FileMaker does not have triggers that can be set at the data level. It DOES have triggers that can be set at the interface level.
This type of automatic creation of related records usually isn't really needed. The related record in Table 2 can be very easily created on an "as needed basis", but it can be done:
First the relationship:
Table 1::__pkRecID = Table 2::_fkRecID
Double click the relationship line and select the "allow creation of related records..." check box for Table 2.
On the layout where you will create new reocrds in Table 1, go to Layout Setup and select the OnCommitRecords trigger. Set it to run this script:
Set Field [Table 2::_fkRecID ; Table 1::__pkRecID ]
The first time around, this script step will create a new related record in table 2. Subsequent trips of this trigger--such as after editing a field in Table 1, will make no change to the data in Table 2 as it then is setting an existing field to a value that it already contains.
Thanks PhilModJunk...your solution worked perfectly.