sequence of tenses (optional and obligatory back shifting )

Consider a sentence:

1) The president learned that the earthquake has caused havoc all across the country.

Here present perfect tense is used. First tell me is it correct to use 'has caused' ?

I read once in a grammar book that if the verb in the main clause is in the past tense the the verb in the subordinate clause will also be in the past tense.

So according to this rule it should be 'had caused' instead of 'has caused'.

But at the same time some of them say that if the emphasis is laid on the subordinate clause then present perfect tense can be used. While some say if the emphasis is laid on 'noticing' then past perfect tense to be used. So by this logic one can use present perfect tense as well.

I'm confused.

P.S. -- I'm aware that past perfect tense can be used in every situation but I have no idea when to use present perfect tense in the cases when the verb in the main clause is in the past tense. Help me out.

The use of present perfect has caused indicates that the event happened in the recent past and its effects are still current.

Imagine a meeting within the first hour of the earthquake:

We held a meeting in Washington.
The president learned that the earthquake has caused havoc all across the country.
The National Guard was mobilised.

All of those simple verbs describe a particular event which happened instantaneously (held, learned, mobilised). The present perfect indicates that havoc was caused and is still ongoing. Compare to the simple past again:

The president learned that the earthquake caused havoc all across the country.

That sentence indicates an instantaneous event (it caused havoc), but it's not explicit that it's still going on: the havoc may well have been countered by the time that sentence was said.