problem merging iscgem373782 with usp00048gt

On April 26, 1990, we and GCMT located an M6.5 event WSW of Xining, China (event usp00048gu). It was preceded by an M6.3 foreshock about 5 seconds earlier (event usp00048gt). They were followed about 30 seconds later by an M6.3 aftershock (event usp00048gv). ISCGEM and GCMT also located the aftershock (which merged successfully with the automatic association algorithm), but ISCGEM only located a single event where we have the foreshock and mainshock 5 seconds apart.

Using the event admin pages, I have tried to merge iscgem373782 to the foreshock usp00048gt, and when a couple attempts at that preferred merge, I tried to merge it to the mainshock usp00048gu. This merge has also failed. Since the admin pages allow me to merge events for many other cases, it seems to me that the system is refusing to do the merge because the ISCGEM event is by origin time between the two US events that are only 5 seconds apart.

Our preferred option is to merge iscgem373782 to the foreshock usp00048gt.