Seismotectonics - Science topic

Earthquake or what I sometimes call geo-quake builds up becuse of stored energy that is lurking within the subsurface. The position of the epicenter, earth's surface above the focus of an earthquake where this energy lurks does not depend on the shape of the earth nether can the shape of the earth be used to predict, but it relates to the mobile plates, which create disequillibrium above, below and around the position of the lurking energy. The resuling disequilibrium causes the sudden release of energy, which is disastrous whenever it occurs. Its prediction can be achieved by assessing the seismogenic activities few hours before and few hours after the earthquake/geo-quake.

Julian, If you are using Excel for your computations, please consider the value of R-squared coefficient. It is estimated routinely, but you should select the appropriate box, if you want to see its value. A value of R-squared close to 1, like 0.9 or 0.85 will indicate a good fitness by a straight line. I suppose you will obtain such a value for the whole data set in your Figure1 above. So, you may evaluate that first point by following what is happening with the R-squared values. If continuously decreasing the number of points used in your computations just makes R-squared remain high (close to 1), with fluctuations in the range +/_ 5%, it means your data set may be indeed approximated by a single straight line. At some point, the R-squared will be (maybe) out of that range and that is what you are looking for. Yet, the main problem is here, i. e. IF your data set may be indeed fitted by such a single line or not. So, first of all, try to fit the whole set with a single straight line and see R-squared value here. If the obtained value is low, as I expect with the data set in your Figure 2 above, you should first identify the reasons for such a low value. Myself, I estimate at least two straight lines, with quite different slopes, may be fitted to the data set in Figure 2. So, if you are looking for the point where the whole data set may be fitted by two straight lines (with different slopes), R-squared may be also of use. R-squared value for the first data subset will be high, it will remain also high for the second data subset, but it will be low for the whole data set.

Please take a look at the GMT manual. There are 20 examples with scripts. So you will find your answer for PSMECA and PSVELOMECA.

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.

The resources of IRIS, USGS, GEE may cater the need of required dataset.

 Each event is characterized by its location-time-magnitude parameters (x, y, z, t, m). In the following, we shall neglect the z (depth) coordinate only for sake of simplicity.

There are many optimal parameters of earthquake clustering models such as:

Failure rate fr which is a measure of the proportion of events that can be considered truly independent and constitute the spontaneous background seismicity.

K and a are constant parameters

 c and p are characteristic parameters of the time dependence process .

r is the distance from the point (xi, yi) and  is a free parameter determining the fall off of the induction effect with distance.

d and q are two other free parameters of the process

for more information about the optimal parameters of earthquake clustering can be found in the attached pdf file.

Since you say its a big event and big events have finite source area which then radiates energy in all azimuths which is not same because of the Doppler effect.  As Weijia mentioned cross-correlation would be best to detect it, as for as stacking is concerned it would not work from all azimuths. But if the event is deep enough then STF is more simple than the one which shallow (like recent Nepal Eq). You might wanna have a look into these: 

For the cross-correlation

1. http://www.bssaonline.org/content/early/2017/03/02/0120160271.abstract

For big shallow event with multiple sub-events

2. https://academic.oup.com/gji/article-abstract/208/2/992/2556164/The-2015-April-25-Gorkha-Nepal-earthquake-and-its

I hope it helps in some way

 Dear Ramesh, 

                          You may convert your synthetic ground motion such that it matches with bedrock motion response spectra.  You can also determine bedrock motion versus amplification curve and read the value corresponding to bedrock motion. You can check my paper titled " Obtaining the surface PGA from site response analyses based on globally recorded ground motions and matching with the codal values,". 

Abhishek 

At least the magnitude of the main shock itself is the upper limit of the magnitude of aftershocks.

!!!! Have people heard of Photoshopping

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.

Dear Sameera! Since tsunami is a long surface water wave, it has the speed V=(gD)^(1/2). Since g=9.81 m/s2, in the case of D=40 cm, we get V=2 m/s. For D=1 m, we get V=3 m/s. This is the speed with which the whole volume of water flows. Can a person stand in this flow or not? One can try in a mountain river. I guess one cannot do it if V=5 m/s, but perhaps at V=1 m/s this is not difficult. So V=2 m/s, corresponding to wave height 40 cm, might indeed be critical for many people. But this border is likely to be fuzzy (humans are different), so that both 30 cm and 50 cm might be correct answers.

Another question: whether it is dangerous to fall down? I  guess not if water depth is only 30 cm, but might be for somebody if it is 50 cm. All depends also if this is sandy beach or stones. Finally, some tsunami are turbulent, and for a given speed turbulence is more dangerous. However, it propagates at less distance inside because of friction.

To summarize, I think that tsunami less than 30 cm high are not of much danger, apart from children and in rough terrain, while above 1 meter could be dangerous for all.

The final issue is where this height is observed. If approaching tsunami is 30 cm high where the water depth is 10 meters, it can increase its height substantially before reaching the shore. You can look at my attached paper. It is rather mathematical, but I also provide coefficient of amplification of a solitary tsunami wave on the shelf in a Table. https://www.researchgate.net/publication/275581998_Evolution_of_long_nonlinear_waves_on_shelves

P.S. I am not a person who studied human safety. I just know the physics of tsunami waves.

Dear Mahdi, The predominant frequency of a ground motion can be estimated by evaluating the predominant period. This is the period at which the maximum spectral response is observed. 

Many thanks for the answer. I am working on stichtite and pyroaurite, and have not found much information on these relatively rare (in the natural world) minerals. I work at a smaller CSU campus and don't have access to much research instrumentation. Just got back from sabbatical with more questions than answers.

Do you know of a lab that could do this work, and what the cost might be? I am worried about doing just a theoretical estimate of interlayer spacing, as these natural samples have non-endmember compositions.

Hello Sedigheh Farahi ,

I can suggest you these papers

BR

Hi,

I would suggest our paper: http://www.sciencedirect.com/science/article/pii/S0277379113003053

which suggests a new method to investigate Late Quaternary palaeoshorelines. This method, that we called "synchronous correlations method", takes advantage of the fact that (i) sea-level highstands are not evenly-spaced in time, yet must correlate with palaeoshorelines that are commonly not evenly-spaced in elevation, and (ii) that older terraces may be destroyed and/or overprinted by younger highstands, so that the next higher or lower palaeoshoreline does not necessarily correlate with the next older or younger sea-level highstand. 

If you have any comments, suggestions, etc., feel free to contact me.

Bye

EHB bulletin ( http://www.isc.ac.uk/ehbbulletin/).

The focal depths are well constrained using depth phases.

The Richter magnitude reflects the energy released by a given earthquake. Depending upon the distance to the epicenter the acceleration at a given place will be greater or smaller. There is, as well, a large influence of the ground type at the recording site.

To find the value of acceleration as a function of  magnitude and distance, taking into account the type of gound at the site,  you can follow the paper:

Morales-Esteban, A., Justo, J.L., Martínez Álvarez, y Azañón, J.M. (2012). “Probabilistic method to select calculation accelerograms based on uniform seismic hazard acceleration response spectra”. Soil Dynamics and Earthquake Engineering, ISSN 0267-7261, 43:174-185. DOI: 10.1016/j.soildyn.2012.07.003. 4 citations.

There are other factors that influence the acceleration from a given magnitude, as it is the whole geology between the epicenter and the site. But this factor is too complex to be taken into account.

Looked at this topic in the late 1970's Here are a  couple references.1971 Peter L. Ward and Sveinbjorn Bjornsson, Microearthquakes, Swarms, and the Geothermal Areas of Iceland, Journal of Geophysical Research, June 10, 1971,Vol 76, NO 12 pp3953-3982

1974 Lister, C. R. B., On the Penetration of Water into hot Rock, Geophys. J. R. astr. Soc. 39, 465-509

1985 Bratt, Steven R., Eric A. Bergman, and Sean C. Solomon, Thermoelastic Stress: How Important As a Cause of Earthquakes in Young Oceanic Lithosphere? Journal of Geophysical Research, Vol. 90, No. B12, PP 10249-10260. –concludes it is very important

thanks stoffel!

i was also thinking on same line. if u have any reference of publish result, pl share.

This is a good question. In geohazards, aleatoric and epistemic uncertainties are difficult to distinguish. Separation of these two uncertainties is arbitrary, even like "splitting a hair."

you can use FAULTKIN or WINTENSOR, but i think that wintensor is better for many raison, with this softawre you can calculate de R ratio and you can deduce the stress regime.

best regards

Pushover analysis is the common name of a type of procedures that uses simplified nonlinear static analysis. A modal response spectrum analysis is a dynamic linear analysis. Modal response spectrum analysis is more suitable for problems involving the structural design of new structures, while pushover analysis is more indicated for assessing the seismic vulnerability of existing structures. There are many pushover analysis procedures. The most popular are the ATC40 capacity spectrum method (as an example, see the following paper: http://www.sciencedirect.com/science/article/pii/S1350630714003732), the displacement coefficient method (FEMA273), and the N2 method (Eurocode 8).

Max,

I guess that there are only theoretical macroseismic maps related to this earthquake (e.g. http://www.jaee.gr.jp/event/seminar2012/eqsympo/pdf/papers/175.pdf). I've been searching in the NEMC and there is no field observation macroseismic information about the Van earthquake, or I have been unable to find it!!

 I am not sure if in 2011, the Turkeys agencies had a protocol for the macroseismic calculation from field observation. I figure that you have to ask to Turkish agencies, because of I don't know any paper dealing with this so far.

Regards from Spain

Hello Hamid,

Denote the first by X and the second by Y.

What Fernando and Maaruf answered could be super helpful because cross correlations tells you how much information one random variable tells you about the other, but you could also study the first and second order moments of a prior known relation (if you know it or have a feeling that such relation might work). For example, if you know X and Y might be linearly related then study the first and second order moment of Y = aX + b where a and b are constants. If it's a non-linear relation of prior known form ( i.e. Y = exp{X} ) , study that form.

Hope this helps :) 

         

I think you should read a text book. These things are explained. The corner frequency is important because this is the peak of energy radiated (you see this when you consider the power spectrum) and like an antenna radiates best at is own dimension the wave length corresponding the the corner frequency is approximately equal to the source dimension.

The moment can be estimated from the low frequency constant amplitude of the displacement spectrum from the amplitude of any frequency because at these long wavelength the source can be modeled as a point.

Of course you can estimated the energy radiated seismically by integrating first the energy at one station in the spectrum and then integrate in space considering the variations of amplitudes according to the fault plane solution, and then you need to add the energy in the P and the S-waves. After that you would have the energy radiated, but would know nothing about the energy that went into heating the fault plane by friction and the energy possibly used to break rocks, plus there is also the potential energy stored by uplift,

As I said, it's best to study a text book, perhaps Aki and Richard.

The seismic moment depends on the average slip (displacement at rupture) and rupture area, as well as the driving shear stress (roughly stress drop) during the earthquake. The maximum rupture area relates to the strike dimension ('length') and dip dimension ('height' or 'width') of the rupture (slip) plane, and so does the slip. The maximum values of all these factors, and thus the moment, depend on the size of the seismogentic fault zone (or part of the zone) within which the earthquake occurs. For an earthquake to rupture the entire seismogenic fault zone, the local stress field in the entire  zone must be everywhere favourable to that type of fault slip, that is, stress-homogenised. There are certainly limits to how large a rock body - seismogentic fault zone or part of it - can develop stresses (that, in turn, relate to the strain energy stored in the body, a part of the elastic energy) that are everywhere similar and generally  favourable to a given type of slip at a particular time (the time of the earthquake). Thus the dimensions of the rock body/fault zone with favourable stresses for a particular earthquake at a particular time put limits on the maximum rupture area and slip and thus the moment (and the moment magnitude) of the earthquakes generated. Further discussion of these points is in: Gudmundsson A (2014) Elastic energy release in great earthquakes and eruptions.Front.EarthSci. 2:10. doi:10.3389/feart.2014.00010

Dear Jagan,

The answer that Shahid has given you is correct.  It is used in seismology a lot to determine movement direction with respect to your recording station.  It is explained in detail by Cronin (2008) in his paper: "Cronin, V.S., Millard, M.A., Seidman, L.E. and Bayliss, B.G. 2008. The seismo- Linearment Analysis Method (SLAM). A reconnaissance tool to help find seismogenic faults: Environmental and Engineering Geoscince, v. 14, no. 3, 199-219 p.

In essence what you are looking for is depicted in the attached figure.  You can also look at the frequency content.  The forward content may be a little bit higher than the backward content.

Hope this helps.

Regards

Stoffel

If you are working with a local seismic network, a simple equation may be good enough:

M(local) = log A + 1.7 log r - 0.15

A = horizontal displacement amplitude ( peak to peak) in um, if you are observing vertical components, multiply them by 1.7. Normally your seismometer will give you velocities of the ground motion,dividing them by 2 pi f yields displacements ( f being the dominating frequency)

r = epicentral distance in km

the last coefficient can be adjusted by looking for events, which are listed in seismological catalogues (USGS etc.)

Dear Alessandro, (dear all)

It is very easy after the earthquake occurrence to find that there was some kind of acceleration before it, especially when the earthquake is anticipated by a seismic sequence of small/intermediate shocks. From this perspective a simple answer could be: yes, L'Aquila showed some sort of seismic acceleration although it looked as evolving as a chaotic process (see for example my article:

http://www.sciencedirect.com/science/article/pii/S0040195110004270 ).

On the other hand, when some sequence is evolving, the problem to understand what is going on is also related to which data to use (e.g. instantaneous or cumulative strain or moment release or other real or pseudo physical quantities) and how to handle them in order to eventually identify an acceleration. Literature is full of great examples, and only very few exceptions were published before the earthquake really happened.

My opinion agrees with many (e.g Massimo and Ian above) i.e. that the problem is very complex and difficult to cope with. To what previously said I would add that we really need to analyse as many kinds of data as possible in order to establish with some confidence that something unusual is happenning. (Of course it will not be only question of amount of data but also of their quality). For this reason, I would prefer to change the question to: what was the physics underlying the L'Aquila seismic sequence (or any other) that brought it to culminate with the mainshock of the 6 April, 2009?

Although still controversial, it will be of great help also to identify possible anomalies due to the eventual lithosphere-atmosphere-ionosphere coupling that seems oto provide some typical manifestations, for instance, in the form of thermal atmospheric anomalies (e.g. see my article about the 2012 Emilia earthquake:

http://www.annalsofgeophysics.eu/index.php/annals/article/view/6123 )

or ionospheric anomalies (e.g. see my article:

http://www.ann-geophys.net/32/187/2014/angeo-32-187-2014.html about two Chinese earthquakes).

In particular that the problem is complex and difficult can be deduced from the results of the latter article where we show that ionospheric anomalies do not always appear, because the conditions to occur are not simple, depending on the solar magnetic activity, magnetic latitude, lithospheric conditions and, likely, kind of fault mechanism, sufficient energy of coupling, etcetera.

Although statistical analysis is important to grasp something of the question, I believe we need of something more "physics-oriented" to identify those fore-patterns that eventually preceed a large earthquake.

In general, I agree with Wyss. For detail, you can use the depth of earthquake hypocenters in studied region. You could use also GPS measurement at two fault's sides to modelling fault locked depth by OKADA's dislocation model. For practical case when you have no information of rupture width, you could consider maximum width is equal rupture length for estimate maximum earthquake. I discuss in my paper: Phan Trong Trinh et al., 2012. Late Quaternary tectonics and seismotectonics along the Red River fault zone,North Vietnam. Earth-Science Reviews 114, 224–235.

It is difficult only with this figure. Both in acceleration and velocity you can see a significant and energetic pulse in the FN component with a clear period. In the spectrum, this period must appears clearly. After a better filtering, you must also observe this pulse in the displacement.

Moreover, in the velocity hodogram you can see a clear directivity of the ground movement. It must be also observed in the acceleration and displacement hodograms, after to consider only the S phase and, as I told you, modify the filter parameters.

Lot of things can be learned even from small earthquakes, From getting first ideas on scaling laws (earthquake energy and size of fault), to effects of wave propagation. All this information can be exploited for modeling larger earthquakes, which may have occured in the past. Indeed, being strong events rare and therefore lacking of instrumental data, seismologists often have to extrapolate somehow from smaller earthquakes (with all the caveats implied). As Jose said, valuable seismotectonic information can be obained, both from fault plane solutions, moment tensor inversion but also from the distribution of the seismicity, which may delineate tectonic structure. Many papers have been published on high-precision location with astonishingly high resolution of the fault geometries.

Dear Jagan, There are many softwares like SEISAN are available which can have facility of P phase picking etc. But I still feel manual picking of the phase is the best. Because you are from Civil background, it will be little difficult for you. But in your city CSIR-NGRI is situated. Sometime visit their and you will get all the answers.

The directivity effect is a phenomenon which appears when the velocity of the fault rupture is very close to the velocity of the shear wave. This leads to the appearance of long period pulses which may or may not be visible in the acceleration traces, but they are readily distinguishable in the velocity traces (which are basically low-passed versions of the accelerograms). These velocity pulses appear to be stronger when the rupture propagates towards the site (forward directivity).