Multidimensional associative arrays in Bash

I'm trying to create a multidimensional associative array but need some help. I have reviewed the page suggested in this SO answer but it confused me even more. So far here is what I have:

The script:

#!/bin/bash
declare -A PERSONS
declare -A PERSON
PERSON["FNAME"]='John'
PERSON["LNAME"]='Andrew'
PERSONS["1"]=${PERSON[@]}
PERSON["FNAME"]='Elen'
PERSON["LNAME"]='Murray'
PERSONS["2"]=${PERSON[@]}
for KEY in "${!PERSONS[@]}"; do
 TMP="${PERSONS["$KEY"]}"
 echo "$KEY - $TMP"
 echo "${TMP["FNAME"]}"
 echo "${TMP["LNAME"]}"
done

The output:

1 - John Andrew
John Andrew
John Andrew
2 - Elen Murray
Elen Murray
Elen Murray

As you can see trying to access a specific index of the $TMP array in the for loop returns the whole array.

[Q] What do I need to do in order to separately access the "FNAME" and "LNAME" indexes of the $TMP array inside the for loop?

Thanks.