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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16
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1answer
331 views

Is Iceland an example of a hot-spot overlying a mantle plume?

Iceland has been cited as the location of a hot-spot overlying a mantle plume (similar to that of the Hawaii chain in the Pacific), though for some time this model has been challenged (see Gillian ...
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Can impact events cause widespread volcanic activity on the other side of the planet?

The currently accepted theory for P-T mass extinction is environmental change triggered by the Siberian Traps volcanic activity. A paper(1) suggests that the Siberian Traps were caused by a hotspot ...
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Interpretation of a seismogram (three components)

In most cases (as shown in the figure below), a seismogram shows data from three components: North-South East-West Vertical/depth(z) However, if these components are not marked and all we have are ...
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When a tectonic plate subducts, does any of the subducted material melt, or is it just the mantle above the subducted slab that melts?

I know that water released from oceanic crust causes melting of the mantle in subduction zones, but does any part of the subducted slab melt as well - such as the sediments on the slab or the basalt? ...
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What does it mean when the depth of earthquakes get near the surface over a period of time?

First of all, I am not expert at this so correct me. My hometown is Shiraz and since last year I can sense the earth is moving. I call them mini earthquakes. But many people around me can not sense ...
15
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What is this strange feature on Mars in Valles Marineris

While I was browsing Mars on Google Earth, I stumbled upon an interesting feature on one of the slopes of Valles Marineris. The feature seems unique in the sense that I couldn't find any similar ...
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Why is there a line of volcanoes along the northwest coast of North America?

Mount Hood in Oregon is a dormant volcano, and in Washington Mount St. Helens and Mt. Ranier are both active volcanoes. What causes this line of volcanoes running parallel to the coastline along the ...
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How are subsurface wave speeds determined without subsurface sensors?

This is something I've never quite understood from a geology class I took years ago: Consider the following picture (courtesy of wikipedia) Obviously, we can't possibly have sensors deep in the ...
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Why is a seismogram interpreted as a convolution?

I remember reading in a geology book that a seismogram is a convolution between a source signal and propagation effects. In layman's terms, what does this really mean?
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How are Earth's rotational changes due to large earthquakes calculated?

According to NASA (and many other sources), Japan Quake May Have Shortened Earth Days, Moved Axis and in the answers to the question here What geophysical events can (temporarily) increase the Earth's ...
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Would oceans regenerate if removed?

On Earth, there is enough Hydrogen and Oxygen to make 13,88 million km$^3$ of water (calculation below). However, oceans contain only a tenth of that. Clearly, most of the hydrogen must be stored in ...
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What are the causes of the supercontinent cycle?

Throughout geologic history, Earth's continents have broken apart and come together to form supercontinents multiple times, in a somewhat regular period, known as the supercontinent cycle. The length ...
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How accurately can explosions be triangulated from the IRIS seismogram data?

There's a bunch of armed conflicts going on right now. What are the lower boundaries on accuracy of triangulating and timing man-made events from the IRIS datasets (accessible, for instance, with the ...
14
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How are Richter magnitudes of past earthquakes estimated?

In reading about historical major earthquakes, in particular, the Great Shaanxi Earthquake that killed approximately 830,000 people in July, 1556, there is a claim made about the approximate Richter ...
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What are the ground motion prediction equations for 3-D ruptures?

Ground motion prediction equations (GMPEs) estimate ground motion at any given site due to an earthquake at a distance. There are many such equations, each with different parameters. Can somebody ...
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Has an entire plate ever subducted?

We know that plates can subduct, causing one plate to be pushed into the core by another. As the plates move, the subduction continues, pushing one plate under the other. If this process continues, ...
13
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1answer
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Why is the temperature between the earth core and surface not distributed linearly?

So I read somewhere that the inner core temperature of Earth might be as high as 7000 °C. Depending on the composition of the different layers towards the surface, the temperature should decline ...
13
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1answer
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P wave to S wave conversion

While passing through layers inside the earth some P waves get converted to S waves and then back to P waves while returning towards the surface. Is this statement true? If yes, then why? (...
13
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How is known that the Earth core is solid?

As I know, the Earth core is solid. This is known, because it conducts also transverse waves, while liquids conduct only longitudinal waves. But, how was it found? The inner core is in the outer core,...
13
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698 views

Successful Earthquake predictions

Have there been any instances where seismologists have successfully predicted the occurrence of earthquakes? If so, then why has the number of scientists working on this area has declined (as ...
13
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363 views

How much silicon is in the Earth's core, and how did it get there?

With some informal conversation with a peer of mine, he had suggested that there is evidence (which he couldn't find,but had remembered reading) that there was Silicon in the Earth's core. I referred ...
13
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1answer
219 views

Phase changes deep in planetary interiors and their implications for surface tectonics

Earth's core mantle boundary represents a phase change from a solid (though convecting) mantle to a liquid Iron/Nickel core. This dramatic transition is likely the origin of the D" boundary, as well ...
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The relation between the magnitude and duration of earthquake

I am asking this question in reference to the recent earthquake that struck Nepal last month. I read that the magnitude 7.8 richter scale earhtquake would have caused more damage had it lasted for ...
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How do you calculate the depth of penetration in a Schlumberger array?

In a resistivity survey, how do we calculate the depth of penetration for a Schlumberger array?
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Epicenter location of the 900-930 A.D.,7.4 Magnitude Seattle Earthquake?

I am preparing a seismic hazard map of Seattle and I was curious about the great 7.4 magnitude earthquake that occurred in the Seattle area during 900-930 A.D. On a second note, is it possible to ...
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2answers
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Change in earth mass since the time of the dinosaurs

Is there a significant difference in the mass of the Earth between now and the time of the dinosaurs (250 - 75 million years ago)? I was just wondering if the force of gravity on dinosaurs would have ...
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What do the derivative or the integral of amplitude of a seismogram mean?

I'm doing a project in which I'm analyzing earthquake seismogram waves. I used a program to graph the exact amplitudes and how they changed over the course of a single earthquake. For the project I ...
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5answers
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Are there water molecules in the oceans which will almost never fall down as rain?

Some oceans are very deep. But is there also current (convection) deep in the ocean so that all water molecules will ones be evaporated and fall down as rain or is it very quite at the bottom so some ...
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How do I derive the formula for lithostatic (overburden) pressure?

The title pretty much says it. I have the formula: $P = \rho g h$ where $\rho$ is the density, $h$ is how deep the pressure is in the Earth and $g$ is the gravitational acceleration(?). I don't get ...
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1answer
781 views

What are the non-anthropogenic causes of The Netherlands' low elevation?

A large area of The Netherlands is below sea level. There are two non-anthropogenic reasons that I can think of: Compaction of delta sediments that lie below the country, A side effect of the ...
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Why is colored seismic inversion called 'colored'?

One of the seismic inversion algorithms is called 'colored' inversion. It is performed in the frequency domain and the point is in building an operator that directly transforms a seismic trace into ...
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4answers
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When will the Final Ice Age happen?

As the Sun's luminosity slowly rises, the Earth's surface temperature will climb. Will Earth ever be too warm to have any more glacial periods? If so, when will that be? Edit: The existing answer ...
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Temporal Resolution of Seismic data

Radius of the Fresnel zone is given by $$Rf=(v/2)(t_0/f_\mathrm{dom})^{1/2}$$ where $v$: velocity of layer $t_0$: two way travel time $f_\mathrm{dom}$ :dominant frequency in the spectrum This shows ...
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What geophysical knowledge have we learned by the construction of IceCube?

The IceCube is a particle detector at the South Pole that records neutrino interactions. It has lead to many fascinating new discoveries in the field of astrophysics (e.g., 1, 2) and it was awarded "...
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Why is ocean surface velocity around 3% of wind velocity?

Many introductory level textbooks suggest that, as a rule of thumb, the velocity of the ocean surface is around 3% the wind velocity at 10 meters above the sea surface. For instance, Ocean ...
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1answer
216 views

Do seismic travel times from one location to another differ based on factors other than distance?

Bit puzzled why it appears that seismic travel times from one location to another appears to just be a function of the distance, and not any other factors. Do seismic travel times from one location ...
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1answer
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How do mantle plumes travel from the core of Earth to the crust?

As mantle plumes begin in the core and move towards the crust, I would have thought that the heat in the mantle plume would disperse to the surrounding mantle, and the plume would cease to exist by ...
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1answer
210 views

Why does seismic activity shed light on the inner core rigidity?

Reading Introduction to Geology (MIT 2005) and Wikipedia's article on Earth's inner core, it is specified that: Earth was discovered to have a solid inner core distinct from its liquid outer ...
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Probability distribution of fault throw displacement and height limiting mechanisms

First, what is the probability distribution of fault throw displacement. Uniform distribution seems unlikely, since then small changes would add up to huge huge elevation differences that require a ...
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2answers
178 views

Mechanism for Pluto's young surface

According to recent reports (e.g. in Nature), Pluto is geologically active. It has some mechanism by which it has "recycled" its surface. I originally thought we had a similar case to Jupiter's moon ...
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Should one extract wavelet from seismic or well log for the generation of synthetic traces?

Synthetics are generated by convolving reflectivity series with the known wavelet. I have seen most of the wavelet are extracted from seismic data itself. Is there any hard and fast rule, or can one ...
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957 views

What's the distance between the center of mass and geometrical center of Earth (CM-CF offset)?

I asked the same question on Physics StackExchange site. I now know that there are several types of "center" and I can tell, I'm interested in the CM-CF offset (CM = geocenter, CF = center of figure). ...
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Do normal modes of oscillation cause permanent deformation?

It is known that when a large earthquake occurs, say $M \ge 9.0$, The surface waves travel around Earth over and over, "ringing the surface like a bell". The GIF below is an example (Image Source): ...
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converting SU file to ASCII format in seismic unix using OpenSeaSeis

I have tried to convert a Seismic SU file to ASCII format in seismic unix using openseaseis module named "sutoascii". I have already tested the SU file by opening it in SeaView Seismic Viewer and ...
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Is the cause of Old Faithful's bimodal distribution for eruption times straightforward?

From wikipedia: With a margin of error of 10 minutes, Old Faithful will erupt 65 minutes after an eruption lasting less than 2.5 minutes or 91 minutes after an eruption lasting more than 2.5 ...
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Does gravity differ from place to place on Earth

Does a particular object have the same weight on every part of Earth or does it vary?
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Why does Earth's outer-core rotate in the opposite direction to the inner-core?

Is it true that Earth's outercore rotates in the opposite direction to Earth's inner-core? Is there a plausible explanation for why this phenomenon occurs and what is the available evidence ...
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Equatorial bulge and tectonic plates

It is well known that the Earth is not a sphere, but rather it bulges at the equator. Also it is well known that the Earth's crust is composed of 7 or 8 (depending on definition) major tectonic plates,...
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Are there any other earthquake magnitude scales other than Richter's?

There are sometimes confusion about the magnitude of Earthquakes. What scales, other than Richter's, are used to measure the magnitude of an earthquake? Is there a scale where magnitude 9.0 is ...
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Is the epicenter always directly above the hypocenter?

All the graphics I've seen showing epicenters with a hypocenter (labeled focus in the graph below) appear to show that epicenters are always directly above their related hypocenters. Is this correct?

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