How do you know an ISP is using subsea cables or satellite through tracert command

I don't think there is an easy way to do this. Probably your only resolution is to GUESS, resolve the DNS names of the hops in the trace and google them, or use a whois service/search engine. You might get what you want. If two hops are placed geographically very far away (i.e crossing continents), they are likely to be a satellite connection, but this is NOT a strict rule.

Also in some text I read if you see a reply of less than 250ms then it is a fiber link against our normal 560ms satellite link

I think thats a good point.

Hi
I don't think there's much correlation between ping responses and physical links between source and destination hosts.
I've got terminal servers and standard hosts on a customer network which take more than 250ms and sometime literally touching the 1 second mark. But I know the link that I use is neither VSAT or subsea fibre optics.
An easy way to logically figure out is to determine if your target is in another country. Now check how your ISP communicates with that country. Also check if in some shape or form, the service changes hands between several other ISPs who uses links which has to be subsea. Even then, there's always the bone of contention that how your packets are being routed.
I don't believe there is any way of finding out from a tracert command, whether the packets are being routed via a satellite link or a subsea cable.

visualroute.visualware.com/

try the live demo in the above site. In there chose a server, may from outside your country and then press start, it will show you all the hops that the traffic is passing to reach your computer, in most cases you can even tell which internet wholesale provider they are using.