Questions tagged [seismology]

For questions about the study of earthquakes and various seismic sources.

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7
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0answers
314 views

What geological structure(s) is responsible for the recent Queensland earthquakes?

Recently, south-east Queensland has been rattled by 2 moderate earthquakes - a 5.3 a couple of days ago (News report) and a 5.7 tremor just a few hours ago as of writing this post (News Report). These ...
6
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1answer
403 views

Why is it necessary in seismic imaging to calculate an image of reflection coefficients when one of the inputs is the velocity model?

Note: I'm not at all an expert in this field. I read in the first few pages of Robein (2010; Seismic Imaging, A Review of the Techniques, their Principles, Merits and Limitations, EAGE) that both ...
7
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1answer
82 views

Publicly-available real-time world-wide seismographic information?

Is there a list of websites supplying real time seismographic information for around the world? I could find for specific places. But I'm looking for a list so I can check for anywhere (providing, of ...
6
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1answer
98 views

Querying Seismic Databases

I'm trying to find 3-component records of the P-wave arrivals of a variety of earthquakes at seismic stations (specific earthquakes or stations aren't important, I just want a small library of these ...
14
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2answers
517 views

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?
7
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1answer
2k views

What is the meaning of seismic spectral blueing?

What is the meaning of seismic spectral blueing? Please cite any good introductory materials if possible.
12
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4answers
967 views

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 ...
10
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1answer
2k views

How does one determine the optimum offset in a seismic survey?

I was going through a report on MASW (Multi Station Analysis of Surface Wave) and found this "To avoid the aliasing in the space domain, geophone spacing (Δx) needs to be less than half of the ...
12
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1answer
2k views

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 ...
9
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1answer
84 views

Groundwater unloading and corresponding changes in fault zone stick-slip behavior

I was intrigued by this Slate piece, more or less a summary of Amos et al. (2014)'s Nature article, which essentially states that groundwater depletion and subsequent crustal unloading causes a ...
14
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0answers
143 views

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 ...
7
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1answer
638 views

Why do most seismic inversion methods ignore high frequencies?

Different post-stack inversion methods such as model based, sparse spike, colored and recursive inversion methods use high cut frequency impedance logs (low frequency) and mid-frequency seismic trace ...
7
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1answer
1k views

Why does part of the P-wave convert into a S-wave with an increase of incidence angle?

With the increase of incidence angle, a portion of a P-wave converts into a S-wave, how does this behaviour occur?
3
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1answer
378 views

How to determine the number of bytes in the SEGD Revision 1 interblock gap

How can one determine the number of bytes in the SEGD Revision1 interblock gap? The quantity is present on page 5 of the standards document.
22
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1answer
132 views

Placement of crustal thickness estimation from 1D inversion of surface wave dispersion curves

Seismic surface waves present a characteristic dispersion behavior in which different frequencies travel at different speeds. This characteristic dispersion curve depends on the shear and ...
10
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3answers
2k views

Is there a correlation between hot springs and earthquakes?

Is there a correlation between how many hot springs an area has, and how frequent or severe the area's earthquakes are?
8
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2answers
2k views

Distance to epicenter vs distance to focus

I am not really a "budding seismologist." I am a chemistry/physics teacher teaching an Earth science class (low academic level) in a small-town high school. (My college coursework in earth sciences = ...
12
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1answer
1k views

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 ...
18
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2answers
1k views

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 ...
6
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1answer
413 views

Earthquake probabilities

A recent report estimated the probability of an earthquake greater than magnitude 7 on the southern section of the San Andreas fault at approximately 60% over the next thirty years. How is that ...
8
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1answer
2k views

Calculating the displacement of a fault

In the calculation of scalar moment magnitude of an earthquake we have the formula $$M_0=\mu AD$$ where: $\mu$ is the shear modulus of the rocks involved in the earthquake (in Pa) $A$ is the area ...
7
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1answer
235 views

About Earthquakes and their properties

I know this sounds like a crazy observation but San Francisco has a lot of HUGE buildings in the downtown area , millions of tons or probably more. Many Scientists think a big earthquake there is '...
11
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1answer
158 views

What efforts have been made to separate the microseismic events related to wind-related ocean waves from the components of volcanic origin?

I have read the question What generates the microseism? and it's accompanying answer. In [#1, cited below], they use the azimuth values of seismographic activity on the flanks of the volcano ...
12
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2answers
966 views

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 ...
14
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1answer
179 views

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 ...
17
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1answer
387 views

Can earthquakes contribute to Antarctic ice loss?

I read about the earthquake that took place in Japan in 2011, led to some small calving events in Antarctica (link). So, it makes me think if there is a big earthquake near or in Antarctica, can it ...
12
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1answer
202 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 ...
12
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1answer
226 views

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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1answer
694 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 ...
12
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1answer
343 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 ...
12
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1answer
587 views

What causes “shallow” moonquakes?

It is thought that "deep" moonquakes are caused by tidal forces exerted on the Moon by the Earth and Sun. Some other sorts of moonquakes are thought to be caused by impacts, or by thermal expansion (...
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1answer
137 views

What are the factors that dictate a given topology for seismometer placement around a volcano?

The image below (borrowed from [#1]) shows the topology of the seismometers around the volcano Stromboli. In the text, they explain the following: The seimometers were set on the flanks of the ...
11
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1answer
333 views

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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1answer
1k views

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 ...
11
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1answer
310 views

Relation between fault rupture aspect ratio and slip rate?

I am modeling a fault surface (which I consider to be a plane rectangle). I got the area of the surface, but the orientation is unknown, which can be found out if the aspect ratio of the rectangle is ...
13
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1answer
209 views

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 ...
12
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1answer
194 views

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 ...
13
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1answer
5k views

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? (...
17
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3answers
538 views

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 ...
12
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2answers
3k views

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 ...
12
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1answer
2k views

Is there any correlation between La Niña/El Niño and seismic activity?

I've read in the past that extreme precipitation levels may have an effect on seismic activity, and wondered if anyone has ever analysed the La Niña / El Niño cycles to see if there are any ...
8
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2answers
299 views

Is seismology really the only way to measure the thickness of Earth's layers?

Answers from these two questions: How can we guess the size of the earths inner core? & How can we measure the thickness of the earths mantle? use seismic waves as the method for detirmining ...
11
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1answer
163 views

How do we determine subsurface composition?

Let's assume that a seismogram $s(t)$ is the convolution $s(t)=r(t)g(t)$ between a source signal $r(t)$ and propagation effects $g(t)$. If the source signal $r(t)$ is known, then we can obtain the ...
12
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1answer
178 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 ...
22
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3answers
8k views

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?
11
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1answer
527 views

What generates the microseism?

Looking at seismic noise around the Earth there is commonly a peak in the seismic noise around a frequency of 200 mHz. This peak is typically referred to as the microseism (an example is shown below)....
14
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2answers
326 views

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 ...