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We can calculate the dimension of a fault plane for a particular magnitude earthquake using Wells and Coppersmith (1994) relation. But how can we locate it on map.  
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I am also seeking answers to this question in 2022.
Has anyone been able to obtain a definite procedure to estimate the location of the surface projection of a buried fault plane?
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One way to display multi-attributes in seismology is to use 2D colormaps. Can anyone advise how to use 2D colormap in MATLAB in the imagesc command?
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Perhaps you may check MathWorks community, there are many similar Qs with helpful As. For example:
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If a rigid plate is bounded by two transform faults and the plate is moving, with the translatory motion of the plate will there be oscillatory motion as well? If not, why and if there is an oscillatory motion then what will be the mechanism of it?
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In my article on RG 'The driving forces of tectonic activity' I propose a mechanism that can explain an oscillatory motion of moving plates.
It is well documented that tectonic activity has a seasonal variation. The article gives a mechansm based on the axis tilt of the earth with a different velocity ( and centr@ifugal force) of the earth hemispheres in the rotation around the sun according to the seasons.
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Can rainfall affect the amount of fundamental frequency (fundamental period) and shear wave velocity profiles from the HVSR technique?
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The effect of rainfall on the fundamental frequency and shear wave velocity profile is limited. Various articles have been reviewed on the effect of saturation or non-saturation on shear wave velocity and fundamental frequency. yang 2001, yang 2006 has investigated that the effect of full saturation and partial saturation on the shear wave velocity is negligible, and on the other hand, the compressive wave velocity can be significant.
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Hi,
I need the digitized data (Acceleration time history) of 1968 Tokachi-Oki Earthquake (Hachinohe harbor).
Here you can see the graph of this record (Acc. time history) that used in this article:
And also an old report of this event is available in Port and Airport Research Institute of Japan website: [pari.go.jp] (Strong-Motion Earthquake Records on The 1968 Tokachi-Oki Earthquake And Its Aftershocks)
I wonder if someone can help me find this record. Thanks.
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Do you find it. Could you send me a copy? I find a record but the time seems to be the right.
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Dear researchers,
Please before any of you find my question incorrect or even blame me for it, be patient until this conversation continues!
Today, for scholars, earthquake is an understandable concept, somewhat of course non unique and imprecise. If it is true, please stay with me!
This natural phenomenon varies greatly in size. Occurs at different depths of the earth's crust or lithosphere. They have different mechanisms. They can happen anywhere and anytime. Although the location of many of them is explained by plate tectonic theory, their occurrence is possible anywhere on Earth. Their magnitude on the known Richter scale can vary from small numbers (negative) to about 10. It can be happen even if be greater than 10!?!
In seismology, where the magnitude of an earthquake is proportional to the moment (Mo=µSD relation), by the same value of the shear modulus (µ) the amount of area (S) as well as the amount of displacement (D) at their very low level is ambiguous (for examples, a bulk of materials and grains size, crystal or molecule-atom scales). They are also very different in terms of origin. They originate by falling caves, erupted volcanoes and around the magma chambers, between plate boundaries (Interplate), induction such as around dam reservoirs, vary in focal depth from a few kilometers to several tens of kilometers. They also occur inside lithospheric plates (Intraplate), which may not be well understood in relation to the plate tectonics theory. In terms of duration time on waveforms (seismograms), they fluctuate between less than 10 seconds to more than 1 minute and have variation in frequencies from 0.001 up to 1000 Hz and more between 0.01 up to 100 Hz. By improvement of instruments and methods, can be sensed and detected as small amplitude as possible. If they consider as strong ground motion in earthquake engineering views because of human and financial losses (greater than 4 up to 4.5 as threshold magnitude), the task is somewhat clear. But this limitation in magnitudes does not solve the scientific problem of the source and the initiation of this phenomenon and how it was really created. Should they be considered as the propagation of elastic waves on the ground? Do they come only from the release of the elastic energy of the strain of the crust materials? As the famous scientist Reid said? Apart from breaking (fault and failure), can other phenomena produce such violent and destructive waves? As we know, Aki and Richards in their effort “Quantitative Seismology” tried to point out that seismology is the scientific study of mechanical vibrations of the Earth due to earthquakes. We also know that any small earthquake can be a pre-earthquake (foreshock) or a post-earthquake (aftershock) of a larger earthquake. Without knowing which of them, are the main earthquake (main shock), it will take a long time (hours to several days) to distinguish it. I have not yet found a powerful answer for the question. I will be very grateful if someone can satisfy me with a reasonable answer. If is not, I together with interested researchers ready to define it as a joint project for finding the proper answer.
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I latch on to it as an event that generates seismic waves -- natural or human-made. Right or wrong, this take put me in a better position to understand Dr Stephen Hicks' discovery that COVID-19 lockdown caused 50% global reduction in human-linked Earth vibrations. My RG question about this highly significant research didn't fetch a single reply or recommendation. https://www.researchgate.net/post/Have_you_heard_that_most_pronounced_silence_in_these_COVID-19_days
Seismic or not, it's the "shaking of the surface of the Earth" that makes it a disaster.
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Hello everyone.
Any one can help me with the computation of the ray parameter (p) for seismological phases?
If a code is available in Matlab, it would be most useful!
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Good morning,
I tried converting seismic SAC data into SAF using Geopsy, but the results were not satisfactory. Is there any other way to do that conversion from SAC to SAF?
Thank you
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i am using seisaf program to convert 1.man file of seisan in sAF format but it convert only one top station in saf format and not converting others...any one please healp me in this matter
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Initial surface absorption test
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This is a good question.
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Actually I've had done it, but the result only show tsunami generated by landslide. Somehow the earthquake just disappeared in the model.
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Can any one tell me how to run the comcot model for tsunami generation.
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Sylhet in Bangladeh, experienced mini seismic jolts frequently.
Sylhet is on the Assam the Indian tetronic juncture.
Induces are must to release the mounted Tremor pressure.
How quickly can this be done?
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Hi, You in Bangladesh have a good earthquake forecaster... One person of them is present at Facebook: Naeem Ahmed with his earthquake prediction account: https://www.facebook.com/seismobd/; https://www.facebook.com/groups/1335828209784002;https://www.facebook.com/naeem.ahmed2188/
You can ask him because he has to have a very acceptable... concept for explanation...
About my earthquake forecasting, you can get information from my works:
and mainly at the nexts (discussion and question):
From the next my article: you can get an opposition view against the PT theory: that is why such an explanation that wants to resolve such a problem with the mentioned theory cannot be very good... The real tectonic structure of the East area of Bangladesh same we can get such 'correct' ('' -not worked out) conclusion which negates explanation of the plates tectonics in connection to the East Banglades... I have a presumption that arose mentally a few days ago I will try it in the case of Banglades...
Regards,
Laszlo
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I am just curious to know, Is there a publically available catalogue of explosion occurred?
Just like the earthquake catalogue available from ISC or USGS or GCMT? Or a catalogue with the combination of both explosions and earthquake?
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You could try the International Seismological Centre's Ground Truth reference events catalogue http://www.isc.ac.uk/gtevents/
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I working on radiation pattern to seismology ,please help me about how plot it for seismic wave at an earthquake?
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Seismic Radiation From Simple Models of Earthquakes R. Madariaga
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I am looking for a way to increase the number of sensors in acoustic emission lab experiments. Fiber optics (DAS) is a natural candidate but the standard resolution is several meters. Is it possible to increase the resolution to cm and use the method on laboratory scale?
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I highly recommend you to dig into the difference between OFDR and OTDR methods. If you want mm gauge length, you might need to make OFDR DAS system, or ask manufacturer like LUNA to customize one for you. OFDR is not recommended for length more than 50 m.
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Good morning.
I'm trying to fix a proper velocity model for waveform inversion. I thought that if I get a good "rms" with the localisation I can start the inversion with that velocity model.
The thing is that I get a good rms (under 0.15) and an acceptable erh and erz (under 1km). The gap, the itr and the v1/v4 are also acceptable in all trials. But each time I get a different locations, far away with almost 5 km in some results.
How can we choose with certitude a proper velocity model when all trials give a good output parameter?
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First of all, are all your earthquakes crustal ones ? If so, try to identify extra information available, like faults existing in the epicentral area. And see how the epicenters are matching the faults path. Maybe some Seismic Prospecting data or tectonic information are available too and could be compared to the obtained fault plane solutions too. Maybe some large refraction profiles are available in your area to fix the depth to Moho and so on. You may use other codes for joint hypocentral determination, like VELEST and see the results too.
To conclude, simply using some rms values is not enough and extra information should be used.
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Could you suggest any python module that is made for dealing with statistical seismology?
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Dear Vivek,
Please check the website https://pyrocko.org/.
You shall find a large variety of descriptions for seismology toolboxes and libraries, written in Python. Enjoy!
With best regards,
ALEX
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Hello,
I need a small clarification on artificial and synthetic accelerograms. To my knowledge, synthetic accelerograms are those which can be derived from seismological parameters and artificial accelerograms those which can be derived from spectrum compatible. If my explanation is wrong, kindly correct me. 
Another clarification on synthetic accelerogram is, why do we multiply source, path and site terms in generating synthetic accelerogram. To my knowledge, source is related to magnitude, path is related to hypocentral distance and site is related to local geology. If my explanation is wrong, kindly provide detailed information.
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This is an interesting question.
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I am using ocean bottom seismometer (OBS) data for ambient noise H/V with a target of nearly 5 Km. To consider the water layer effect, it is important to know the theoretical concept of P-wave contribution to ambient noise H/V peaks. The frequency range I use is 0.03 to 2 Hz.
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ambient noise consist of body and surface waves and their complex interference (diffarciton, scattering, dispersion etc.). Within this scope P waves echos in the range of 'broad band' frequencies between 0.1-2 Hz. You can use therotical p wave/s wave amplitude spectrum in order to obtain h/v transfer function for deep basin (as your case-5 km)
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NASA’s latest robotic geologist is starting to reveal the red planet’s pulse.
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1. Mars catastrophic past.
2. Real forces of celestial mechanics
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I am working in statistical seismology and we are running into a HIGHLY controversial topic. What can we say about the largest possible event (earthquake) that could happen in an area based on data? We make estimates, but what reliability do these estimates carry? There are epistemic and random uncertainties involved. There are many theoretical estimators for this quantity but many scientist doubt that they are of any practical value. I do not believe we seismologists are qualified to do more than "rambling" about the problem and I think some input from philosophers would be extremely enlightening.
I refer to papers:
Pisarenko VF (1991). Statistical evaluation of maximum possible magnitude. Izvestiya Earth Phys 27:757–763
Zöller, G. & Holschneider, M. (2016). The Maximum Possible and the Maximum Expected
Earthquake Magnitude for Production-Induced Earthquakes at the Gas Field in Groningen, The
Netherlands. Bull. Seismol. Soc. Am. 106, 2917-2921.
Zöller, G. (2017) Comment on “Estimation of Earthquake Hazard Parameters from Incomplete Data
Files. Part III. Incorporation of Uncertainty of Earthquake‐ Occurrence Model” by Andrzej
Kijko, Ansie Smit, and Markvard A. Sellevoll. Bull. Seismol. Soc. Am. 107: 1975-1978.
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and Albania ...
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I have been trying to model subsurface slip with GBIS software. However, after the geodetic inversion, i don't know how to draw the subsurface slip as shown in the screenshot. can anyone please help me with it ?
the example screenshot is taken from
Jónsson, S., Zebker, H., Segall, P., & Amelung, F. C. (2002). Fault slip distribution of the 1999 Mw 7.1 Hector Mine, California, earthquake, estimated from satellite radar and GPS measurements. Bulletin of the Seismological Society of America, 92(4), 1377-1389. https://doi.org/10.1785/0120000922
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Jiansheng Yu i have obtained the fault parameters through GBIS, but i dont know about how to write GMT scripts that produces a subsurface slip. if you have any idea, please share. Thanks
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Dear members of the Geophysics, Geoscience and seismology communities,
I am new in the areas of Geophysics and seismology; and I would like to get clear understanding of some technical concepts proper to these fields. Please, kindly spare few minutes of your time to answer this question so as to provide me with some tips to move on. Any suggestions would be greatly appreciated.
Thank you for your time
Best regards,
Patrice
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Dear Patrice:
There are 3 basic steps in seismic works, chronologically such as:
1) Design and Acquisition.
2) Processing the data, from 1).
3) Interpretation the data, from 2).
The objective of the point 2), seismic processing (your question) is to try to convert the acquired seismic data (using artificial “earthquakes” source: impulsive / vibrators / air-gun; and several receivers: geophones / hydrophones) to a seismic image.
Due that the data are recorder in time-sequences, and you use the multiple-fold coverage, you need to re-order the field data by CMP / CDP. Therefore, the basic processing sequence usually involves the following steps: Read the acquired data and assign its geometry; amplitude recovery; deconvolution, noise filtering; static corrections; rearrangement of traces by CMP; velocity analysis; correction for normal move-out NMO; residual static; Stacking; Migration.
On the other hand, you are talking about seismic interpretation, the third step. I recommend to read this wonderfull synthesis by Alistair Brown, AAPG, only 4 pages, a clear ideas, a better understanding what we (me too) do everyday.
If you are interesting to find a little more knowlegde, there are a lot of papers and books ... but please, you do not try to start with Oz Yilmaz´s bible for example ...a lot !!!!!!
Cheers, Mario E. Sigismondi
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Hello!
How can I quantify the uncertainty in the seismic wave incidence angle calculated with a single station? I have several earthquakes recorded by a single station and would like report the uncertainty to the hypocenter depths.
I will be grateful for the help.
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Would need math model of angle incidence estimator for helping with uncertainty
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A professor remarked that after a couple thousand kilometers from impact the length of a Rayleigh wave would be in the 200 meter range. Can anyone verify this and perhaps discuss their size when they are initially formed?
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Hi John,
I've been working on Chicxulub for the last 20 years, and this question never had come up!, with that you can imagine that I don't have a very good answer. To the best of my knowledge nobody has produced a model on this. All the models I know deal with the formation of the crater and the rheology of the target rocks.
Large meteorite impact structures on the terrestrial bodies of the Solar System contain pronounced topographic rings, which emerged from uplifted target (crustal) rocks within minutes of impact. To flow rapidly over large distances, these target rocks must have weakened drastically, but they subsequently regained sufficient strength to build and sustain topographic rings. The mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering are largely unknown and have been debated for decades. In 2016 we drilled Chicxulub and it has produced a record of brittle and viscous deformation within its peak-ring rocks. In a recent Nature paper, we show how catastrophic rock weakening upon impact is followed by an increase in rock strength that culminated in the formation of the peak ring during cratering. The observations point to quasi-continuous rock flow and hence acoustic fluidization as the dominant physical process controlling initial cratering, followed by increasingly localized faulting, but no estimates of Rayleigh wave-length what so ever.
Nature volume 562, pages511–518 (2018) .
Cheers.
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Is there a way or a simple code / software that can eliminate aftershocks of a main event with respect to time and distance?
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Dear Redouane,
There is no sure-fire way to way to "automatically" decluster earthquake catalogues! Methods of declustering have evolved from the generally inefficient deterministic (e.g. Gardner and Knopoff, 1974; Reasenberg, 1985) to the more complicated stochastic (e.g. Zhuang et al., 2002; Marsan and Lengliné, 2008). An excellent review is provided by van Stiphout et al, (2012). The former identify aftershocks using temporal and spatial windows that usually depend on the main shock magnitude while ignoring aftershocks of aftershocks (higher order events). The latter allow for aftershock triggering within a cluster and use Omori’s law as a measure of the temporal dependence of aftershock activity. Both approaches ignore fault elongation for larger magnitude events, assuming circular (isotropic) spatial windows. Stochastic declustering was pioneered by Zhuang et al. (2002) and is based on space-time branching techniques to describe how each event triggers its successors. Nevertheless, it is parametric (model driven). It improves on previous methods in that the choice of space-time distance is optimized by fitting an ETAS model to the earthquake data. Moreover, instead of associating an aftershock with one main shock, each earthquake is assigned with a probability that it is an aftershock of its predecessor. This means that all earthquakes are possible main shocks to their short-term aftermath and neatly circumvents the problem of having to make committing binary decisions in the frequent cases of nearly equal space-time distances between successive events. Marsan and Lengliné (2008) carried stochastic declustering one step forward by introducing a generalized triggering process without a specific underlying earthquake occurrence model, although they still assume that background earthquakes occur at constant and spatially uniform rate density.
So there you have it... simple way there is not! Better use stochastic methods, although they require significant effort to understand, and depending on the quality of the catalogue hope for the best...
References
1. Gardner, J. K., and Knopoff, L., 1974. Is the sequence of earthquakes in Southern California, with aftershocks removed, Poissonian? Bull. Seism. Soc. Am., 64 (5), 1363-1367.
2. Reasenberg, P. 1985. Second-order moment of central California seismicity, 1969-82, J. Geophys. Res., 90, 5479, 5495.
3. Marsan, D. and Lengliné, O., 2008. Extending earthquakes’s reach through cascading, Science, 319, 1076; doi: 10.1126/science.1148783.
4. van Stiphout, T., Zhuang J, and Marsan D., 2012, Seismicity declustering, Community Online Resource for Statistical Seismicity Analysis, doi: 10.5078/corssa-52382934. Available at http://www.corssa.org.
5. Zhuang J., Ogata Y. and Vere-Jones D., 2002. Stochastic declustering of space-time earthquake occurrences, J. Amer. Stat. Assoc., 97, 369-380.
6. Zhuang J., Ogata Y. and Vere-Jones D., 2004. Analyzing earthquake clustering features by using stochastic reconstruction, J. Geophys. Res., 109 (B5), B05301; doi: 10.1029/2003JB002879.
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I found on Wikipedia that the equation for primary/secondary wave speed in solids in 3D is
C_{solid,p} = sqrt((K+4/3*G)/rho)
C_{solid,s} = sqrt(G/rho)
where K is the bulk modulus, and G is the shear modulus of the elastic material, and rho is the material density.
  1. How was this equation derived? A source of literature will be helpful.
  2. Is this equation the same in 2D?
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Derivation of equation for velocity of P wave & S wave
P-wave propagates with the help of expansion and compression of the medium, so the motion of the particles is in the direction of propagation of the wave whereas the S-wave propagates with the relative perpendicular motion of the particles. P-waves are also called longitudinal wave/compressional wave and S-waves are also called transversal wave/shear wave. The derivation of equation for velocity of P-wave/S-wave is quite complicated and is very difficult to understand so here, we would only deal with the 1 dimension accoustic wave equation.
You can derive the velocity of S-wave or P-wave if you know 3 equations. First is the Newton's ssecond law of motion (F=ma), Hooke's law for elasticity and equation of sound waves. Easy, isn't it ?
Let us consider that P is the pressure that is exerted on the subsurface layer by the wave incident on it and x is the distance travelled by the wave in order to do so. þ is the density of the formation on which the given wave is incident. ø and µ are the modulus of elasticity and modulus of rigidity.
As we know that the Newton's 2nd law is given by:
dP/dx = þ* dx²/dt² (1)
As we know that as per Hooke's law, the ratio of stress and strain is equal to the modulus of elasticity;
so,
P = ø* dy/dx (2)
differentiating equation (2) w.r.t. x, we get
dP/dx = ø* dy²/dx²
putting equation (1) in above equation, we get
þ* dx²/dt² = ø* dy²/dx²
dx²/dt² = (ø/þ)* dy²/dx²
comparing above equation with equation of sound wave we can directly obtain
V² = (ø/þ)
V = (ø/þ)^½ (3)
Now, for s-wave we can write modulus of elasticity(ø) = modulus of rigidity(µ)
so, by replacing the above value ø in equation (3) by the above relation, we can write velocity of S-wave which is given by,
V = (µ/þ)^½
Similarly you can derive the equation of velocity of p-wave in which the modulus of elasticity is the function of modulus of rigidity and bulk modulus(K).
i.e. ø = K + (4/3µ).so, by replacing the above value ø in equation (3) by the above relation, we can write the velocity of P-wave which is given by,
V = [{K + (4/3µ)}/þ]^½
That's it !!!
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I need to asses what would be the consequences of earthquakes over a cylindrical water tank embedded in soil (roof is at the surface of the soil).
I was wondering to do a spectral response analysis but does this makes sense if the whole structure is below the surface?
What analysis can I do over the structure to asses seismic risk? Any recommendation is appreciated!
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In general the answer of your question is yes and I explain more below about the conditions and applications to do a spectral response analysis for a water tank when it is supposed to be embedded in the soil. In water tanks embedded in soil, at least to some extent, for many cases, the conditions of embedment are complicated. For example, structures are not supported uniformly around their circumferences because of adjacent structures and cuts in the soil, such as for the connected pipes, etc. Water embedment has a significant effect on soil-structure interaction: in comparison with a surface foundation, both the water tank input motion and the water tank impedances change for an embedded water tank. For vertically propagating waves, a horizontal shear wave produces both a horizontal translation and rotation of the embedded massless foundation; a vertical compression wave produces a vertical translation and rocking of the embedded massless water tank. In general, the amplitude of a water tank input motion for embedded water tanks is less than that for surface water tanks, especially in the high-frequency range. Structural responses are thus reduced for embedded water tanks. For water tanks, during the seismic design of a soil-foundation-structure system, if the water tank is embedded under the soil surface, design response spectra at the control point under the soil surface. However, location of the water tank is not always known at the time when the design response spectrum is constructed. Thus, design response spectra at several depths of the site profile need to be established considering the free-field ground response; the effect of soil-structure interaction is not considered. Besides, because soil parameters usually exhibit large variabilities, it causes uncertainty of the design response spectra at various depths of the site profile. Thus, probabilistic design response spectrum at a control point under the soil surface may be required to accurately reflect the seismic hazards at corresponding locations.
I hope my answer is helpful and responded to your question.
Best of luck.
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Can anyone give me some reasons why we should use Python language programming instead of Matlab in seismology?
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If you are looking a python solution for signal seismic processing because you are looking for something easier to work than MathLab I have bad news. I think learn and work wiht python will demand to you a similar effort than working with mathLab.
But if the problem is to pay a license I think python Could be a solution for your processing problems. The advantage of python over MathLab despite the cost is you will gain much more flexibility by accesing tens of specific libraries that can help your work
Apparently a library for seismic signal exists and is call ObsPy:
And also you can access to different free GIS packages like GMT, QGIS that give you the possibilitty to create maps too.
I hope this comments will help you.
Cheers Gabriel
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Hi,
I am working on Travel Time Tomography in seismology. I am looking for an algorithm for ray bending method using conjugate gradient method. If there is an existing code for the ray bending method, then it would be useful as well.
Thanks
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International Association of the Seismology and Physics of the Earth's Interior (IASPEI)
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Good morning,
I'm trying to generate synthetic seismograms for an observed seismic event.
I did compare the amplitude in the time domain, and applied the FFT for both observed and synthetic waveforms.
although all the signals are beneath 0.3Hz, I'm asking about the tolerance range in the frequency domain.
How near the frequency ranges need to be in the FFT, to tell if my two signals are similar.
Thank you in advance
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thank you very much for your quick answer, that's very helpful.
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Hello,
I am currently working on a software on Travel Time Tomography of refracted rays.
I have an under-determined problem and I am using sparse matrix solver like LSQR, to solve Ax = b .
Since this is an ill-posed problem, I want to apply Tikhonov regularization to the system and hence determine the "best" Tikhonov parameter, to achieve our target chi-square, after constructing the L-curve.
We are trying to minimize the cost function:
F(dx) = || Ax - b ||2 + lamba2 || Dx ||2 + n2 I dx
Where lamba is the Tikhonov parameter. and n is the damping parameter. Both are collectively known as the tuning parameters.
D is the first derivative matrix.
What should be the range of the tuning parameters while constructing the L-curve? Should it lie between 0 and 1 OR higher?
I appreciate your help.
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I'd like 2 suggest to see the book written by Zadahanov on Inversion.
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I am trying check if earthquakes record located around 950 km has the pP phase.
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Second step is run a programe like TAU_P Code to generate arival time of pP phse for your Source_Receiver distance.
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About the HVSR method, I am interested to know:
1) The depth coverage for depicting regional structure
2) The window length, frequency range, etc. for such works.
3) Should the data be broadband or short period data would do?
4) Also wish to know if it was really possible by using data of surface seismometers.
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Thanks a lot.
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Since 1988 to present began The Scientific Consensus on Climate Change. Over this period of time we have not advanced neither in climatology nor in other related sciences. Hydrology,meteorology,seismology all related sciences in the same state as 40 yeas ago.
Science is the ability to build models. Models are patterns. And the patterns somethimes are wrong. Science is the ability to be wrong.
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The yardstick with which we measure the progress of atmospheric sciences in our time is the predictability across the scales from minutes to weeks and in extreme cases to seasons. Even if this measure seems to be unreasonable, there is agreement on using it to judge our models. In the field of numerical weather forecasting, the progress is spectacular, as the recent review by the group of leading scientists shows:
At the same time, there are voices pointing out the severe limitations of our "across the scale" forecasts, as the atmospheric system is chaotic (this fact was discovered by Lorentz in 1960s)
The situation in climate modeling is even more complicated, but it is agreed that our models are sufficiently accurate to make a climate prediction based on known boundary and initial conditions. Most importantly, in climate modeling, knowledge of the boundary conditions is crucial, and actual progress depends on how accurately we can evaluate them; this subject requires the extensive interaction between all fields of geosciences.
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I am working on rotational seismology, and I want to give rotational ground motion data as a input in SAP 2000, and want to check the torsional mode shapes of structure, and want to study about effects of rotational component of ground motion data, If any other software is available for this purpose then please suggest me that also.
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Hi Ankit Goyal , you may input the rotational ground motion as a rotational acceleration load in SAP2000. To do this, first define a time history function based on the ground motion data you have. Next, define a load case for the acceleration load. Select "Time History" under the load case type. Under "Loads Applied", select "Accel" load type and the rotational degree of freedom under "Load Name". Use your defined function for the rotational acceleration. You may refer to the following websites for more information:
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I want a scholarship
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Dear Arshad,
Thank you for your interest. I moved from Kamchatka to Mexico 25 years ago. Now I am working with the seismic events of volcanoes. We can not support your scholarship at our Colima University but if you could find any grants, we´ll be glad to receive you here for any joint investigations.
Best regards,
Vyacheslav
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The PGV to PGA ratio is known as a significant parameter for the damage assessment of structures under earthquake shakings. As a matter of fact, it is considered as a descriptor of the frequency contents of the seismic input motion. I am interested in understanding the physical and seismological significance of that ratio, and finally the engineering meaning, and its correlation with the structural damage.
I could not find technical treatments except empirical measurements.
Many thanks in advance for your contribution.
danilo
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Consider a SHM for which displacement y = Acos(wt+B), Then velocity v = -wAsin (wt+B) and acceleration = -Aw2cos(wt+B). Thus the ratio PGV/PGA = 1/w i.e. the inverse of the circular frequency = 1/(2πf) = T/(2π ).
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Geophone used in falling weight Deflectometer-to measure deflections.
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EGL Equipment Services Co, Ltd offers high-quality geophones for sale at competitive prices to clients from all over the globe.
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My primary goal is to find out Rayleigh wave dispersion from array of seismometer for several 100s of meters to depict shear wave velocity layers in the ocean bottom.
I am a beginner with programming.
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In my experience, python as a lot more seismic librairies such as obspy, and also a lot more seismic file read/write such as segyio librairies.
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I'm going to perform seismic analysis on LUSAS, FEM software. Downloaded ground motion data (accelerograms) from CESM database in the form of a text file. I have no clue how to move forward. I just know that I need two columns in a spreadsheet where one represents time, while the other one- acceleration.
Any help would be appreciated!
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Here you go, you should be able to work it out from this example file I made.
If you're smart you'll change the equation for the list under "column" so that you don't even need to split the time and acceleration columns.
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Expensive types of gravimeters are used to detect small changes in gravity. High-precision simple pendulums, about 2 m long and using automated timing cost significantly less. In addition, they have less components and so less sources of potential errors. Also , there are issues with the springs used in gravimeters. Why, then, are the more expensive gravimeters preferred over the less expensive simple-pendulum type of gravimeter?
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Dear Dharanjit,
In fact, pendulums do not make it possible to obtain absolute measurements of gravity, which is why they are not used to measure gravity changes in seismology.
Best regards
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I'm using Seisan for Regional earthquakes. I append one event from several stations (More than 3, at list 60) and picked their phase mainly P. But I cant able to locate them. Its showing some strange error. I'm here by posting one screen shot also. But I picked one phase from at least 60 stations. Please help me.
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I think your stations didnt define well. Please check out your station file.
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Please suggest me how to calculate stress accumulation and strain using gps displacements for understanding the occurrence of failure (earthquakes).....
Thank you
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The simple answer to get to strain from displacements is to find the deformation matrix that connects initial to final positions. If you are working in 3D that would be a 3D tensor. If you could assume plane strain the matrix would be simpler. Basically the displacements would be longitudinal and angular and you could go about quantifying those depending on your problem. If your data consist of GPS displacements, it is the longitudinal strain (typically N and E) that is significant and you can look at "baselines" that shorten or extend in the direction that is most important to you. As Stress and Strain tensors are connected through the Rheology tensor, you would need to have information about the rheology of the deforming material to be able to go from strain to stress (as Martijn correctly pointed out above). If the deformation is near surface then elastico-frictional laws typically apply. Other wise you could opt for quasi-plastic or viscoelastic rheologies.
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As you know that Mw is related to released energy for specific earthquake, so why their recorded accelerations vary for the same distance and Mw for different seismotectonic regions?
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Another effect can also play an important role when it comes to reverse fault. Indeed, the sectors on the hanging wall of the fault may exhibit greater acceleration equidistant from the epicenter than the areas on the overlapped compartment.
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In following file you can see spectrum energy.
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I am particularly interested in the ability of rammed earth walls in a simple, one-story house to resist tornado debris and tornadic winds. I am aware of the Matta et al. paper on Compressed Stabilized Earth Blocks and high winds, "Earthen Masonry Dwelling Structures for Extreme Wind Loads."
Have any studies been done on RE (wind-borne) debris resistance?
How is a continuous load path created for a house with rammed earth walls? Rebar? Geogrid? Are there articles which address this?
Thank you.
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I don´t think that a brittle rammed earth house may be able to withstand extreme winds like the induced by tornados. This material behaves brittle even when subjected to reduced stress levels due to the intrinsic poor strength and lack of structural integrity among structural elements (lateral loading induced by earthquakes, extreme winds and so on).
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It is very important to study the time-acceleration history for all seismotectonic units in all overall the world to establish new type of ground motion attenuation and for data truth.
regards
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The resources of IRIS, USGS, GEE may cater the need of required dataset.
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Hi
Rock characteristics such as porosity, density, mineralogy and mechanical properties have correlation with wave propagation. Can i achive a base method for modeling the rock with all properties?
We can make model of deep ground with seismology. Than how can optimized these methods?
Thanks
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Wave speed in different directions give an indication of density and rigidity, which together with other data make a model.
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It is well known that SAR (Synthetic Aperture Radar) interferometry is based on the SAR technology. How SAR can detect the deformation in three dimensions after earthquake happen? is it possible to measure the slip rate and fault parameters from SAR technology?
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To answer your questions you need to first make interferograms from SAR acquisitions.
So say you have interferograms from scenes captured before and after an earthquake, and you unwrap the interferogram, you essentially have a map of surface displacement caused by the earthquake (with resolution depending on how coherent pixels on the ground are). Now, that allows you to easily invert for coseismic slip distribution on a fault in 3D. But these are only static offsets. You cannot investigate the rupture process with InSAR.
Now, the more fun parts are while dealing with other quasi-static processes like interseismic and post seismic velocity fields (and possible debris flow/landslides). If you collect enough SAR scenes over a particular frame on the ground, you can create a time series of the surface velocity field. Now you can invert that data for slip rates/locking depth of faults/frictional parameters/strain rates (for afterslip/visco-elastic relaxation studies). 
The links that have been provided by some of the other responses to this thread are excellent, and should give you a more detailed description of the possibilities with SAR interferometry.
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The moment magnitude of the earthquake would be calculated by following formula
Moment magnitude Mw=2/3 log (Mo-9.1)
Seismic moment (Mo) = μ*S*D
My doubt is how could we get rupture length (S) and Slip of an area (D) immediately. Is there any standard model to calculate these parameters?
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Dear Ramesh,
consider that, as a general property, the value of the amplitude spectrum of displacement at frequency=0 is proportional to the seismic moment Mo (see Aki & Richards “Quantitative Seismology” ed. 2009, chapter 10).
So, if you take the signal of your seismic event, compensate for attenuation and geometrical spreading, convert it to displacement and compute the amplitude spectrum then the value at f=0 (I call it Ao) gives you a measure of Mo. Depending on the type os sensor you are using, probably you don’t get the recording of signals down to f=0, but you can approximate it by considering the behaviour of the spectrum at low frequencies.
To get the final value of the Mo, and so of Mw, you need to link Ao to Mo. This can be done assuming some model of the rupture which allows to link the kinematic parameteres to the geometrical/seismic parameter of the rupture. A model often used is the Brune-Madariaga model that assumes circular rupture and is suited for moderate (let say up to Mw=5) and shallow (into the crust) earthquakes. In this case you get:
Mo=2πρv^3Ao/0.6
Where ρ is density and v velocity at source, and 0.6 accounts for average radiation pattern.
Hope the above can help.
Kind regards,
Lorenzo
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It is clear that both systems keep the general shape of signal similar. But do they have differences in saving same signal in both systems?
digital save it in binary mood so what is the effect of sampling rate and digital recording system on signal saving?
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Digital mode are stored in zero and one, and there are more easier to handle and manipulate , while analog data are continuous with great fidelity, but very difficult to handle. Because of this,most times analog data are digitized and converted into digital data.most state of the art equipment work with digital data.
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Hello,
someone knows a program available to calculate synthetic Receiver Function?
I tried to use the Matlab toolbox FuncLab, written by Kevin C. Eagar but I think that it works only functions for RF analysis ...
Someone can help me, please?
Thanks in advance,
Leonardo
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Hi 
There are different types of tools to generate a synthetic Receiver Function. For example an iterative deconvolution process (Ligorría and Ammon,1999). It required an velocity model. Please see the following link for more details,
Best wishes
Nagaraju Kanna
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As far as I know, in seismology, we usually assume the dislocation on the fault is unidirectional thus we only see a positive part on displacement record. However, I could see not a few traces with a large negative part. Dose it mean the dislocation reverse it direction? Thanks!
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Yeah, it could be one possible reason. But this phenomenon doesn't not observed at a majority of stations. Only a potion of them have a large negative cycle. Could some other source reason or local structure have this effect?
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Seismic Image issues are very challenging in thrust fold areas, specially in highly undulated terrain. However, in recent years the Passive Seismic Tomography has emerged as a solution to the problem. I would like to know if anyone has experience and provide about case studies & papers with expert advice on how to perform the Passive Seismic Tomography in thrust fold areas for undulated terrains?
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Passive seismic tomography will help remarkably in thrust belt area if the data is processed properly. The technique is tried in Baramura and Tulamura antiforms with thrusts. There are shadow zone problems in the crestal part and that require radon processing and re-imaging.
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I read that there is a direct relation between variation of pressure and seismic noise: high pressure correspond to an increase of noise, low pressure correspond to a decrease of noise.
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A reasonable answer is in the first page of this paper
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i designed 8 story rigid frame building using static equivalent seismic load as lateral load
when i did linear time history analysis as lateral load (SE not used anymore), some of its members are overstress.
somebody told me that SE is always larger than THA and it's impossible that my members are overstress
is there possibility that THA is larger than SE in member internal forces?
i'm pretty sure that my step is based on ASCE 7-10
thank you
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It is certainly possible for time history analysis to result in a more severe response than static equivalent. You need to look at the method used to select and modify the ground motions used in the time history analysis. Compare the mean spectrum of the records (which will determine the level of response to the time history analysis) to the code-based design spectrum used for the static equivalent. You must also consider how bidirectional effects are included in each method if you are employing a 3D model as opposed to a 2D model. Recall, as well, that forces from a static equivalent analysis are reduced by the R-factor. Frankly, a linear time history analysis does not reveal much new information beyond static equivalent. Inelastic time history analysis, on the other hand, is very revealing. So I am unsure how much you gain by performing the linear THA.
If every mode of vibration were on the acceleration plateau of the spectrum (they never are) and if the response spectrum of every THA ground motion perfectly matched the target response spectrum (none of them will) then you could expect the same results from SE and linear THA.
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Good morning everyone,
I should parameterize in a 3D grid my shear-wave velocity model deduced from receiver function analysis. Considering that the best velocity model which represents a discontinuity in the receiver functions is represented by a step function, how can I solve in 3D the problem of singularity (Dirac delta in mathematical terms) keeping constant (no flexibility) the discontinuity value? Someone knows or can suggest me some papers about this key point, please?
Thank you very much for your big help,
Leonardo 
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Sorry, but for what purpose are you making a 3-D grid?  If it is for display or comparison with other observations, a discontinuity would seem to not be a problem.  If it is to then do wave propagation, it depends on the software or algorithm you are intending to use. Most applications are content with a strong gradient rather than a true discontinuity (and receiver functions are sensitive to gradients above some threshold, so the presence of a converted arrival only reflects the presence of a strong gradient, not necessarily a discontinuity).
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If a source is distant and shallow, then the incident wave to a basin will consist mainly of surface waves. When surface waves reach the basin, a part of the incident wave energy reflected back but the rest is impinging into the basin. It means the energy is decreased significantly but it still has large amplitude.
What are the causes of larger amplitude of basin-transduced surface waves?
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The cause of large amplitude of basin transduced surface waves are
1. Transmission coefficient at the basin-edge is much larger than what we expect in case of body waves.
2. Sudden drop in impedance in basin causes the amplitude amplification
3. Further, the amplitude amplification due to decrease of wavelength in basin is much larger in case of surface waves since amplitude decrease with depth is exponential in nature.
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Some think that 25 December 2016 magnitude 7.7 earthquake might be aftershock of the 1960 M9.5 earthquake. My question is how M7.7 earthquake could be considered aftershock? Isn't it too big for aftershock? To me, there should be upper limit of the magnitude of the aftershock! 
Anyone help me to understand this phenomenon.
Best,
Mehmet
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At least the magnitude of the main shock itself is the upper limit of the magnitude of aftershocks.
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The wave diagram has been attached herewith.What is the reason of such wave?Is it noise or signal?
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Hi Vukalp, Can you increase the amplitudes on the screen and see if there is any signal looking like P-wave before the signal that you show? Stretch the traces almost exactly in the same way for all sensors so that we can compare them. Plot also the traces aligned with the distance. Please provide images with better quality.
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I have to locate the microseismic event at the site.In this regard,how after recording the waveform I can calibrate the magnitude?
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We expect to see the same law acting in small scale (wells) and big scale (seismic) when dealing with fractures and corridor of fractures. Fracturing has this advantage to cross over different scales.
Can we compare orientation in seismic, using long/short wavelength curvature approach, with orientation we see in well rose diagrams ?
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Yes, you can do that mainly for short wavelenght curvature data, but the issues in doing that still remain the same, and care must be taken when you perform up or downscalling in structural interpretation. For the long wave structures, and because the strain is lower in those cases as a general rule, the downscaling is more problematic, but still possible in my opinion.
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Dear All
I want to have the point of view from different experts given below to adopt an integrated approach.
1. Geologist
2. Engineering Geologist
3. Mining Geologist
4. Geomorphologist
5. Geographer
6. Civil Engineer
7. Mining Engineer
8. Meteorologist
9. Structural Geologist
10. Landslide Expert
11. Earthquake Geologist
12. Seismologist
Thanks for a quick response.
Regards
Ijaz
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Dear Ijaz,
re:    Landslides: failure mechanisms and triggering factors.
The scope of what you ask is vast and different disciplines approach them in different ways.  However, a landslide occurs due to two sets of factors :
1.         pre-disposing factors
2.         triggering factors
The best starting point, I suggest, is to read Varnes (1958).  His classification is sound and the different slides are well described.  It is clear that he divides landslides into falls, slides, flows and complex, and into bedrock and soils forms (p.21).  Brunsden (1979) is good for a more comprehensive approach.  The other literature I have appended gives an indication of the breadth of approaches to specific types of slide, e.g. Jaboyedoff (2011) gives a comprehensive study of rockfalls/slides, Campbell (1975) examines debris flows and Winter et al. (2005) gives the road engineer’s approach.
To return to pre-disposing factors, these include rock type, strike/dip of bedding planes, jointing patterns, susceptibility to weathering (both physical and chemical), soil characteristics, drainage patterns, groundwater movements, slope gradient, possibility of seismic activity, human interactions (mining activity/road or dam building in area), vegetation cover, climate, day-to-day weather experienced in area, among others.
Triggering factors include intense rainfall, excessive porewater pressures in rock/soil, gravity, seismic activity, undercutting by e.g. river or road building, overburden adding excess weight to slope
Models for landslide prediction will contain a selection of such factors relevant to the specific type of landslide involved.  I would assume that in Pakistan rockfalls, rockslides, debris slides and debris flows would loom large along with snow avalanches.
I hope this goes someway to answering your question.
George Strachan
BRUNSDEN, D. 1979. Mass movements. In Embleton C. & Thornes J. eds., Process in Geomorphology, Edward Arnold, p.130-186.
CAMPBELL, R. 1975. Soil slips, debris flows, and rainstorms in the Santa Monica Mountains and vicinity, Southern California. US Geological Survey Professional Paper, 851.
HENCHER, S.R. & LEE, S.G. 2010. Landslide mechanisms in Hong Kong. From Calcaterra D. & Parise M (eds.) Weathering as a predisposing factor to slope movements. GSL Engineering Geology Special Publications, 23, 77-103.
IVERSON, R.M. 1997. The physics of debris flows. Review of Geophysics (American Geophysical Union), 35, 245–296.
IVERSON, R.M. & LaHUSEN, R.G. 1993. Pore-pressure dynamics in debris-flow experiments. Abstract - Transactions (American Geophysical Union), 75, 274.
JABOYEDOFF, M. 2011. Slope tectonics. Geological Society Special Publication, 351.
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I need to design an RCC structure for a useful life of 300 years. The available Peak Ground Acceleration (PGA) value is 0.20 for Zone 2B of Pakistan. But this value is for structures with a useful design life of 50 years only. How to determine the PGA value for a structural design life of 300 years?
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Hi Shafi, if you have access to the original hazard curve of PGA for or near the site of your project, you can get easily the PGA for 300 years of lifetime. For example, 50 years lifetime with 10% of probability of exceedance yields about 500 years return period of ground motion (T=50/0.1) is the usual case, it  means that the number of earthquakes per year in this case is 1/500 = 0.002. Then if you have the hazard curve look for the number of earthquakes per year that matches 300 years life time with 10% of probability of exceedance (300/0.1=3,000 years return period) that is equivalent to 0.0003 earthquakes per year in the "y" axis. So just intercept the hazard curve to this value (0.00033) and get in "x" axis the PGA you are looking for. If you need the PGA for another probability of exceedance (i.e. 2% instead of 10%) you must divide all the former calculations by 0.02 instead of 0.1. If you do not have the hazard curve, you have to perform a hazard assessment for your site using available information. Hope it helps.
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My goal is to obtain the spectra of earthquakes: frequent, occasional, rare and very rare. The problem is that Latin American codes just define the spectrum of an earthquake with 10% probability of exceedance in 50 years, which would correspond to rare earthquake according to VISION 2000.
So, how can I get the remaining seismic spectras: frequent, occasional and very rare? Is it correct to scale the spectrum of the rare earthquake?. Conservatively, what scale factors would you suggest?
(Please mention your source, code or etc.)
Attached seismic performance objectives proposed by VISION 2000.
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Dear Arturo:
Thanks for the reference, that's what i was looking for.
Now, I have reviewed Roberto Aguiar's paper and I found that the investigations referred are based on codes of 96 (Chile),97 (Peru), 98 (Colombia), etc. And naturally, current codes are more exigent. So, if you know about recent publications, it would help me a lot.
best regards.
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Hi guys
I am performing a fault inversion for a pair of SAR SLC images. For my dinSAR map, the extents of the map is insufficient to envelop the entire seismic displacement area.
Just wondering, if I perform my inversion using such a map, what effects would it have on my results? I noted that the source modelled is accurately along the lines of existing fault boundaries. I'm am however unsure of the accuracy, especially regarding slip values.
Also, I noticed the fault inversions are iterative processes. How can I judge what should be a good result? I am processing using SARSCAPE.
Thank you
Regards
Ben
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Hi Ben 
Go with this article .may be it will help you
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I need some databases except PEER and ISESD.
I'm looking for an earthquake record (Hachinohe 1968 , Japan) that is not in those sites.
thank you so much
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The U.S. Geological Survey maintains an excellent online database of earthquakes, which can be filtered by several attributes, such as time, location, size, depth, etc.
I found records of two large (M>6) earthquakes in Japan in 1968:
I hope this helps.
Scott Bennett, USGS
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Hi,
does anyone know if secondary Love waves can be generated by Rayleigh wave interaction with a sedimentary basin boundary?
I have found prior work that showcases generation of secondary Rayleigh and Love waves due to the incident of S-waves on sedimentary basin boundaries for both the observational case and numerical calculations. From a purely simplified point of view the horizontal energy of a Rayleigh wave should excite Love waves when hitting a perpendicular sedimentary boundary.
Does anyone know of any results pointing towards or against such mechanism.
Any help is greatly appreciated.
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Thanks for the potential references, I will have a look through.
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I used Wells & Coppersmith, (1994) paper (has 4417 citations) to determine the rupture width and length when the moment magnitude (Mw) was given. This paper is little bit old paper. I did not find any new paper of ground breaking idea against this paper. Do you use another approach to calculate the rupture width  formulas published by Wells & Coppersmith, (1994)? I know that the theoretical way is too complex. I am searching a simple procedure (empirical or semi empirical).
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Dear Sameera,
The research on scaling relationships between earthquake rupture parameters has advanced significantly in the more than twenty years elapsed since the paper of Wells & Coppersmith (1994).
These improvements are based on datasets which are larger than the one in W&C, and which also embrace a wider range of faulting types and tectonic environments.
For example, the W&C dataset was biased, since it was dominated by earthquake ruptures with low stress drop. In consequence, for a given rupture length, earthquakes with large stress drops have magnitudes larger than expected from the W&C relations (for example the 2011 Darfield earthquake in New Zealand).
The best reference I can recommend is this review:
Stirling, M.; Goded, T.; Berryman, K. & Litchfield, N. (2013) Selection of earthquake scaling relationships for seismic‐hazard analysis. Bulletin of the Seismological Society of America, 103, 2993-3011.
Regarding the works by Leonard (2010 & 2012), mentioned in a different answer, note that these self-consistent relationships were recently updated by the same author:
Leonard (2015) Self-consistent earthquake fault-scaling relations: Update and extension to stable continental strike-slip faults. Bulletin of the Seismological Society of America, 104, 2953-2965.
I hope this helps. Best regards,
Álvaro
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I would like to retrieve the best fitting seismic moment tensor from given pressure and tension axis orientations, even in the case of non-double couple seismic source mechanisms. I did not find such function in MoPad, any suggestion, at least for pure double-couple case ?
Figure:  for a given seismic source, I have a probabilistic representation of pressure and tension axis orientations (Left and middle plots), what is the moment tensor of the corresponding  source mechanism (right plot) ?
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The mean P and T may be computed by vector summation, and will represent the best fitting P and T in the mean square sense. Then, the full moment tensor may be given in the principal axis frame of reference (P, T, N) and rotated to the working frame of reference as the orientation of the P, T, N vectors is known. If for some reason <P> and <T> are not strictly orthogonal, once they are normalized as unit vectors, it may be shown that <P>+<T> and <P>-<T> are orthogonal, and normal to the nodal planes, and the geometry of the moment tensor defined on this basis.
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I want to drive (draw) a seismic fragility curve for the four damage states (Slight, Moderate, Extensive, and Complete) for an existing building. I performed a nonlinear static pushover analysis (NSP) and I got the spectral capacity curve (spectral acceleration vs spectral displacement curve). As the last step to draw the fragility cure, I need to determine the lognormal mean modal displacement and lognormal standard deviation of modal displacement values from the capacity curve. How can I do that according to FEMA (or HAZUS)? pictures for Base shear-Displacement and spectral acceleration-displacement curves are attached. I appreciate your help.
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Dear Jahangir Alam
Refer to my last answer above.
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-An earthquake shook Yokadouma on September 19, 2012
-It was recorded by our station at 18h33 UTC
-We need P and S waves arrival times, the  codas, Amplitude and period of the signals and if possible the traces of the signals and location
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De rien, mais je pense que je n'ai pas beaucoup apporté.
Ce séisme n'est pas répertorié dans la base ISC. Je ne vois pas où on pourrait avoir des infos
Anne
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Hello everyone.
There have been a lot of research in Theoretical Geophysics in the past like Plate boundaries,  Earth's interior, Seismology etc. But has there been any theoretical Geophysics analysis of Landslides in particular, as to how these earlier research topics are connected to Landslides.
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Dear Aadityan, try any textbook on engineering geology and look for failure conditions, that means.:When does the shear stress due to the weight of a rock mass exceed the normal stress across a plane of weakness. An old classic e.g. is Elasticity, Fracture and Flow by J.C. Jaeger, Methuen London, 1969.
Regards
Rainer
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I am interested in analyzing large earthquakes around Indonesia from 1910 until 1960. I obtained the arrival time data from ISC website. However, I need seismogram to conduct further analysis. Is there any open access seismogram data available ( the scanned image or digitized version) for this period?
Thank you
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If raster files can be useful you can try SISMOS database. 
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I read in many papers like this, is this because of different methodology?
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I think for large earthquakes  moment tensor is better because moment tensor is stable rather than Polarities but for small events polarities will be better .
as well as moment tensor is more suitable to describe the source  as you know MT is linearly related to ground displacement