Strong motion data of any earthquake can give us the acceleration time history of the earthquake at the recording station, how do we calculate the ground displacement from these records? i have tried a few numerical integration techniques but am not satisfied with the values.
Ok use SeismoMAtch software to get displacement. It well known that you need to integrate the acceleration time history in order to get displacement.
Good luck
You can also use SAC (Seismic Analysis Code) that is free and very useful for such processing. You will have to use integration for going from acceleration to velocity and then displacement but definitely have to apply few things before you do that (some basic processing)
The acceleration record contains the ground acceleration along with noise due to ground and instrument. So, when you integrate the accelrogram twice to get displacement, the noise also get integrated twice . Therefore, the displacements are not true displacement. Thus, before integration of the record, go through basic processing of the records like, base correction, filtering etc.
@Anup Kumar Sutar, Sir the data that i am referring to here is from MOES.gov.in on the sikkim 2011 earthquake strong motion data. There are two strong motion data sets, one is from IIT KGP and another from IIT kanpur, they have something called ASCII data (Filter and Original ASCII) and EVT data so which one of these are advisable to be used for the displacement calculations. Also sir i would like to know why they have multiple files for strong motion records of the same place, like the folder called filter data contains PV394_1,PV394_2,PV394_3 & PV403_1, PV403_2, PV403_3 under the same date in this particular case 110918(18thSep2011) folder
@ Aadityan:
1. The two strong motion data sets belong to IIT, Roorkee and IIT, Kharagpur.
2. The EVT folder contains the original binary files of ETNA instrument.
3. Each folder contains 3 files with extension_1,_2 and _3.
4. The extension_1 is for Z-component of the accelerogram where as _2 &_3 belongs to the horizontal components
5. In most cases Maximum PGA is observed in horizontal components of accelerogram, so you can used them for estimation of maximum displacement.
6. It is suggested to experiment with all three componets
@Anup Kumar Sutar
Sir thanks for such a detailed reply, i have one final question, i would like to know if these data have been already filtered from noise and have they been through Baseline correction process as well.
An elementary way of calculating the displacement from the horizontal records have been found to be Numerical integration. Although it is exhaustive and time consuming by nature we get rigourus robust values. I tried it out myself using the Newmark's algorithm and arrived at the displacement using acceleration time histories.
TIME HISTORIES by H. A. Gabefson. TN-1590 ... DISPLACEMENT SINGLE RECURSIVE EQUATION, ACCELERATION ... transform time histories into shock spectra. ... The explosively generated mechanical shock motion or the earthquake
The seismic displacement can be deduced from an Acceleration time histories (a) as follow:
- Integrate the acceleration array to obtain the velocity time history
- Integrate the velocity array to obtain the displacement time history
To integrate these vectors, you can use the function “cumtrapz” under Matlab.
Velocity= cumtrapz(t,a)
displacemnt= cumtrapz(t,v)
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