如何在现有的关联数组中插入新的键值对？

I'm having following associative array:

Array
(
    [0] => Array
        (
            [user_id] => 9def02e6337b888d6dbe5617a172c18d
            [user_first_name] => Ashutosh
            [user_last_name] => Modi
            [user_email] => ashutosh.modi@gmail.com
            [user_status] => enable
            [user_subscription] => lifetime
            [user_registered_type] => online
            [user_reg_date] => 1325581397
        )

    [1] => Array
        (
            [user_id] => a6d22e4cc3f65778a60b359842bcec82
            [user_first_name] => Dilip
            [user_last_name] => Modi
            [user_email] => dm.modi@gmail.com
            [user_status] => enable
            [user_subscription] => period
            [user_registered_type] => online
            [user_reg_date] => 1325152066
        )


)

It is having two keys. Now I'm having another array named $user_data which has the following output:

Array
(
    [user_state] => Rajasthan
    [user_city] => Jhunjhunu
)

I want to add this key value pair to the above array. Above array is just first iteration of for loop so the above values get inserted into first array element. the second array element will have somethong different values. I want the result in following manner. Can you help me in achieving this? Thanks in advance.

Array
    (
        [0] => Array
            (
                [user_id] => 9def02e6337b888d6dbe5617a172c18d
                [user_first_name] => Ashutosh
                [user_last_name] => Modi
                [user_email] => ashutosh.modi@gmail.com
                [user_status] => enable
                [user_subscription] => lifetime
                [user_registered_type] => online
                [user_reg_date] => 1325581397
                [user_state] => Rajasthan
                [user_city] => Jhunjhunu
            )

        [1] => Array
            (
                [user_id] => a6d22e4cc3f65778a60b359842bcec82
                [user_first_name] => Dilip
                [user_last_name] => Modi
                [user_email] => dm.modi@gmail.com
                [user_status] => enable
                [user_subscription] => period
                [user_registered_type] => online
                [user_reg_date] => 1325152066
                 [user_state] => Tamilnadu
                [user_city] => Chennai
            )


    )

<?php
    foreach($user_data as $key => $val){
        $original_array[$key]['user_state'] = $val['user_state'];
        $original_array[$key]['user_city'] = $val['user_city'];
    }

assuming the 2 arrays have the same keys

Try with array_merge

foreach ($users as &$user)
{
    $user = array_merge($user, $user_data);
}

var_dump($users);