# Questions tagged [geophysics]

Geophysics is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment.

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### Why is the pond in my backyard not frozen when it is -15 °C (5 °F) outside?

I am in O'Fallon, Missouri and today it is -15 °C (5 °F) outside. I was taught water freezes at 0 °C (32 °F). I could understand if it was exactly 0 °C (32 °F) that the water might not be turning to ...
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### Are Richter-magnitude 10 earthquakes possible?

The largest earthquake since 1900 according to the United States Geological Survey (USGS) was Richter-9.5 magnitude quake in Chile in 1960. Are magnitude 10 earthquakes possible? If so, what is the ...
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### Farthest point from the center of the Earth

At first glance, this seems like such a simple question of "What's the highest point on Earth". However, I also know that the Earth isn't perfectly round. So that "highest point" may be in a ...
31k views

### Why is Earth's inner core solid?

I have never understood why earth's inner core is solid. Considering that the inner core is made of an iron-nickel alloy (melting point around 1350 C to 1600 C) and the temperature of the inner core ...
12k views

### How is the mass of the Earth determined?

According to textbook knowledge, the mass of the Earth is about $6 × 10^{24}\,\mathrm{kg}$. How is this number determined when one cannot just weight the Earth using regular scales?
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### Similarities between grand circulation solvers and mantle convection solvers

My impression is that both ocean grand circulation models (e.g. MITgcm), and Mantle Convection models (e.g. CitcomS), both use Navier-Stoke's as the governing equation. What are the other major ...
12k views

### How can we determine the size and composition of Earth's inner core?

From Wikipedia: Earth's inner core is Earth's innermost part and is a primarily solid ball with a radius of about 1,220 km (760 mi). (This is about 70% of the Moon's radius.) It is believed to consist ...
9k views

### Is it true that earthquakes are not felt in a cave?

I took a tour of a cave in northern California last weekend. The tour guide asked us, "If an earthquake occurred, what would we feel in here?" My answer was, "fear," but she said we would feel ...
7k views

### Where on Earth is the magnetic field intensity stronger?

Are there places on Earth that have a strong magnetic field other than the magnetic north and south poles? Can living where (rare) earth magnetic ore is abundant provide a mini-magnetoshere?
31k views

### Why is Earth's outer-core liquid?

The Earth's inner core is solid because despite the enormous temperature in this region, there is also enormous pressure there, which in turn raises the melting point of iron and nickel to a value ...
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### Is earthquake prediction possible?

After the Tohoku and East Coast quakes, I skimmed over several books discussing the validity of earthquake prediction as a discipline, yet found no significant breakthroughs. What should change in our ...
33k views

### Why is Earth's inner core made of an iron-nickel alloy?

This question has puzzled me for a while. I know that earth's mantle is made of different minerals, metals and rocks etc. and that has always made complete sense to me. But why is the inner core made ...
3k views

### Natural nuclear explosions

I'm aware of the Oklo reactor and other natural nuclear fission reactors, in which geological processes can lead to the formation of a sustained, self-regulating uranium fission reactor. Is it also ...
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### Could earth's core lose its heat?

Will all of the drilling and digging to use the earth's natural heat as geothermal energy be affecting Earth's core, causing it to cool down? If so, would it result in an ice age? If not, how does it ...
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### How to distinguish P, S, Love, and Rayleigh waves in a seismogram?

What features should I look for to determine each of these kinds of waves in a seismogram? What signal processing methods (filters, transforms, etc...) should I use to determine them?
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### What properties must a rocky body possess in order to exhibit plate tectonics?

The Earth exhibits plate tectonics, but the other terrestrial planets do not (though Mars and Venus may have exhibited plate tectonics in the past). What is "special" about Earth that allows it to ...
308 views

### Estimating the permeability tensor of an oil field by remote sensing

I work a lot with numerical methods to solve multiphase flow in porous media for oil applications. In our field, we often use Darcy's law which states that the flux is negatively proportional to the ...
398 views

### Is fracking likely to produce earthquakes?

Post Christchurch-2011 earthquake, there was much concern that fracking in the surrounding areas might lead to further quakes, as was rumoured to have happened elsewhere in the world. Is there ...
375 views

### What are some of the strongest theories against the existence of mantle plumes?

Among the people I interact with in the geodynamics community, it seems that almost all of us are in full support of the mantle plume theory. What are the strongest arguments against this theory? Is ...
785 views

### How does one measure what causes earthquakes?

I know that they occur when energy that was previously stored is released in seismic waves. But how is the energy stored in the earth in the first place, and what can trigger the release of such ...
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### Can the overuse of geothermal energy become an environmental concern? [duplicate]

At what power output would we be using so much geothermal energy that we cool the core enough to endanger the Earth's magnetic field and have to stop using it? Is this a conceivable concern for a ...
60k views

### Why are oceanic plates denser than continental plates?

In the theory of tectonic plates, at a convergent boundary between a continental plate and an oceanic plate, the denser plate usually subducts underneath the less dense plate. It is well known that ...
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### How do seismologists locate the epicenter and focus of an earthquake?

I know the focus of an earthquake is where the earthquake originated from, but what I could never figure out is, how to scientists find out where exactly the focus (and epicenter) are located?
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### What would a replacement for SEGY look like?

I have been having a miserable time this week reading SEGY files. This is data from the largest seismic acquisition company in the world whose client is the 7th largest oil company in the world. So if ...
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### Why Earth's magnetic poles are (and were) in their positions?

This is a sort of a follow-up question to What causes the Earth to have magnetic poles? The Earth has magnetic fields, and according to dynamo theory I roughly understand why. If the Earth's rotation ...
353 views

### To what accuracy and precision do we know the volume of the Earth?

Satellites such as GOCE and GRACE measure the geoid with unprecedented accuracy. Altimeters can determine local surface elevation with millimetre-precision. This makes me wonder: to what precision ...
281 views

### Can large (and wet) storms really trigger large magnitude Earthquakes?

At the 2011 AGU Fall meeting, this poster claimed that the water erosion from Taiwan's wettest storms could prematurely trigger large magnitude earthquakes , $M \ge 6.0$. If this was true, this ...
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### What causes intra-plate faults, such as the New Madrid fault?

There's been news (some recently) about the New Madrid fault and other active intra-plate faults. For those living in the midwest of the United States, it's been a bit of a shock to learn they have ...
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### What fraction of dry land is below sea level?

Someone just asked me if it would be practical to counter the rise of sea level by pumping water into storage on land. It struck me that if there is enough land below sea level, this would require ...
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### What would be the first thing which will render the Earth uninhabitable?

There are quite a few things which can make an otherwise habitable planet uninhabitable, and some of these will eventually happen, sooner or later: engulfed by its star when it becomes a red giant ...
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### Where is the calmest place on Earth?

I have done some research online, and I've found out that Antarctica has the calmest winds (lowest maximum wind speed) recorded on Earth. However, it is uninhabitable for human life. Other very calm ...
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### Will the Earth ever stop rotating?

It is well known that the Earth's rotation is slowing down and that millions of years ago there was a point in time where there was only a mere 20 hours in a day on Earth. My question is in two parts....
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### Why Vp/Vs and not Vs/Vp?

The relation between shear wave velocity (Vs) and pressure wave velocity (Vp) is often expressed as Vp/Vs. Wouldn't the opposite be more logic? Vs/Vp would never lead to division with zero and the ...
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### What geophysical events can (temporarily) increase the Earth's rate of rotation?

My understanding is that the dominant factor behind the slowing of the Earth's rotation (i.e. the lengthening of the day) is tidal friction induced by the Moon's gravity. As seen on the graph below, ...
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### Why does sea level correspond to boundary between oceanic and continental crust?

Is it a coincidence? the first is determined by the amount of water on the Earth and the second comes from evolution of tectonic plates. Still, oceans seem to fill exactly the oceanic crust.
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### Are there any techniques for imaging the deep Earth besides seismic waves?

It is well-known that we can learn a lot about the structure of the lower crust, mantle, and core by observing the ways in which they refract different kinds of seismic waves. Do we have any other ...
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### Why are minerals found in “large” quantities and not scattered throughout the earth as individual atoms?

Heavier elements are created in stars. After stars die they scatter these heavier elements throughout the universe. These elements eventually gather to form planets. But why do we find "chunks" of ...
322 views

### What are the physical upper bounds on the magnitude of an earthquake?

Given what we know about the physical mechanisms underlying earthquakes, what do the theoretical upper bounds on the magnitude of an earthquake look like? What physical phenomena impose those upper ...
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### How to quickly or easily prove the world is spherical?

A relative of mine has recently introduced me to the modern flat earth theory, which she believes in. Setting aside for the moment that it is ridiculous, and that sending up some balloons with cameras ...
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### Did the impact event that caused the Chicxulub-Crater definitively and single-handedly cause the Cretaceous-Paleogene extinction?

Opinions abound on the web. What is the state of the current science regarding this theory and what is the best evidence? Is the theory gaining or losing traction? If it's losing what's the best of ...
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### How long until Earth's core solidifies?

How much longer does Earth have until the core turns solid? Does global warming change these estimates at all?
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### Why won't Yellowstone explode?

From my understanding Yellowstone is a massive super-volcano, so why isn't it active? Where has its (correct me if I'm using the wrong term) hot-spot gone? Can it still erupt?
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### Why is the inside of the Earth so hot?

I have heard that the Earth is made up of four layers, being the crust, the mantle, the outer core and the inner core. I have also heard that the Earth's temperature increases as you move from the ...
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### At what point does plate tectonics stop?

As the core and mantle of the earth cools, it will reach a point where new crust cannot be produced. How can this point be calculated? If we can, has anyone done such calculations? Thanks!
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### Why is there Uranium in Earth's Crust?

Uranium's density is greater than most elements, so you would expect it to settle to the bottom of a volume of fluid. In the case of the Earth, which was molten in the beginning, you might then expect ...
704 views

### Does volcanic activity fluctuate?

According to this person's surmises, volcanic activity appers to be increasing. However, according to this report, volcanic activity is probably not increasing. My question is: Does Volcanic activity ...
1k views

### What causes the Earth to have magnetic poles?

A compass can tell me the directions of the Earth's North and South poles? What is it about the Earth that produces this "polarity" such that a compass can pick it up? The first thing that jumped ...
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### How did tectonic plates originally come to form?

Plate tectonics is a theory which describes Earth's lithosphere as being composed of distinct plates which are able to move atop of the underlying asthenosphere. At plate boundaries, this movement ...