthquakes in a particular province in Japan, based on observed frequencies over many hundreds of years: Source: http://topo.earth.chiba-u.jp/afr/backnumber/no24/24%E5%8F%B702kumamoto.pdf The ...


33

We know the the size of the inner core through seismology. From my answer to this question: How are subsurface wave speeds determined without subsurface sensors?, we can determine the speeds of the different layers of earth. Pictured below is a diagram of raypaths going through the earth from the 1994 Northridge Earthquake in Southern California: (image ...


32

Magnitude 10 earthquakes are indeed possible, but very very unlikely. You see the frequency of an Earthquake is given by the Gutenberg-Richter law: $$N = 10^{a-bM}$$ where $N$ is the number of earthquakes $\ge M (magnitude)$ and $a,b$ are constants. As you can see, the greater $M$ is, the less $N$ is. $a,b$ are generally solved for statistically, through ...


32

Are magnitude 10 earthquakes possible? The idea of a “Mega-Quake” – an earthquake of magnitude 10 or larger – while theoretically possible—is very highly unlikely. Earthquake magnitude is based in part on the length of faults -- the longer the fault, the larger the earthquake. The simple truth is that there are no known faults capable of ...


28

The simple answer is that you can't drill to 50 km depth. The deepest holes ever drilled were to a little more than 12 km, one is named the Kola Superdeep Borehole in Russia, which was a scientific drilling project. The very few others were oil exploration boreholes. Drilling that deep is extremely expensive and hard. If you go and ask anyone who ever ...


26

10 seconds is a worthwhile warning time. The Japanese use it to switch off compressors on gas lines (or open release valves on them), emergency break bullet trains, and in particular shut down nuclear power plants, all in anticipation of a power loss moments later. In the case of Japan, however, the warning time doesn't come from having deep sensors, but ...


25

Ground motion results due to passage of elastic waves. Now there are different kinds of waves, e.g., P waves, S waves, surface waves, etc. Most of the shaking (and therefore damage) is caused by surface waves. So if you are in a deep cave or mine then the amount of shaking you might experience can be much lower than on the surface. This of course assumes ...


20

There are two important ways to recognize different types of waves in seismic records: Their velocity. These waves travel at different speeds: P-waves are fastest, then S-waves, then Love waves, then Rayleigh. Since seismic recordings are measures of earth displacement, particle velocity, or water pressure over elapsed time, this means the waves show up at ...


20

It's not too too likely, but it can happen. A few earthquakes have either been attributed to fracking, or the wastewater produced from fracking. According to the USGS (for more information, visit that page): Many questions have been raised about whether hydraulic fracturing — commonly known as “fracking”— is responsible for the recent increase of ...


20

Earthquake prediction really is a contentious issue, especially after the l'Aqula trials. However, let me try to elaborate how predictions might be possible in the future and what is inhibiting this development. We do have some understanding of earthquakes and rupture mechanisms. However, for prediction in a scale of hours (sufficient for evacuation), we ...


19

Perhaps this is not what you had in mind, but it seems to be generally agreed that the Chicxulub asteroid impact generated earthquakes in excess of magnitude 10.


17

In simplest terms, it simply means that: if the source signal is shifted by some amount of time Δt, but otherwise unchanged, then the seismogram will also be shifted by Δt, but otherwise unchanged; and the seismogram generated by the sum of two (or more) source signals is the sum of the seismograms that would've been generated by each of the ...


17

You ask what we should change to better predict earthquakes, and I'd think almost everything. As geophysicists we might know the what of earthquake detonation, but are relatively blind at the how. There is a strong group of scientists who feel that single event prediction is NOT a realistic goal, and may perhaps be impossible. Some good guesses as to why ...


17

There are three main types of waves produced during an earthquake: P, S, and L waves, which stands for Primary, Secondary, and Love. (There was a mnemonic I read many years ago that went P=pressure, S=Shear, and L=Long.) The P and S waves are body waves. That is, they propagate inside the earth. The P wave is basically a sound wave; as the mnemonic goes, a ...


16

P and S waves are fundamentally different, when it comes to properties of the wave. An example might be that P waves can travel through fluids while S waves cannot. However, when it comes down to wave theory, these two are just different polarizations of a mechanical wave. Seismology In seismics this concept may be puzzling as we make some very ...


15

Earthquake epicenters are located using triangulation, this is possible once seismograms of the earthquake - coming from at least three locations - have been analyzed properly. Here is a good explanation on a site for seismology students at Michigan Tech which takes its seismogram illustrations from Bolt's textbook on earthquakes (1978). Read this page and ...


14

There are a number of causes (this list is probably not complete): Elastic Rebound of tectonic faults. This is the most common and well known. Here the energy is elastic energy stored as two blocks of rocks move against each other. There is a point where elastic deformation cannot take up the entire movement, and the rock breaks releasing the elastic energy....


14

This is a good question, and the basic answer is earthquake seismology. To answer this question, lets accept a fact: Waves propagate through the least time pathway, and not the least distance path. This property of physics is known as Fermat's principle. When an Earthquake occurs, energy propagates similar to a ripple of water, and spreads. Each point on ...


14

After quite a bit of conversation on Twitter, I think it's arbitrary. Tradition is probably the prevailing reason. It would be interesting to go back through the literature to see who first used it. My hunch is that it goes back to the Zoeppritz equations (Zoeppritz 1919), which feature both $V_\text{S}/V_\text{P}$ and $V_\text{P}/V_\text{S}$. I bet Aki &...


14

Googling leads to a very old document: EFFECTS OF AN EARTHQUAKE IN A MINE AT TOMBSTONE, ARIZONA stating that in many cases, mine workers did not notice earthquakes which were felt above ground. A newer book, Earthquake effects on tunnels, check the "Look Inside" option for the introduction) confirms this. According to this source, a possible reason is that ...


13

Besides the theoretical limitations that @Neo talks about, there is also a great data gap in our knowledge. To predict an earthquake, we would need to know: The 3D geometry of all major, and possibly minor, fault zones The distribution of stress in the lithosphere, at least close to the fault zones but possibly more The physical characteristics of the rocks ...


13

This is a good observation. The reason we can measure S-wave (transverse) propagation in the inner core is because P-waves can set up S-waves and vice versa. When an S-wave hits the mantle-outer core boundary at an angle it has a vibration component which is normal to the boundary and this sets up a P-wave in the liquid inner core. The opposite happens at ...


12

This is a very good question, not just important to seismic inversion, but also modeling in general. Lets set this problem up differently. Lets say point's A and D are nodes. Each node represents a system of equations, and these equations are only calculated on these points. Therefore, the model can only exist on the points in which they are calculated. ...


12

This is a very simple answer, and it depends on the what the seismometer is measuring. I'm assuming you mean the time derviative/intdegral $\frac\partial{\partial{}t}$ or $\int{dt}$ Most seismometers measure displacement over time or velocity over time (series). So taking the time derivative will give you the spectral velocity or the spectral acceleration ...


12

This phenomenom is called velocity pull-up. The seismic waves that reflected off the top of Layer 2 beneath the carbonate layer have also travelled through the carbonate. Because carbonate (at least in this case) has a faster P-velocity than the surrounding shale, waves that have travelled through the carbonate will return to the surface receivers in a ...


11

I've done work with SEGY files, and the fixed length headers with ignored fields were an issue. Also, endian issues. You have to remember SEGY is the present exchange and archiving standard. That's a good thing. The issue is that SEGY was designed for tape, so it's a single file. In this day and age, that may not be a good thing. It might be better to ...


11

Tomography! In essence, we guess some velocities, compute the arrival times our guess implies, compare them with actual arrival times, tweak our answer, and repeat. Seismic tomography is an ill-posed, ill-conditioned inverse problem, and one upshot of this is that the solutions are non-unique — there are infinitely many answers! We have to choose one (or, ...


11

Well the dinosaur-killing asteroid that struck the Yucatan peninsula in the gulf of Mexico (65 million years ago!) generated a seismic shock or earthquake that went around the world and registered magnitude 13 on the Richter scale the reason for this was the object was 6 miles in diameter and its mass was equal to all the construction-materials used for ...


11

Yes, the vertical component of the seismogram looks different than the horizontal components. There are surface seismic waves (Love waves or Q-waves) that are horizontally-polarized. The ground motion due to these waves is horizontal and parallel to the plane of the ground surface. Therefore these waves will be most visible in the horizontal components of ...


11

The Haicheng Earthquake is the only successful evacuation of a devastating earthquakes. It's notable that the Chinese scientists thought they had figured out ot predict earthquakes, but have subsequently failed to predict many catastrophic earthquakes and many people's lives have been ended, ruined, changed. It is news to me that this research is in ...


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