8 votes
Accepted

Strange circular structures found on a photo from Mars rover Curiosity at Dingo Gap

There are no circles, it is an image artifact. Here is another picture from Dingo Gap that shows nothing at the exact same position. Your mind is a well-trained pattern-matching machine that makes ...
Jan Doggen's user avatar
  • 2,679
8 votes
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Terracing in Mahad

The Deccan Traps are the geological formation that make up the Western Ghats in India. They were formed by massive volcanic eruptions that formed flood basalts. These are layers of lava that are ...
Andy M's user avatar
  • 2,008
7 votes
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What causes these circular swirls of islands?

Near the Lake of the Woods, the island swirl or vortex is due to structures in bedrock beneath the lake. The rocks in this area are old and have been folded by tectonic action. The area has either ...
Earth Science Expatriate's user avatar
7 votes

Megathrust earthquakes on subduction zones

Megathrust is not a particularly well defined term but in my experience it generally refers to very large earthquakes that occur on the subduction interface. The subduction interface is the main ...
bon's user avatar
  • 2,221
7 votes

An approximate, piecewise continuous analytical model for Earth's radial density profile useful for numerical integration?

From Table I in the admittedly dated Preliminary Reference Earth Model, $$ \rho = \begin{cases} 13.0885 - 8.8381 x^2 & \quad \phantom{000}0\phantom{.0} \le r < 1221.5 \\ 12.5815 - 1.2638 x - 3....
David Hammen's user avatar
  • 23.5k
6 votes
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In Geology - True Dip versus Apparent Dip: When dip is estimated along a line of section, how is that dip determined in relation to true dip?

This is an excellent question. The answer requires that one visualize a 3-dimensional space with a dip plane, a vertical plane coincident with, and aligned along, our line of interest, and the trace ...
Thomas Perry's user avatar
5 votes

Megathrust earthquakes on subduction zones

Yes, mega thrust earthquake can occur in any point of any subduction zone. However, some areas areas are much more active than others, meaning that the frequency of earthquakes and energy released per ...
Camilo Rada's user avatar
  • 17.6k
5 votes
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Why should this be a thrust fault?

First don't rotate the whole thing, you are just confusing yourself by rotating the bedding plane. You can't rotate the bedding planes and expect faults to match up like that. Your eye is treating the ...
John's user avatar
  • 6,906
5 votes

From how deep in the mantle has any rock ever been brought to the surface? Have scientists found anything they believe originated in the outer core?

Diamond is stable at high temperatures only under very high pressures. Mineral inclusions in a diamond, and the rocks in which a diamond are embedded, can offer further clues as to the depth from ...
nigel222's user avatar
  • 161
4 votes
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Plotting stereonets in R

You might try the RockFab package. I am not a structural geologist but I use other R packages for geological endevours. Documentation.
Ton's user avatar
  • 316
4 votes
Accepted

Do discordants dykes ever travel concordantly (are transgressive dykes a thing)?

Yes, they are. It's not the sills or dykes that "jump", it's the magma. Depending on the various parameters such as viscosity, stress, temperature, pressure, and local conditions and availability of ...
Gimelist's user avatar
  • 23.1k
4 votes
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Does flow banding only occur in silicic rocks?

Flow banding can occur in all igneous rocks, regardless of their composition. Any kind of molten rock that flows may eventually cause some flow banding. Sometimes the flow banding is not even obvious ...
Gimelist's user avatar
  • 23.1k
4 votes
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How does Vertical Electrical Sounding Work?

The diagram is perhaps a little mis-leading. Think of the ground/rock between the electrodes as a big resistor. The surrounding rock can be modeled as a set of parallel resistors. Most of the ...
winwaed's user avatar
  • 3,903
4 votes
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Relay structures in Rupes Recta

From Nahm & Schultz (2013): Detailed structural mapping of Rupes Recta has revealed the presence of four distinct fault segments (Fig. 6). Analysis of throw distributions can clarify which ...
Jean-Marie Prival's user avatar
4 votes

From how deep in the mantle has any rock ever been brought to the surface? Have scientists found anything they believe originated in the outer core?

As far as I know the best estimate is "upper mantle" from mantle xenoliths but that's not terribly specific. I am not sure if knowing more than that is possible right now.
Ian's user avatar
  • 41
3 votes

Could the LA County Museum of Art fall into the LaBrea Tar pit during an earthquake?

The two geological faults that may be responsible of large earthquake in proximity of the museum are: Hollywood fault; Santa Monica fault (actually many branches, but they all go together as Santa ...
EarlGrey's user avatar
  • 461
3 votes
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Do earthquakes produce folds on rocks?

No, earthquakes are sudden, often very energetic events which produce faults and discontinuities. There is a sharp break in the strata when subjected to a powerful earthquake. The folding of strata is ...
Michael Walsby's user avatar
3 votes

What is meant by Massif?

A massif is an undisturbed solid rock mass, which is demarcated by e.g. faults. Massifs keep their internal structure and are displaced as a whole. Only mountains of mountain ranges fulfilling this ...
JulPal's user avatar
  • 734
3 votes

What did tunnel digging teach us about the formation of chains of mountains?

Tunnels have provided nothing more than what was learned from conventional geological drilling and surface mapping. Tunnels provide supplemental information. Very rarely do they provide "make or break"...
Fred's user avatar
  • 24.7k
3 votes
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Gravitational Anomaly of a subsurface body

The gravitational anomaly (delta_g) changes linearly with the density contrast, and proportionally to the inverse square of depth. That's simply a version of the 'Universal Law of Gravitation'. Here ...
DrGC's user avatar
  • 1,753
3 votes

Can we determine strike when dip is given? What about the reverse?

No. Strike is a line value whose direction is referenced with respect to true north. Dip can be any 0-90 degree angle (below horizontal) perpendicular to that line. It must be physically measured in ...
Knob Scratcher's user avatar
3 votes

Is there any intuitive and easily understandable way to help students understand the triangular facet of outcropted stratigraphy?

This is a tale of two three dimensional coordinate systems. You may need to take a bit of a side track if your students are not already familiar with the concepts of three dimensional coordinate ...
David Hammen's user avatar
  • 23.5k
3 votes

How can smartphones help geologists in the field?

Part of the answer lies in where the geologist will be working and if there will be coverage by cellular/mobile telephone networks. It is my experience that a number of geologists, particularly ...
Fred's user avatar
  • 24.7k
3 votes
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How can smartphones help geologists in the field?

I know a young geologist using his smartphone as a compass. When we were in the field doing structural measurements together, I would: Record a waypoint using my hiking GPS Take the measurement with ...
Jean-Marie Prival's user avatar
2 votes

Structural geology, regarding cross section of two outcrops with similar characteristic but very distinct dip

Is this a homework question? These are quite steep dips, strongly implying that substantial deformation (folding) has taken place. The interlayering of steep mudstone pretty much rules out your ...
Gordon Stanger's user avatar
2 votes

Which type of convergent boundary creates the tallest mountains?

The type of convergent boundaries is not the only factor. From the current configuration of the world one could be tempted to say that Continental-Continental collisions would form the tallest ...
Camilo Rada's user avatar
  • 17.6k
2 votes

Where can I find information about the basic concepts of sedimentary basins?

In general, a good answer to "where can I learn the basic concepts of X" is "a textbook on X". For sedimentary concepts, you might try Nichols (2009), for instance. Academic papers are a publication ...
Pont's user avatar
  • 5,429
2 votes

How big were the Siberian Traps originally?

Short answer, there are various estimates, with large uncertainties, ranging from 4 to 7 million km2. Pulling from the link provided by Keith McClary in the comments: Estimating the original extent ...
GrapefruitIsAwesome's user avatar
2 votes

Why is Venus so cracked?

I found the picture with a small write up on a JPL site. It's a picture of the Aine Corona with pancake domes. P-38340 MGN-48 5/21/91 This Magellan radar image shows a region approximately ...
Fred's user avatar
  • 24.7k

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