CPR PLT OF SMT ACFT LANDED SHORT OF TEMPORARY DISPLACED THRESHOLD DUE TO INADEQUATE MARKINGS.

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PREFLT PLANNING REVEALED THAT RWY 13R AT BOEING FIELD HAD A TEMPORARY DISPLACED THRESHOLD WITH THE FIRST 5000 FT CLOSED. BOEING FIELD'S ATIS ALSO INDICATED THAT THE FIRST 5000 FT OF RWY 13R WAS CLOSED. ON FINAL; TWR ALSO ADVISED THAT THE FIRST 5000 FT OF RWY 13 WAS CLOSED AND THE DISPLACED THRESHOLD WAS MARKED. I PLANNED TO LAND 1/2 WAY DOWN RWY 13R (10000 FT RWY) OR E OF THE TWR AS ADVISED; AND BETTER YET; PAST THE TEMPORARY DISPLACED THRESHOLD MARKINGS. I WAS CONCENTRATING ON LNDG AND LOOKING FOR THE MARKINGS. I NEVER SAW THE THRESHOLD MARKINGS AT ALL AND LANDED AT LEAST 1/2 WAY DOWN THE RWY PAST THE LAST OF THE WORKING EQUIP OFF THE SIDE OF THE RWY. AFTER CLRING THE RWY; GND CTL ASKED ME TO CALL THE TWR. THE TWR SUPVR SAID I HAD TOUCHED DOWN 1000 FT OF THE DISPLACED THRESHOLD. I NEVER DID SEE THE MARKINGS. HE SAID THAT A NUMBER OF OTHER ACFT HAD DONE SO ALREADY THAT MORNING AND DON'T WORRY BUT BE MORE ALERT IN THE FUTURE AS WORKING EQUIP WERE FREE TO CROSS THE CLOSED PART OF RWY 13R AT ANY TIME. AS WE WERE TALKING HE SAID 'THERE GOES ANOTHER ONE NOW' AND EXPLAINED ANOTHER ACFT HAD JUST LANDED SHORT. LATER I WALKED OVER TO THE EDGE OF TRANSIENT PARKING NEAR WHERE THE DISPLACED THRESHOLD WAS AND STILL COULD NOT SEE ANY MARKINGS. IF TEMPORARY MARKINGS ARE TO BE USED THEY SHOULD BE MORE CONSPICUOUS THAN THESE WERE.