You will have to know or determine the interval velocities.

Hi,

depth conversion needs a book to talk about  :)  but let's keep it simple...

it is important to know which is the purpose of the depth conversion  (GBV calculation, hydrocarbon volume calculation, fluid analysis etc..),  not always the depth conversion has to be very precise... so you can obtain acceptable results also with very few data. If you have well data you should start with the check shot data at the well(s) location to build up a Time/Depth curve for instance. If  lateral variation in velocities is a key issue you should introduce seismic velocities in the study and calibrate them with the wells data.  If you do not have any information from wells around and no seismic velocities (stacking velocities) it is hard. In case you do not need a precise depth conversion (let's say to evaluate something on which bulk depth shift has a minor impact) than you should look for some regional data that provides some kind of velocity gradient/trend or some key horizons information. Usually seismic survey are shooted in areas of some interest so probably there will be data available around.

You need to know the definition intervel velocity. You can check if there is any acoustic logging data on the line or around the work area.

Hello Redouane, 

wich software do you use for your time to depth conversion ? 

thank you very much, all of you, for your answers,

#Stephano Angella; your explanation is so clear, but unfortunately there's only one well , but it's shallow and the rest of the cross section remain unidentifiable in thickness and depth (km) terms.

#Gaël Lymer; I'm not using any software, the cross section is built and I took it from an article, I tried to contact the autors about the conversion, I'm still waiting.

i'm working on a 3D seismic cube across the Iberian Margin. I use a velocity model published from wide angle seismic data (https://www.researchgate.net/publication/297658786_Fault-controlled_hydration_of_the_upper_mantle_during_continental_rifting) to build my model and convert the data from time to depth.

Maybe there is such data that you can find in publications in your area? 

Also from your well, composition of the layers and tables that are probably possible to find on the web (IODP?) you can get an estimation of the velocities in the different layers. 

Then you can convert your lines.

What is the goal for ? 

Article Fault-controlled hydration of the upper mantle during contin...

Your work is extremely fabulous. Did you use magnetic or gravimetric data as well, or only seimic data?.... I'll read it anyway thank you.

-I'm working on the north-west of algeria, ibero-maghreb zone. i found some publications on this area, but they provide only TWTT depth.

-Thank you for (IODP) I'll start looking there.

-The goal is for seismological study. we need a good velocity model for studying an historical earthquake.

I totally agree with #Stephano Angella's professional answers. But as you mentioned, you got the cross section from an article, so that you have the image only, which means you don't have to do too much over-interpretation since your data is quite limit. So the most conservative way is degitizing the image to allow you read more precise TWT first, then convert from the emperical velocity function (maybe from the one well or IODP) mark the TWT from your target spots which you are interested to interpret in your study. Good luck!

TWT * Velocity (m/sec.) = Depth (m)

it give approximate results.

I have been using the SeisCom conversion spreadsheet by Christopher L. Liner which can be downloaded from the Stanford website.

Quite practical, if you don't need much accuracy:

http://sepwww.stanford.edu/oldsep/cliner/files/download/SeisCom.xls

Cheers!