A B767 CREW NOTICES A 'THUMP' SOUND DURING AN ENCOUNTER WITH THE WAKE OF A PRECEDING B757 THAT WAS DETERMINED BY MAINT TO BE AN ENGINE SURGE.

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THE REASON FOR THIS RPT IS TO ALERT CREWS THAT AN ENGINE SURGE CAN OCCUR WITH A WAKE TURBULENCE ENCOUNTER. A B757 HAD DEPARTED IN FRONT OF US AND WAS APPROX 5 MILES AHEAD. WE ENCOUNTERED A WAKE TURBULENCE EVENT WHICH INDUCED AN ENGINE SURGE ON THE R ENGINE. WE HAD NO IDEA THAT A SURGE HAD OCCURRED UNTIL DSCNT INTO LAX WHEN MAINT SENT A MSG STATING SAME. ALL INDICATIONS IN THE FLT DECK WERE NORMAL. I BELIEVED THE TURBULENCE AND 'THUMP' WE HEARD WERE ALL RELATED TO THE WAKE TURBULENCE EVENT ONLY. PLEASE ADVISE ALL OF OUR FLT CREWS THAT AN ENGINE SURGE IS POSSIBLE WHEN ENCOUNTERING WAKE TURBULENCE. THIS COULD BE CRITICAL DEPENDING UPON WHEN A WAKE TURBULENCE EVENT IS ENCOUNTERED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THEY CLBED THROUGH THE WAKE OF A 'STRETCH' B757 THAT CAUSED A ROLL OF 10 TO 15 DEGS AND WAS ESTIMATED AS MODERATE. MAINT DETERMINED THAT THERE HAD BEEN AN ENGINE SURGE AT THAT TIME EVEN THOUGH IT WAS NOT NOTED BY THE CREW ON THE ENGINE INSTRUMENTS. THERE WAS NO DAMAGE TO THE ENGINE. THE ENGINE TYPE IS SUBJECT TO AN AIRWORTHINESS DIRECTIVE TO PREVENT ENGINE POWER LOSSES DUE TO HPC SURGES (2003-19-15).