Questions tagged [structural-geology]

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What is the history behind the present day geology of California? What processes took place that led to the formation of each region as shown in fig?

This is the image showing the different geomorphic provinces of California. What led to the formation of these provinces, and what events took place that resulted in the diverse geological setting of ...
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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?

The map presents a summary example of topography and mapped units X and Y. From the information presented, can someone help me determine or estimate the actual dip along the line of section, A-A'? I ...
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2 answers
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How can smartphones help geologists in the field?

Smartphones have incorporated many sensors and some of them can be helpful for a geologist in the field: They have GPS, so it is possible to register your route in a Google Maps map. I find this may ...
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1 answer
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Is there any intuitive and easily understandable way to help students understand the triangular facet of outcropted stratigraphy?

I find it difficult to teach college students about using the triangular facet on remote sensing images to judge the dip direction of sedimentary formations. Is there any intuitive way that can help?
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3 votes
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How can we distinguish fold and cycle of sedimentation on a remote sensing image or in the field?

A fold is composed of stratigraphy that is symmetric and repeated. Cyclic sediments (also called rhythmic sediments) are sequences of sedimentary rocks that are characterised by repetitive patterns of ...
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1 answer
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Terracing in Mahad

my first time here! I was going down the rabbit hole after watching a video on YouTube that made me want to read about it on Wikipedia. It led me to this Picture: (View from Varandha Pass near Mahad ...
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Is there a way to convert from Dip direction to Strike direction?

I have some set of recorded data in dip direction/dip format. I wish to transform then to strike/dip. I am currently having a hard time imagining how to convert from dip direction to strike direction. ...
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regarding four-way closure in structural geology

I am a little bit confused on the two concepts in structural geology, i.e., what is the relationship of anticline and four-way closure. My understanding is that anticline belongs to four-way closure. ...
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What local formation am I drilling?

I'm having a water well drilled on my property. The drilling crew has been working since Wednesday. They are using an airlift rig with a 6in bore. They are at 300ft and only have 4gpm. I would really ...
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1 vote
1 answer
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Have cosmic ray muons or solar neutrinos been used to probe inside the Earth?

By looking at the attenuation of cosmic ray muons passing through pyramids as a function of their direction, it seems it is possible to "look inside" by mapping their 3D density distributions. ...
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1 answer
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Why is Venus so cracked?

Wired.com's Space Photos of the Week: Perfectly Safe Celestial Coronas includes radar images of the surface of Venus taken from spacecraft in orbit around it. One of them shown below. What causes ...
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Could the LA County Museum of Art fall into the LaBrea Tar pit during an earthquake?

LACMA (the Los Angeles County Museum of Art) is built right next to the famous La Brea Tar Pits and that keeps me up at night†. Question: What is the subsurface structure like adjacent to the Lake ...
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4 votes
2 answers
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Can we separate a sandy, clayey & salt layer on basis of their rheological properties?

Since, given enough compaction, salt is able to behave like a fluid & buoyant too if it's overlain by a higher density rock (it could be fine grained clay or a sandy sequence). But in another case,...
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How can one find the true dip angle and quadrant when an apparent dip and strike is provided?

I am trying to solve the following question but cannot figure out how: A layer of limestone has a strike of East to West on a hilltop, and an apparent dip of 40 degrees on the vertical hillside ...
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3 votes
1 answer
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How did these dark lenticular features form? (Near Hoganekkal Falls India.)

These photos were taken near Hoganekkal falls in south India. The darker lenses appear to be the same rock type but have varying thickness and do not form a continuous layer. How did this structure ...
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Does fold tightness correlate to deformation intensity?

I'm studying a migmatite with two overprinting fold structures. The first (Dn+1) is tight and the second (Dn+2) is gentle. Would it be fair to assume that, since Dn+1's tightness is, well, tighter, ...
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Calculate normal and shear stresses with fault plane dimensions, slip, orientation and regional stress tensor

I'm trying to verify that some code I have is running correctly when calculating the Coulomb stress change. So for a example I have a fault with : Length = 70 m, Slip= 0.004 m, Orientation(strike/dip/...
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1 answer
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Do earthquakes produce folds on rocks?

Earth rocks are frequently folded at surface. Folds in alternating layers of limestone and chert in Crete, Greece. Source: commons.wikimedia Are earthquakes the main mechanism ...
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1 answer
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How big were the Siberian Traps originally?

252 million years ago, Siberia was subject to a mass series of flood basalt eruptions, creating a large igneous province called the Siberian Traps. Today, it measures three million square miles (7.77 ...
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5 votes
1 answer
355 views

What is meant by Massif?

In India, Panchchuli, Kun Nun and Shilong only these mountain are claimed to be massif. Why other mountain formations are not termed as massif...? What are the characteristics of massif..? Anybody ...
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ALOS Palsar SLC data products for geological mapping

I have some ALOS palsar SLC data products which are downloaded from ESA database and they are processed with ESA ALOS-PALSAR IPF processor which is different from JAXA. Formerly it was not possible to ...
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2 votes
1 answer
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What did tunnel digging teach us about the formation of chains of mountains?

Since tunnelling is like making a giant horizontal core sample, what did the analysis of the extracted rocks teach us? Is the inside homogeneous or layered, are there "deformations", etc?
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2 votes
1 answer
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Which type of convergent boundary creates the tallest mountains? [closed]

Which type of convergent boundary creates the tallest mountains? Continental-Continental Ocean-Ocean Ocean-Continental
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5 votes
2 answers
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Megathrust earthquakes on subduction zones

I am a beginner in geology and earthquake studies, and learning about subduction zones recently. Question is: do large earthquakes (sometimes referred to as megathrust quakes) occur on any point in ...
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2 votes
1 answer
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Where can I find information about the basic concepts of sedimentary basins?

There are a lot of papers on the web but they don't explain the concepts, they just mention them, taking for granted that the reader knows the concepts. I mean piggyback basin, forearc, back arc, ...
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2 votes
1 answer
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Why should this be a thrust fault?

Why should this figure represent a thrust fault? I know this might be a stupid question, but I really want to understand. Since thrust faults are reverse faults why in the figure above if we turned ...
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12 votes
1 answer
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What causes these circular swirls of islands?

I was following the boarder of the US and Canada on Google Maps, because, and found these interesting circular patterns of islands near the Northwest Angle. I have heard of geologic folding but I have ...
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3 votes
0 answers
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Drawing strike lines when given strike and dip

Map 1 shows a hillside with topographic contours at 50 m intervals. At Locality A a coal seam is exposed at the surface. The strike and dip of the seam is as indicated on the map. Use this information ...
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3 votes
2 answers
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what is a transverse isotropic rock?

I know isotropic means equal properties in all directions , but the term "transverse" is not making it easy for me to understand.
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3 votes
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measuring fracture length and width using PKN and KGD models for hydraulic fracturing?

I am trying to understand PKN and KGD models for hydraulic fracturing. I am wondering why equations for fracture width and length does not include 'breakdown pressure' (pressure at which fracture ...
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4 votes
1 answer
2k views

What are the differences in terms of appearance between sandstone and limestone?

On the field, I find it very difficult to differentiate the two types of rocks just by looking at them.I know that you should do some analysis of the sample before any conclusions. But, for example in ...
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3 votes
2 answers
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Can we determine strike when dip is given? What about the reverse?

In any geological plane, strike gives the direction of a line formed by intersection of horizontal plane and geological plane. And dip shows the orientation of the geological plane. While studying, I ...
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3 votes
1 answer
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How can oil can escape from a shale source rock into a reservoir rock?

How can oil can escape from a shale source rock into a reservoir rock if the shale itself is impermeable?
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1 vote
1 answer
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are laccolith, lobolith, dikes and sills formed of porphyritic texture?

Laccolith, lobolith and batholith are shapes of igneous rocks which exist below the surface of the earth, dikes and sills too. And the way they formed by makes me think that they have a porphyritic ...
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1 vote
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Do reverse faults tilt the underlying layers of rocks to form an angular unconformity?

I came across this question while studying in my text book: What does the existence of strata containing a reverse fault and above them parallel strata refer to? I thought that referred to an angular ...
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2 votes
2 answers
2k views

How to understand Mohr diagram?

Structural geologists use Mohr diagram to evaluate stress on rock's surface, but I find it difficult to understand how this diagram works (Though I am good at math). Where can I find a good ...
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4 votes
2 answers
1k views

Plotting stereonets in R

Is there a package for R to plot Schmidt nets, like it is done in geology? So far, I only know software like Stereonet. However I think it would make a lot of sense to handle these data in R, to have ...
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1 answer
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Strange circular structures found on a photo from Mars rover Curiosity at Dingo Gap

What are all these gaps / circular structures found on a photo taken by Mars rover Curiosity at Dingo Gap? Have a look at the image I made to see what gaps I mean. (I know the quick paint job looks ...
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1 vote
1 answer
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Structural geology, regarding cross section of two outcrops with similar characteristic but very distinct dip

I found an outcrop of sandstone interbedded with claystone which strike/dip is N 195 E/42. Then, around 4 km at the south of previous outcrop, i found another outcrop with similar characteristic, but ...
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5 votes
1 answer
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How does Vertical Electrical Sounding Work?

I recently conducted a brief training exercise with VES equipment, although it had to be called off due to rain. I can't help but wonder about the basic physics of it, why is it that increased ...
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4 votes
1 answer
380 views

Gravitational Anomaly of a subsurface body

How does the gravitational anomaly measured at the Earth's surface and produced by a subsurface body depend on its depth and on the density contrast of the body relative to its surroundings?
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4 votes
0 answers
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How to differentiate between normal and reverse fault, given a stress tensor?

I want to generate synthetic fault slip data using a known stress tensor. I am using a rotation matrix to get the orientation of the principal stress axes, and rotating the tensor [1 0 0, 0 phi 0, 0 ...
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3 votes
1 answer
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Do discordants dykes ever travel concordantly (are transgressive dykes a thing)?

Transgressive sills "jump" between bedding planes, following joints: ...
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3 votes
1 answer
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Does flow banding only occur in silicic rocks?

I made a video about what I learnt in my A Level Geology course so far, about igneous rocks. One thing I mentioned was that flow banding is mostly only found in silicic rocks (and so mostly rhyolite) ...
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4 votes
1 answer
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State of Stress in rotated 2D system

I'm working on the rotation of the state of stress using the book Geodynamics of Turcotte page 101. The 2D coordinate system $x'$ and $y'$ is inclined at an angle $\phi$ with respect to the $x$, $y$ ...
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3 votes
1 answer
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How to determine if this fault is normal, sinistral?

Studying for an exam tomorrow and stumped on this question (parts d and e). The region show in Map 2 consists of a series of sedimentary strata that have been tilted and then eroded, producing an ...
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13 votes
1 answer
768 views

What is the definition of a continent?

Is there a scientific definition of a continent? Is there an academic reference for such a definition? There's a tendency to correlate with tectonic plates, but of course lots of plates don't have ...
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25 votes
1 answer
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How much of a mountain is below the surface?

Is there some kind of math rule for how much does a mountain extend (depth) below the surface? I found an article like this http://www.livescience.com/6595-depth-himalayan-mountain-roots-revealed....
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8 votes
1 answer
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Measuring bed dip angle from contour lines, which lines to pick?

Measuring dip angle of a bed, I choose any 2 contour lines that cross the bed, and then project lines off and measure the angle (I'm assuming this is standard technique that doesn't require ...
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6 votes
2 answers
326 views

What geologic features could this video game environment be modeled from, and how do they form?

I have been playing this game for a while and I like the city's setting. It seem to be placed on a rock platform, or a mesa maybe, connected to the mainland on the bottom-left. It also has some ...
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